Search

Crop phenology is fundamental for understanding crop growth and development, and increasingly influences many agricultural management practices. Water deficits are one environmental factor that can influence crop phenology through shortening or lengthening the developmental phase, yet the phenological responses to water deficits have rarely been quantified. The objective of this article is to describe the science and general evaluation of a decision support technology software tool, PhenologyMMS (Modular Modeling Software) V1.2. PhenologyMMS was developed to simulate the phenological response of different crops to varying levels of soil water. The program is intended to be simple to use, requires minimal information for calibration, and can be easily incorporated into other crop simulation models. New and revised developmental sequences of the shoot apex correlated with phenological events and the response to soil water availability are provided for proso millet (Panicum milaceum L.), hay/foxtail millet [Setaria italica (L.) P. Beauv.], sunflower (Helianthus annuus L.), and sorghum (Sorghum bicolor L.). Model evaluation consisted of testing algorithms using “generic” default phenology parameters for a crop (i.e., no calibration for specific cultivars was used) for a variety of field experiments to predict developmental events such as seedling emergence, floral initiation, flowering, and physiological maturity. Additionally, an application of the program predicting mean dates of winter wheat (Triticum aestivum L.) phenology across the Central Great Plains based on historical weather records is presented. Results demonstrated that PhenologyMMS has general applicability for predicting crop phenology and offers a simple and easy to use approach to predict and understand how phenology responds to varying water deficits. PhenologyMMS software may be downloaded from http://www.ars.usda.gov/services (select “Software”) or http://arsagsoftware.ars.usda.gov.

The potential impact of global temperature change on global crop yield has recently been assessed with different methods. Here we show that grid-based and point-based simulations and statistical regressions (from historic records), without deliberate adaptation or CO2 fertilization effects, produce similar estimates of temperature impact on wheat yields at global and national scales. With a 1 °C global temperature increase, global wheat yield is projected to decline between 4.1% and 6.4%. Projected relative temperature impacts from different methods were similar for major wheat-producing countries China, India, USA and France, but less so for Russia. Point-based and grid-based simulations, and to some extent the statistical regressions, were consistent in projecting that warmer regions are likely to suffer more yield loss with increasing temperature than cooler regions. By forming a multi-method ensemble, it was possible to quantify ‘method uncertainty’ in addition to model uncertainty. This significantly improves confidence in estimates of climate impacts on global food security. The potential impact of global temperature change on global crop yield has recently been assessed with different methods. Here we show that grid-based and point-based simulations and statistical regressions (from historic records), without deliberate adaptation or CO2 fertilization effects, produce similar estimates of temperature impact on wheat yields at global and national scales. With a 1 °C global temperature increase, global wheat yield is projected to decline between 4.1% and 6.4%. Projected relative temperature impacts from different methods were similar for major wheat-producing countries China, India, USA and France, but less so for Russia. Point-based and grid-based simulations, and to some extent the statistical regressions, were consistent in projecting that warmer regions are likely to suffer more yield loss with increasing temperature than cooler regions. By forming a multi-method ensemble, it was possible to quantify ‘method uncertainty’ in addition to model uncertainty. This significantly improves confidence in estimates of climate impacts on global food security.

Flowering is a crucial determinant for plant reproductive success and seed-set. Increasing temperature and elevated carbon-dioxide (e[CO2]) are key climate change factors that could affect plant fitness and flowering related events. Addressing the effect of these environmental factors on flowering events such as time of day of anthesis (TOA) and flowering time (duration from germination till flowering) is critical to understand the adaptation of plants/crops to changing climate and is the major aim of this review. Increasing ambient temperature is the major climatic factor that advances flowering time in crops and other plants, with a modest effect of e[CO2].Integrated environmental stimuli such as photoperiod, temperature and e[CO2] regulating flowering time is discussed. The critical role of plant tissue temperature influencing TOA is highlighted and crop models need to substitute ambient air temperature with canopy or floral tissue temperature to improve predictions. A complex signaling network of flowering regulation with change in ambient temperature involving different transcription factors (PIF4, PIF5), flowering suppressors (HvODDSOC2, SVP, FLC) and autonomous pathway (FCA, FVE) genes, mainly from Arabidopsis, provides a promising avenue to improve our understanding of the dynamics of flowering time under changing climate. Elevated CO2 mediated changes in tissue sugar status and a direct [CO2]-driven regulatory pathway involving a key flowering gene, MOTHER OF FT AND TFL1 (MFT), are emerging evidence for the role of e[CO2] in flowering time regulation.

Unraveling the complexity underpinning nitrogen (N) use efficiency (NUE) can be physiologically approached via examining grain N sources and N internal efficiency (NIE) (yield to plant N content ratio). The main objective of this original research paper is to document and understand sorghum NUE and physiological mechanisms related to grain N dynamics. The study of different grain N sources, herein defined as the reproductive-stage shoot N remobilization (Remobilized N), reproductive-stage whole-plant N content (Reproductive N), and vegetative-stage whole-plant N content (Vegetative N), was pursued with the goal of synthesizing scientific literature for sorghum [Sorghum bicolor (L.) Moench] crop. A detailed literature review was performed and summarized on sorghum NUE (13 studies; >250 means) with three Eras, defined by the year of the study, named as Old Era (1965-1980); Transient Era (1981-2000); and New Era (2001-2014). The most remarkable outcomes from this synthesis were: (1) overall historical (1965-2014) cumulative yield gain was >0.5 Mg ha(-1) (yields >7 Mg ha(-1)); (2) NIE did not change across the same time period; (3) grain N concentration (grain %N) accounted for a large proportion (63%) of the variation in NIE; (4) NIE increased as grain %N diminished, regardless of the Eras; (5) Remobilized N was strongly (>R (2) 0.6) and positively associated with Vegetative N, presenting a unique slope across Eras; and (6) a trade-off was documented for the Remobilized N and Reproductive N (with large variation

EF-Tu proteins of plastids, mitochondria, and the cytosolic counterpart EF-1α in plants, as well as EF-Tu proteins of bacteria, are highly conserved and multifunctional. The functions of EF-Tu include transporting the aminoacyl-tRNA complex to the A site of the ribosome during protein biosynthesis; chaperone activity in protecting other proteins from aggregation caused by environmental stresses, facilitating renaturation of proteins when conditions return to normal; displaying a protein disulfide isomerase activity; participating in the degradation of N-terminally blocked proteins by the proteasome; eliciting innate immunity and triggering resistance to pathogenic bacteria in plants; participating in transcription when an E. coli host is infected with phages. EF-Tu genes are upregulated by abiotic stresses in plants, and EF-Tu plays important role in stress responses. Expression of a plant EF-Tu gene confers heat tolerance in E. coli, maize knock-out EF-Tu null mutants are heat susceptible, and over-expression of an EF-Tu gene improves heat tolerance in crop plants. This review paper summarizes the current knowledge of EF-Tu proteins in stress responses in plants and progress on application of EF-Tu for developing crop varieties tolerant to abiotic stresses, such as high temperatures.

Drought tolerance was investigated in ‘C306’, one of the most drought tolerant wheat cultivars bred in India in the 1960’s. An intervarietal mapping population of recombinant inbred lines of the cross ‘C306’ × ‘HUW206’ was evaluated for drought tolerance components, namely potential quantum efficiency of photosystem (PS) II (Fv/Fm), chlorophyll content (Chl), flag leaf temperature (Lt), and grain yield per plant (Gyp) under stress. Three independent experiments were conducted under well-watered and water-stressed conditions in greenhouses and growth chambers at Kansas State University (USA). Five hundred and sixty microsatellite markers covering the entire genome were screened for polymorphism between the parents. A QTL (QLt.ksu-1D) for Lt (low flag leaf temperature under stress) on the short arm of chromosome 1D between markers Xbarc271 and Xgwm337 at LOD 3.5 explained 37% of the phenotypic variation. A QTL for Fv/Fm (QF v /F m .ksu-3B) and Chl (QChl.ksu-3B) controlling quantum efficiency of PS II and chlorophyll content under stress were co-localized on chromosome 3B in the marker interval Xbarc68–Xbarc101 and explained 35–40% of the phenotypic variation for each trait. A QTL (QGyp.ksu-4A) for Gyp on chromosome 4A at a LOD value of 3.2 explained 16.3% of the phenotypic variation. Inconsistent QTLs were observed for Fv/Fm on chromosomes 3A, 6A, 2B, 4B, and 4D; for Chl on 3A, 6A, 2B and 4B; and for Lt on 1A, 3A 6A, 3B and 5B. The identified QTLs give a first glimpse of the genetics of drought tolerance in C306 and need to be validated in field experiments using the marker-phenotype linkages reported here.

Aims Sorghum is commonly grown under dryland conditions, where yields are limited by soil water deficits. Yield increase may be possible by selecting genotypes that express traits that are desirable for water-limited conditions. Water conservation is one possible trait for increasing yield since this trait could increase water availability during critical stages of crop development. Water conservation could be achieved by slower transpiration rate with soil drying initiated at a high fraction of transpirable soil water (FTSW) so that the use of soil water is extended over a longer period of time. This water conservation strategy may allow the crop to have water available during the critical phase of grain filling. Therefore, the objective of this study was to compare genotypes of sorghum for possible differences in the threshold for the decline in transpiration.

Sorghum is one of the most drought-tolerant grain crops and is used in biofuel production. Since sorghum is often exposed to drought and high temperature (heat) stress, this study investigated the effect of stress applied at different phenological stages of crop development on the glucose levels in grain and subsequent ethanol production. Short season sorghum hybrid DK-28E grown under controlled environment was exposed to drought and heat stress at five different stages of growth, namely: (1) pre-flowering (boot leaf emergence) to flowering, (2) flower to seed-set, (3) seed-set to early seed-fill, (4) early seed-fill to mid seed-fill, and (5) mid seed-fill to late seed-fill stage. Drought stress at any of the growth stages did not statistically affect either the glucose content or the ethanol production compared to the control (337 mg/g), although the ethanol yield increased up to 4.5% (352 mg/g) in flowering to seed-set stage. Heat stress, on the other hand, significantly reduced the glucose release and ethanol yield compared to the control (322 mg/g). Marginal ethanol yield reduction by 9% (293 mg/g) and 8.3% (295 mg/g) was seen in plants stressed during early seed-fill to mid seed-fill and mid seed-fill to late seed-fill stages, respectively. The results suggest that the phenological stage when sorghum is exposed to stress affects the ethanol yield. Overall, from the point of ethanol yield, it appears that grain sorghum cultivated in semi-arid regions where heat and drought stress are prevalent can be used for biofuel production. However, economic viability of ethanol production, especially of grain sorghum from high temperature stress needs to be investigated.

Simulation studies have demonstrated that limited maximum transpiration rate (TR) at high air vapor pressure deficit (VPD) in water-limited environments could result in significant increases in sorghum yield. However, such a restriction on TR at high VPD has not been documented in sorghum. The objective of this study was to search within sorghum germplasm for the possibility of restricted TR at high VPD. Twenty six genotypes were selected for measurement of VPD response based on field observations including yield, leaf temperature, and the stay-green phenotype. These genotypes were grown in a greenhouse for about 24-d growth, and then placed into individual chambers in which VPD was varied and TR measured. The results of this study showed marked variation among sorghum genotypes in TR response to VPD. Seventeen genotypes were identified as exhibiting a breakpoint in their VPD response in the range from 1.6 to 2.7 kPa, above which there was little or no further increase in TR. Therefore, these genotypes with a breakpoint have the possibility of soil water conservation when VPD during the midday cycle exceeds the breakpoint VPD. This trait would be desirable in less humid environments for increasing yields in water-deficit seasons. The observed range in the value of the BP among genotypes offers the possibility of developing genotypes with BP appropriate for specific environments.

Chloroplast protein synthesis elongation factor, EF-Tu, has been implicated in heat tolerance in maize (Zea mays). Chloroplast EF-Tu is highly conserved, and it is possible that this protein may be of importance to heat tolerance in other species including wheat (Triticum aestivum). In this study, we assessed heat tolerance and determined the relative levels of EF-Tu in mature plants (at flowering stage) of 12 cultivars of winter wheat experiencing a 16-d-long heat treatment (36/30 degrees C, day/night temperature). In addition, we also investigated the expression of EF-Tu in young plants experiencing a short-term heat shock (4h at 43 degrees C). Heat tolerance was assessed by examining the stability of thylakoid membranes, measuring chlorophyll content, and assessing plant growth traits (shoot dry mass, plant height, tiller number, and ear number). In mature plants, relative levels of EF-Tu were determined after 7 d of heat stress. High temperature-induced accumulation of EF-Tu in mature plants of all cultivars, and a group of cultivars that showed greater accumulation of EF-Tu displayed better tolerance to heat stress. Young plants of all cultivars but one did not show significant increases in the relative levels of EF-Tu. The results of the study suggest that EF-Tu protein may play a role in heat tolerance in winter wheat.

Rising carbon dioxide (CO2) concentrations and associated changes in global temperature and precipitation are major concerns for future weed management and crop production. This review focuses on the impacts of climate change factors on the growth of weeds and the potential variations in the efficacy of herbicides under changing climate conditions. Weeds are likely to show greater resilience and better adaptation to changes in CO2 concentrations and rising temperature in competition with crops due to their diverse gene pool and greater physiological plasticity. Weeds with C3 and C4 photosynthetic pathways may exhibit differential responses to higher CO2 levels and temperatures, which can affect the dynamics of crop–weed competition. In addition to its positive impact on weed growth, climate change factors could influence the efficacy of many herbicides, making weed management a major challenge for sustainable crop production. To enhance our understanding of the impact of climate change factors on herbicide efficacy, it is important to evaluate the effects of environmental conditions on various herbicide modes of action. Environmental factors such as CO2, light, temperature, relative humidity, and soil moisture differentially affect the uptake, translocation, and activity of different herbicide chemistries. Furthermore, interactions among these environmental factors may have unpredictable effects on herbicide activity. Existing literature suggests that climate change factors impacts vary not only within herbicide modes of action but also among herbicides belonging to same mode of action, so making generalized assumptions for each mode of action is difficult. Extensive research on the impact of climate change factors and their interactions on all commonly used herbicides is necessary to understand the implications for weed management in future climate scenarios.

Determining mechanisms associated with heat tolerance and identifying screening methods are vital for improvement of heat tolerance in plants. The objectives of this study were to investigate the relationship between the heat stability of thylakoids and loss of chlorophyll in winter wheat (Triticum aestivum L.) under heat stress, and to examine whether chlorophyll loss can be used as an indicator of heat tolerance in wheat. We assessed heat tolerance and measured chlorophyll content in 12 cultivars of winter wheat at fl owering stage during exposure to 16-d-long heat stress. Heat tolerance was assessed using fl uorescence to determine the heat stability of thylakoids, and chlorophyll content was measured with a chlorophyll meter. Experiments were conducted under controlled conditions. Heat stress caused damage to thylakoids in all cultivars as indicated by the increase in the ratio of constant fl uorescence (O) and the peak of variable fl uorescence (P). Heat stress also caused a decline in chlorophyll content in most cultivars. A strong negative correlation between heat-induced increases in O/P and chlorophyll content was seen. The results suggest that heat-induced damage to thylakoids and chlorophyll loss are closely associated in winter wheat. Measurements of chlorophyll content with a chlorophyll meter could be useful for high throughput screening for heat tolerance in wheat.

High temperature stress-induced male sterility is a critical problem in grain sorghum (Sorghum bicolor L. Moench) that significantly compromises crop yields. Grain sorghum plants were grown season-long under ambient (30/20 degrees C, day-time maximum/night-time minimum) and high temperature (36/26 degrees C) conditions in sunlit Soil-Plant-Atmospheric-Research (SPAR) growth chambers. We report data on the effects of high temperature on sugar levels and expression profiles of genes related to sugar-to-starch metabolism in microspore populations represented by pre- and post-meiotic "early" stages through post-mitotic "late" stages that show detectable levels of starch deposition. Microspores from high temperature stress conditions showed starch-deficiency and considerably reduced germination, translating into 27% loss in seed-set. Sugar profiles showed significant differences in hexose levels at both "early" and "late" stages at the two temperature regimes; and most notably, undetectable sucrose and approximately 50% lower starch content in "late" microspores from heat-stressed plants. Northern blot, quantitative PCR, and immunolocalization data revealed a significant reduction in the steady-state transcript abundance of SbIncw1 gene and CWI proteins in both sporophytic as well as microgametophytic tissues under high temperature conditions. Northern blot analyses also indicated greatly altered temporal expression profiles of various genes involved in sugar cleavage and utilization (SbIncw1, SbIvr2, Sh1, and Sus1), transport (Mha1 and MST1) and starch biosynthesis (Bt2, SU1, GBSS1, and UGPase) in heat-stressed plants. Collectively, these data suggest that impairment of CWI-mediated sucrose hydrolysis and subsequent lack of sucrose biosynthesis may be the most upstream molecular dysfunctions leading to altered carbohydrate metabolism and starch deficiency under elevated growth temperature conditions.

Background Pearl millet is a staple food for people in arid and semi-arid regions of Africa and South Asia due to its high drought tolerance and nutritional qualities. A better understanding of the genomic diversity and population structure of pearl millet germplasm is needed to support germplasm conservation and genetic improvement of this crop. Here we characterized two pearl millet diversity panels, (i) a set of global accessions from Africa, Asia, and the America, and (ii) a collection of landraces from multiple agro-ecological zones in Senegal. Results We identified 83,875 single nucleotide polymorphisms (SNPs) in 500 pearl millet accessions, comprised of 252 global accessions and 248 Senegalese landraces, using genotyping by sequencing (GBS) of PstI-MspI reduced representation libraries. We used these SNPs to characterize genomic diversity and population structure among the accessions. The Senegalese landraces had the highest levels of genetic diversity (π), while accessions from southern Africa and Asia showed lower diversity levels. Principal component analyses and ancestry estimation indicated clear population structure between the Senegalese landraces and the global accessions, and among countries in the global accessions. In contrast, little population structure was observed across in the Senegalese landraces collections. We ordered SNPs on the pearl millet genetic map and observed much faster linkage disequilibrium (LD) decay in Senegalese landraces compared to global accessions. A comparison of pearl millet GBS linkage map with the foxtail millet (Setaria italica) and sorghum (Sorghum bicolor) genomes indicated extensive regions of synteny, as well as some large-scale rearrangements in the pearl millet lineage. Conclusions We identified 83,875 SNPs as a genomic resource for pearl millet improvement. The high genetic diversity in Senegal relative to other regions of Africa and Asia supports a West African origin of this crop, followed by wide diffusion. The rapid LD decay and lack of confounding population structure along agro-ecological zones in Senegalese pearl millet will facilitate future association mapping studies. Comparative population genomics will provide insights into panicoid crop evolution and support improvement of these climate-resilient crops. Electronic supplementary material The online version of this article (doi:10.1186/s12864-015-2255-0) contains supplementary material, which is available to authorized users.

A common theme in plant physiological research is the trade-off between stress tolerance and growth; an example of this trade-off at the tissue level is the safety vs efficiency hypothesis, which suggests that plants with the greatest resistance to hydraulic failure should have low maximum hydraulic conductance. Here, we quantified the leaf-level drought tolerance of nine C4 grasses as the leaf water potential at which plants lost 50% (P50 × RR ) of maximum leaf hydraulic conductance (Ksat ), and compared this trait with other leaf-level and whole-plant functions. We found a clear trade-off between Ksat and P50 × RR when Ksat was normalized by leaf area and mass (P = 0.05 and 0.01, respectively). However, no trade-off existed between P50 × RR and gas-exchange rates; rather, there was a positive relationship between P50 × RR and photosynthesis (P = 0.08). P50 × RR was not correlated with species distributions based on precipitation (P = 0.70), but was correlated with temperature during the wettest quarter of the year (P < 0.01). These results suggest a trade-off between safety and efficiency in the hydraulic system of grass leaves, which can be decoupled from other leaf-level functions. The unique physiology of C4 plants and adaptations to pulse-driven systems may provide mechanisms that could decouple hydraulic conductance from other plant functions.

Herbicide efficacy is known to be influenced by temperature, however, underlying mechanism(s) are poorly understood. A marked alteration in mesotrione [a 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor] efficacy on Palmer amaranth (Amaranthus palmeri S. Watson) was observed when grown under low- (LT, 25/15 °C, day/night temperatures) and high (HT, 40/30° C) temperature compared to optimum (OT, 32.5/22.5 °C) temperature. Based on plant height, injury, and mortality, Palmer amaranth was more sensitive to mesotrione at LT and less sensitive at HT compared to OT (ED50 for mortality; 18.5, 52.3, and 63.7 g ai ha-1, respectively). Similar responses were observed for leaf chlorophyll index and photochemical efficiency of PSII (Fv/Fm). Furthermore, mesotrione translocation and metabolism, and HPPD expression data strongly supported such variation. Relatively more mesotrione was translocated to meristematic regions at LT or OT than at HT. Based on T50 values (time required to metabolize 50% of the 14C mesotrione), plants at HT metabolized mesotrione faster than those at LT or OT (T50; 13, 21, and 16.5 h, respectively). The relative HPPD:CPS (carbamoyl phosphate synthetase) or HPPD:β-tubulin expression in mesotrione-treated plants increased over time in all temperature regimes; however, at 48 HAT, the HPPD:β-tubulin expression was exceedingly higher at HT compared to LT or OT (18.4-, 3.1-, and 3.5-fold relative to untreated plants, respectively). These findings together with an integrated understanding of other interacting key environmental factors will have important implications for a predictable approach for effective weed management.

Global climate change, especially, increases in carbon dioxide (CO2) concentration and the associated increases in temperature willhavesignificantimpact onthecropproduction.Grain-sorghum[Sorghum bicolor(L.)Moench]cultivarDeKalb28Ewasgrown at daytime maximum/nighttime minimum temperature regimes of 32/22, 36/26, 40/30 and 44/34 8C at ambient (350 mmol CO2 mol � 1 ) and elevated (700 mmol CO2 mol � 1 )C O2 from emergence to maturity in controlled environments to quantify the effects of temperature and CO2 on the reproductive processes and yield. Growth temperatures of 40/30 and 44/34 8C inhibited panicle emergence. Growth temperatures � 36/26 8C significantly decreased pollen production, pollenviability, seed-set, seed yield and harvestindexwhen compared to 32/22 8C. Percentage decreases inpollenviability,seed-set, seedyield and harvestindexdue to elevated temperature were greater at elevated CO2 when compared with ambient CO2. Elevated CO2 increased seed yield (26%) at 32/22 8C, but decreased seed yield (10%) at 36/26 8C. At high temperatures, elevated CO2 increased vegetative growth but not seed yield, thus, leading to decreased harvest index. We conclude that the adverse effects of elevated temperature on reproductive processes and yield of grain-sorghum were more severe at elevated CO2 than at ambient CO2; and the beneficial effects of elevated CO2 decreased with increasing temperature. The adverse temperature sensitivity of reproductive processes and yield at elevated CO2 was attributed to higher canopy foliage and seed temperatures. # 2006 Elsevier B.V. All rights reserved.

SUMMARY Atmospheric carbon dioxide concentration ([CO2]) and other greenhouse gases have risen over the past few decades. If this continues, it could indirectly lead to increases in global temperature. Responses of grain legume crops (soybean, dry bean, peanut and cowpea) to elevated [CO2] and interactions with temperature are summarized. Our research shows that, in the absence of biotic (pests, diseases and weeds) or abiotic (temperature, water and nutrients) stresses, elevated [CO2] will increase yield due to increased photosynthesis and growth. However, at above optimum temperatures, the beneficial effects of elevated [CO2] are more than offset by negative effects of temperature on yield and yield-components, leading to lower seed yield and poor seed quality Future research should focus on developing genetic and agronomic crop management practices to improve crop productivity under changing climates.

Kidney bean ( Phaseolus vulgaris L. cv. Montcalm) plants were grown under daytime maximum/nighttime minimum temperatures of 28/18, 34/24 and 40/30 °C at ambient carbon dioxide concentration (CO 2 ; 350 μmol mol −1 ), and 28/18, 31/21, 34/24, 37/27 and 40/30 °C at elevated (twice-ambient) CO 2 , to characterize how increases in growth CO 2 and temperature affected kidney bean leaf photosynthesis and carbohydrate metabolism. Elevated CO 2 enhanced leaf photosynthetic rates by about 57% across the temperature regimes, compared with plants grown an ambient CO 2 . As growth temperature increased from 28/18 to 40/30 °C, leaf photosynthetic rates decreased at both ambient and elevated CO 2 . Growth at either elevated temperature or CO 2 decreased activity, protein content and activation of the primary photosynthetic enzyme ribulose 1,5-bisphosphate carboxylase-oxygenase (Rubisco). Elevated CO 2 increased activities of sucrose-phosphate synthase (SPS) and adenosine-5′-diphosphoglucose pyrophosphorylase (AGP) and accumulation of soluble sugars and starch across all temperatures, compared with plants grown at ambient CO 2 . At elevated CO 2 , growth temperatures above 34/24 °C significantly increased leaf carbohydrates (total soluble sugars and starch) and activity of AGP. The up-regulation of leaf carbohydrate metabolism enzymes under elevated CO 2 plus temperature would be beneficial for growth and productivity of kidney bean in future climates.

Continuing increases in atmospheric carbon dioxide concentration (CO2) will likely be accompanied by global warming. Our research objectives were (a) to determine the effects of season-long exposure to daytime maximum/nighttime minimum temperatures of 32/22, 36/26, 40/30 and 44/341C at ambient (350lmolmol � 1 ) and elevated (700lmolmol � 1 )C O2 on reproductive processes and yield of peanut, and (b) to evaluate whether the higher photosynthetic rates and vegetative growth at elevated CO2 will negate the detrimental effects of high temperature on reproductive processes and yield. Doubling of CO2 increased leaf photosynthesis and seed yield by 27% and 30%, respectively, averaged across all temperatures. There were no effects of elevated CO2 on pollen viability, seed-set, seed number per pod, seed size, harvest index or shelling percentage. At ambient CO2, seed yield decreased progressively by 14%, 59% and 90% as temperature increased from 32/22 to 36/26, 40/30 and 44/341C, respectively. Similar percentage decreases in seed yield occurred at temperatures above 32/221C at elevated CO2 despite greater photosynthesis and vegetative growth. Decreased seed yields at high temperature were a result of lower seed-set due to poor pollen viability, and smaller seed size due to decreased seed growth rates and decreased shelling percentages. Seed harvest index decreased from 0.41 to 0.05 as temperature increased from 32/22 to 44/341C under both ambient and elevated CO2. We conclude that there are no beneficial interactions between elevated CO2 and temperature, and that seed yield of peanut will decrease under future warmer climates, particularly in regions where present temperatures are near or above optimum.

Water is a primary concern for producers in the Great Plains; as such, research is warranted to quantify how much cover crops affect the amount of soil water available to subsequent cash crops. Cover crop mixes have been marketed as a means to conserve water in no-till cropping systems following winter wheat (Triticum aestivum L.) harvest. The objectives of this study are to quantify changes in soil profile water content in the presence of different cover crops and mixtures of increasing species complexity, to quantify their biomass productivity and quality, and to quantify the impact of cover crops on subsequent corn (Zea mays L.) yields. We hypothesized the change in soil water brought on by the cover crop treatments would be correlated to the quantity of biomass produced and the species composition, rather than mixture complexity. Soil moisture was measured using a neutron probe to a depth of 9 ft. Results from 2013–14 showed no difference in water use between cover crop mixtures and single species. Cover crops depleted the soil profile by a maximum of 3.5 in. during growth, but fallow was able to gain 0.75 in. of water during the same period. At the time of corn planting, soil moisture under all cover crops had replenished to levels at cover crop emergence, except for the brassicas, which had extracted water from deeper in the profile. Corn yields were reduced following the grass cover crops and the six-species mix. Corn yields were more closely related to the carbon:nitrogen (C:N) ratio of the cover crop residue than to profile soil moisture at corn emergence. The fact that yields were similar for corn after fallow and for corn after brassica cover crops implied that water was not the cause of yield reductions after the other cover crops.

Integrated use of organic and inorganic fertilizers can improve crop productivity and sustain soil health and fertility. The present research was conducted with an objective to study the influence of application of farmyard manure in combination with three levels of chemical fertilizers [80 : 40 : 30, 120 : 60 : 45 and 160 : 80 : 60 kg N, P2O5 and K2O ha−1, respectively] on yield and yield components of irrigated lowland rice. The experiment was conducted in split-plot design during the rainy season with and without farmyard manure as main plots and three inorganic fertilizer levels as subplots. Data on grain and straw yield, number of tillers, panicle length, filled grains per panicle, 1000-grain weight and nutrient uptake were collected. The results showed that application of farmyard manure at 10 t ha−1 increased grain yield of rice by 25% compared to no farmyard manure control. Similar observations were also made on straw yield, tiller number, filled grains per panicle, and 1000-grain weight....

It is important to quantify and understand the consequences of elevated temperature and carbon dioxide (CO2) on reproductive processes and yield to develop suitable agronomic or genetic management for future climates. The objectives of this research work were (a) to quantify the effects of elevated temperature and CO2 on photosynthesis, pollen production, pollen viability, seed-set, seed number, seeds per pod, seed size, seed yield and dry matter production of kidney bean and (b) to determine if deleterious effects of high temperature on reproductive processes and yield could be compensated by enhanced photosynthesis at elevated CO2 levels. Red kidney bean cv. Montcalm was grown in controlled environments at day/night temperatures ranging from 28/18 to 40/30 °C under ambient (350 µmol mol−1) or elevated (700 µmol mol−1) CO2 levels. There were strong negative relations between temperature over a range of 28/18–40/30 °C and seed-set (slope, − 6.5% °C−1) and seed number per pod (− 0.34 °C−1) under both ambient and elevated CO2 levels. Exposure to temperature > 28/18 °C also reduced photosynthesis (− 0.3 and − 0.9 µmol m−2 s−1 °C−1), seed number (− 2.3 and − 3.3 °C−1) and seed yield (− 1.1 and − 1.5 g plant−1 °C−1), at both the CO2 levels (ambient and elevated, respectively). Reduced seed-set and seed number at high temperatures was primarily owing to decreased pollen production and pollen viability. Elevated CO2 did not affect seed size but temperature > 31/21 °C linearly reduced seed size by 0.07 g °C−1. Elevated CO2 increased photosynthesis and seed yield by approximately 50 and 24%, respectively. There was no beneficial interaction of CO2 and temperature, and CO2 enrichment did not offset the negative effects of high temperatures on reproductive processes and yield. In conclusion, even with beneficial effects of CO2 enrichment, yield losses owing to high temperature (> 34/24 °C) are likely to occur, particularly if high temperatures coincide with sensitive stages of reproductive development.

Detailed spatial and temporal data on plant growth are critical to guide crop management. Conventional methods to determine field plant traits are intensive, time-consuming, expensive, and limited to small areas. The objective of this study was to examine the integration of data collected via unmanned aerial systems (UAS) at critical corn (Zea mays L.) developmental stages for plant height and its relation to plant biomass. The main steps followed in this research were (1) workflow development for an ultrahigh resolution crop surface model (CSM) with the goal of determining plant height (CSM-estimated plant height) using data gathered from the UAS missions; (2) validation of CSM-estimated plant height with ground-truthing plant height (measured plant height); and (3) final estimation of plant biomass via integration of CSM-estimated plant height with ground-truthing stem diameter data. Results indicated a correlation between CSM-estimated plant height and ground-truthing plant height data at two weeks prior to flowering and at flowering stage, but high predictability at the later growth stage. Log–log analysis on the temporal data confirmed that these relationships are stable, presenting equal slopes for both crop stages evaluated. Concluding, data collected from low-altitude and with a low-cost sensor could be useful in estimating plant height.

The tubers of yam, principally those of Dioscorea rotundata (white Guinea yam) and D. alata (water or greater yam), are important staple foods and sources of carbohydrate in West Africa. Yams are grown in diverse environments – from the high-rainfall forest zone on the coast to the seasonally arid savannas of West Africa, that is in situations in which the duration and the timing of the onset of the growing season vary appreciably. Dormancy in both underground and aerial tubers of the Dioscoreaceae is an important adaptive mechanism that helps to maintain organoleptic quality during storage and also ensures that tubers germinate at the start of the growing season. Plant breeders are especially keen to manipulate the duration of the dormant period in order to synchronize growth periods and, therefore, to produce more than one generation per year. The control of tuber dormancy, however, is poorly understood. This review examines critically those factors that affect tuber initiation, dormancy and sprouting, and makes recommendations for future priorities in research.

Groundnuts (Arachis hypogaea L.) are frequently exposed to high temperatures in the semi-arid tropics. The objectives of the present research were: (i) to determine the response of groundnuts to different nitrogen sources; (ii) to quantify the effects of high air and soil temperatures on nodulation, dry matter production, partitioning and pod yields; and (iii) to discover whether plants dependent on symbiotic dinitrogen are more sensitive to heat stress than those dependent on inorganic nitrogen (N). Plants were grown at optimum air and ambient soil temperatures from sowing until the first flowering. Thereafter, plants were exposed to a factorial combination of two air temperatures [optimum: 28°/22°C (day/night) and high: 38°/22°C], two soil temperatures (ambient: 26°/24°C and high: 37°/30°C) and three N-sources [inoculated with Bradyrhizobium strain NC 92 (symbiotic N2); inoculated and supplied with 20 ppm inorganic N (symbiotic N2 plus 20 N); or not inoculated and supplied with 100 ppm inorganic N (inor...

Groundnut is an important crop of the semi-arid tropics where potential yields are frequently reduced by heat and water stress. Eight groundnut genotypes varying in heat tolerance were grown in controlled environments and exposed to either high (40/28°C) or near-optimum (30/24°C) temperature from 32 days after sowing (DAS) to maturity. There was significant variation among genotypes in mainstem leaf number and total flower number at 30/24 and 40/28°C and rates of appearance were faster at 40/28°C than at 30/24°C. Days from sowing to first flowering varied among genotypes from 28 to 41 days and therefore the time plants were exposed to high temperature relative to first flowering ranged from −4 to 9 days. Fruit number for seven out of eight genotypes at 40/28°C was linearly and negatively related to the time of first flowering relative to the onset of high temperature (r2 = 0·93; n = l7; P < 0·001), indicating that ‘escape’ was an important component of heat tolerance in this experiment. Further analysis showed that fruit number in all genotypes at 40/28 °C was closely associated with the cumulative number of flowers that had opened between first flowering and 3 days after the onset of the high temperature regime (r2 = 0·95; n = 8; P < 0·001). Variation in fruit number was therefore due both to the timing of flowering and the initial rate of flower production. These data also suggest that the most sensitive stage of development to high temperature in groundnut occurred around 3 days before flowers opened. Therefore, it was the timing of flowering, rather than heat tolerance or susceptibility, that was the dominant attribute determining fruit number.

Global production of annual crops will be affected by the increases in mean temperatures of 2–4°C expected towards the end of the 21st century. Within temperate regions, current cultivars of determinate annual crops will mature earlier, and hence yields will decline in response to warmer temperatures. Nevertheless, this negative effect of warmer temperatures should be countered by the increased rate of crop growth at elevated atmospheric CO2 concentrations, at least when there is sufficient water. Of more importance for the yield of annual seed crops may be changes in the frequency of hot (or cold) temperatures which are associated with warmer mean climates. The objectives of this paper are to review evidence for the importance of variability in temperature for annual crop yields, and to consider how the impacts of these events may be predicted. Evidence is presented for the importance of variability in temperature, independent of any substantial changes in mean seasonal temperature, for the yield of annual crops. Seed yields are particularly sensitive to brief episodes of hot temperatures if these coincide with critical stages of crop development. Hot temperatures at the time of flowering can reduce the potential number of seeds or grains that subsequently contribute to the crop yield. Three research needs are identified in order to provide a framework for predicting the impact of episodes of hot temperatures on the yields of annual crops: reliable seasonal weather forecasts, robust predictions of crop development, and crop simulation models which are able to quantify the effects of brief episodes of hot temperatures on seed yield.

Iron (Fe) chlorosis is a major nutritional constraint to groundnut (Arachis hypogaea L.) productivity in many parts of the world. On‐farm research was conducted at a Fe‐chlorotic site to evaluate the performance of three genotypes (TMV‐2, ICGS‐11, and ICGV‐86031), three fertilizer practices [no fertilizer control, fanners practice (125: 200: 0 kg NPK ha−1), recommended practice (20: 50: 30 kg NPK ha−1)], and two Fe treatments (non‐sprayed control and foliar FeSO4 sprays) for their effect on Fe‐chlorosis and haulm and pod yields. These treatments were tested in a strip‐split plot design with four replicates. Results revealed that TMV‐2 and ICGS‐11 were susceptible to Fe‐chlorosis and produced significantly smaller haulm and pod yield, whereas, ICGV‐8603 1 was tolerant to Fe‐chlorosis. Farmer's fertilizer practice had the highest incidence of Fe‐chlorosis. Extractable Fe and chlorophyll content in the fresh leaves were the best indices of Fe‐status and were significantly (P

Peanut (Arachis hypogaea L.) crops grown in the semi-arid tropics are commonly exposed to damaging hot temperatures of above 40°C. The objectives of this research were to identify the time(s) during reproductive development when hot days reduce yield, and to examine relations between flower production and sensitivity to heat stress. At start of flower bud initiation (21 d after planting, DAP) plants of the cvs ICGV 86015 and ICGV 87282 were grown either at 28/22°C (optimum temperature, OT) or at 38/22°C (high temperature, HT) or were reciprocally transferred at 3-d intervals between the OT to HT regimes and vice versa, until 46 DAP. Transferred plants remained in the new temperature regime for 6 d before being returned to their original regime. All plants were harvested at 67 DAP. In cv. ICGV 86015, transfers between 6 d before and 15 d after flowering (DAF) significantly (P < 0.001) affected total number of pegs (i.e., pegs and pods) and reproductive (peg and pod) dry weight, with the greatest effect occurring at 9 DAF. In cv. ICGV 87282, number of pegs and reproductive dry weights were also significantly reduced by transfers at 9 and 12 DAF. Heat stress had no effect on flower production or the proportion of pegs forming pods, but did significantly reduce the proportion of flowers producing pegs. Data presented suggest that it is heat stress during floral bud development that determines peg number.

Hot days and warm nights are important environmental factors limiting fruit yields of groundnuts in the semi-arid tropics. The objective of the present research was to quantify the eects of short episodes of heat stress on pollen production and viability, and fruit yield. Plants of cultivar ‘ICGV 86015’ were grown at a day}night temperature of 28}22 ∞C from sowing until 9 d after flowering. Cohorts of plants were then exposed to a factorial combination of four day (28, 34, 42 and 48 ∞C) and two night (22 and 28 ∞C) temperatures for 6 d. Thereafter, all plants were maintained at 28}22 ∞C until final harvest 9 d later. Number of flowers per plant (FN), the proportion of flowers setting pegs (fruit-set), the number of pegs and pods per plant (reproductive number, RN t ), pollen production per flower and pollen viability were determined during the 6 d stress period. There were strong negative linear relations between day temperature over the range of 28 to 48 ∞C and FN (slope, fi1‐1 ∞C’"), fruit-set (fi2‐8%∞C’"), RN t (fi0.90 ∞C’"), and pollen production (fi390 ∞C’") and viability (fi1‐9%∞C’"). Warmer night temperature (28 as .2 2∞C) had no eect on FN, but reduced fruit-set (31 to 19%), RN t (8 to 5), and pollen production (4389 to 2800) and viability (49 to 40%). There were no significant interactions between day and night temperature. Reduced fruit-set was a consequence of fewer pollen grains and reduced pollen viability. The threshold day temperature for pollen production and viability was 34 ∞C and there were strong negative linear relations between both pollen production and pollen viability and accumulated temperature " 34 ∞C. # 1999 Annals of Botany Company

Short episodes of high temperature (HT) stress during reproductive stages of crop development cause significant yield losses in wheat (Triticum aestivum L.). Wheat plants of cultivar Chinese Spring were grown at various temperature regimes at several stages of reproductive development for different durations. The objectives of this research were to (i) identify the stage(s) most sensitive to HT stress during reproductive development, and (ii) determine threshold temperature and duration of HT stress that decrease floret fertility and individual grain weight. Two periods (first at 8–6 days before anthesis and second at 2–0 days before anthesis) during reproductive development were most sensitive to short episodes (2 or 5 days) of HT stress, causing maximum decreases in floret fertility. Short episodes (5 days) of mean daily temperatures >24°C imposed at start of heading quadratically decreased floret fertility, with the values reaching close to 0% around mean daily temperature of 35°C; and floret fertility and individual grain weight decreased linearly with increasing duration (in the range from 2 to 30 days) of HT stress when imposed at start of heading or start of grain filling respectively. HT stress caused morphological abnormalities in pollen, stigma and style. The combination of lower floret fertility (leading to decreased grain numbers) and decreased individual grain weights can cause significant decreases in grain yield. Further research to search for genetic variability for these traits and use them in breeding programs to develop tolerant genotypes that can provide yield stability under current and future climates is warranted.

Sorghum [Sorghum bicolor (L.) Moench] grain yield is severely affected by abiotic and biotic stresses during post-flowering stages, which has been aggravated by climate change. New parental lines having genes for various biotic and abiotic stress tolerances have the potential to mitigate this negative effect. Field studies were conducted under irrigated and dryland conditions with 128 exotic germplasm and 12 adapted lines to evaluate and identify potential sources for post-flowering drought tolerance and stalk and charcoal rot tolerances. The various physiological and disease related traits were recorded under irrigated and dryland conditions. Under dryland conditions, chlorophyll content (SPAD), grain yield and HI were decreased by 9, 44 and 16%, respectively, compared to irrigated conditions. Genotype RTx7000 and PI475432 had higher leaf temperature and grain yield, however, genotype PI570895 had lower leaf temperature and higher grain yield under dryland conditions. Increased grain yield and optimum leaf temperature was observed in PI510898, IS1212 and PI533946 compared to BTx642 (B35). However, IS14290, IS12945 and IS1219 had decreased grain yield and optimum leaf temperature under dryland conditions. Under irrigated conditions, stalk and charcoal rot disease severity was higher than under dryland conditions. Genotypes IS30562 and 1790E R had tolerance to both stalk rot and charcoal rot respectively and IS12706 was the most susceptible to both diseases. PI510898 showed combined tolerance to drought and Fusarium stalk rot under dryland conditions. The genotypes identified in this study are potential sources of drought and disease tolerance and will be used to develop better adaptable parental lines followed by high yielding hybrids. Electronic supplementary material The online version of this article (doi:10.1186/2193-1801-2-650) contains supplementary material, which is available to authorized users.

Agriculture is extremely sensitive to climate and weather conditions. The resilience of our crop production systems to changes in climate can be enhanced by improved understanding impacts and responses of crops to changing climates. Several countries in Asia and Africa are at the risk of losing about 280 million tons of potential cereal production as a result of climate change factor, particularly increasing temperatures and prolonged dry periods. The most significant negative changes for developing countries in Asia, where agricultural production declines of about −4% to −10% are anticipated under different socioeconomic and climate change scenarios. Rising temperatures will reduce the amount of fertile farmland, and by 2050, the amount of maize grown is expected to decline by 6–23% and wheat by 40–45%. The majority of the world’s food supply comes from the consumption of seeds from grain crops (wheat, rice, maize, soybean, barley, and sorghum), which are most vulnerable to changing climates. The growth in food production is lower than the population growth; therefore, there will be challenges of food security. Major impacts of climate change will be on rain-fed crops that account for nearly 60% of cropland area. As predicted, South Asia and sub-Saharan Africa will be highly vulnerable to climate change. Crop production can be increased by the use of quality seeds of high-yielding stress-tolerant varieties, combined with judicious use of inputs, particularly water and nutrients. Climate changes affect all four dimensions of food security, that is, availability, access to food, stability of food supplies, and food utilization. The seed industry plays an important role in increasing food production. It provides high-quality seeds of high-yielding varieties in adequate quantities at the right time and right place. Climate change influences the population dynamics of insects, emergence of new pests, changing status of pest and disease development, and evolution of new races of pests. Quality seed production is also affected by crop/weed interactions, loss of pollinator biodiversity, and genetic diversity. The seed crop is also affected by climate change regarding change in crop phenology, reproduction, flowering, anthesis/pollen viability, and pollination/fertilization, length of seed-filling duration, seed setting, seed size, seed dormancy, seed yield, and ultimately seed quality. Therefore, the cost of seed production is likely to increase in changing climate due to scheduling of operations, land and water management, herbicide/insecticide applications, pollination management, and postharvest seed management. Issues regarding intellectual property rights (IPR) related to seed, including patent infringements, prevalence of monocultures, consolidations of transnational corporations through acquisitions and mergers, and biodiversity and pollinator-loss related issues further complicate the problem. The lack of trained conventional plant breeders, crop physiologists, and seed technologists and stronger interdisciplinary collaboration between agronomists and biologists need attention. Further, acceptance of engineered crop or seed, increasing cost of genetically engineered (GE) seed as compared with conventional seed with no yield advantage, increasing number of herbicide applications, culminate in loss in net farm income in developed countries. In this article, the issues regarding the impact of climate change (particularly increasing temperature and carbon dioxide concentrations) on seed production, the present trend of the global seed industry, are discussed.

Low plant hydraulic conductance has been hypothesised as an approach to decrease the rate of soil water use, resulting in soil water conservation for use during late season water deficits. The impact of leaf hydraulic conductance (Kleaf) on water use characteristics was explored by comparing two sorghum (Sorghum bicolor (L.) Moench) genotypes that had been found to differ in Kleaf. Genotype SC15 had a much lower leaf conductance than genotype SC1205. Four sets of experiments were undertaken to extend the comparison to the impact of differences in Kleaf on the plant water budget. (1) Measurements of hydraulic conductance of intact plants confirmed that leaf conductance of SC15 was lower than that of SC1205. (2) The low leaf conductance of SC15 was associated with a decrease in transpiration during soil drying at a higher soil water content than that of SC1205. (3) SC15 had a restricted transpiration rate at vapour pressure deficits (VPD) above 2.1 kPa, whereas SC1205 did not. (4) Treatment with aquaporin inhibitors showed substantial differences in the sensitivity of the transpiration response between the genotypes. These results demonstrated that low Kleaf in SC15 was associated with conservative water use by restricting transpiration at higher soil water content during soil drying and under high VPD. Tests with inhibitors indicate that these differences may be linked to differences between their aquaporin populations. The differences between the two genotypes indicated that the traits exhibited by SC15 would be desirable in environments where soil water deficits develop.

Salinity is an important abiotic stress that limits growth and yield of many crop species. The effects of salinity on crop plants are exerted by presence of excess salts (ionic effect) and associated water deficits (osmotic effect). Plant responds to salinity in two phases: in a rapid phase, (plants exhibit osmotic effects and inhibits growth of young leaves), and in a slower ionic phase, (plants accelerates senescence of mature leaves). Salinity stress causes changes in ion homeostasis and osmotic adjustments. Some of adaptations to salinity stress in plants include (i) accumulation of osmoprotectants, (ii) sodium (Na+) or chloride (Cl−) exclusion (iii) tissue tolerance to accumulated Na+ or Cl−, and (iv) detoxification of reactive oxygen species (ROS). Salinity stress causes membrane damage, decreases photosynthetic rate, chlorophyll fluorescence traits, changes leaf water potential, relative water content, increases ROS level, and modifies antioxidant enzymes production system. Intensity of the membrane deterioration processes are proportional to ionic concentrations. Plant species and genotypes within species show differential responses to salinity stress. Various traits that govern salinity tolerance can be identified by studying physiological and biochemical mechanisms, which can lead to identification of new genetic sources of salinity tolerance. The ability of plants to accumulate osmoprotectants to maintain water status and detoxify ROS under salinity stress are some traits that can help to improve salinity tolerance in crop species. This chapter provides a brief overview of effects of soil salinity on plant growth and tolerance mechanisms that help plants to avoid or tolerate stress, with particular emphasis on ion homeostasis, osmotic and oxidative response and tissue tolerance.

Solar energy is the primary energy source for almost all of the world’s ecosystems and drives primary production. Solar radiation is also the heat source for the earth and fuels optimum ecosystem functions. Incoming infrared radiation is retained within the atmosphere by heat-trapping gases such as carbon dioxide; this creates a natural greenhouse effect (Rogers 1990). The world’s industries discharge about 15 × 109 tons of carbon dioxide (CO2) into the atmosphere every year. About half of this amount is fixed by planetary photosynthesis, a quarter is devoured by the oceans, and another quarter is deposited in the atmosphere. Atmospheric CO2 is essential for maintaining temperatures that support life systems; without CO2 the average global temperature would be −18◦C (Abrahamson 1989; Surasinghe 2009). However, infrared irradiation absorption by CO2 and other greenhouse gases such as methane, nitrous oxide, and sulfur dioxide may cause warming of the earth’s climate. Global surface temperatures are predicted to rise by about 2–5◦C by the end of this century, leading to significant changes in crop productivity, water supplies, and associated economic value (IPCC 2007). An overall increase of 2◦C in temperature and 7% in rainfall would lead to an almost 8% loss in farm level net revenue. These changes are already occurring. For example, in India, rainfall has decreased in July, and greater rainfall has been recorded in August in key cropgrowing areas. Another major change is that the monsoon pattern has shifted westward; this confines the rainfall to certain pockets and may result in floods and, in turn, food shortages for many people. The effects of global warming on food security will likely be more severe in India than in other parts of the world. For a 2◦C rise in temperature, the reduction in gross domestic product (GDP) is 5%, and for the next 6◦C increase, GDP would be reduced 15–16%. In Haryana, wheat (Triticum aestivum L.) production declined from 4106 kg/ha in 2001 to 3937 kg/ha in 2004, and the maximum temperature during February and March (booting and grainfilling) rose by about 3◦C in the last 7 years (Gahukar 2009). In addition, water supply will suffer because of scant rainfall in the Himalayas. South Asia’s prime wheat-growing land—the vast Indo-Gangetic Plain, which produces about 15% of the world’s wheat crop—will shrink 51% by 2050 because of hotter, drier weather and diminished yields; this loss will place at least

Drought stress is an important abiotic factor limiting wheat yield. Thirty-one accessions of Aegilops species belonging to five species were screened to identify species/accessions tolerant to drought stress and to measure traits associated with the tolerance. Plants were grown at full irrigation, 25/19°C day/night temperature and an 18 h photoperiod. At anthesis (Feekes 10.5.1), drought stress was imposed by withholding water for 16 days. Controls were continuously irrigated. Drought stress decreased chlorophyll content, grain number, individual grain weight and grain yield by 31, 25, 68 and 76% compared with the control. Aegilops geniculata Roth had greater tolerance to drought stress for yield (48% decline from control) compared with other species (>73% decline from control). The tolerance was associated with higher grain number spike–1 and heavier grains. A. geniculata, GenBank accession number TA 10437, was highly tolerant to drought stress with

Evapotranspiration (ET) is an essential component of the water balance and a major consumptive use of irrigation water and precipitation on cropland. Remote sensing based surface energy balance algorithms are now capable of providing accurate estimates of spatial-temporal ET. Uses of these spatial ET estimates are innumerable including hydrological modeling, irrigation scheduling, drought and flood monitoring and global climate change studies. The objective of this study was to evaluate the ability of the Surface Energy Balance System (SEBS) to estimate hourly ET fluxes using very high resolution (0.5-1.8 m) aircraft images acquired during the BEAREX07 (Bushland ET and Agricultural Remote Sensing Experiment 2007). Accuracy of the predicted ET fluxes were investigated using observed data from 4 large weighing lysimeters, each located at the center of 4.7 ha field in the USDA-ARS Conservation and Production Research Laboratory, Bushland, Texas. The uniqueness and the strength of this study come from the fact that it evaluates the SEBS for irrigated and dryland conditions simultaneously with each lysimeter field planted to irrigated forage sorghum, irrigated forage corn, dryland clumped-grain sorghum, and dryland row-grain sorghum. Eleven images acquired during early and mid cropping seasons (June 24 - July 27) were used in the study. SEBS algorithm performed equally well for both irrigated and dryland conditions in estimating the hourly ET with overall mean bias error and root mean square of -0.01 and 0.11 mm h 1 (-1.53% and 20.27%), respectively.

High temperature stress is an important abiotic stress limiting sorghum (Sorghum bicolor (L.) Moench) yield in arid and semiarid regions. Climate models project greater increases in the magnitude of night temperature compared with day temperature. We hypothesise that high night temperature (HNT) during flowering will cause oxidative damage in leaves and pollen grains, leading to decreased photosynthesis and seed-set, respectively. The objectives of this research were to determine effects of HNT on (1) photochemical efficiency and photosynthesis of leaves, and (2) pollen functions and seed-set. Sorghum plants (hybrid DK-28E) were exposed to optimum night temperature (ONT; 32 : 22°C, day maximum : night minimum) or HNT (32 : 28°C, day maximum : night minimum) for 10 days after complete panicle emergence. Exposure to HNT increased thylakoid membrane damage and non-photochemical quenching. However, HNT decreased chlorophyll content, quantum yield of PSII, photochemical quenching, electron transport rate and photosynthesis of leaves as compared with ONT. Exposure to HNT increased the reactive oxygen species (ROS) level of leaves and pollen grains. Lipid molecular species analyses in pollen grains showed that HNT decreased phospholipid saturation levels and altered various phospholipid levels compared with ONT. These changes in phospholipids and greater ROS in pollen grains may be responsible for decreased pollen function, leading to lower seed-set.

Crops are often exposed to multiple factors of climate change including: (1) enhanced ultraviolet-B (UV-B) radiation, (2) elevated carbon dioxide concentrations (CO2), and (3) episodes of elevated temperatures and water stress during critical stages of crop development. Our understanding of crop responses to individual climate change stress factors has significantly advanced in recent years. However, crop responses to a combination of stress factors are less understood and need attention. In addition to direct effects on various physiological, growth, and yield traits of plants, the interaction of plants with biotic factors (particularly insects and pathogens) will play an important role in determining crop productivity. The objective of this chapter is to provide a summary of crop responses to UV-B, CO2, temperature, drought, and a combination of multiple stresses. Exposure to above ambient UV-B radiation decreases crop productivity through negative effects on photosynthesis, growth, dry matter production, yield, and grain quality. Elevated CO2 often improves photosynthesis, growth, and yield of most crop species. Alternatively, exposure to both above optimum temperatures and water stress significantly decreases crop productivity and quality, particularly when stress occurs during sensitive stages (reproductive phase) of crop development. The positive effects of elevated (CO2) on photosynthesis and growth do not generally overcome the negative effects of UV-B radiation, elevated temperatures, or water stress on productivity and quality of grain crops. Crop species and cultivars within crop species vary in their responses to both individual and a combination of stress factors, suggesting a scope for genetic improvement. Further research should be focused on breeding for tolerance to multiple stresses of regional and local importance. An increased knowledge of crop responses to multiple stresses and genetics may also improve crop simulation models resulting in a better understanding, prediction and management of crops in a changing environment.

Rising atmospheric carbon dioxide (CO

Protein elongation factors, EF-Tu and EF-1α, have been implicated in cell response to heat stress. We investigated the expression (accumulation) of EF-Tu and EF-1α in mature plants of spring wheat cultivars Kukri and Excalibur, and tested the hypothesis that cultivars with contrasting tolerance to heat stress differ in the accumulation of these elongation factors under prolonged exposure to high temperature (16 days at 36/30°C). In addition, we investigated the expression of EF-Tu and EF-1α in young plants experiencing a 24-h heat shock (43°C). Excalibur showed better tolerance to heat stress than Kukri. Heat stress induced accumulation of EF-Tu and EF-1α in mature plants of both cultivars, but to a greater extent in Excalibur. Young plants did not show appreciable accumulation of EF-Tu in response to heat shock. However, these plants showed increased accumulation of EF-1α and the accumulation appeared greater in Excalibur than in Kukri. The results support the hypothesis that EF-Tu plays a role in heat tolerance in spring wheat. The results also suggest that EF-1α may be of importance to wheat response to heat stress.