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Thirteen cultivars of elephant grass (Pennisetum purpureum) were grown in the wet tropics over a period of 30 months for evaluation as a source of paper pulp. The first five ratoon harvests were at 3-month intervals, and the following two ratoon harvests at 6-month intervals. Mean annual yields were similar under both harvest regimes. At 3-month harvest intervals four cultivars were consistently high yielding and averaged 69.5 t ha−1 of total dry matter and 47.1 t ha−1 of stem dry matter, but at 6-month intervals yield rankings were less consistent due to variable lodging. Limited pulping studies suggested that cultivars did not differ greatly in pulping characteristics. Crude protein content ofleaves averaged 15% and quality was generally adequate for direct feeding to cattle. In crops harvested at intervals of 3 months mean temperature was the environmental variablwe mostclosely associated with total dry matter yield.

International audience; The nitrogen economy of the crop is a critical driver of biomass and grain production, and its importance is reflected in a large, worldwide research effort to link nitrogen, growth and yield. Particular research questions require measurement of specific traits, hence the need to quantify multiple, often complementary traits including crop nitrogen uptake, nitrogen use efficiency and its components, nitrogen concentration in the crop and its parts, down to relevant enzymes (e.g. nitrate reductase) and other products of gene expression. Nitrogen uptake, however, is co-regulated by both soil nitrogen availability and crop biomass accumulation; hence, crop nitrogen uptake or shoot nitrogen concentration reflect univocally crop nitrogen status only if comparisons are made at similar biomass. Although the allometric relationships between biomass and nitrogen uptake have been established for over two decades, many studies still report results in terms of nominal treatments, e.g. high vs low nitrogen, which are uninformative; curves relating yield and fertiliser rate, which are of local interest but provide little insight on the underlying processes and have low generic value; and nitrogen-related traits that are incomplete or inadequate to quantify crop nutrition status. Often, the allometric relationships between nitrogen and biomass are overlooked. In this opinion paper, we summarise the already well established concepts of dilution curves and nitrogen nutrition index, outline the standard partitioning of nitrogen use efficiency, and highlight the confounded effects in nitrogen use efficiency when the allometric relationship between nitrogen uptake and biomass is ignored. A sample of recent papers is used to survey the most common approaches to characterise nitrogen related traits. We illustrate the application of dilution curves and nitrogen nutrition index in the assessment and interpretation of crop responses to agronomic practices and comparisons of wheat cultivars and maize hybrids.

Even though planting cotton early in the season is advantageous, the cold sensitivity of cotton seedlings and low germination rates, especially in the areas experiencing low temperatures, are the main obstacle for the early seasonal planting. A total of 106 genotypes from three different species; Gossypium hirsutum L., G. barbadense L., and G. herbaceum L. were screened for cold tolerance using three different approaches. Furthermore, the best screening method to differentiate between the genotypes for cold tolerance, and to predict their field emergence rates was also determined. In detail, optimal germination percentages were measured at 30 °C with the results ranging from 61% to 99%. On the other hand, cold temperature germination rates and emergence percentages ranged from 8% to 82% in paper test and from 8% to 88% (the 7th day after planting) in sand test at 18 °C, and field emergence percentages ranged from 44% to 77% at 28 days after planting. A significant difference between cotton species in terms of their tolerance to cold was observed. That is, G. barbadense genotypes had higher germination rates than the other two species in the three methods used. There was no correlation between optimal germination rates and field emergence percentages. Among cold temperature germination methods, the 18 °C paper test was better in predicting of field emergence percentage, in differentiating between genotypes in terms of their cold tolerance and in determining seed vigor. G. hirsutum cultivars; 8106-2, AYDIN-110, CORINA, DP-388, DPL-50, DPL-5614, NAZILLI-342 and one G. barbadense cultivar, GIZA 70 were more cold tolerant among all the cotton cultivars screened in this study.

The paper investigates management and cultivar type effects on pearl millet stover yield and fodder quality. Sixteen pearl millet cultivars available to farmers in India were selected to represent three cultivar types: (1) traditional landrace germplasm from the arid/semi-arid millet production zones, (2) improved dual-purpose (grain and stover) open-pollinated varieties incorporating differing amounts of traditional landrace germplasm and (3) commercial, grain-type F1 hybrids, bred for use in the arid/semi-arid zone. The cultivars were grown for 2 years (2000 and 2001) at high fertility (HF: 65 kg N ha −1 and 18 kg P ha −1 ) and low fertility (LF: 21 kg N ha −1 and 9 kg P ha −1 ). Within each fertility level high (HP) and low (LP) plant population densities were established by varying sowing rate and then thinning to the target populations (HP: 11 plants m −2 and LP: 5 plants m −2 ). Stover fodder quality traits (nitrogen concentration, sugar content, in vitro digestibility and metabolizable energy content) were analyzed using a combination of conventional laboratory analysis and near infrared spectroscopy. In general, fertility level and cultivar type had strong effects on grain and stover yields, and on a range of stover nutritional quality traits, but with significant year interactions. In contrast, the effect of population density on these variables was largely insignificant. Higher fertilizer application significantly increased grain and stover yields and stover nitrogen concentration, in vitro digestibility and metabolizable energy content. As a result, fertilization resulted in significant increases in the yields of both digestible and metabolizable stover. Landrace cultivars as a group produced higher quality fodder than modern hybrids, but at a significant cost in grain yield. Dual-purpose, open-pollinated cultivars were generally intermediate between the landraces and hybrids, in terms of both stover quality and grain yield, but produced the highest yields of both digestible and metabolizable stover. The paper discusses the implications of these findings for Indian pearl millet farmers with various resource levels and farming objectives.

Field experiments with soybean demonstrated that the extension of photoperiod after flowering increases both the duration of the post-flowering phase and the production of seeds. These results suggest that cultivars with increased duration of the post-flowering phase could be selected to improve soybean yields. The aims of this paper were to: (a) evaluate the ability of the CROPGRO-soybean model to reproduce the experimental relationships between seed number and duration of the critical phase between first and last pod, and (b) assess the putative benefits and trade-offs of variable durations of the critical phase in a south–north transect in the Pampas of Argentina. We varied the genetic coefficients accounting for photothermal requirements and photoperiod sensitivity of soybean A5409-RG (maturity group V), reducing pre-flowering phase while maintaining time to maturity. The model produced sound estimates of crop phenology and reproduced the positive relationship between seed production and the duration of the critical period between first and last pod found in field studies. Linking the model with long-term climate records for six locations between 31 and 37°S, indicated that substantial yield gains could result from increasing the relative duration of post-flowering phases. A hypothetical cultivar with flowering time typical of cultivars of maturity group III and total cycle typical of cultivars of group V, outyielded the traditional cultivar of group V in most cases. For well-watered crops, extension of the critical period had a positive effect in yield in all seasons and locations, whereas for rainfed crops, the extension of the critical period increased yield in 95% of the simulated scenarios. The magnitude of the effect was strongly asymmetric: yield gains were up to 1 Mg ha −1 whereas losses were below 0.2 Mg ha −1 . The modelled results in this paper indicate that shortening pre-flowering period without changing the duration of the whole cycle should increase yields in a broad range of latitudes and environmental conditions.

Cotton (Gossypium hirsutum L.) cultivars containing the cryIAc gene accounted for 81% of South Africa's cotton production in 2004. Current research on Bt cotton in developed countries has revealed that this transgenic crop provides a key means for enhancing yields and boosting profits. Our study was designed to assess the agronomic efficiency of Bt cotton particularly in South African commercial (Paper 1) and small-scale (Paper 2) farming systems. Over several consecutive years, we compared yield boll distribution patterns (using a plant mapping analysis) of a Bt cultivar (NuOpal) with a conventional nearly isogenic line (DeltaOpal). Compared with the non-Bt cultivar, Bt cotton had better early boll retention rates at the first and second positions on the fruiting branches. Beyond the third position this trend was reversed, indicating that non-Bt cotton varieties offset losses occurring at the first two positions by producing fruits at further positions. Bt cotton thus had a higher average boll weight, shorter vegetative cycle, earlier boll opening, and 13% higher yield potential on average than the conventional control. These results indicate that using the transgenic variety provided better protection against bollworm as compared to chemical treatments—which are likely not effective at the onset of bollworm infestation and do not protect the first bolls. These observations demonstrate the advantage of transgenic Bt cotton when grown under near optimal conditions.

Pearl millet (Pennisteum americanum L.) is an essential crop in farming systems of the dry areas of the semi-arid tropics and its tillering habit is an important adaptive feature. This is the first paper in a series aiming at developing and validating a pearl millet simulation model that recognises tillers as functional entities, analogous to intercrops. The objective of this paper is to quantify the effects of total leaf number per axis (TLN), cultivar, plant density and axis number on parameters that are used to simulate potential leaf area per plant. Four cultivars with different phenology and tillering habit were grown under well-watered and well-fertilised conditions at two locations in India, covering a range of daylengths and plant densities. For selected plants, the area of fully expanded leaves was measured non-destructively. A bell-shaped function adequately described the relationship between individual leaf area and leaf position on an axis. Its shape was determined by the position (X0) and area (Y0) of the largest leaf and by the breadth and skewness of the leaf area profile curve. TLN affected all four parameters, although the association with Y0 was weak. Cultivar only affected Y0, suggesting that parameterising new cultivars is straightforward. The observed density effect confirmed that competition for light between axes started during stem elongation. The results highlighted the consistent differences between leaf area profiles of main shoots and tillers. For a high-tillering crop like pearl millet, modelling leaf area dynamics through individual leaves is justified, as this approach can potentially deal with cultivar and environmental effects on tillering.

Birch, C.J., Carberry, P.S., Muchow, R.C., McCown, R.L. and Hargreaves, J.N.G., 1990. Development and evaluation of a sorghum model based on CERES-Maize in a semi-arid tropical environment. Field Crops Res., 24: 87-104. This paper reports on the development and evaluation of a grain sorghum model (CERESSorghum ( SAT ) ) for use in the semi-arid tropics. The model was developed from a version of CERESMaize, previously adapted for use in this climatic zone. Functions for phenology, leaf growth, leaf senescence, assimilate accumulation and grain growth were modified using a small subset of sorghum data and validated against a much larger field-data set. When tested with cultivar De Kalb DK55 at Katherine, Northern Territory, the model successfully predicted grain-yield with a root mean square deviation of 0.972 to ha- ~ over a range of sowing dates and water regimes resulting in observed yields ranging from 1.56 to 6.28 t ha -~. Deviations of predicted from observed yields were no greater than those of maize predictions by the parent model. Prediction of components of yield and biomass were also satisfactory. Calibration required 28 changes to the CERES-Maize(SAT) model, of which 15 were changes to coefficients in equations rather than substantial changes to the model. Because of the ease of conversion and the time-use efficiency found in these analyses, the techniques used in this paper could have application where locally calibrated models are required.

The paper compares food and straw fodder traits in wheat lines of 6 different CIMMYT wheat trials tested across 32 environments of South Asia (India, Nepal, Bangladesh and Pakistan). Experiments were conducted in the main spring wheat season with sowing time of mid-November to mid-December and harvest between March to April. Investigated and compared were grain yield (GY), straw yield (SY), straw nitrogen (N) content, neutral (NDF) and acid (ADF) detergent fiber, acid detergent lignin (ADL), and in vitro organic matter digestibility (IVOMD). Highly significant (P 60%), considerable (45%) for HI and straw N (40%), moderate for ADL (18%), and minor for NDF, ADF, and IVOMD ( Across all cultivar types only ADF was significantly (P 0.05) relationships were observed between N, ADF and IVOMD and SY. Among cultivars consistent relationships were only observed between N and GY which were significantly (P = 0.03 to 0.009) inversely correlated in five out of the six cultivar types. Within cultivars types ADF varied by at least 2.3% units in HTNM and 1st DRYT and up to 4.9% units in ESWYT. By extrapolation such cultivar-dependent differences will matter at wheat straw trading.

This paper reviews the results of published and unpublished experiments over 30 years looking at the effect on yield of planting density and row spacing, and of raised bed planting, of modern irrigated short wheat cultivars under the favourable climatic conditions of northwest Mexico. With optimum planting dates (mid Nov. to mid Dec.), regardless of row spacing, wheat yield was remarkably insensitive to planting density within the range normally studied (80–400 plants/m2). However yield was sensitive to row spacing: the most sensitive cultivars (erect dwarf cultivars) lost yield at spacing 30 cm and greater, while the least sensitive (some taller vigorous semidwarf cultivars) tolerated spacing up to at least 50cm without yield loss. Yield sensitivity to wide spacing was unaffected by density but varied between years, being less in favourable cooler years, and was markedly greater with later plantings (Jan.). The response to yield on narrow raised beds (2–3 rows per bed, 75–90 cm between bed centres), which have many agronomic advantages, could be explained by the aforementioned yield responses to spacing, in this case the furrow gap or distance between rows on adjacent beds being critical. Yield testing with a furrow gap of 44–50 cm appeared to select cultivars more suited to this system, but it wasn’t clear whether such cultivars represented the best option under normal 20 cm row spacing in the absence of raised beds. When testing was extended to very low plant densities, yield was remarkably insensitive (maximum yield often achieved with only 16/m2), provided the planting date was normal and the planting arrangement did not deviate greatly from a square grid, with the honeycomb design giving an additional small yield advantage. These yield responses reflect the great plasticity in wheat imparted especially by tillering, and appear to be reasonably well explained by the notion that maximum yield requires close to full light interception no later than just before flag leaf emergence, being the onset of dry weight accumulation in growing spikes. Greater leaf greenness and probably higher radiation use efficiency with very low densities (and wide gaps), and associated delays in 50% flowering, may also assist in compensation for gaps. In contrast to much conventional wisdom, it is suggested that a worthwhile breeding objective would be selection for high per spaced-plant yield, with a view to achieving normal (or better) commercial yields at very low plant densities (

ORYZA version 3, as the successor to ORYZA2000, is an ecophysiological model that can simulate rice growth and development for targeted yield with different nitrogen (N) fertilizer rates and planting densities in a given rice production system. Currently, there is little published information on the application of ORYZA (v3) and ORYZA2000 in simulating high-yielding rice cultivars under different N rates and planting density schemes in central China. This paper combines field experimentation with ORYZA (v3) to calibrate the crop growth characteristics of widely grown high-yielding inbred and hybrid rice cultivars. The calibrated model was applied to simulate yields under different N rates, planting densities, and seedlings per hill, using historical weather data from 1986 to 2015. ORYZA (v3) reliably simulated the dynamics of crop biomass and leaf area index, and seasonal yield, with relatively small normalized root mean square error (RMSEn) and high adjusted linear correlation coefficient (R2), but slightly over-estimated leaf N concentration. Scenario analyses indicated that the maximum differences in simulated yields were 72.1 kg ha−1 due to planting density, 112.8 kg ha−1 due to seedlings per hill, and 3266.2 kg ha−1 due to N rates. The simulations demonstrated that further field experiments are crucial in investigating the effects of rice genotype, N management and their interactions on yield for optimal crop management.

An understanding of genotype × environment (G × E) interactions for phenological adaptation in crops can help identify traits that facilitate genetic improvement and cultivar selection. Such understanding is also necessary to identify environments that facilitate identification of cultivars with better environmental adaptation. Process-based crop simulation models including APSIM are valuable tools to investigate G × E interactions and traits conferring adaption to particular conditions. However cultivar parameters relating to crop phenology in crop model are difficult to determine directly through field experiments. Within this paper, we present a simulation study to explore the environmental and genotypic control of time to flowering and maturity in lupin and its grain yield, by using the APSIM model. In the model, lupin cultivar parameters were optimized by combining prior knowledge and PEST (Parameter ESTimation), a model-independent parameter optimiser. The parameterisation was for nine lupin cultivars with contrasting maturity (early vs late) and vernalization requirement (non-responsive vs responsive) across 13 sites × years across Australia. We showed that phenological differences among the cultivars were well explained by the optimized set of parameters, mainly reflected in vernalization response and photoperiodic sensitivity before flowering. Simulated flowering days and grain yield agreed well with the observations, with RMSEs (root mean squared error) of 4 days and 0.34 t ha−1 for all cultivars together. The simulation results showed that lupin yield was significantly affected by temperature and water availability. An early-maturity cultivar would yield better than the late-maturity one at the warm and low rainfall region, while at high rainfall or long-season regions, cultivar types should be chosen tactically based on the climatic conditions for that season. Thus, lupin breeding in Australia should therefore focus on temperature regimes and rainfall gradients. These results indicate that the parameter-optimized APSIM model could be used to explore the adaptation of genotypes to a particular environment to provide guidance for a more efficient breeding program and develop optimal agronomic management practices.

Genetic variation in traits affecting transpiration efficiency has been reported in sugarcane, but the impact of this variation on yield in a range of production environments needs to be estimated for assessing the priority and selection weightings to apply to these traits in crop improvement programs. A modelling approach may be useful and even necessary for reasonable assessment of these traits across production environments with different and temporally variable levels of water availability. Earlier theoretical modelling using the Agricultural Production Systems Simulator (APSIM)-Sugar module, found that traits affecting transpiration efficiency (TE) and water uptake by roots were important for improving sugarcane grown with highly variable rainfall. However, there were limitations of APSIM-Sugar in accommodating key physiological mechanisms, and this led to a revision of the APSIM-Sugar module described in this paper. Four key features were added to enable genetic variation in TE traits and root water supply (RWS) known to exist, to be modelled and assessed for predicted impact. These features were 1) the response of TE to water stress, 2) the midday flattening of hourly transpiration when plants are stressed, 3) conductance limits to hourly transpiration, which can apply even without stress and 4) the separation of soil hydraulic conductivity ( k) and root length density ( l) rather than the use of combined kl for determining RWS. A dataset of 182 observations of above ground biomass from 13 field experiments of sugarcane were used to check firstly that the new sugarcane module did not affect the simulation results when all the new features were disabled (model stability), secondly to check that the new features did not greatly reduce model performance, and thirdly, to determine the response or sensitivity of yields to the new features. Variation in parameter settings for the new features were based on the best evidence available for genetic variation in these traits, and were set before any testing against observations were made. With these features enabled in partial factorial combinations, the accuracy of the simulation of observed biomass, changed only to a minor extent compared to when no features were enabled. Separating k and l had the most consistent effect on improving model performance. Three additional published experiments with varying levels of imposed water stress were also simulated, with and without the new features. The simulation of biomass yield from two of the experiments was remarkably accurate regardless of which features were used in the simulation. Dry stalk yields reported for the third experiment were simulated accurately when no features were enabled and when midday flattening of transpiration was enabled and separate k and l enabled, one at a time. When a limit was placed on hourly transpiration, simulated TE and yield increased substantially when water was limiting but not in well-watered conditions; where yield was reduced. The new APSIM-Sugar features address the limitations of the original module (developed in 1999) for assessing water use related traits, including TE component traits and root growth. Effects of conductance on TE can now be simulated by limiting maximum hourly transpiration at the leaf level or k and specific root length at the root level. The new sugar module will also allow for better discrimination between sugarcane cultivars, now that vigour traits such leaf area development and radiation use efficiency are linked to root water uptake.

In a previous paper (Field Crops Res. 203, 114-127), we showed that the difference in yield potential between a contemporary and a traditional cultivar was due to differences in fruiting efficiency, likely derived from differences in spike fertility (fertile florets per spike) while having similar spike dry weights at anthesis. In this study, we determined the mechanistic bases of these genotypic differences in spike fertility analysing the initiation of all floret primordia per spike (up to 8), the maximum number of florets initiated per spikelet, and the associated floret developmental rates and their fate to become fertile florets under contrasting photoperiod (natural vs extended) and nitrogen availability (50 or 200 kg N ha−1) during the stem elongation phase. Under potential growing conditions (natural photoperiod, high nitrogen availability), the contemporary cultivar owed its higher spike fertility to the improved rate of floret development, which mainly determined an improved level of floret primordia survival to produce fertile florets. The sensitivity of the floret developmental patterns to faster development due to exposure to an extended photoperiod and, to a larger extent, a reduction in N availability was similar for both cultivars, providing a basis for the consistent differences in spike fertility across a range of environments. The response again determined a main effect through increasing floret mortality reducing therefore the level of fertile florets per spikelet in these conditions. Funding was provided by project AGL2009-11964 granted by the Spanish Ministry of Science and Innovation. AF held a FPU scholarship from the Spanish Government.

Improving grain yield and adaptation is achieved by synchronising crop phenology with the environment. Phenology research is complex and encounters analytical challenges in characterising genotype x environment (GxE) interactions. This paper presents a simple approach that helps to explain the environmental drivers of phenology. Photoperiod and temperature are major environmental cues for expression of crop developmental genes, and sensitivity to photoperiod is thought to be the major cause of maturity differences among Australian spring barley varieties. However, temperature and photoperiod show similar seasonal trends and strong autocorrelation makes it difficult to distinguish their relative importance in crop development. Partial Least Squares regression (PLS) was developed to handle large data sets with many correlated explanatory variables and only one dependent variable. Across 35 environments encompassing a wide range of temperature and photoperiod regimes in southern Australia, a PLS model described more than 90 % of the phenotypic variation in time to anthesis of three adapted barley cultivars. The PLS outputs defined the critical periods when photoperiod and temperature were most influential, and revealed that temperature effects are of equal or greater importance than photoperiod in determining anthesis date, which is a new finding for genotypes adapted to Australian environments. Insight into the previously elusive differential responses to changes in daily average, maximum, and minimum temperatures will assist in developing flowering models for growers that are more accurate, and assist breeders in the genetic dissection of phenology for target environments.

Yield potential studies can assist in identifying the production constraints in any cropping system and economics at the farm level dictate a continual need to increase yield and profit for most crops. Cotton is a tropical indeterminate perennial grown as an annual crop for fibre (lint), oil and meal for animal feed. Its growth habit means a production season can have a long duration up to 180 days. Here we define yield potential as yields that can be obtained with current cultivars and systems under ideal conditions in the absence of poor weather, disease, soil or nutritional constraints with management and genetics optimised. This paper aims to review yield potential in cotton and particularly identify factors, such as climate, soil health, nutrition, water, weeds, pests and diseases which affect yield. Worldwide, average cotton lint yield is about 800 kg/ha and is increasing at rates of 10–20 kg/ha/year, especially where irrigation is available. Under irrigated conditions, lint yield of 3500 kg/ha is now being obtained and we use this value for yield potential under full season irrigated conditions. Yield potential for raingrown cotton production systems depends on soil water storage and rainfall but is about 800 kg lint/ha. Thus, yield potential is not a fixed value but it is increasing through time as crop management and genetics are improved—but it is also strongly affected by local conditions. We derived the theoretical yield of cotton from potential growth or photosynthesis and respiration rates by growth analysis, from radiation use efficiency or by simulation modelling. All three methods indicated theoretical yield to be about 5000 kg lint/ha. To achieve this yield, a long season is required, possibly with slower initial fruit set so canopy size is not restricted by high fruit load. Estimates of resource requirements for lint yields of 5000 kg/ha indicated that nutrient uptake of 384 kg/ha N and K and 83 kg P/ha would be a more challenging constraint than the 10.7 Ml/ha of total evapotranspiration required. Future research opportunities were identified in crop agronomy (nutrient uptake and use efficiency), plant physiology (modelling fruiting dynamics), breeding (longer season plant types with slower initial fruit setting) and biotechnology (increased photosynthesis).

Future increases in grain number may be achieved through improving fruiting efficiency (FE; grains set per unit spike dry weight at anthesis). In recent experiments it was found a negative relationship between the average weight of the grains and FE. The objective of this paper was to determine whether this negative relationship was constitutive (i.e. the increased FE caused all grains to be smaller) or resulted from the increased proportion of grains of smaller potential size. Four experiments, involving 8 different environmental conditions, were carried out during two consecutive growing seasons (2008–2009 and 2009–2010) in which two durum wheat cultivars contrasting in FE and average grain weight were compared. In these conditions we determined FE and carried out a comprehensive study analysing in detail the weights of each individual grain along each of the spikelets. Averaging all experimental conditions, there was a negative relationship between average grain weight (GW) and fruiting efficiency (FE). Donduro with low FE produced in average heavier grains than Vitron. However, when considering individual grains there were, in general, no differences in GW. Therefore, the negative relationship between average grain weight and FE would not be constitutive, and would mostly represent the increase in the proportion of distal grains within the spikelets or of grains from apical spikelets as a consequence of an increased FE, reducing the average size of the grain but mostly unaffecting the size of particular grains. This provides further and stronger support to the idea of using FE as a criterion to further raise yield potential in wheat breeding programmes.

Drought is a major problem for rainfed lowland rice in Laos as well as for other countries in the Mekong region, and different drought screening methods under managed environments have been used to develop varieties adapted to drought prone environments. This paper evaluates the appropriateness of on-research station screening methods conducted under intermittent and terminal drought conditions, using the yield results of 12 on-farm multi-location trials with 25 genotypes some of which had been selected for drought tolerance. In these multi-location trials drought stress was rather mild, even in the intermittent or terminal drought trials which tended to develop in the higher fields of the rainfed lowlands. The high position generally produced low yielding crops but no significant interaction between position and genotypes were found for grain yield of 25 genotypes grown at 4 pairs of high and low field positions. Genotypes that performed well under higher yielding conditions in the on-(research) station experiments also performed well in on-farm multi-location trials. Genotypes that were identified as drought tolerant using drought response index as a criterion in the on-station experiments generally performed well in the on-farm multi-location trials (r= 0.49**), particularly in high yielding environments, but not under low yielding environments where low soil fertility appeared to be a major limitation for high yield. Similarly, genotypes that were identified to have high potential yield in flooded conditions in the on-station experiments also performed well in on-farm multi-location trials (r= 0.43*). Drought tolerance determined on-station either intermittent or terminal drought was similarly effective and was at least as effective as potential yield determined on-station in predicting on-farm yield. On-farm multi-location trials in combination with on-station experiments identified several promising lines that were well adapted to rainfed lowland conditions. It is concluded that genotypes selected for high yield potential under favorable conditions and for high drought tolerance determined in the on-station experiments would result in the development of well adapted cultivars suitable for drought-prone rainfed lowlands, and that either intermittent or terminal drought conditions developed at a research station is suitable for this purpose. The intermittent drought condition had the added advantage that genotypes selected directly for high yield, performed well in farmer's fields in the rainfed lowlands.

It is frequently assumed that durum wheat is more tolerant to stress than bread wheat. Unfortunately few research papers compare the performance of both species side-by-side under a wide range of environments in field conditions. We aimed to compare durum and bread wheat performance in a field study under contrasting treatments of water and nitrogen during three experimental seasons. In addition we compiled a comprehensive database with data from field experiments in which both species were grown in the same field conditions. A cross-over interaction of yield from bread vs. durum wheat was found, but oppositely to the hypothesis, bread outyielded durum wheat in the low-yielding conditions while durum wheat tended to have higher potential yield. We then divided the database in decades in which the cultivars were released and found that in the 1960s bread wheat outyielded durum wheat in almost any comparison whilst in the 2000s durum wheat outyielded bread wheat in most comparisons. Grain weight was constitutively higher in durum than in bread wheat, likely associated with a lower fruiting efficiency in the former; but in both types of wheat grain number per m2 was the component responsible for yield sensitivity to environmental changes. Differences in yield were also related to differences in water and nitrogen use efficiencies: under low-yielding conditions bread wheat was consistently more efficient than durum wheat and under high-yielding conditions durum wheat was more efficient.

This paper combines the analysis of rice growth data with crop modeling to quantify the changes in single rice cultivars over three decades from 1981 to 2009 at four sites in China. Crop data include timing of main developmental stages, aboveground biomass, grain yield, 1000-grain weight, grain number per spike, percentage filled grains, and plant density. The APSIM-Oryza model was used to quantify the rice cultivar changes and their impact on growth and yield. The results showed that cultivar changes could be explained by the changes in rice physiology captured in APSIM-Oryza and changes in yield components. Cultivar changes mainly involved: (1) the increase in actual thermal time requirements during the growing period as a result of reduced development rates and photoperiod sensitivity and extended grain filling period, which compensated the negative impact of warming to shorten growing period and stabilized or increased aboveground biomass and (2) the increase in grain numbers and harvest index as a result of the dwarfing and improved growth. Once these changes could be captured in the parameterization of model, APSIM-Oryza could explain 61.7% of the variation in observed aboveground biomass and 55.1% of the variation in grain yield. This demonstrates that crop modeling is an efficient means to study the impact of environmental and cultivar changes on crop productivity in the future. It also highlights the needs to quantify the physiological changes in new cultivars by combining field observations and crop modeling in future research.

Understanding the confounding impacts of climatic and varietal changes on crop phenology is of importance to help make appropriate adaptation measures and target future directions for crop breeding. This paper investigated the changes in winter wheat phenology and analysed the impact of climatic, varietal and sowing date changes on crop phenology during the last three decades by combining field data with modeling. The APSIM crop model was used to quantify the changes in wheat phenology in terms of vernalization and photoperiod sensitivity as well as the changes in thermal time of pre- and post-flowering stage among wheat varieties at six sites in the North China Plain (NCP). The results showed that APSIM model could capture the phenological changes of winter wheat caused by interannual climatic change. There was a large spatial difference in the response pattern of wheat phenology to climatic and varietal changes across NCP. At most sites the increase in temperature shortened the growth duration of winter wheat mainly by shortening the growth period from sowing to jointing. The delayed sowing of winter wheat further shortened the growth period from sowing to jointing at two northern sites (Tianjin and Huimin). Continuous adoption of new wheat varieties shortened the growth period from sowing to jointing at Huimin, Xinxiang and Zhumadian, from jointing to flowering at Tianjin, but helped increase the length of growth period from jointing to flowering at Huimin, Tangyin and Xinxiang and post-flowering growth period at all the sites except for Tangyin. The findings of the study suggest that past cultivar changes in wheat in the NCP have been varied geographically.

Yield differences among wheat cultivars and its responsiveness to resource availability are usually related to grain number per m 2 , and further increases in grain number are required, but now beyond differences in time to anthesis and plant height (that are mostly optimised in traditional growing regions). The objective of this paper was to determine and quantify differences in yield physiology between different modern well adapted durum wheats grown in contrasting conditions (in addition we also tested if a higher amount of resources due to removal of competition could affect yield through the same determinants to nitrogen (N) availability). Four experiments were carried out during two growing seasons (2008–09 and 2009–2010); all in all under eight different growing conditions (Gc1–Gc8). In the first season four different modern cultivars were used and in the second season we selected the two highest-yielding cultivars, which differed in their responses to N in terms of spike fertility. Yield was closely related to biomass and N uptake due to both growing conditions and genotypic effects in all experiments. The existence of variation among modern cultivars in these yield determinants is relevant as further increases in yield must be achieved beyond further increases in partitioning. Yield differences among cultivars were based on their differences in grains per m 2 or average grain weight depending on which cultivars were compared. Overall grain number was related to spike dry weight at anthesis, and no evidences were found for a direct involvement of N in grain number determination, beyond the general effect of N availability on spike dry matter. However, this overall effect was mainly driven by growing conditions whilst differences between genotypes seemed associated with either spike dry weight at anthesis or fruiting efficiency, which varied significantly between cultivars. Interestingly, grain weight was consistently higher in the cultivars with lower fruiting efficiency than in cultivars maximising the number of grains set per unit of spike dry weight at anthesis suggesting a constitutive component for the commonly reported negative relationship between grain weight and grain number. In conclusion, the main differences in yield between modern, well adapted wheats were related to their biomass and N uptake and to the sink-strength during post-anthesis, being this strength increased either by having more grains or grains of potentially greater size, depending on the specific cultivar and as a consequence of a trade-off between fruiting efficiency and grain size.

Sclerotinia stem rot caused by the fungus Sclerotinia sclerotiorum is one of the most damaging and difficult-to-manage diseases of oilseed rape (Brassica napus) and mustard (B. juncea). Identifying oilseed Brassica genotypes with effective resistance offers the best long-term prospect for improved management of the disease. Despite some significant interactions between oilseed Brassica genotypes and S. sclerotiorum isolates reported in earlier studies, mostly a single pathogen isolate has been used to identify resistant genotypes. This paper reports the results of studies involving 53 isolates of S. sclerotiorum from the northern and southern agricultural regions of Western Australia where Sclerotinia stem rot is a serious disease of oilseed rape. Colony characteristics of isolates on potato dextrose agar were determined, and two field virulence (i.e., levels of disease severity) studies conducted. The first field study included 14 Brassica genotypes against three S. sclerotinia isolates and the second had eight Brassica genotypes against 50 S. sclerotinia isolates. Only colony diameter of isolates growing on potato dextrose agar was correlated with stem lesion length in the field. In both field experiments, there were significant effects of isolates and host genotypes, as well as a significant interaction between isolates and genotypes in relation to stem lesion length. In the first field experiment, mean stem lesion length ranged from 1 cm in the highly resistant B. napus ZY006 to at least 9 cm for susceptible genotypes Brassica juncea #2 and B. juncea Montara. The latter genotype was the most susceptible with a mean stem lesion length of 11.1. Expression of high-level resistance in B. napus ZY006 was largely independent of S. sclerotiorum isolate. In contrast, responses in B. napus genotypes, Zhongyou 821, 06-6-3792, RT108 and Charlton were much more isolate-dependent. In the first field experiment, with a greater number of host genotypes than S. sclerotiorum isolates, a higher variance ratio occurred for isolates (VR = 158.4) than for host genotypes (VR = 10.7). In the second field experiment, with a larger number of S. sclerotinia isolates than hosts, host genotypes had a higher variance ratio (VR = 458.9) compared to the isolates (VR = 71.2). Increasing the number of isolates greatly improved the capacity to differentiate levels of resistance among test genotypes. In this experiment, some genotypes showed more consistent resistant reactions (e.g., B. napus Mystic and B. juncea Xinyou 9) across different isolates and these are ideal targets for commercial exploitation of this resistance in oilseed Brassica breeding programs. From this experiment, a standardized set of three B. napus and three B. juncea genotypes were shown to be suitable for use as universal differentials to characterize pathotypes of S. sclerotiorum using octal nomenclature. Eight distinct pathotypes of S. sclerotiorum were delineated and characterized and these six host differential genotypes can now be utilized to identify and monitor the incidence and distribution of current and future pathotypes of S. sclerotiorum. Further, by providing a reliable means to characterize pathotypes of S. sclerotiorum, for the first time not only allows identification of resistance(s) against the predominant pathotype(s) of S. sclerotiorum prevailing in a particular region, but also now allows oilseed rape breeding programs to combine host resistances against several specific pathotypes of S. sclerotiorum into future cultivars.

Narrow-leafed lupin (Lupinus angustifolius L.) is a grain legume well adapted to sandy soils of a Mediterranean climate and is the major grain legume in Australia. Improved herbicide tolerance of lupin cultivars is now considered as top priority by the industry for effective weed management. This paper reports induced mutation by seed mutagenesis in metribuzin-sensitive but anthracnose resistant cv. Tanjil, selection for metribuzin tolerant mutants in the field and evaluation of the tolerant mutants to metribuzin and anthracnose resistance. Two highly tolerant mutants Tanjil-AZ-33 and Tanjil-AZ-55 were identified and they were the first reported metribuzin tolerant mutants. The estimated mutation rate was 2.5 × 10−5. Tanjil-AZ-33 was six times and Tanjil-AZ-55 was four times more tolerant to metribuzin than the original cultivar Tanjil and they were also more tolerant than the tolerant cv. Mandelup. Tanjil-AZ-33 was the most tolerant lupin germplasm. Disease nursery assessment over 2 years revealed that both mutants also retained anthracnose resistance. Seed yield under irrigation was 4.2 t/ha for Tanjil-AZ-33 and 1.9 t/ha for cv. Tanjil when the seedlings were treated with metribuzin at 300 g/ha at the six-leaf stage. Clearly the mutation process has created new tolerance to metribuzin, but did not alter the anthracnose resistance. The mutant Tanjil-AZ-33 has been used as a parent in the lupin breeding program as a source of both metribuzin tolerance and anthracnose resistance. Seed mutagenesis followed by field selection in M2 proved to be an effective method to develop new tolerance to herbicides.

Several crop simulation models calculate grain yield by assuming that the rate of change of harvest index (δHI/δt) is constant (at rate k) during grain growth. Such behaviour has been identified in many crops, although the literature contains many examples of variations in k. The concept is useful if it approximates the truth in most circumstances, or if departures from both linearity and constancy are predictable from either the environment or the state of the crop. In this paper we examine the hypothesis that much of the variation in k is related to both crop biomass at the start of grain filling (BGF) and the crop growth rate during grain growth (CGF). Calculations using simple partitioning rules indicated that both factors are important. We showed that k increases rapidly as BGF decreases below about 9.0 Mg DM/ha, but decreases only slowly with increases of BGF above 9.0 Mg DM/ha. The analysis also showed that the increase in HI with time is quadratic rather than linear. We analysed data from 68 field grown wheat crops with variation in cultivar, location, irrigation, ambient CO2 concentration and sowing dates. These showed an almost three-fold variation in k (0.0058–0.0164 day−1). Across all data sets, there was a negative linear relationship (y = 0.02 − 0.0006x, R2 = 0.41, p

Many of the world's rice-growing regions lack adequate irrigation facilities, and drought frequently reduces yield. This paper reviews drought-resistance traits in rice and their quantitative trait loci (QTLs), with emphasis on CT9993/IR62266, one of the most widely studied mapping populations, and suggests ways to develop cultivars that will perform well in drought-prone environments. Information about the type of drought faced in the target region – particularly the timing of the drought (late season terminal drought, early stage vegetative drought, and intermittent drought) and the intensity of the drought – are important in determining the specific plant traits required to improve drought resistance in rice. Most of these traits are related to drought avoidance strategy, so that the drought-resistant genotypes are able to maintain better internal water status, either by taking up more water through a better root system or by reducing the rate of plant water use. We identified and listed a number of QTLs for many drought-resistance traits, such as deep roots. We identified four key genomic regions on chromosomes 1, 4, 8, and 9 on which are co-located a number of QTLs for traits considered to be directly or indirectly responsible for grain yield under stress. These regions, once they have been more finely mapped, appear promising for eventual use in marker-assisted selection for development of drought-resistant rice varieties. In addition to selecting for specific traits or specific genomic regions, screening under managed drought conditions on the basis of yield itself or on spikelet fertility adjusted for flowering time appears useful, because of the relatively high degrees of heritability of these characters, for the development of drought-resistant rice cultivars, and it is currently practiced in some breeding programs.

Genotype by environment (G × E) interactions were investigated in Vandana and a subset of 13 BC2 and BC3 lines of an improved indica upland rice cultivar, Vandana, backcrossed with a drought-tolerant traditional japonica cultivar, Moroberekan, which has a thick and extensive root system, in response to eight hydrological field environments conducted at Los Banos, in the Philippines, between 2001 and 2003. The G × E interaction accounted for 13% of the total sum of squares with environment and genotype responsible for 84 and 3%, respectively. Cluster analysis identified four environment and six genotype groups, which accounted for 70% of the G × E sums of squares. Of this, AX1, AX2 and AX3 accounted for 27, 22 and 21% of the G × E-SS, respectively. AX1 represented yield potential; AX2 was related to soil conditions, aerobic status and possibly VPD; and AX3 to change in phenology (days to flowering) with stress. The four environment groups were considered as broadly representative of contrasting rice production environments, including lowland-type, upland-wet season and upland-aerobic environments that experienced vegetative- or anthesis-stage drought stress. Genotype groups differed in adaptation to these diverse environments. For genotype groups G1–G6, G3 (VM150) had stable yields across environments; G1 (VM134) had the greatest grain yield in lowland-type environments (E2); G5 (VM135) in wet season environments (E3); G6 (VM168) in anthesis-stage drought (E4); G2 (Vandana and VM26) in vegetative- and anthesis-stage drought (E1 and E4); G4 had average yields across environments. Implications for breeding of rice adapted to contrasting hydrological environments are discussed, with the caution that adaptation to more than one environment type is desirable, because, as is demonstrated in this paper, an untimely climatic event can transform one environment type into another. Our results suggest that selection in one environment type may not give benefit in other environment types, so testing in more than one environment type is essential.

This paper is a response to Sinclair and Jamieson [Sinclair, T.R., Jamieson, P.D., 2006. Grain number, wheat yield, and bottling beer: an analysis. Field Crops Res. 98, 60–67] who propose that bulk carbon and nitrogen accumulation are fundamental to grain yield determination in wheat (Triticum aestivum L.), while challenging the common approach to yield through the separate processes of grain number determination, followed by grain filling, as governed by source–sink balance then. The response focuses on yield determination under potential conditions for which genetic and agronomic progress is clearly associated with increased grain number, herein abbreviated to KNO (kernels m−2). It argues that grain yield in modern cultivars is still limited by post-anthesis sink (KNO) and that understanding KNO determination is therefore useful for predicting physiological routes to higher yield. KNO determination appears to be strongly related to dry matter accumulation in spikes at anthesis (g m−2), governed by events in the last 20–30 days before anthesis, while some modern cultivars show higher grain number per unit spike weight. Post-anthesis photosynthesis and crop dry weight accumulation have increased as KNO has increased with breeding. There is no evidence for effects of N on KNO apart from those operating via dry matter accumulation, or for grain N demand limiting post-anthesis photosynthesis. Beyond this simple model, several other linkages that might exist between the pre- and post-anthesis periods are explored. Such linkages could help maintain the balance between the post-anthesis sink and the source required to fill the sink, and constitute common underlying processes which to some extent reconcile the model of Sinclair and Jamieson (2006) with current mainstream thinking about grain yield in wheat. Reports of an increasing amount of pre-anthesis carbohydrate reserves in the crop with breeding progress is a good example, but overall it is concluded that at least under potential conditions, the commonly accepted approach to grain yield determination is not invalidated by Sinclair and Jamieson (2006).

The paper investigates the variation in laboratory fodder quality traits in stover of 16 cultivars of pearl millet grown over 2 consecutive years and subjected to two different fertilizer regimes and planting densities. Stover quality traits were nitrogen and sugar content, in vitro digestibility and metabolizable energy content as well as yield of digestible and metabolizable stover. Significant (P 0.05) suggesting that high stover quality will not be achieved on the expense of grain yield. Heritabilities for stover quality traits were high (h2 > 0.73) except for stover nitrogen content (h2 > 0.56).

The aim of this paper was to compare different field, laboratory and physiological methods for the evaluation of frost tolerance in barley; as well as to show both the possibilities and limitations of these individual methods and approaches. The tolerances of 39 barley cultivars and breeding lines were evaluated by four direct methods (based on the exposure of plants to frost) and three indirect (based on diagnostic traits and markers). The direct methods included the evaluation of: (1) field survival after five winters 1999–2004; (2) winter survival in a provocation pot test under natural conditions; (3) lethal temperature (LT50) of plants taken from a field in winter; and (4) LT50 of plants grown and hardened in a growth chamber. The indirect methods were based upon: (1) endogenous levels of abscisic acid (ABA); (2) water content (WC); (3) osmotic potential (OP) of the plants cultivated and hardened in growth chambers. All four direct methods correlated well with one another, and resulted in similar sequences of frost tolerance of the tested barley cultivars and lines. While it was only possible to distinguish individual barley cultivars based on field survival after the 2002/2003 winter, by using the provocation method it was possible to distinguish between barley cultivars after all of the winters. Moreover, the average winter survival of barley from multi-year pot tests was in correlation with the minimal LT50, evaluated in plants hardened in both the field or in growth chambers. From indirect indicators, the levels of ABA increased slightly, while WC and OP clearly decreased in all cultivars during cold hardening. No correlation was observed between LT50 and the ABA content. A significant correlation between LT50 and WC, and between LT50 and OP was found, but only after 1 or more weeks of cold acclimation of the plants had been completed, since both the duration and the rate of decline of these parameters differed in individual cultivars during the cold hardening. The LT50-values of barley cultivars not only accurately characterized their field tolerance to frost, but also were indicative of changes associated with the induction of frost tolerance in plants under the given conditions, when comparing the direct and indirect methods.

Drought is by far the most important environmental factor contributing to crop yield loss, especially in soyabean [Glycine max (L.) Merr.] where symbiotic fixation of atmospheric nitrogen (N2) is sensitive to even modest soil water deficits. Decline of N2 fixation with soil drying causes yield reductions due to inadequate N for protein production, which is the critical seed product. In this paper, we present a combined physiological and breeding research effort to develop soyabean lines that have diminished sensitivity of N2 fixation to drought. A preliminary physiological screen was used to identify lines that potentially expressed N2 fixation drought tolerance. One hundred progeny lines derived from a cross between Jackson, a cultivar proven to have N2 fixation tolerance to drought, and KS4895, a high-yielding line, were tested in the screen. Seventeen lines were identified for subsequent yield trials in moderate- and low-yielding rainfed environments. Two lines, found to have higher yields than commercial checks in these environments were then tested in the greenhouse for their N2 fixation activity in drying soil. Nitrogen fixation activity was found to persist at lower soil water contents than exhibited by the sensitive parent. These two soyabean lines offer a genetic resource for increased yields under rainfed conditions as a result of decreased sensitivity of N2 fixation to water deficit

Grain number has long been considered to be a key determinant of yield in wheat crops and cultivars. In this paper, we argue that both yield and grain number are constrained by a crop's ability to gather resources. In this sense, grain numbers can be considered more as a consequence of yield than a determinant. We examine published literature on the effects of variations in development, light, nitrogen, and water supply on grain number determination and yield. We conclude that most of the variation in both grain number and yield is likely caused by variations in resource accumulation, particularly nitrogen, by the crop.

Pod and seed number are the most important yield components in soybean ( Glycine max (L.) Merrill) crops. Crop growth rate during post-flowering and the duration of the period when pod and seeds are formed explain much of the variation of soybean yields across genotypes and environments. Exposing post-flowering stages to long photoperiod has been found to extend the period R3–R6 and to increase seed number in soybeans grown under field conditions. In this paper, post-flowering development and yield components responses to photoperiod were quantitatively analysed and the degree of coupling between both responses was investigated. Indeterminate soybean cultivars, A-5409 (maturity group V) and Dekalb CX-458 (maturity group IV), were grown under field conditions and exposed to natural photoperiod from sowing to the beginning pod stage (R3). From then onwards, they were either kept under natural daylength or exposed to four photoperiod regimes that were artificially extended in relation to natural daylength by 1.5, 3.0, 4.5 or 6.0 h. All the extended photoperiod regimes increased the duration of R3–R6 period. Both cultivars showed a quantitative type of response through the whole range of explored photoperiods, though A-5409 exhibited a stronger sensitivity. Development responses during the R6–R8 phase were less noticeable and more variable. Exposing plants to extended photoperiod increased the number of nodes per plant and improved node fertility, thus increasing the number of pods and seeds produced per unit area. Average seed weight tended to be reduced in plants exposed to extended photoperiod and the magnitude of these effects depended both on cultivars and treatments. However, seed size was reduced in ca. 20% while seed number was increased by more than 75% due to the treatments. These results strengthen the hypothesis that manipulating photoperiod sensitivity during post-flowering in indeterminate soybean may actually be an avenue to increase seed number and yield.

Sucrose yields in sugarcane (Saccharum spp.) could be improved by increasing the efficiency of biomass production per unit of intercepted radiation and/or by increasing the fraction of total biomass partitioned to stalk sucrose, or both. In theory, this could be achieved by optimally matching the physiology of genotypes to the driving environmental conditions. Quantitative knowledge of the subtle effects of climate and genotype is therefore required to optimise cultivar choice, time of harvest, irrigation and chemical ripening. The objective of this paper is to review existing knowledge of the effect of time of harvest and cultivar on the assimilation and partitioning of biomass in sugarcane by comparing modelling theory and published literature with observations from selected experiments conducted at Pongola, South Africa. Simulations were compared with observations for well-watered crops harvested at different times of the year at Pongola, South Africa. Crops started in April and May seem to have higher radiation use efficiencies than other crops, thereby compensating for lower interception of radiation during this time of the year. Winter-harvested crops partitioned a smaller fraction of final biomass to leaves and more to stalks than summer-harvested crops. This trend was not simulated by the Canegro model. Simulations were partially improved by refining the model to account for temperature control of photosynthesis and respiration. The observed seasonal peak of stalk sucrose content also occurred later than simulated, while the observed decrease in sucrose content from January to April could not be reproduced by the model. These shortcomings have serious implications for the relevance of the model as a tool for identifying crop improvement and management strategies. However, the Canegro model successfully mimicked partitioning of assimilate to stored sucrose using two cultivar parameters. Results suggest that there is scope for improving yields but that the optimisation process should include all components of the sucrose production process in sugarcane, including radiation capture, net photosynthetic efficiency and stalk partitioning. Sufficient understanding of the interactions between these components is lacking. There is a need for models to distinguish between photosynthesis and respiration and the strong dependence of both on temperature should be taken into account. Sinks for leaf, stalk structure and sucrose need to be considered separately to adequately understand the effect of temperature on partitioning.

The presence of suckers, late-formed tillers, in mature sugarcane crops reduces the sugar concentration of harvested material to the detriment of profitability. The amount of suckering varies with cultivar and season. However, the environmental stimuli promoting suckering, i.e. the number of suckers, are not understood. This paper describes the effects on suckering of increasing soil moisture, nitrogen, and the level of light penetrating the canopy. Light was manipulated by plant spacing or removal of dead leaf from mature stalks. Increased nitrogen availability late in the crop's growth cycle promoted suckering, even in a cultivar of low suckering propensity. Higher levels of nitrogen applied at the beginning of the growing season had inconsistent effects, possibly due to variation in rainfall. Increased soil moisture late in the growing season greatly increased suckering and also had a positive effect when combined with high levels of nitrogen. The effect of plant spacing on sucker number was only significant in the plant crop, and then only when expressed as sucker number per mature stalk. Removal of dead leaves had a significant effect on suckering at one site but not another. In all cases, higher plant spacing and dead leaf removal increased light levels recorded under the canopy. The quality and quantity of light required to promote suckering still remain unknown, as does the means by which the plant perceives the light stimuli. The differences in suckering between the plant and ratoon crops suggested that not all stimuli were tested in the treatments applied, or that other factors negated stimuli that were present or that suckering is inherently more prevalent in ratoon crops. All cultivars tested responded similarly to the environmental stimuli that produced a significant effect.

Through reduction of water demand by defoliation during the vegetative growth period of wheat, it may be possible to optimize use of soil water and in-crop rainfall for enhanced grain yield and water use efficiency. Trials conducted in the field in the sub-tropical and semi-arid region of central Queensland (CQ), Australia, over 3 years (1997–1999) were set up under various water and fertility regimes to test this hypothesis. With an early maturity wheat (cv. Sunstate), under rainfed conditions with no fertilizer application, defoliation treatments at early (DE), or middle (DMT) tillering had not effect on grain yield while those imposed at late (DLT) tillering and booting (DB) reduced grain yield. In 1998, with 76 kg basal N ha −1 and 100 mm irrigation during cropping, an early-sown late maturity wheat (cv. Batativa at the end of April) responded to DLT with an increased grain yield (by 7.3%) through an increase of harvest index (HI by 10.7%) and grain water use efficiency (WUE by 22%) compared to the control, but DB had negative effects on almost all components. Both defoliation treatments of a crop sown 2 months later resulted in yield reduction. In 1999, a similar late maturity wheat cultivar (Batavia 2) was sown on 27 April with 55 kg basal N ha −1 under entirely rainfed conditions. DMT had similar positive effects on grain yield (7.4%), HI (5.9%) and WUE (12.7) to DLT in 1998, but reduced protein content compared to the control. Reduction of plant density by 30% at middle tillering was without effect on grain yield; while DLT raised grain WUE it had no effect on grain yield due to a reduction of above-ground dry matter (AGDM). It also reduced grain protein content. Defoliation treatments of a crop sown one month later had no effect on grain yield. Analysis of physiological data collected in 1999 suggests that defoliation suppressed vegetative growth, optimized the ratio of AGDM at anthesis to that at final harvest (0.5–0.8, peak 0.66) and led to more AGDM post-anthesis for maximal grain production. Defoliation that led to a yield increase also increased the leaf area ratio and enhanced stomatal conductance and photosynthetic capacity at anthesis. It is concluded that defoliation of early (April)-sown wheat defoliated at the middle to late tillering stage could let to greater yield and WUE, and would not result in yield reduction. The value of foliage removed and overall economic and risk analyses are discussed in a further paper.

Cereal crop residues are important feed resources for ruminants in developing countries. However, they are poor in nutritive value because digestible energy, crude protein and mineral contents are all low. Techniques to improve the feeding value of crop residues by chemical or biological means have not been adopted widely by small farmers in developing countries. Genetic enhancement may provide an alternative and practical strategy for improvement of nutritive value in cereal straws and stovers. This paper reviews the opportunities for the improvement of nutritive value by plant breeding, with particular reference to dual-purpose cultivars of sorghum ( Sorghum bicolor ) and pearl millet ( Pennisetum glaucum ) in South Asia.

Edaphic factors constrain bean production in most areas where this crop is grown. They include nutrient constraints particularly N and P deficiency, soil acidity including Al and manganese toxicity, and drought. The Bean/Cowpea Collaborative Research Support Program (CRSP) has supported research on edaphic constraints to bean production since its inception, the major partnerships involving the University of Wisconsin and EMBRAPA, Brazil (1981–1989) and the University of Minnesota and INIAP, Ecuador (1989–2002). Research over this period has emphasized cultivar and strain variation in nodulation and nitrogen (N2) fixation, host strain interaction and coevolution, host and strain tolerance of soil acidity and nitrogen fixation under phosphorus limited conditions. This paper reviews recent developments in these areas of nitrogen fixation research, but does so from the perspective of the Bean/Cowpea CRSP project.

This paper reviews accomplishments in cowpea cultivar and germplasm development by the Bean/Cowpea Collaborative Research Support Program (CRSP) which was funded by the United States Agency for International Development for a period of about 20 years. Drought-adapted, pest and disease resistant cultivars ‘Mouride’, ‘Melakh’ and ‘Ein El Gazal’ were developed for rainfed production in the tropical Sahelian zone of Africa. Cultivars ‘CRSP Niebe’ and ‘Lori Niebe’ which have seed and pod resistance to cowpea weevil and some disease resistance were developed for rainfed production in the tropical Savanna zone of West Africa. Cultivar ‘California Blackeye No. 27’ was developed for irrigated production in subtropical California, USA and is a semidwarf with heat tolerance and broad-based resistance to root-knot nematodes and Fusarium wilt. Various cultivars with persistent-green seed color including ‘Bettergreen’ and ‘Charleston Greenpack’ were bred for use in the food freezing industry in the USA. Germplasms were developed with unique traits including: snap-type pods, green manure/cover crop capabilities, heat tolerance during reproductive development, chilling tolerance during emergence, delayed leaf senescence as a mechanism of adaptation to mid-season drought and high grain yields, differences in stable carbon isotope discrimination, harvest index, rooting and plant water- and nutrient-relations traits, broad-based resistance to root-knot nematodes and Fusarium wilt, and resistance to flower thrips, cowpea aphid, lygus bug and cowpea weevil, and various quality traits including all-white and sweet grain. These germplasms provide a valuable resource for breeding additional cowpea cultivars for Africa and the USA.

Accurate prediction of leaf area is critical for precise forecasting of crop growth and yield by most crop simulation models. Most maize ( Zea mays L.) models simulate canopy growth using generic functions. In this paper, we present a new leaf area model that can simulate cultivar-specific growth of individual leaves of maize. The new model was linked to CERES-Maize and validated for several cultivars and environments. The model describes three processes of the life cycle of leaves articulated in a dynamic thermal time framework: expansion, longevity and senescence. Calculations are performed on a per leaf basis since current environmental conditions and stresses affect specific processes on individual leaves. Three cultivar-specific inputs are used to distinguish genotypes. These are: area of largest leaf (cm 2 ), longevity of most longevous leaf (growing degree days, base temperature 8 °C), and final leaf number. We tested the model by linking it to CERES-Maize and making the expansion and senescence processes responsive to the canopy-based carbon balance and stress indices of CERES. Model predictions were compared with field measured leaf area for different genotypes and with data available in DSSAT (version 3.5). The new model improved the accuracy of leaf area prediction compared to the original CERES-Maize. Our evaluation also showed that the carbon balance in CERES does not simulate correctly the effect of reduced assimilate supply for leaf growth caused by inter-plant competition. A sensitivity analysis revealed that this new leaf area model is very sensitive to the number of leaves predicted. The new model provides a flexible system to simulate area of leaves in maize. It also facilitates the evaluation and calibration of carbon, water, and nitrogen balances at the leaf level.

Pearl millet landraces from Rajasthan, India, yield significantly less than improved cultivars under optimum growing conditions, but not under stressed conditions. To successfully develop a simulation model for pearl millet, capable of capturing such genotype×environment (G×E) interactions for grain yield, we need to understand the causes of the observed yield interaction. The aim of this paper is to quantify the key parameters that determine the accumulation and partitioning of biomass: the light extinction coefficient, radiation use efficiency (RUE), pattern of dry matter allocation to the leaf blades, the determination of grain number, and the rate and duration of dry matter accumulation into individual grains. We used data on improved cultivars and landraces, obtained from both published and unpublished sources collected at ICRISAT, Patancheru, India. Where possible, the effects of cultivar and axis (main shoot vs. tillers) on these parameters were analysed, as previous research suggested that G×E interactions for grain yield are associated with differences in tillering habit. Our results indicated there were no cultivar differences in extinction coefficient, RUE, and biomass partitioning before anthesis, and differences between axes in biomass partitioning were negligible. This indicates there was no basis for cultivar differences in the potential grain yield. Landraces, however, produced consistently less grain yield for a given rate of dry matter accumulation at anthesis than did improved cultivars. This was caused by a combination of low grain number and small grain size. The latter was predominantly due to a lower grain growth rate, as genotypic differences in the duration of grain filling were relatively small. Main shoot and tillers also had a similar duration of grain filling. The low grain yield of the landraces was associated with profuse nodal tillering, supporting the hypothesis that grain yield was below the potential yield that could be supported by assimilate availability. We hypothesise this is a survival strategy, which enhances the prospects to escape the effects of stress around anthesis.

This paper tests PARJIB, a simple but powerful model to analyse and forecast yield responses to nutrients in annual crops. The model was calibrated for maize using data obtained under a very wide range of conditions in New Zealand from 1996 to 1999. The calibration process used a genetic algorithm technique. After a preliminary calibration using about half of the available data and only one cultivar, the model performed well, accounting for 66–73% of the observed yield variation in independent datasets that included five cultivars. When simulating the test datasets, the largest errors were associated with one long-season cultivar. The model was then recalibrated against all available data. That dataset spanned five cultivars, four regions of New Zealand, a wide range of soil and weather conditions, and a range of fertiliser application treatments. Grain yields varied from 4 to 18 t/ha. The root mean square (RMS) error of calibration was 0.92 t/ha (9.3%), and the model accounted for 83% of the observed variation in yield. We checked various model predictions against previously published results, and found good agreement. The model indicates strong interactions between water stress, plant population and the need for nutrients. The PARJIB model has substantial potential to aid growers in fertiliser decisions, and to assist researchers in the analysis and interpretation of field experiments.

The objective of this paper is to assess the effectiveness of alfalfa (Medicago sativa L.) improvement efforts over the last century, and with the advent of molecular biology, identify challenges for alfalfa improvement in the future. Yield trials conducted between 1986 and 1998 from around the US were used to compare yield and persistence of older alfalfa cultivars to those released in the 1990s. First and second harvest forage yield of recently released alfalfa cultivars were not improved over those of older cultivars. New cultivars had higher forage yield at fourth harvest, in early September, possibly due to a reduction in fall dormancy. Efforts to improve alfalfa persistence by breeding for improved disease resistance and greater winter hardiness also have not been effective at most locations. Use of molecular biology for alfalfa improvement depends upon identifying genes that control important agronomic traits that translate into greater yield, improved persistence, and enhanced forage quality. Few such genes have been identified in alfalfa, and their use might be complicated by the polyploid nature of this outcrossing species. The Medicago truncatula genome project is providing large amounts of sequence information, but little is known about the regulation of these genes and the function of their protein products in planta. Uncertainty exists regarding the effectiveness of transferring these genes to alfalfa to obtain a desired phenotype. Much remains to be done to identify key genes that determine agronomic performance of crop plants, including alfalfa, and to clarify mechanisms that regulate the expression of genes and the function(s) of their protein products under field conditions. Future efforts to improve agronomic performance of alfalfa will be enhanced by partnerships between public and private scientists because companies now dominate commercial release of new alfalfa cultivars.

The contribution of genetic improvement to overall soybean (Glycine max (L.) Merrill) yield improvement has been estimated to range from 0.5 to 0.7% per year in continental North America. Therefore, breeding has had and potentially will play an important role in yield improvement. An understanding of the physiological traits associated with genetic improvement in yield holds the promise of increasing the efficiency of further advances in yield improvement. A number of theories have been put forward as to the physiological traits that may contribute to genetic yield improvement. However, in reviewing the research literature, a number of incongruencies among the theories become apparent. The objective of this paper was to discuss some of the contradictory theories on the physiological traits associated with yield, especially as they address the role of assimilate supply to genetic yield improvement. The genetic material used, the means of parameter calculation, the phenological stage at which treatments were imposed can all impact the conclusions that may be drawn from a study. The conclusions from a study must thus be seen within the constraints of its experimental approach. Total dry matter (DM) accumulation appears to be a more important contributor to yield improvement than harvest index. The association between DM accumulation and yield is most apparent after the beginning of reproductive development, although the physiological traits associated with this increase is contentious: neither selection for maximum leaf carbon exchange rate (CER) nor maintenance of leaf CER during the seed filling period (SFP) has proved to consistently improve yield. Soybean cultivars have a complex feedback system which maintains a cultivar-specific source–sink ratio. Manipulation of the ratio of source supply to sink demand has shown that plants generally readjust to maintain their inherent source–sink ratio. A possible explanation for the lack of gain in yield through selection for greater assimilate supply alone may be because it was ineffective in increasing the source–sink ratio of the cultivar. The source–sink ratio may prove to be a more potent trait than assimilate supply alone to further soybean genetic yield improvement.

The common bean crop (Phaseolus vulgaris L.) occupies 5.5 million hectares in Brazil and provides about 30% of the population’s protein needs. Yield remains low mainly due to limited availability of N and P, and to the often acid soil conditions. Surprisingly, there have been only very limited studies in Brazil in which the isolation and evaluation of efficient N2-fixing bean strains has been attempted. This paper reports the selection of bean rhizobia for the “Cerrados”, the savannas that represent one-fourth of Brazilian land. Two-hundred strains were selected from large pink-colored nodules collected in the Cerrados region and biological nitrogen fixation was evaluated under optimal (27/21 °C, day/night) and high (37/21 °C) temperature conditions. Thirty-six strains were selected and their nitrogen-fixing capacity and competitiveness further evaluated with black-seeded “Negro Argel”, and colored “Carioca” cultivars. One-fifth of the strains showed low genetic stability of nodulation genes, but some strains were as or more competitive than the strains currently recommended for use in commercial bean inoculants in Brazil. The superior performance of five strains was confirmed under field conditions and re-inoculation in the second year increased bean yield. The DNA fingerprintings obtained by the ERIC–REP-PCR analyses indicated a high level of genetic diversity, and among the 36 strains, six different patterns of RFLP-PCR of the 16S rRNA gene region were detected. The 16S rDNA sequences of the most efficient and competitive strains were genetically similar to Rhizobium tropici, suggesting that further studies on inoculant strains in the hot and acid soils of the Brazilian Cerrados and Africa should emphasize this species.

Chronological and physiological age of seed tubers have major impacts on potato yields. This paper presents a new, simple and reliable physiological age index (PAI) that considers and reconciles the effects of chronological and physiological age. PAI calculation is based on the haulm killing date of the seed crop (T0) and the end of the incubation period of seed tubers, measured under standardized conditions. The PAI formula is T1/T2, where T1 is the time from haulm killing date (T0) to possible planting date and T2 the time from T0 to the end of the incubation period. The PAI expresses physiological ageing of seed potato tubers within a range from 0 (for physiologically young) to 1 (old) tubers. To test the PAI existing data were re-evaluated and re-elaborated and specific experiments regarding seed origin and storage conditions for different cultivars were performed during 1994–1999. The PAI proved useful in assessing differences due to differences in growing conditions, cultivar, haulm killing, seed origin and storage system, and pre-planting treatments. For example, for cv. Spunta 6 days after haulm killing the PAI was 0.025 and after 100-storage days the PAI was 0.56, 0.52 and 0.49 for seed tubers stored in heaps in the field, at relatively high temperatures, natural diffuse light and a cold (4°C) and ventilated store, respectively. The PAI is related to ground cover duration and yield of the future crop. For a PAI of 0.55 tuber yield was 55 t ha−1, while for a PAI of 0.80 tuber yield was 40 t ha−1. The PAI is easy to measure, non-invasive, objective, reproducible and reliable and could be used for modelling purposes to describe performance of seed tubers.

Parasitic flowering weeds of the genus Striga (Scrophulariaceae) cause substantial losses in sorghum [Sorghum bicolor (L.) Moench] production in sub-Saharan Africa. Striga-resistant sorghum cultivars could be a major component of integrated striga management, if resistance was available in adapted, productive germplasm. In this paper we review methodologies for breeding striga-resistant sorghums. The agar-gel assay is an excellent tool to screen host genotypes in the laboratory for low production of the striga seed germination stimulant. Further laboratory assays are needed which allow the non-destructive, rapid and inexpensive evaluation of individual plants for additional resistance mechanisms. Field screening for striga resistance is hampered by high microvariability in African soils, heterogeneity of natural infestations, and concomitant large environmental effects on striga emergence. An improved field testing methodology should include one or several of the following practices: field inoculation with striga seeds; appropriate experimental design including elevated replication number; specific plot layout; use of appropriate susceptible and resistant checks; evaluation in adjacent infested and uninfested plots; and the use of selection indices derived from emerged striga counts, striga vigor, and grain yield or a host plant damage score. Due to the extreme variability of the parasite and significant genotype×environment interaction effects, multi-locational screening is recommended to obtain materials with stable performance. Additional strategies include: careful definition of the target environments; determination of the most important selection traits in each target environment; characterization of crop germplasm and improvement of available sources of resistance for better agronomic performance; transfer and pyramiding of resistance genes into adapted, farmer-selected cultivars; development of striga-resistant parent lines for hybrid or synthetic cultivars; and development of random-mating populations with multiple sources of resistance. The development of marker-assisted selection techniques for broad-based, polygenic striga resistance is underway. This approach is particularly promising because striga resistance tests are difficult, expensive, and sometimes unreliable; the parasite is quarantined; and some resistance genes are recessive. Transgenic, herbicide-tolerant sorghums could contribute to an immediate, cost-effective control of striga by herbicides, but such cultivars are not yet available. The selection of sorghum cultivars with specific adaptation to integrated striga management approaches could contribute to sustainable sorghum production in striga-infested areas of sub-Saharan Africa

This paper describes results of a three-year field experiment and a simulation study to quantify the magnitude of improvement in yield potential at different levels of management and climatic variability. In two crop seasons for crops planted on time, there was a significant increase of 1.0–1.3% per year in yield of cultivars but it was negligible in the third season when March was relatively warmer. In late plantings done in one season, the rate of improvement in yield varied between −0.16 and 0.57% per year. This indicates that in warm conditions, particularly during grain-filling period, there was only a negligible difference among the cultivars. It suggests that new cultivars yield more than the older ones only when the temperatures are favorable for growth and development. The trends in simulated yields were similar in direction but lower in magnitude compared to the trends in observed yields in field experiments. The simulated rate of change in yield was always greater in the potential production conditions compared to the modest level of management as is practiced today. Simulation always showed a negative trend in yielding ability of cultivars in seasons when grain-filling duration was less than 29 days. When the grain-filling duration exceeded 29 days, the trend in most cases was positive varying up to +0.67% per year. The late-released cultivars used in this study have long vegetative duration that extends grain-filling to high temperatures. Crop seasons that favored long vegetative duration or had high March temperatures that shorten grain-filling showed a negative trend in yield improvement whereas seasons with cool March showed a positive improvement. Conclusions based on limited experimentation in field studies, therefore, can be biased depending upon the agro-environment experienced by the cultivars. Simulation studies can supplement such field studies and assist in reducing this bias.

This paper reviews the factors determining flowering time and phenology requirement in rainfed lowland rice. Recent developments in understanding of the temperature and photoperiod effects on flowering time of rice resulted in phenology models that can predict flowering time accurately in the irrigated field. However, in the rainfed lowland ecosystem drought and low soil fertility commonly delay flowering time. Genotypes with a long delay are often those with a large yield reduction under the adverse conditions. In rainfed lowland rice, there may not be standing water at the appropriate time for transplanting and the use of old seedlings for transplanting on a later date results in delay in flowering. Optimum time of flowering for high yield is often related to water availability, and early flowering cultivars are favoured in areas where the probability of occurrence of late season drought is high. However, short duration cultivars are less tolerant to stress such as early season drought if the stress develops during the vegetative stage. The variation in water availability in paddies would cause genotype phenology-environment interaction for yield. Further understanding of water balance in the rainfed lowlands would assist determination of the optimum phenology groups for different regions of the rainfed lowland system. (C) 1999 Elsevier Science B.V. All rights reserved.

The grain yield of rainfed lowland rice (Oryza sativa L.) in many Asian countries is reduced by drought and low soil fertility. This paper reviews recent work on the interactions of these effects on grain yield and also work on cultivar requirements for production under low soil fertility conditions, particularly in Thailand and Laos, Fertiliser application trials in the held and nutrient omission pot trials showed that low soil fertility resulted from inadequate levels of many essential nutrients, but especially of nitrogen (N) and phosphorus (P), When standing water disappeared from the paddy, yield was reduced even if there was no apparent problem of water stress. Simulation modelling indicated that this was associated with reduced nutrient availability. In multi-location trials involving a large number of genotypes, the variance component for grain yield was often greater for genotype by environment interaction than for genotype alone. While the genotype by fertiliser interaction was often significant, its contribution to the genotype by environment interaction was rather small. These results indicate that the current practice of direct selection for yield under rather high fertiliser application rate may be justified in breeding programs. The limited information from research conducted with irrigation and under rainfed lowland conditions suggests that both uptake of N and P and their utilisation efficiency (grain yield/unit nutrient uptake) to produce grain yield are important for adaptation to low soil fertility environments. Genotypic variation in utilisation efficiency appears to be consistent across environments, and the efficiency can be improved by the development of cultivars that require a low nutrient concentration in the plant and a higher nutrient allocation to the grain. The amount of genetic variation for these specific traits, the ease with which these traits can be incorporated in an appropriate genetic background and the extent of the specific nutritional problem will determine the usefulness of selection for a specific nutrient disorder, and they need to be identified in the future research. (C) 1999 Elsevier Science B.V. All rights reserved.