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Phenology shifts are one of the most prevalent responses to climate change across taxa. Temperature increases have resulted in many species shifting the timing of seasonal behaviours such as bud-burst or nest-building. Interspecific variation in the level of response has given rise to previously interacting species diverging in their phenologies, leading to the possibility of temporal mismatch. One system in which this has been predicted, and in some cases evidenced, is pollination networks. There are several underdeveloped areas of understanding that restrict our ability to anticipate and accurately predict the impacts of phenology shift in pollination networks. There is limited research quantifying the demographic fitness impacts of mismatch, which hinders understanding of the risks of mismatch. The drivers of interspecific variation in phenological sensitivity to temperature are uncertain, limiting capacity to predict which species may undergo divergent rates of shift. Finally, current methods do not account for how phenology shifts may also change how species population are distributed through time, which affects predictions of mismatch. This thesis seeks to examine each of these knowledge gaps. First, a manipulative field experiment was conducted using a generalist plant to quantify how continuous variation in pollinator phenology impacts on seed-set. Pollinator abundance and species composition was found to vary significantly over the field season, resulting in large variation in seed-set depending on flowering phenology. Second, the phenology of a group of key pollinators, Syrphidae (hoverflies), was examined using a UK recording scheme from 1980 onwards. Syrphidae were generally found to be advancing their flight phenologies, although response was asymmetrical over their flight period and first date of flight advanced at a greater rate than peak abundance date or last date of flight. Life history traits that were used 8 to predict phenology response in Lepidoptera were applied to the data set but were not found to be predictive in Syrphidae, potentially indicating that these traits are not general predictors of phenology response in arthropods. Finally, simulations of phenology shift in pollination networks were run using an individual-based model in which the shape of population distributions were also allowed to shift in response to temperature. These predicted large rates of species loss in networks and demonstrated that accounting for the shape of phenology events results in larger rates of species loss, indicating that current predictions may underestimate risk. These findings advance understanding of phenology shifts by showing that they can have severe fitness impacts and that it is necessary to model phenology in a way that takes account of the shape of phenology events.

Native pastures present an opportunity to diversify that can support an array of animals, including pollinators and livestock. A variety of insect pollinators, important for both crop production and wild fauna persistence, are in population decline and benefit from native floral resources to sustain across the landscape. The goals of our work were to document blooming and forage characteristics of a variety of native forbs and to determine their establishment, persistence, and forage characteristics under different grazing rest regimens. We also sought to measure animal productivity between grass and diversified pastures under continuous stocking. Forbs established and persisted differently based on life history characteristics, competitive advantages, and grazing preference. During all three trials, black-eyed Susan (Rudbeckia hirta L.; BESU), lanceleaf coreopsis (Coreopsis lanceolata L.; LCOR), purple coneflower (Echinacea purpurea (L.) Moench; PURC), oxeye sunflower (Helopsis helianthoides (L.) Sweet; OSUN), ticktrefoil (Desmodium (L.) DC.; TTFL), cup plant (Silphium perfoliatum L.; CUPP), and Maximilian sunflower (Helianthus maximiliani Schrad.; MSUN) were the most regularly observed species and demonstrated moderate to high establishment and persistence success. Of these species, LCOR, OSUN, and TTFL were grazed the most frequently by cattle (Bos taurus L.), and of these species both OSUN and TTFL showed the best persistence in pastures. Forb populations declined over multiple grazing seasons in both grazing trials; however, a combination of grazing and pasture rest appeared to develop the best persistence compared to long term grazing or rest. Forbs improved forage nutritive composition and stabilized crude protein levels throughout the season while reducing the concentration of fiber components later in the season compared to the maturing grass species. When combined with native warm-season grasses (NWSG), the forbs produced high quality forage that sustained cattle throughout the grazing season. Cattle produced higher overall ADG, and total bodyweight gain on pastures interseeded with forbs compared to NWSG alone, but animal days were most impacted by grazing management decisions and stocking density throughout the season. Overall, a blend of LCOR, OSUN, BESU, TTFL, PURC, CUPP, and MSUN could improve the diversity of NWSG pastures to support both cattle and critical pollinators.

As plants are sessile organisms, processes controlling plant growth and development must react to fluctuations in the external environment to aid plant survival. However, as the climate of the Earth changes and becomes more extreme, plants become less able to develop to their optimal capacity and this can have an adverse effect on crop yield and biofuel feedstock production. Thus, it is becoming increasingly important to understand the molecular mechanisms used by plants to respond to external stimuli. One important system that plants utilise in their response to environmental fluctuations is the circadian clock. The circadian clock is a time-measuring device that buffers the timing of plant growth and development against fluctuations in the local environment, such as temperature, light quality and light intensity. Importantly, the circadian clock is also able to measure day-length (photoperiod). Thus, plant development and growth is co-ordinated with photoperiod that is closely linked to seasonal changes. A key example of this is the time taken for a plant to flower. Flowering of Arabidopsis thaliana occurs specifically in long-days (LDs) of spring/summer months. Thus, the circadian clock is a key regulator promoting flowering in LD conditions. In conjunction with experimental studies, mathematical modelling has proven to be a successful method of elucidating the mechanisms that underlie complex biological systems. One example of this 'systems biology' approach is in uncovering the components that make up the Arabidopsis circadian clock mechanism. Previous research in our group has also led to the development of a model describing photoperiodic flowering that is tentatively linked to the circadian clock mechanism. In this thesis I shall develop on these models to highlight five key results: 1. using rhythmic PHYTOCHROME INTERACTING FACTOR 4 (PIF4) and PIF5 mRNA as an example, I shall show that multiple circadian regulators are required to describe rhythmic transcription of target genes across multiple photoperiods; 2. the stabilisation of CONSTANS (CO) protein by the blue light-signalling component FLAVIN-BINDING, KELCH REPEAT, F-BOX 1 (FKF1) is required to for flowering in LDs and has a relatively larger impact on photoperiodic flowering than FKF1-dependent degradation of CYCLING DOF FACTOR 1 (CDF1), an inhibitor of flowering; 3. multiple components of the circadian clock play specific post-translational roles in photoperiodic flowering to promote the acceleration of flowering specifically in LDs; 4. temperature regulation of photoperiodic flowering can be explained through an interaction between CO and PIF proteins, limiting the effects of temperature to a specific time-window in a 24-hour day; 5. red light- and temperature-control of the circadian clock can be explained by altering the post-translational regulation of circadian clock components.

In this study, theoretical and experimental approaches were combined, using Arabidopsis as the studied species. The multi-scale model incorporates the following, existing sub-models: a phenology model that can predict the flowering time of plants grown in the field, a gene circuit of the circadian clock network that regulates flowering through the photoperiod pathway, a process-based model describing carbon assimilation and resource partitioning, and a functional-structural module that determines shoot structure for light interception and root growth. First, the phenology model was examined on its ability to predict the flowering time of field plantings at different sites and seasons in light of the specific meteorological conditions that pertained. This analysis suggested that the synchrony of temperature and light cycles is important in promoting floral initiation. New features were incorporated into the phenology model that improved its predictive accuracy across seasons. Using both lab and field data, this study has revealed an important seasonal effect of night temperatures on flowering time. Further model adjustments to describe phytochrome (phy) mutants supported the findings and implicated phyB in the temporal gating of temperature-induced flowering. The improved phenology model was next linked to the clock gene circuit model. Simulation of clock mutants with different free-running periods highlighted the complex mechanism associated with daylength responses for the induction of flowering. Finally, the carbon assimilation and functional-structural growth modules were integrated to form the multi-component, whole-plant model. The integrated model was successfully validated with experimental data from a few genotypes grown in the laboratory. In conclusion, the model has the ability to predict the flowering time, leaf biomass and ecosystem exchange of plants grown under conditions of varying light intensity, temperature, CO2 level and photoperiod, though extensions of some model components to incorporate more biological details would be relevant. Nevertheless, this meso-scale model creates obvious application routes from molecular and cellular biology to crop improvement and biosphere management. It could provide a framework for whole-organism modelling to help address global issues such as food security and the energy crisis.

Post-fire recovery in terrestrial ecosystems is a complex, long-term process with outcomes that depend on the interaction of abiotic and biotic factors before and after fire. Understanding these processes helps to inform conservation efforts so that these natural ecosystems and the services they provide may be preserved. With anthropogenic activities changing fire regimes worldwide, there has been increasing interest in investigating the dynamics of recovery post fire. While comparisons of vegetation at different stages post fire are well documented, less is known about recovery in the form of comparisons of post-fire vegetation to pre-fire stands. Furthermore, recent fire history can not only affect vegetation cover, but also flowering and pollinator interactions. These effects on flowering and pollination should also be examined to better understand recovery patterns in the long-term. The first chapter examines vegetation recovery in two southern California ecosystems through a long-term (15Y) monitoring dataset and compares pre- and post- fire differences in plant community composition with chronosequence differences from the 2017 canyon 2 fire. Burned areas in coastal sage scrub had lower native shrub cover and greater forb cover, along with higher vegetation diversity from greater forb diversity, with changes in species composition persisting four years after fire. In contrast, vegetative cover recovered quickly in grasslands. The inclusion of pre-fire data allowed identification of a pre-existing difference in non-native grass composition between grassland field sites that would have otherwise been interpreted as a direct effect of fire. These results demonstrate the importance of long-term monitoring to allow for the separation of the effects of disturbance vs pre-existing differences. The second and third chapters focus on flowering and pollination in coastal sage scrub. I sampled 22 transects with three burn statuses (recent = 0.5-1.5 y after fire, intermediate = 3.5-4.5 y after fire, and old burned = >10 y after fire) across two years. Chapter 2 explores how recent fire history affects flowering abundance, diversity, and flower size. Recent burn history increased flowering diversity and affected flowering community composition, but in a way that was mostly predicted by vegetation recovery rather than changes in flowering patterns, suggesting vegetation can serve to predict flowering diversity and composition. Flower abundances differed across the two sampling years rather than burn statuses, and most species showed no change in flowering intensity after fire. The third chapter explores how recent fire history impacted flower visitation by pollinators and pollen deposition. Burn status alone had little effect on pollinator visits, with visits and number of visitors strongly associated with flower abundance per area observed. Differences across burn statuses and year did impact how pollinator visits increased with flower count. Types of pollinators also differed, with Apis mellifera, the most common visitor, showing the greatest increase in visits in relation to flower count. Pollen deposition on five common flowering species (Salvia mellifera, Gilia angelensis, Eucrypta chrysanthemifolia, Hirshfeldia incana, Erodium cicutarium) was mostly not affected by burn status, expect for conspecific pollen deposition in S. mellifera, which was higher in intermediate burn sites. Overall, we saw that while grasslands recovered quickly in both cover and composition, coastal sage scrub remained changed for longer after fire. Increased forb diversity in CSS after fire contributed to increased flowering diversity, and though effects of burn status on pollinator diversity were not directly detected, we did find an increase in pollinator diversity with increased flowering diversity at our sites. However, overall flowering abundances and their positive effects on pollinator visits were impacted by the annual changes in flower production in native forbs and shrubs, and less clearly associated with recent burn history. Combined, these chapters help to highlight facets of post-fire recovery beyond burned/unburned comparisons and vegetation recovery, including the importance of separating the effects of burn from pre-fire community differences, and impacts of flower number on pollinator visits.

Leptospermum scoparium is a shrub native to New Zealand and holds high cultural value (taonga = a treasure) and economic value due to the antimicrobial mānuka honeys produced from its nectar. Previous studies demonstrated a high frequency of association between microorganisms and the leaves, stems and roots of L. scoparium, with some modifying the secondary metabolite profile of L. scoparium leaves and improving growth. Flowers are an important niche for microorganisms; however, no research has focused on the L. scoparium anthosphere (flower), despite its potential impact on the honey industry. The aim of this research was 1) to characterize the endophytic and epiphytic microbial communities associated with L. scoparium flowers, 2) to characterize the effect of floral development on the anthosphere community of L. scoparium, 3) to determine the origin of the microbial communities associated with L. scoparium flowers, and 4) to determine the effects of soil on the bacterial communities associated with L. scoparium flowers. To answer these objectives, bacterial and fungal communities were characterized using 16S rRNA and ITS1-based community profiling (or cultivation independent approach) by high throughput sequencing. Host contamination (plastid and mitochondrial sequences) in 16S rRNA amplicon sequencing from plant samples impedes plant microbiota studies, thus I first optimised the 16S-sequencing method for L. scoparium bacterial microbiota studies (overall increase of bacterial sequences by 30%) based on modifications to the published Cas9-16S seq method. I then characterized for the first time which bacteria and fungi that live in (endophytic community) and on (epiphytic community) L. scoparium flowers. The results showed that nectar-consuming yeasts from Aureobasidium and Vishniacozyma genera, functionally diverse filamentous fungi from the Cladosporium genus, and bacteria from Candidatus Phytoplasma, Pseudomonas and Pantoea dominated the L. scoparium anthosphere. The L. scoparium epiphytic community was richer (5.6 times and 2.5 times more bacterial and fungal OTUs) and differed in composition relative to the endophytic community (p < 0.001), demonstrating filtering by the plant. This study demonstrated that a wide diversity of microbial taxa inhabit the L. scoparium anthosphere. As flower morphology and biology change rapidly over time, dynamic niches for microorganisms are formed and lost. Floral physiology at each life stage can therefore influence arrival, persistence, and loss of microbial species; however, this remains poorly understood despite its potential consequences for host reproductive success. Thus, I characterized the effect of transition through five floral stages on the flower-inhabiting bacterial and fungal communities, from immature bud to spent flower, and subsequent allocation to seed. The results showed a core microbiota (representing >80% of all fungal reads and between 47.5% and 94.0% of all bacterial reads at each floral stage) persisted across this dynamic niche despite high microbial turnover, as observed in shifts in community composition (p = 0.001) and diversity (increase in alpha diversity between closed and open floral stages, p25% bacterial community potentially originated from bee visitations). The selection or specialisation of microorganisms was demonstrated across flowering season with a few highly prevalent and abundant taxa (representing >90% of the reads for fungal and bacterial communities in both years). However, most of the taxa retrieved were not prevalent in flower samples indicating stochasticity in the anthosphere assembly process that may depend on environmental conditions, vectors and the microbial community surrounding the flower at the time. Finally, as the rhizosphere is an interface for plant microbial acquisition, soil is an important factor for microbial colonisation of plants. To date there has been little research conducted on the contribution of soil bacteria to the anthosphere bacterial community. Thus, seedlings of L. scoparium were planted in pasteurized potting mix and in soils collected from three contrasting sites. Once the first flowers appeared (~1.5 years), flowers and soil were collected for 16S rRNA gene community profiling. I found that soil played a relatively small role in bacterial community composition of L. scoparium flower, as the anthosphere bacterial community for plants grown in only one soil, ‘home soil’, was different compared to the anthosphere bacterial community for the plants grown in the other soils or pasteurize potting mix (p

‘Whatawhata’ is a naturalised genotype of subterranean clover in New Zealand that has been identified as different to the parent of origin ‘Mt Barker’. A field experiment was conducted from the 10th of May 2021 to the 2nd of May 2022 to characterise and quantify key aspects of growth and development of the ecotype and compare it with the cultivars ‘Denmark’ and ‘Woogenellup’. Evaluation against ‘Denmark’ and ‘Woogenellup’ allowed recommendations to be made for the establishment and management of the cultivar for New Zealand grazing systems. ‘Whatawhata’ is a small leaved plant with a prostrate growth habit and exceedingly hairy petioles, trifoliate leaves, and runners. It is differentiated from ‘Denmark’ by the visible leaf mark and structural pubescence, while ‘Woogenellup’ has a large light green leaf with inconsistent hairiness on structural components. ‘Whatawhata’ can be classified as a ‘Late’ flowering cultivar with phenological development consistent with that of ‘Denmark’ at all stages. In comparison with ‘Woogenellup’, the ‘Whatawhata’ strain is slightly later to produce its first trifoliate leaf and reach flowering. ‘Whatawhata’ required 260±21.2 Cd to produce its first trifoliate with phyllochron thereafter 64.4±7.0 Cd/leaf. ‘Woogenellup’ thermal time requirement in the field (230±21.2 Cd) and controlled experiment (188±9.29 Cd) was consistent with published values. Thermal time requirement up to the fourth trifoliate leaf stage was between 417-489 Cd. Runner initiation occurred with a change in photoperiod. The first runner leaf appeared at the same time for all cultivars (683±39.5 Cd). Runner phyllochron was not different for ‘Whatawhata’ (83.3±9.45 Cd) and ‘Denmark’ (64.5±9.45 Cd) but was longer for ‘Woogenellup’ (96.1±9.45 Cd). ‘Whatawhata’ (952±10.9 Cd) and ‘Denmark’ (962±10.9 Cd) required the same amount of thermal time after the 21st of June to produce their first flower. This was longer than for ‘Woogenellup’ (883±10.9 Cd). Legume yield of ‘Whatawhata’ (1898±166 kg DM/ha) was consistent with that of ‘Denmark’ (1986±166 kg DM/ha) and ‘Woogenellup’ (2482±166 kg DM/ha). ‘Whatawhata’ herbicide tolerance is comparable to ‘Denmark’ and ‘Woogenellup’ with a similar response reported for pastures sprayed with flumetsulam and imazethapyr. However, the application of recommended herbicides for weed suppression did not increase total DM yield compared with unsprayed pasture. Phytotoxicity scores supported the lack of difference, with none of the pasture components reaching the commercial threshold (7) for high yield suppression. Cooler temperatures (

This research aimed to understand the growth and development of hemp (Cannabis sativa L.) crops and determine their impact on hemp fibre quality. An experiment was sown using four cultivars, ‘Ferimon’, ‘Kompolti’, ‘Futura 75’ and ‘Carmagnola’, on three dates (22/10/2020 (SD1), 11/11/2020 (SD2) and 09/12/2020 (SD3)) in Canterbury, New Zealand. The duration of important phenophases was quantified using temperature and photoperiod. Components of dry matter (DM) growth patterns were calculated and explained by differences in light interception, canopy architecture and radiation use efficiency (RUE). Secondary fibre (F2) production was related to key physiological drivers to determine optimum harvest stage. The facultative photoperiod response meant the duration of the vegetative phase, from emergence to flowering, was described in thermal time (Tt), and was progressively longer (P

The movement of nutrients from old vegetative tissue to young leaves and reproductive organs is known as senescence. Senescence can be influenced by the environment of a plant, such as, drought, heat, and nutrient stress. These environmental stressors can also influence canopy architecture. Crop canopy consists of several traits including: leaf number, angle, length and width. Past research in crops like maize and rice have shown significant influences of more erect leaves, including, the ability for increased planting density, which optimizes light interception and increases yield. In a field trial of a sorghum association panel including 345 different sorghum varieties grown in a replicated design under nitrogen sufficient and nitrogen deficit conditions, we have found that sorghum leaf angle is plastic in response to nitrogen deficit stress. While the response of individual varieties varied, an overall statistically significant trend was observed towards smaller leaf angles (e.g. more erect leaves) under deficient nitrogen conditions. In parallel with field experiments, greenhouse experiments utilizing sorghum plants grown under different levels of nitrogen availability were also conducted. These confirmed the increased erectness of sorghum leaves under nitrogen deficient conditions. In addition, RGB and hyperspectral images collected from this experiment were used to train machine learning models to classify individual pixels into six classes: nonplant pixels, panicles, stems, green leaves, senescing leaves, and dead leaves. With this new method, we were able to track the progression of senescence through the life cycle of individual sorghum plants grown under different nitrogen treatments. Adviser: James C. Schnable

Lettuce (Lactuca sativa) is one of the most popular leafy vegetables in the United States. A popular leafy vegetable harvested in its vegetative stage, cultivated lettuce has been selected for delayed flowering and insensitivity to photoperiod, both intentionally and unintentionally. In the past decades, the advancement in functional genetics in model organisms and the development of marker technologies have allowed fast and accurate mapping of quantitative trait loci (QTL) that control flowering time in lettuce. These past endeavors have been summarized in Chapter Two of this dissertation. In Chapters Three and Four of this dissertation, I mapped QTLs for two distinct and understudied components of flowering time in lettuce: daily floral opening time and photoperiod sensitivity. Chapter Three reported the discovery of two QTLs, qDFO2.1 and 8.1, that controlled daily floral opening time in lettuce. These are the first genetic loci reported to regulate floral opening. The study in Chapter Four revealed five QTLs on Chromosomes 1, 2 and 4 that explained photoperiod sensitivity in lettuce; these QTLs were distinct from loci associated with long-day flowering-time in lettuce. Chapter Four also identified a candidate gene as the functional ortholog of Arabidopsis CONSTANS in lettuce. These results supported the complex, networked architecture of the flowering time regulatory pathways in lettuce. Chapter Five highlighted the importance of microRNAs (miRNAs) in floral development. This chapter provided updated, tissue-specific miRNA and miRNA target annotations for lettuce. The diversity of DNA sequence variations at miRNA regions within the genus Lactuca was also characterized. The differential expression pattern of miRNAs between vegetative and floral tissues supported a model where archetypal miRNAs, miRNA156 and miRNA172, and their regulatory functions were conserved between Arabidopsis and lettuce. Chapter Six of the dissertation proposed promising future experiments to extend the novel methodologies developed in this dissertation and to further elucidate the molecular regulatory network for flowering time in lettuce. Overall, this dissertation found new angles to provide knowledge in the realms of genetics and genomics of flowering time regulation in lettuce. Results from these studies can be used to effectively accelerate vegetable breeding efforts.

In recent years, the North American region has seen increased usage of grafted vegetable transplants to reduce soil-borne disease incidence, increase tolerance to abiotic stress, enhance fruit quality, and increase yields over conventional nongrafted transplants. Grafting itself is a unique agrotechnology that merges a vegetable crop (scion) with the root system of another plant (rootstock) to form one transplant that benefits from both traits. In North America, a recent survey showed nearly 60 million grafted transplants are produced annually for fruiting vegetable crops, including tomato, watermelon, cucumber, pepper, eggplant, and muskmelon. Due to the limited number of nurseries in North America, transplants are commonly shipped 3-5 d to distant producers and have reportedly experienced chilling stress during transportation that reduces transplant quality and may affect post-transplanting performance. However, few studies have explored the specific effects of transport-related chilling stress on seedling quality and post-transplanting development. Using watermelon (Citrullus lanatus), a highly chilling sensitive member of the Cucurbitacea family, we examined effects of acute chilling stress on seedlings quality and post-transplanting development. When grafted and nongrafted seedlings were exposed to 0 - 48 h of 3 °C chilling, we found that seedling quality and post-transplanting development were unaffected by chilling. However, when the chilling temperature was reduced to 1 °C, seedlings exhibited increased visual damage of seedlings with longer durations, decreased chlorophyll fluorescence (Fv/Fm), and increased delays in the number of days it took for plants to reach male and female flower anthesis after transplanting. Nongrafted plants had longer delays in days to flower anthesis than grafted plants, indicating that grafted plants may have been more resistant to chilling or had enhanced flower primordia development that reduced the effects of acute chilling. Based on these findings, we chilled nongrafted watermelon for various durations at chilling temperatures between -0.4 and 1.2 °C to determine if the chilling stress could be a cumulative response below a specific threshold temperature. Threshold temperatures, or base temperatures (BT), between 3 and 15 °C were found so that various measures of seedling quality were highly correlated with chilling degree hours (CDH). We found that seedling damage and reductions to Fv/Fm were highly correlated with CDH accumulation at base temperatures of 15 and 3 °C, respectively. Further, delays in female flower development increased linearly with CDH when a BT was selected as 4 °C. Therefore, reproductive development was directly inhibited by the chilling temperatures, and 4 °C was a critical temperature that caused post-transplanting reproductive delay. This result was confirmed when using the CDH model to analyze our previous results, indicating that this model can be used to predict delays in plant reproductive development when given various chilling conditions. Our results suggest that long-distance transportation of transplants above 4 °C will allow proper post-transplanting development without delays.

Temperature is recognized as a primary influence on grapevine phenology and has been used to classify the climates and regions suited for growing specific grapevine varieties. Many models utilize average temperature to correlate with phenological stages and predict the timing of specific phases. Because average temperature does not account for the hourly temperature or the change in temperature from day to night, it is not known to what degree diurnal temperature range (DTR) influences grapevine phenophases. Utilizing controlled growth conditions (phytotrons) the objective was to determine if DTR impacted the rate of leaf appearance, time of flowering or percent fruit set separate from average temperature (Experiment 1); and to determine if thermal time measured as growing degree hours (GDHs) impacted the rate of leaf appearance, time of flowering and or the degree of fruit set (Experiment 2). For Experiment 1, the time of flowering occurred 3.5 (P

The challenge to produce more food under sustainable agricultural practices is to develop more efficient systems in the use of natural resources, avoiding agrochemical contamination, and prediction of yield under a changing environment. This dissertation has focused on providing information of the physiological and floral gene expression behavior of avocado trees under different environmental conditions building upon three different chapters: (1) the identification of water-use efficient avocado varieties using leaf carbon isotopic composition (δ 13C), (2) the analysis of the physiological behavior of salinity-tolerant avocado rootstocks, and (3) the analysis of the effects of temperature, soil moisture, and light intensity on the temporal pattern of floral gene expression and floral intensity in avocado. In the first chapter, we found carbon isotope composition measurements to be useful for identifying water-use efficient plants. In the second chapter, the relationship between the physiological performance, health and productivity of avocado exposed to a salinity treatment is described. Low photosynthetic rate and canopy damage describe the effect of salinity on avocado yield. In the third chapter, we successfully identified the gene expression profile of putative floral genes when avocado flowering is promoted by low temperature. The results from the floral gene expression analysis in avocado suggest that the significantly greater bud expression levels of LFY and AP1/FUL promoted by low temperature were sufficient to confer bud determination, since transferring the trees from low to warm temperatures did not prevent flowering. Overall, the first two chapters successfully allowed the identification of trees or cultivars that are saline tolerant or water-use efficient while the gene expression analysis showed how the expression of putative floral genes are coordinated with bud determination, suggesting a role during the reproductive development in P. americana.

Plants constantly engage and interact with the environment and respond to the changes in conditions like temperature, water, and photoperiod, by regulating expression of genes of multiple regulatory and signaling pathways. Insight into these pathways and their participants has provided and will provide candidates to improve various agronomically important traits in crops through marker-assisted breeding and genetic manipulation. With this aim in mind, in the present study, I attempted to identify key candidate genes that are involved in the regulation of; i) plant response to low temperature stress, ii) plant roots’ response to soil moisture content and iii) flowering time. identified and studied the expression of C-repeat binding factors (CBFs)-like genes and CONSTANS (CO)-, FVE- and FCA-like genes in alfalfa (Medicago sativa L.), a major forage crop in United States and worldwide. C-repeat binding factors (CBFs) are key transcription factors involved in plants’ response to low temperatures. The results based on the gene expression and its correlation with freezing tolerance in alfalfa suggested that two MsCBFl genes might play important role in freezing tolerance in alfalfa. Through expression analysis of CO-like, FVE-like and FCA-like genes in different tissues, at differential stages, and under circadian control, I identified several genes in CO-, FVE- and FCA-like gene families that are potential functional homologues involved in flowering time control. These candidate genes, once function is confirmed, can be used to delay flowering in alfalfa which will lead to higher biomass production and higher quality forage due to delayed senescence, a trait associated with flowering. An enhancement in biomass production can also pave the way for its use in cellulosic-based biofuel production. To understand the molecular basis of plant roots’ response to soil moisture gradient in major crops, a phenomenon known as hydrotropism, I attempted to identify the functional homologue of Arabidopsis MIZ1, one of the key regulators of hydrotropism, in maize (Zea mays L.). Through analysis of expression of MIZ1-like genes in maize, one gene, ZmMIZ1l-K appeared to be the candidate functioning in hydrotropic response. This study is the first attempt at understanding molecular players in hydrotropism in a crop plant and could be potentially used to enhance water acquisition of crop plants and thus their performance especially under drought conditions. My research demonstrated that the candidate gene approach I took can be a first step to effectively identify the key players in the regulatory pathways in major crops. Through studying these genes, I also provided great insight into the complexity of molecular processes in responding to environmental cues in crop plants. Additional studies are needed to confirm the gene functionalities and their key roles in these processes. The molecular participants can then be used as resources to develop better crop varieties that could perform efficiently especially under more severe environmental stresses like drought and harsh temperatures.

Transport is an essential component of the regulation of polyamines, but to date only onefamily of Polyamine Uptake Transporters (PUTs) have been characterized in plants, and theirimpact on polyamine regulation has not been defined. Here we show that knockout mutants ofput5 in A. thaliana, promote early flowering and result in plants with smaller leaves, thinnerstems, and fewer flowers. In contrast, heterologous expression of the rice gene OsPUT1 in A.thaliana using the Put5 promoter at 22°C produced plants with larger leaves, a two-week delayof flowering and more flowers and siliques. Similar effect on leaf size, flowering time andnumber of siliques also were observed in transgenic plants with constitutive expression ofOsPUT1 or OsPUT3. The delay of flowering was associated with significantly higher levels ofspermidine and spermidine conjugates in the leaves prior to flowering. These experiments outlinethe first genetic evidence for the control of flowering by polyamines. How polyamine levelscontrol the timing of flowering at a molecular level is not yet known, but this delay of floweringhas been demonstrated to be upstream of the stimulation of flowering by the gibberellin andtemperature sensitive response pathways.It has been assumed that there exists a single cytosolic pathway for the synthesis ofputrescine in A. thaliana. Here we show that A. thaliana and Glycine max, have a chloroplastlocalizedputrescine biosynthetic pathway. This pathway comprises of arginine decarboxylaseand an agmatinase to synthesize putrescine from arginine. Analysis of expression data suggeststhat it is the major route of putrescine synthesis in response to stress signals.Since compartmentation of polyamines has been demonstrated to play an essential role inpolyamine homeostasis, the identification of other types of polyamine transporters is a criticalknowledge gap. We show here that PDR11 is an important long-distance transporter ofpolyamines in plants and that OCT5 functions as a vacuolar transporter for polyamines. Taken ,these findings will accelerate interest in manipulating polyamine metabolism to generate morestress responsive crop plants.

Four thousand years ago, maize began migrating out of Mexico and into the geographically diverse Southwestern US (1, 2). Maize spread quickly through the lowland deserts, but full maize agriculture in the uplands lagged for another 2,000 years (1, 3). Why did maize agriculture fail to fully develop, despite the persistent presence of maize in the uplands? I tested the hypothesis that early maize in the Southwest US was not adapted to the uplands, specifically testing archaeological maize from the uplands at the beginning of agricultural intensification for early flowering. To better understand temperate adaptation in maize, I led a project to generate tools for accurate imputation and projection of maize inbred haplotypes onto related individuals. We then projected whole genome sequence onto five diverse modern inbred maize populations to further elucidate the genetic architecture of maize flowering through mapping, machine learning and cross population predictions. We find that the genetic architecture of flowering is tightly linked to the temperate-tropical differentiation in American germplasm for four of the five populations, and suggest an independent temperate adaptation occurred in China after 1500. We also find that populations with individuals across the North American temperate adaptation predict others well. We further test that good cross population prediction extends to modern Southwestern landraces by developing a mapping population for flowering time, and show that modern inbred populations can predict divergent modern landraces with high prediction accuracy for days to flowering. We extend flowering predictions to archaeological maize samples dating to the early period of agricultural adoption, and find that this population was already adapted. Using SNPs with the greatest population differentiation over the extremes of temperate-tropical adaptation, we find that temperate adaptation happened in situ in the Southwest, and early southwestern peoples selected on primarily standing variation. 1. J. B. Mabry, ed. Las Capas: Early Irrigation and Sedentism in a Southwestern Floodplain (Center for Desert Archaeology, Tucson, 2008), Anthropological Papers. 2. E. K. Huber, in Fence Lake Project (Statistical Research Inc., Tempe, 2005), vol. 1: Introduction and Site Descriptions of Technical Series. 3. R. G. Matson, B. Chisholm, Basketmaker II Subsistence: Carbon Isotopes and Other Dietary Indicators from Cedar Mesa, Utah. Am. Antiq. 56, 444–459 (1991).

AbstractPlant phenology, climate and climate changeJuliet OshiroPhenology, or the timing of life cycle events, is often cued by climate in plants. Many studies of plant phenology and climate use climate data from models, such as PRISM (prism.oregonstate.edu), which are generated from data collected at 2 m above the ground (above many plants), and are averaged over 4 km2 grid cells. We compared temperature recorded near-the-ground, at vegetation level, to PRISM’s temperature at ten study sites in Santa Cruz County representing grassland and sandhill habitats and a range of distances from the coast, elevations, and slope/aspects. Temperature near-the-ground was generally larger than PRISM’s, and the difference between the two sources varied with elevation, distance from the coast, and aspect. We reconstructed microclimate near-the-ground at the 10 sites from 1982-2016, and assessed how it has changed over time. Changes were minimal, but minimum temperature increased, and inter-annual variability in maximum temperature and winter rainfall changed. We then examined how these data have influenced plant phenology using historical records (1989-1998) and resurveys (2011-2015) of the 10 study sites. Higher minimum temperature and lower precipitation caused earlier first and last flowering dates in the resurveys (versus historical) and at the coast (versus inland), though variation among species was high. We also examined how functional traits influenced species-specific phenological responses to climate. We hypothesized that phenological response to climate varied among species that avoided versus tolerated warm, dry summers, but our results did not support this. Responses varied among species with different leaf flatness, and whether the species was native or not native to California. The season in which species were sensitive to climate also influenced phenological response. Finally, we manipulated minimum temperature, maximum temperature and precipitation in growth chambers. In higher maximum temperatures, plants began flowering earlier, and in drought and high maximum temperatures, plants stopped flowering later, and flowered for a shorter period. In these conditions plants also used water more efficiently, and therefore were smaller and had lower fitness. Overall, this dissertation shows that phenological response to climate near the ground is trait based, and that phenological change impacts plant performance.

Changing climate has been linked to changes in phenology, the timing of biological events such as leaf out and flowering. Phenological changes of herbaceous plants and shrubs remain less studied and thus less understood. This study takes place within the Boreal Forest Warming at an Ecotone in Danger (B4WarmED) project in Minnesota, examining phenological responses of herbaceous plants, shrubs, and tree seedlings to warming and reduced rainfall over. Warming extended the growing season, primarily through earlier leaf unfolding in the spring. Flowering advanced under warming, though more so for fall blooming species than for spring blooming species. Warming did not alter senescence for most species, though several species did delay senescence with warming. Community level phenological responses of the groundlayer and tree seedlings were not altered by rainfall treatments. Fall blooming species altered flowering phenology to rainfall manipulation. Two species diverged in flowering time in the warmest, driest treatment.

A field experiment was conducted to quantify the carbohydrate distribution in perennial (Lolium perenne L.) and Italian ryegrass (Lolium multiflorum L.) seed crops from anthesis to harvest. To do this, first year crops of diploid perennial ryegrass (‘Samson’) and a diploid Italian ryegrass cultivar (‘Progrow’) were sown on 14th May and 16th September 2015. A subsequent application of Moddus® (a.i. 250 g/l Trinexapac ethyl) plant growth regulator at three rates (0, 1,600 and 3,200 ml/ha) was applied at Zakoks growth stage 32. Moddus® increased perennial and Italian ryegrass seed yield by approximately 29% from 1,600 ml/ha (1,651 kg/ha) to 3,200 ml/ha (2,134 kg/ha), with similar yields between 0 ml/ha (1,296 kg/ha) and 1,600 ml/ha. The seed yield increase in perennial and Italian ryegrass was achieved through increased number of seed produced per spikelets. The vegetative stem length in perennial and Italian ryegrass was reduced from 62 cm to 41 cm by application of 1,600 ml/ha of Moddus® and further reduced to 36 cm with 3,200 ml/ha. The perennial ryegrass’s stem component dry weight and water soluble carbohydrate (WSC) concentration were constant from anthesis through untill harvest. Despite Moddus® reducing the stem length and its storage capacity a large amount of WSC remained in the stem components. Perennial ryegrass had the capacity to fill and improve seed yield accumulating WSC simultaneously and converting this into starch up to harvest at 37 days after anthesis (DAA) with little or no remobilisation of WSC in the stem. Moddus® decreased Italian ryegrass’s stem components dry weight by 37% and WSC by 42% . The effect of Moddus® suggests the source and sink relationship between the stem and developing seed has been modified.The Italian ryegrass seed dry weight increased up to 7 DAA and declined until harvest with WSC and starch illustrating a similar pattern. When maximum seed weight, WSC and starch was achieved the stem component begun to decline. This demonstrates that Italian ryegrass stem may play a role in seed filling under conditions of limited assimilate supply with stem assimilate reserves remobilised to the developing seed. Moddus® reduced overall lodging at the highest rate of 3,200 ml/ha and delayed the onset of lodging at the lower rate. Lodging progressed more quickly and had a greater effect on perennial ryegrass than Italian ryegrass. Lodging reduced perennial ryegrass seed yield with less WSC in the seed of control plants of 0 ml/ha (49.91 mg) compared to the highest Moddus® treatment of 3,200 ml/ha (59.63 mg). Italian ryegrass showed similar seed WSC between the control (88.6 mg) and the two Moddus® treatments of 1,600 ml/ha (94 mg) and 3,200 ml/ha (85.5 mg). This showed the degree which two ryegrass species seed sinks can compete for available assimilates. The relative lower seed depression in lodged Italian ryegrass compared to the perennial indicates a higher compensation potential. The Italian showed the ability to partition more assimilate reserves from the stem and leaves to support seed growth and development.

Abstract: Southeast Asian dipterocarp forests are highly diverse tropical forest communities, with the family Dipterocarpaceae alone comprising hundreds of species. Dipterocarps are remarkable in that they exhibit supra-annual mass flowering events, which occur in irregular intervals of two to ten years, normally involving several dipterocarp species and sometimes including many other plant families as well, a phenomenon known as general flowering event. Dipterocarps are a leading species group on 85% of Southeast Asia’s forested land base and they are also commercially important, representing a quarter of global consumption of tropical timbers. Southeast Asia’s dipterocarp forests are also one of the most threatened tropical ecosystems in the world. Only 16% of the total original forested area remains classified as primary forest in Southeast Asia and less than 6% in the Philippines, which is a focus of this thesis. The overall objective of this thesis is to support and improve reforestation and community forestry initiatives in dipterocarp forests by contributing ecological insight and compiling local community knowledge, and by addressing major impediments to successful forest restoration in Southeast Asia. The first issue is the biology of dipterocarp reproduction that makes it hard to manage natural regeneration as well as reforestation. It is logistically difficult to mobilize resources to collect short lived dipterocarp seed without knowing in advance when flowering will occur. This thesis research investigates what environmental factors drive dipterocarp mass flowering and tests alternative resource accumulation and trigger models to predict mass flowering. Using a variety of candidate predictor variables (precipitation, cloud cover, minimum temperature and El Niño indices) a plausible environmental trigger could not be found (median AUCs around 0.55 indicating near random predictions), while the best resource accumulation model had a median AUC of 0.70, which could be improved to 0.75 when the date of previous flowering was included in the model. Further, the analysis revealed that a simple resource accumulation by individual trees can cause inter- and intraspecific flowering synchronization leading to community-wide general flowering events. The second issue is a lack of knowledge of which dipterocarps and which other native species are suitable for reforestation. Community based forest management programs typically use readily available exotic species that may not be desired by the local communities. Choosing species for reforestation programs or community forestry in species-rich tropical rainforest ecosystems is a complex task. Reforestation objectives, social preferences, and ecological attributes must be balanced to achieve landscape restoration, timber production, or community forestry objectives. In a case study for an upland tropical rainforest in the Philippines, socioeconomic preference in five forest-dependent communities were surveyed. In addition, ecological suitability of tree species for open-field plantations was inferred from growth rates, density and frequency of native tree species in long-term monitoring plots. Notably, ecological suitability indicators and socioeconomic preference ranks were generally negatively correlated, with few species being classified as both ecologically suitable and socioeconomically valuable. The results also highlight that reforestation species must be carefully chosen, and that species-rich tropical rainforests are not an easily renewable natural resource. Secondary and planted forests do not serve socioeconomic needs of forest-dependent communities as do original native forests

Subterranean clover cultivars available in New Zealand have been currently and historically reliant on the Australian market and research. Currently there is very little information available which is related to cultivars performance under a cooler New Zealand climate. This study evaluated 11 subterranean clover cultivars and their performance in mixed swards. On average cultivars throughout this experiment performed poorly in their germination ability, under lab conditions (15°C). Large proportions of these seeds remained hard with the earliest flowering culivar ‘Monti’ consisting of 67% hard seed, while a later flowering cultivar ‘Napier’ consisted of 33% hard. Along with hardseededness a small proportion of seed throughout all cultivars were unable to germinate and defined as ‘dead’, suggesting issues during the development stage of the seeds. ‘Narrikup’ a mid-flowering cultivar, outperformed all other cultivars during the emergence stage, with 293 seedlings/m2 on the 5th a March and consisted of a high potential to bury its burrs (7/9) (Nichols et al. 2013). ‘Narrikup’ showed the ability to regenerate and survive throughout the 2015 season, still consisting of a 15% sub clover cover by the end of September. The cultivar ‘Antas’ showed huge potential in its first year with the highest overall yield in September 2014 (760 kgDM/ha) and highest sub clover content in November 2014 (2710 kgDM/ha). However in the following year ‘Antas’ performance dropped drastically, with its inability to regenerate. This was attributed to its subspecies family brachycalycinum, unlike subterraneum and yanninicum, brachycalycinum cannot actively burr its burrs and is therefore not protected from the aerial environment, effecting its seed potential to develop seed (Francis et al. 1972; Collins et al. 1976). Both ‘Narrikup’ and ‘Antas’ presents how essential the burial process can be under the cooler New Zealand climate. Older cultivars including both ‘Mt Barker’ and ‘Woogenellup’ (late flowering cultivars) began poorly in their ability to regenerate reaching only 47 seedlings/m2 and 78 seedlings/m2 respectively by the 5th of March. By the final visual score in spring however these cultivar had recovered with ‘Woogenellup’ consisting of around 17% sub clover cover and ‘Mt Barker’ roughly 10%. ‘Denmark’ a later flowering cultivar (Nichols et al. 2013) also showed an increase in performance by the end of spring with 11% sub clover cover. Currently studies throughout New Zealand have claimed late flowering cultivars will out compete both mid to late flowering cultivars (Chapman 1992; Collins et al. 1976; Smetham and Ying 1991; Sheath and Richardson 1983), under this experiment however this was not an obvious trend.

Abstract: Understanding the flowering gene complex in bread wheat is important to utilize the maximum production potential in a time-limited growing season. Vernalization (Vrn), photoperiod (Ppd) and earliness per se are the three genetic constituents of the flowering gene complex. A series of experiments were conducted to explore the role of each genetic constituent in Canadian spring wheat germplasm. The first experiment revealed vernalization and photoperiod gene frequency and effects in Canadian germplasm released between 1885 and 2008. Vernalization insensitive Vrn-A1a is the most frequent allele in the Canadian hard red spring class and Vrn-B1 is more frequent in Canadian soft white spring class. The photoperiod sensitive allele (Ppd-D1) is being replaced with the insensitive allele, Ppd-D1a, in all modern Canadian germplasm. An overall analysis of the data for the CWRS class revealed an average reduction of 0.04 days/year in maturity and an increase of about 8 kg/ha/year in grain yield. A second study was conducted on the Cutler × AC Barrie population to map and characterize the earliness per se QTL. Three QTLs of earliness per se affecting days to flowering and maturity were mapped on chromosomes 1B (QEps.dms-1B1 and QEps.dms-1B2) and 5B (QEps.dms-5B1). Two grain yield QTLs were mapped on chromosome 5B. The photoperiod insensitive allele Ppd-D1a interacted in an additive fashion with QTLs for flowering and maturity times. The earliness per se QTL QFlt.dms-5B.1 together with Ppd-D1a can induce earlier flowering and could help to elongate grain filling duration for higher grain yields. A comparative study of Vrn alleles suggests that the presence of Vrn-D1 along with Vrn-A1a and Vrn-B1 confers higher grain yield with similar maturity compared to all other Vrn gene groups in soft white spring wheat and we suggested the inclusion of Vrn-D1 allele in elite Canadian germplasm, which has been overlooked in the past. In a final study we found that early flowering and maturity conferred by insensitive vernalization alleles Vrn-A1a and/or Vrn-B1 has not conferred any yield advantage under organic conditions. The results also revealed that there is significant genotype × environment interaction and breeding for organic production should be practiced under organic conditions.

This dissertation is divided into two parts. Chapters 1 through 3 are interdisciplinary and focus on legal and scientific perspectives regarding the regulation of genetically engineered crops. Chapters 4 and 5 evaluated the environmental factors that control flowering in Pennsylvania sedge (Carex pensylvanica Lam.). The commercial potential of genetically engineered (GE) crops has not been fully realized in the United States due to environmental litigation that dramatically affected the pace of GE crop development and deregulation. The USDA's Animal and Plant Health Inspection Service (APHIS) regulates GE crops. However, litigation initiated by nongovernmental organizations exposed APHIS's vulnerability to lawsuits under the National Environmental Policy Act. We concluded in chapters 1 and 2 that APHIS did not adequately evaluate the environmental risks of novel crops, and thus left itself open to litigation. In Chapter 3, we described how the biotechnology industry is attempting to avoid regulation of GE crops through the creation of a non-plant pest loophole.Pennsylvania sedge is an upland forest sedge with horticultural potential as a low maintenance groundcover. For large plantings, achenes are preferred, but Pennsylvania sedge typically produces few achenes in its native habitat. As a first step in improving achene production, Chapter 4 evaluated the effect of vernalization and photoperiod on floral initiation and development. We concluded that Pennsylvania sedge is an obligate short day plant that does not require vernalization for flowering. Plants flowered when exposed to daylengths of 6 to 12 hours. Flowering was completely inhibited with 14-hour photoperiods. Chapter 5 examined the environmental factors that control floral gender sequence and inflorescence culm heights. Plants were found to be determined and florally initiated in the fall in the northern United States. A post-floral induction chilling treatment (winter) was necessary to produce protogynous flowering and normal inflorescence culm elongation.

Vernalization is defined as the response to prolonged cold exposure required for acquiring the molecular competence necessary to undergo floral transition. FLOWERING LOCUS C (FLC), a potent floral repressor in Arabidopsis, is highly expressed before vernalizing cold treatment but is repressed during prolonged vernalization. VERNALIZATION INSENSITIVE 3 (VIN3) is a Plant HomeoDomein (PHD)- containing protein that is required for establishing vernalization-mediated repression of FLC. The induction of VIN3 is one of the earliest molecular events in vernalization response and its expression is intimately linked to prolonged cold exposure. However, mechanisms underlying VIN3 induction remain poorly understood. The constitutive repression of VIN3 in the absence of cold is due to multiple repressive components, including a transposable element-derived sequence, LIKE-HETEROCHROMA TIN PROTEIN 1 (LHP1), and POLYCOMB REPRESSION COMPLEX 2 (PRC2). Furthermore, the full extent of VIN3 induction by vernalization requires activating complex components, including EARLY FLOWERING 7 (ELF7) and EARLY FLOWERING IN SHORT DAYS (EFS). Dynamic changes in the histone modifications present at VIN3 chromatin during vernalization were also observed, indicating that chromatin changes play a critical role in regulating VIN3 induction. However, VIN3 induction by vernalization still occurs in the absence of activation complexes and de- repression of VIN3 in the absence of the repressive complexes is not sufficient for achieving complete induction. Thus, unknown cold-influenced regulators responsible for achieving maximum VIN3 induction during vernalization must exist. Therefore, forward genetic screening was undertaken to elucidate upstream regulators of VIN3. Molecular characterization of T-DNA mutant populations elucidated two interesting mutants: a mutant that ectopically expressed VIN3 before cold (ectopic VIN3 induction, evi1) and mutants that failed to induce VIN3 during vernalization (defects in VIN3 induction, dvi1). FLC is over-expressed in dvi1 despite its failure to induce VIN3 expression during vernalization, suggesting that this mutant may regulate both VIN3 and FLC. In evi1, FLC is hyper-repressed after 40 days of vernalization, leading to an acceleration of flowering time. These results indicate that regulators of VIN3 in the vernalization pathway exist and that these regulators may use different mechanisms in order to influence VIN3 expression.

Lucerne (Medicago sativa L.) is the highest yielding temperate forage legume, and fixes as much as 360 kg N/ha/year. Its establishment in dryland Canterbury depends on understanding critical factors such as sowing time and inoculation techniques that increase chances of seedling survival and stand persistence. Measurements occurred for a complete growing season after sowing ‘Stamina 5’ lucerne inoculated with peat, lime coating, ALOSCA ® granules and a bare seed control on 4 October, 4 November, 2 December 2010 and 10 January and 7 February 2011 at Lincoln University Canterbury. No emergence differences were observed from the different inoculants. Coated seed produced a higher initial plant population of 331 plants/m² which was 68% of the 490 seeds/m² sown. It also had the highest population 12 months later although seedling numbers had declined by 27%. Regardless of differences in plant population per treatment, dry matter (DM) yields were not different. Accumulated crop DM yields were however different among sowing dates and decreased with each successive sowing. SD 1 (4 October) gave the highest yield of 15 t/ha whilst SD 5 (10 January) yielded only 2.5 t/ha. Lower DM yields in the later sowing dates were explained by less intercepted light and reduced radiation use efficiency (RUE) probably due to changes in DM partitioning from shoots to roots. Specifically, SD 5 had a longer phyllochron (65 °Cd per node) than SD 1 (44.6 °Cd/node) at a base temperature of 5 oC. No differences were observed in canopy architecture for the different sowing dates as shown by a common extinction coefficient of 0.75. RUE for shoot production (RUEshoot) in regrowth crops of all sowing dates was 1.1±0.065 g DM MJ of intercepted photosynthetically active radiation (PARᵢ). This was 18% higher than the 0.9±0.033 g DM/MJ in seedling crops. Crops from the latest sowing grew 1.84±0.26 kg/ °Cd compared with 3.84±0.22 kg/ °Cd for the earliest sowing. Thermal time accumulation to 50% buds visible (Tt0-bv) decreased from 686 °Cd to 651 °Cd as the photoperiod lengthened in summer from 13 to 15 hours for SD 1 and SD 2. Genotypic characterisation of bacteria isolated from inoculated root nodules and its identification using PCR and 16S methods generated bands for each isolate. These were sequenced and identified to genus level revealing the presence of seven common genotypes. Amongst these, Rhizobium tibeticum was the most dominant species with an occurrence of 14.5%. Ensifer meliloti, the rhizobia responsible for nodulation and subsequently N₂ fixation in lucerne was the second most dominant with an occurrence of 14%. It was also found present in all inoculant carriers characterised but not the bare seed control. These results suggest dominance and effectiveness of resident soil bacteria over introduced Ensifer meliloti in nodulating lucerne. The study emphasises the importance of sowing early in spring or summer to take advantage of the longer growing season and the use of the summer fallow to supplement soil moisture for successful lucerne establishment.

Variety, temperature and viticulture practices (e.g. pruning, trimming, cluster thinning, irrigation etc.) all have an influence on grapevine (Vitis vinifera L.) phenology and berry maturation. Process-based phenological modelling which assumes temperature as the driving factor can be used to predict differences in development among varieties. Management practices including those that alter the Leaf Area to Fruit Weight (LA:FW) ratio may also influence the timing of key phenological stages and berry maturation. Regression modelling the relationship between LA:FW ratio and phenology or maturation parameters will enable a better understanding of these responses for different varieties. The aims of this work were 1) to characterise the differences between varieties for three key phases of development: flowering, veraison and the time to reach a target sugar concentration set at 200g/L using process-based phenological models; 2) to investigate different methods of characterising veraison as a phenological event to define the value of alternate objective measures; 3) to investigate the influence of altering the LA:FW ratio via trimming shoots (reducing leaf area) or removing crop (reducing the fruit weight) on two occasions (shortly after fruit set or at veraison) on the time of veraison and berry maturation parameters (soluble solids, titratable acidity, pH and berry weight). 2) and 3) were considered for two different varieties, Pinot noir and Sauvignon blanc. Linear and non-linear regression modelling was used to explore the relationships in 2) and 3). For the first aim, the Grapevine Flowering Veraison (GFV) model that uses a linear thermal summation of average daily temperatures from the 60th day of the year (in the Northern hemisphere) and a base temperature of 0°C was used to classify 95 varieties for the parameter F* (the accumulation of forcing units) for the time of 50% flowering and 105 varieties for 50% veraison. For maturity, data corresponding to a threshold sugar concentration of 200g/L were calibrated for seven different process-based models and calibrations calculated from either daily mean, daily maximum, average or hourly temperatures. The best fit model was the Sigmoid model in terms of efficiency and parsimony - assessed by the lowest Akaike Information Criterion (AIC), model efficiency, (EF), and Root Mean Squared Error (RMSE) - and the GFV model in terms of parsimony using daily mean temperatures. 35 varieties were parameterised and classified using both models for the day of the year to reach a sugar concentration of 200g/L. Seven different ways of assessing veraison were used to determine the relationship between soluble solids concentration and the measurement considered. Soluble solids ranged from 7 to 9 °Brix for the different methods. 8 °Brix was found to be a simple robust measure that allows comparison between different varieties, seasons and sites and was used in subsequent modelling to investigate the influence of LA:FW ratio on phenology and berry composition. Altering the LA:FW ratios of two varieties (Pinot noir and Sauvignon blanc) by trimming main shoots (leaf removal) delayed veraison, and both leaf removal and crop thinning influenced the dynamics of soluble solids accumulation; leaf removal slowed rates of soluble solids accumulation and resulted in lower concentrations of soluble solids at harvest whereas crop removal had the opposite effect. Titratable acidity, berry weight and pH were unaffected by the LA:FW ratio changes. The method of removing crop (removing all bunches on alternate shoots versus removing alternating bunches-apical then basal- from each shoot) did not influence the response but the presence of laterals advanced soluble solids accumulation. Non-linear exponential regression models across a wide range of LA:FW ratios best described the following different parameters for both varieties: Day of year to 8 °Brix, duration from 8 to 14 °Brix and soluble solids at harvest. The classification of flowering, veraison and the day to reach a sugar concentration of 200g/L are the most extensive to date within the literature. The methodology developed for these classifications and to assess the quality of prediction could also be applied to other crops. LA:FW ratio manipulations can shift the timing of keys events, such as veraison and soluble solids accumulation; the regression results indicated that it is possible to delay timing by the same magnitude of time as observed for between varietal differences in timing. This represents a potential tool to manipulate changes in development under future climate scenarios.

For successful reproduction, angiosperms must form fertile flowers in the appropriate positions and at the appropriate time. The timing of flower formation is especially important for annual plants, such as the model Arabidopsis thaliana used in this study. Floral fate is controlled by a set of genes termed floral meristem identity genes, the most important of which is the plant-specific transcription factor LEAFY (LFY). LFY’s function can be divided into two phases, which are both temporally and genetically separable. In the first phase, LFY controls the expression of genes, such as other floral meristem identity factors, that control phyllotaxy and organ number. In the second phase, LFY is necessary for activation of the floral organ identity genes, which are responsible for differentiating the organs of the flower from each other. LFY is a transcription factor that does not have transcriptional activation or repression activities on its own and therefore must act in multiprotein complexes. Region- and stage-specific control of LFY target genes is provided by co-factors. However, until very recently little information was available about other factors that are present in such LFY-containing complexes. This work aims to identify components of LFY transcriptional complexes and characterize their function(s) in flower development. We demonstrate that LFY acts as a homodimer, which is mediated by a domain that is conserved across land plant LFY orthologs, suggesting that dimerization is important for the function of the entire LFY family. We report the isolation of putative LFY-interacting proteins and their preliminary characterization. Finally, we present an in depth analysis of one such LFY-interacting protein, FRIEND OF LEAFY1 (FOL1), which is a novel C2H2 zinc finger transcription factor. FOL1 is expressed in inflorescence meristems, floral meristems, male and female gametophytes and in embryos. Based on gain of function and loss of function analyses, FOL1 appears to function in control of meristem size and gametophyte development. We also discuss FOL1’s physical and genetic interactions with LFY. The conservation of LFY sequence and functions across angiosperms suggests that most if not all of the LFY-interacting proteins identified in Arabidopsis will also function with LFY orthologs in other plants, including important crops. Therefore this work will provide a basis for the development of new strategies to increase agronomical values such as increased yield by manipulating LFY-interacting proteins in economically important crops.

SHORT HYPOCOTYL UNDER BLUE 1 or SHB1 was previously identified as a negative regulator of the cryptochrome-mediated blue light response in Arabidopsis early seedling development. shb1, a T-DNA insertional loss-of-function allele, showed a short hypocotyl phenotype only under blue light, whereas shb1-D, a gain-of-function over-expression allele, showed a long hypocotyl phenotype under blue as well as red or far red light. SHB1 is a nuclear protein and contains a N-terminal SPX domain and a C-terminal EXS homologous to yeast SYG1 protein family. Using a biochemical approach, I found that SHB1 is anchored to a large protein complex through both of its SPX and EXS domains. In a genetic screen, I identified five mis-sense mutations within or nearby its N-terminal SPX domain and these mutation impaired its biological function and proper assembly into a protein complex. In contrast, the C-terminal EXS domain, when over-expressed, created a dominant negative phenotype and interfered with the assembly of the endogenous SHB1 into a native protein complex. SHB1 also functions in flowering timing control and this involvement is likely related to its light signaling activity. In addition, SHB1 plays a specific role in a quite different developmental phase, seed development. SHB1 regulates the timing of endosperm cellularization and promotes the subsequent embryo development through its control over both cell division and cell expansion. SHB1 associates with the promoters of MINISEED3 (MINI3), a WRKY transcription factor gene, and HAIKU2 (IKU2), an LRR receptor kinase gene in vivo, and activates the expression of these two genes required for endosperm development. In summary, SHB1 plays a novel signaling role in both Arabidopsis seed and early seedling development, and this conserved function may be implicated for some SHB1-like proteins in many other organisms.

Recent studies have indicated that the plant nuclear pore complex (NPC) plays important roles in several processes, including plant-microbe interactions, hormone signaling, and stress tolerance. However, both the protein components of and the various activities associated with the plant NPC are poorly understood. Here, I focused on analyzing two plant NPC-associated proteins located at opposite sides of the NPC. First, I identified an Arabidopsis protein called NUCLEAR PORE ANCHORE (NUA) as the homolog of mammalian Tpr, yeast Mlp1/Mlp2, and Drosophila Megator, long coiled-coil proteins associated with the inner basket of the NPC and involved in mRNA export, telomere organization, spindle pole assembly, and unspliced RNA retention. Four T-DNA insertion mutants of nua were identified, which comprise an allelic series with increasing severity for several correlating phenotypes, such as early flowering, increased abundance of SUMO conjugates, and altered expression of flowering regulators. Together with the genetic interaction between NUA and ESD4 (a SUMO protease), these data suggest that NUA is a conserved component of NPC-associated steps of sumoylation in plants. Defects in SUMO homeostasis affect signaling events of flowering time regulation and additional developmental processes. Secondly, I identified a plant-specific family of NPC-associated membrane proteins, WPP domain-interacting proteins (WIPs), which bind to the WPP domain of Arabidopsis Ran GTPase-activating protein RanGAP and are responsible for the NPC-association of RanGAP. Mammalian RanGAP targeting to NPC during interphase and to kinetochores during mitosis requires interaction of its sumoylated C-terminal domain with nucleoporin Nup358/RanBP2. In contrast, I demonstrated that binding to the coiled-coil domain of WIP is a plant-unique mechanism for targeting RanGAP to the NPC. Moreover, I presented data to suggest that the targeting of plant RanGAP appears to involve different mechanisms during different stages of the cell cycle and in different tissues. Taken together, my research demonstrates the involvement of NUA in regulating SUMO homeostasis and plant development and supports an independent evolution of RanGAP targeting - and thereby the spatial positioning of the Ran cycle - in different kingdoms. The conservation of NUA and the uniqueness of RanGAP anchoring illustrate that evolutionarily the plant NPC is both conserved and diversified.

Japanese stiltgrass is a nonnative invasive grass that occurs in many habitats and is a management concern throughout the eastern United States. Experiments were conducted to address biological and ecological considerations for effective management of Japanese stiltgrass and restoration of native plant communities. Conventional management recommendations emphasize Japanese stiltgrass removal in autumn prior to flowering. Investigations of Japanese stiltgrass reproductive biology were conducted to assess biological considerations that impact such management strategies. Japanese stiltgrass was grown in long day growth chambers (26/22 C) and plants were moved 2, 6, or 10 wk after germination to short day growth chambers (26/22 or 22/18 C). All plants exposed to short days flowered, while under long days no plants flowered. No difference in inflorescence number or shoot dry weight was observed between the two temperature regimes. Japanese stiltgrass populations from North Carolina, Pennsylvania, and Virginia flowered similarly in response short day conditions. Furthermore, inflorescences from natural stands of Japanese stiltgrass were harvested four times; one raceme branch beginning to emerge through the leaf sheath, one raceme branch fully elongated and a second branch visible, fully expanded inflorescence, and in concert with natural dispersal. Following > 90 d storage, seed germination from each harvest averaged 13, 51, 95, and 100%, respectively, suggesting management designed to prevent seed production should be implemented before flowering. In forested areas, herbicides that selectively control Japanese stiltgrass while preserving native vegetation may be desired. The efficacy of three selective postemergence herbicides (fenoxaprop-P, imazapic, and sethoxydim) applied early, mid-, or late season were compared. The herbicides, averaged across application timings, controlled Japanese stiltgrass 83 to 89% and reduced seedhead production 79 to 94%. Seedling emergence was reduced 89, 70, and 78% in spring 2004 by fenoxaprop-P, imazapic, and sethoxydim, respectively, applied in 2003. Additionally, fenoxaprop-P or sethoxydim applied twice (4 wk interval) at half-label or full labeled rates controlled Japanese stiltgrass, providing 92% reduction in biomass and 97 to 98% seedhead reduction. Experiments were conducted to determine if Japanese stiltgrass seeds possess dormancy and if so, to determine conditions required to overcome dormancy and for successful germination. Mature Japanese stiltgrass seeds were collected in autumn 2002 and 2003, cold stratified moist at 4 C or stored dry at 21 C, 0 to 90 d. After storage, seeds were incubated in petri dishes in alternating or constant temperatures and exposed to 14 h or 0 h (total dark) photoperiod. Less than 1% of seeds stored 0 or 15 d germinated while > 95% of seeds stored 90 d germinated, suggesting primary innate dormancy upon natural dispersal. A three-year experiment was conducted in two forest sites to document the ecological impacts of conventional and alternative selective management on Japanese stiltgrass populations and native flora recruitment and establishment. Conventional management treatments included hand-pulling, mowing, or glyphosate (1.1 kg ai/ha) applied in autumn compared to hand-pulling or fenoxaprop-P (0.19 kg ai/ha) applied as needed throughout the season. All management treatments significantly reduced Japanese stiltgrass cover and seed bank over time compared to no management and decreases in relative Japanese stiltgrass cover and seed bank populations were greater in 2004 than 2003, after two seasons of management. However, selective management was more suitable than nonselective management or no management for recruitment and re-establishment of native plants and increasing overall species richness. Additionally, relative cover of other exotic plants decreased 6% over time, suggesting that removal of Japanese stiltgrass did not increase invasion of other exotic plant species.

Rice (Oryza sativa L.) life cycle and yield depend on the partitioning of assimilated carbon to ripening caryopses. Structural and functional aspects of this important process were investigated. First, spatiotemporal dynamics of ripening were assessed. Panicle fresh weight accumulation was maximum after three weeks and had a maximum rate after twelve days. Panicle architecture and ripening asynchrony were reduced to the form of an annotated panicle array. This format permitted a quantitative, computational approach to panicle consensus generation, data analysis and graphical display. Next, the separability of caryopsis tissues was assessed. The caryopsis coat was mechanically isolated from most of the embryonic tissues and facially separated into outer and inner coats from within the tube cell layer. Pectolyase Y-23 compromised adhesion between the maternal nucellus and embryonic aleurone and between endosperm cells. Viable protoplasts were prepared from approximately 10% of the isolated endosperm cells. Low protoplast yield was correlated with low viability of the isolated cells. Third, the mechanism of sucrose uptake by the aleurone was studied. The sucrose concentration-dependence of uptake rate had a nonsaturable component and a relatively small saturable component. Finally, electrophysiology of the caryopsis coat was assessed. Membrane potentials of the aleurone and nucellus were approximately -60 mV and -80 mV, respectively, and invariable over a range of bath conditions. Sucrose negligibly depolarized the aleurone membrane potential. Thus, it was not possible to confirm that the saturable sucrose influx was mediated by a cotransport system. Overall, the work has increased the experimental accessibility of ripening panicles and caryopses for research on the control of carbon partitioning.

The contamination of process pea (Pisum sativum L.) crops by the immature fruit of black nightshade (Solanum nigrum L.) and hairy nightshade (S. physalifolium Rusby var. nitidibaccatum (Bitter.) Edmonds) causes income losses to pea farmers in Canterbury, New Zealand. This thesis investigates the questions of whether seed dormancy, germination requirements, plant growth, reproductive phenology, or fruit growth of either nightshade species reveal specific management practices that could reduce the contamination of process peas by the fruit of these two weeds. The seed dormancy status of these weeds indicated that both species are capable of germinating to high levels (> 90%) throughout the pea sowing season when tested at an optimum germination temperature of 20/30 °C (16/8 h). However, light was required at this temperature regime to obtain maximum germination of S. nigrum. The levels of germination in the dark at 20/30 °C and at 5/20 °C, and in light at 5/20 °C, and day to 50 % germination analyses indicated that this species cycled from nondormancy to conditional dormancy throughout the period of investigation (July to December 2002). For S. physalifolium, light was not a germination requirement, and dormancy inhibited germination at 5/20 °C early in the pea sowing season (July and August). However, by October, 100% of the population was non-dormant at this test temperature. Two field trials showed that dark cultivation did not reduce the germination of either species. Growth trials with S. nigrum and S. physalifolium indicated that S. physalifolium, in a non-competitive environment, accumulated dry matter at a faster rate than S. nigrum. However, when the two species were grown with peas there was no difference in dry matter accumulation. Investigation of the flowering phenology and fruit growth of both species showed that S. physalifolium flowered (509 °Cd, base temperature (Tb) 6 °C) approximately 120 °Cd prior to S. nigrum (633 °Cd). The fruit growth rate of S. nigrum (0.62 mm/d) was significantly faster than the growth rate of S. physalifolium (0.36 mm/d). Because of the earlier flowering of S. physalifolium it was estimated that for seedlings of both species emerging on the same date that S. physalifolium could produce a fruit with a maximum diameter of 3 mm ~ 60 °Cd before S. nigrum. Overlaps in flowering between peas and nightshade were examined in four pea cultivars, of varying time to maturity, sown on six dates. Solanum physalifolium had the potential to contaminate more pea crops than S. nigrum. In particular, late sown peas were more prone to nightshade contamination, especially late sowings using mid to long duration pea cultivars (777-839 °Cd, Tb 4.5 °C). This comparison was supported by factory data, which indicated that contamination of crops sown in October and November was more common than in crops sown in August and September. Also, cultivars sown in the later two months had an ~ 100 °Cd greater maturity value than cultivars sown in August and September. Nightshade flowering and pea maturity comparisons indicated that the use of the thermal time values for the flowering of S. nigrum and S. physalifolium can be used to calculate the necessary weed free period required from pea sowing in order to prevent the flowering of these species. The earlier flowering of S. physalifolium indicates that this species is more likely to contaminate pea crops than is S. nigrum. Therefore, extra attention may be required where this species is present in process pea crops. The prevention of the flowering of both species, by the maintenance of the appropriate weed free period following pea sowing or crop emergence, was identified as potentially, the most useful means of reducing nightshade contamination in peas.

A number of morphological, floral, rhizome, root and herbage characteristics were studied in order to describe genetic variation and environmental responses in T. ambiguum. From each of six lines, 30 genotypes were clonally progagated into five diverse edaphic and altitudinal sites and grown for one season. Comparisons of growth and form were also made between T. ambiguum, T. repens cv. 'Grasslands Huia' and Lotus pedunculatus cv. 'Grasslands Maku'. The polyploid lines were found to have larger leaves than the diploids while all the lines of T. ambiguum had larger leaves than did white clover. Tetraploid lines had longer petioles and were taller and more erect than the diploids or hexaploids. Floral initiation was found to become later as ploidy level increased but the tetraploid lines exhibited a very large variation in flowering date. The cultivar Treeline was found to produce the most herbage under all conditions although not significantly more than cultivar Prairie or C.P.I. 57353. However, as nodulation was not studied it was not possible to determine whether variety differences were due to root nodulating ability or some other genetically determined parameter. None of the T. ambiguum varieties produced as much herbage as cv. Huia or cv. Maku at any site. However, all the T. ambiguum lines performed relatively better under harsher conditions. Because a large proportion of T. ambiguum was below ground the best T. ambiguum line, cultivar Treeiine, produced equivalent total plant dry weight to cv. Huia and cv. Maku at 1200 m. a.s.l., the high altitude site. Cultivar Prairie was found to have the highest proportion of rhizomes to total plant mass bu because cv. Treeline had higher total plant dry weight both cultivars produced equivalent mean rhizome dry weight. The number of rhizomes, number of daughter plants and rhizome dry weight were all highly correlated and these three characteristics showed similar trends among varieties. Rhizome length was found to increase with ploidy level, as did rhizome internode length. However, the number of nodes was found to be higher in the diploids than in the polyploids. Cultivar Treeline was found to have a high proportion of branching nodes on its rhizomes while C.P.I. 57353 and cv. Summit had the least. Rhizome production was restricted in the Wakanui silt loam soil of high bulk density. However, herbage growth and rhizome branching was increased, probably because of the higher fertility. It was shown using factor analysis on genotypic correlations, that rhizome characteristics and herbage yields were relatively independently inherited. However, morphological characters tended to be related to herbage yields. The polyploid varieties were found to be more genetically variable than the diploids . Broad sense heritabilities were calculated for all parameters measured, and in general, morphological characteristics had higher values than agronomic characteristics. As the genetic variation within each line was higher than the variation among lines, it is apparent that selection within lines should result in the largest gains. Therefore, comparison of the mean performance of the presently highly variable lines is relatively uninformative. By sacrificing some genetic diversity, large gains could be made in performance. It is suggested that cv. Prairie be used as the basis for selecting a highly rhizomatous cultivar while cv. Treeline could be used in the selection of a cultivar with higher herbage production suitable for high country conditions. In a second trial, an established stand of cv. Treeline produced up to 13250 kg ha⁻¹ for one season under good growing conditions. The management required to produce this amount of herbage was to irrigate and cut to ground level every two months. The growth rate was considerably depressed when cut monthly. It was also shown that root and rhizome yield reached 12600 kg ha⁻¹, indicating a massive reserve of assimilates, particularly useful for surviving periods of stress. Seed yields were found to be adequate, reaching levels equivalent to 500-700 kg ha⁻¹. These results were discussed in relation to earlier observations on T. ambiguum by workers in Russia, Australia, U.S.A. and New Zealand. Suggestions were made for further genetic and agronomic testing.

Seven vineyards representing three viticultural regions from throughout New Zealand were selected to investigate the influence of site environment on cropping potential, inflorescence development and fruit set of grapevines (Vitis vinifera L. Cabernet Sauvignon). The number and size of inflorescence primordia at bud positions 2-6 from the base of randomly selected canes were determined by dormant bud dissection. Differences between sites were assessed in relation to heat accumulation, bud size and the growth of miniature grapevines from cuttings collected at each site. Site had a significant effect on many of the factors being assessed. Warmer sites are expected to have larger buds, greater numbers of inflorescence primordia within the buds and, in general, to exhibit larger inflorescences with enhanced success of pollination and fertilisation at flowering, resulting in increased yields. In a second series of experiments the effects of modifying the light and temperature environment of developing shoots and inflorescences, as well as that of well developed inflorescences was investigated in two field trials established at Lincoln University. Light and temperature were shown to have a combined effect on early shoot growth and inflorescence development, probably as a consequence of differences in the photosynthetic activity of the developing leaves. The same treatments had few significant effects on the futher development of inflorescences treated 20 days preanthesis to 5-7 days post anthesis. Fruit set in treated inflorescences was reduced by excessively high or cool temperatures. It is suggested that a combination of high light intensity and warm temperature has its greatest effect on the development of the grape inflorescence, in the two weeks following bud break. During the course of this study an investigation into the concept of ‘fitness to flower’ was explored. It was proposed that the limiting factor for inflorescence development and increased fruit set was the size of the peduncle and associated vascular tissues. Evidence is presented which suggests that the grapevine controls flowering by regulating the allocation of available carbohydrates to the developing inflorescence.

In this thesis the author has two aims: (a) to review the literature on flowering in deciduous fruit trees, and (b) to record and discuss, in the light of previous work, experiments designed to elucidate the role of carbohydrates, and the possible role of hormones, in the process of flower-bud initiation in apricot (Prunus armeniaca, L.). The experiments were conducted over the period December 1968, to February 1970. The review is more detailed than may be required for an introduction to the experimental section. This is because most previous work on flower-bud initiation in deciduous fruit trees was carried out some time ago, and there are no recent large reviews on the subject. The review also illustrates how little is known on the process in stone fruits , as most investigations have centred on initiation in apple. The author in the experimental section has looked at the following factors affecting flower-bud initiation in apricot; shading, defoliation, temperature, light, level of carbohydrate metabolites, level of nitrogen compounds. In further experiments the herbicide diuron (DCMU) was used to inhibit photosynthesis and so determine the importance of leaf-produced carbohydrates on initiation of flower-buds in the axil of that leaf. The isotope Carbon-14 was also used to substantiate the results of diuron treatment and to demonstrate translocation patterns within the apricot tree. The experimental results are not recorded chronologically but appear in the following order: Part 1 : Determination of the importance of shading and defoliation on flower-bud initiation in apricot. Part 2: The role of temperature and light in flower-bud initiation in apricot. Part 3 : The role of carbohydrates in flower-bud initiation in apricot.

Flowering and the factors controlling flowering have intrigued scientists and laymen alike for centuries. Over the years, developments in scientific research have revealed that flowering is controlled or at least affected by a wide range of environmental and physiological factors. This should have suggested that flower induction and evocation results from a complicated interaction of physiological processes. However many plant physiologists hoped to find a substance common to all plants which caused flowering. Some were less ambitious and thought that each species or genus may have a specific floral hormone. Such ideas have never been supported by more than a few grafting experiments and many photoperiod studies using the presence or absence of flowers as the criterion of success. These methods gave no information of the biochemical processes operating in intact plants. As techniques were refined the search for specific flowering hormones became intensified only to reveal more and more information which did not support the specific hormone theory. However this intense research has yielded very little information on biochemical and physiological processes. “Quite often as compensation.........there is intensive speculation involving a host of unproved assumptions. Speculation and hypothesis are, of course, an essential part of experimental work. But this does not mean that each hypothesis needs to be published” (Lang, 1970). A decade before writing this Lang (1959) discussed the state of knowledge about flowering physiology and today. Little of significance can be added. When reporting their studies of strawberry plant responses to varying environmental conditions Porlingis and Boynton (1961b) emphasised the need for sequential analyses of endogenous GA-like substances in plants under different photoperiod regimes. The following year, Moore and Hough (1962) applied this concept to endogenous auxin actively in strawberries. But since that time there have been few studies which have attempted to relate the activity of endogenous hormones to growth processes. The present study is an attempt to partially fill this gap. The GA-like activity in strawberry plant tissues is determined and related to the process of floral induction in response to SD conditions. As the study progresses the techniques being used were found to be inadequately accurate and sensitive for a study of this nature. This suggested a reason for the slow advance in the state of knowledge about flowering physiology. A review of the literature revealed a lack of standardisation of techniques making it virtually impossible to realistically compare results from different research laboratories. New techniques now coming into use and the standardisation of the old methods should help to provide the important biochemical and physiological facts now so scarce in the field of flowering physiology.

The production of seed in quality from a new herbage variety in the first step in making it available for use by farmers. This applies equally to “Tama” Westerworlds ryegrass, which is a new winter active annual variety suitable for short term production of heavy yields of high quality herbage in winter and early spring. To achieve rapid adoption of this new variety, which means lowering the price and increasing the supply of seed, attention must be given to methods of producing maximum efficient seed yields from it.