Search

Photosynthetic manipulation provides new opportunities for enhancing crop yield. However, understanding and quantifying the importance of individual and multiple manipulations on the seasonal biomass growth and yield performance of target crops across variable production environments is limited. Using a state-of-the-art cross-scale model in the APSIM platform we predicted the impact of altering photosynthesis on the enzyme-limited (Ac) and electron transport-limited (Aj) rates, seasonal dynamics in canopy photosynthesis, biomass growth, and yield formation via large multiyear-by-location crop growth simulations. A broad list of promising strategies to improve photosynthesis for C3 wheat and C4 sorghum were simulated. In the top decile of seasonal outcomes, yield gains were predicted to be modest, ranging between 0% and 8%, depending on the manipulation and crop type. We report how photosynthetic enhancement can affect the timing and severity of water and nitrogen stress on the growing crop, resulting in nonintuitive seasonal crop dynamics and yield outcomes. We predicted that strategies enhancing Ac alone generate more consistent but smaller yield gains across all water and nitrogen environments, Aj enhancement alone generates larger gains but is undesirable in more marginal environments. Large increases in both Ac and Aj generate the highest gains across all environments. Yield outcomes of the tested manipulation strategies were predicted and compared for realistic Australian wheat and sorghum production. This study uniquely unpacks complex cross-scale interactions between photosynthesis and seasonal crop dynamics and improves understanding and quantification of the potential impact of photosynthesis traits (or lack of it) for crop improvement research.

Main shoot total leaf number (TLN) is a key determinant of plant leaf area and crop adaptation. Environmental factors other than photoperiod can affect TLN in sorghum, implying that leaf appearance rate (LAR) and development rate can differ in response to temperature. The objectives of this study were to determine if (1) temperature effects on TLN can be explained as a consequence of differences in temperature responses across phenological processes and (2) genotypic differences in these responses can be linked to agroecological adaptation.Nineteen sorghum genotypes were sown on twelve dates at two locations in Ethiopia with contrasting altitude, creating temperature differences independent of photoperiod. TLN and temperature were recorded in all experiments and LAR in six sowing dates.Eleven of the genotypes showed a temperature effect on TLN, which was associated with a significantly higher base temperature (Tbase) for LAR than for pre-anthesis development rate (DR). In contrast, genotypes with no effect of temperature on TLN had similar Tbase for LAR and DR. Across genotypes, Tbase for LAR and DR were highly correlated, but genotypes with low Tbase had the greatest difference in Tbase between the two processes. Genotypic differences were associated with racial grouping.Genotypic and racial differences in responses of phenological processes to temperature, in particular in Tbase, can affect specific adaptation to agroecological zones, as these differences can affect TLN in response to temperature and hence canopy size and the duration of the pre-anthesis period. These can both affect the amount of water used and radiation intercepted pre-anthesis. A multi-disciplinary approach is required to identify genotype × environment × management combinations that can best capture the ensuing specific adaptation.

In cereal crops, average leaf angle of the canopy affects the total amount of radiation that is intercepted and how effectively light is distributed through the canopy. Selecting for more erect leaves in maize and rice has allowed higher density plantings and has been associated with significant productivity gains in those crops. The effects of leaf angle on crop productivity depend on how it influences within-canopy light distribution and the plants’ efficiency in using that light to produce biomass. Canopy light distribution is influenced by agronomic interventions such as growing at different locations, sowing on different dates, using different plant densities (leaf area index). For sorghum, which may be grown across a large range of latitudes and plant population densities, the effects of leaf angle manipulations have not previously been studied. We used the APSIM-DCaPST sorghum model to simulate the effects of more erectophile canopies on yield for two locations with different latitudes and planting dates, assuming low-and high- intensity agronomies. The simulations showed that more erect leaves would result in yield benefits in most years at both of those locations. Contrary to the situation in maize, the simulated yield gains were greatest in the low-yielding rather than the high-yielding years. Interestingly also, the simulated productivity gains in erectophile sorghum canopies were not due to enhanced light penetration as suggested in maize, but rather through effects on extent of radiation interception and its implications for early crop growth and crop water balance through the crop life cycle.

The stay-green trait is recognised as a key drought adaptation mechanism in cereals worldwide. Stay-green sorghum plants exhibit delayed senescence of leaves and stems, leading to prolonged growth, a reduced risk of lodging and higher grain yield under end-of-season drought stress. More than 45 quantitative trait loci (QTL) associated with stay-green have been identified, including two major QTL (Stg1 and Stg2). However, none of the contributing genes that regulate functional stay-green are known. Here we show that the PIN FORMED family of auxin efflux carriers induce some of the causal mechanisms driving the stay-green phenotype in sorghum, with SbPIN4 and SbPIN2 located in Stg1 and Stg2, respectively. We found that 9 of 11 sorghum PIN genes aligned with known stay-green QTL. In transgenic studies, we demonstrated that PIN genes located within the Stg1 (SbPIN4), Stg2 (SbPIN2) and Stg3b (SbPIN1) QTL regions acted pleiotropically to modulate canopy development, root architecture and panicle growth in sorghum, with SbPIN1, SbPIN2 and SbPIN4 differentially expressed in various organs relative to the non stay-green control. The emergent consequence of such modifications in canopy and root architecture is a stay-green phenotype. Crop simulation modelling shows that the SbPIN2 phenotype can increase grain yield under drought.

Background and Objectives Injera (a fermented pancake-like product) is a traditional food in Ethiopia but is traditionally made from tef (Eragrostis tef). But sorghum also a traditional Ethiopian crop can be used although considered having a lower quality. A 139 sorghum (Sorghum bicolor) cultivars and their corresponding injera were tested for a range of chemical tests, namely total starch, amylose, and tannin contents, plus a newly developed image analysis program to provide objective measures of the injera. Findings The results showed several sorghums were superior to tef in making injera, based on the chemical, image, and/or sensory analysis. Tannin content was highly positively correlated with color and negatively with taste, while high starch content was more related to softness and rollability. The imaging analysis also provided a rapid and more objective assessment of injera. Two sensory traits, color and eye evenness, were strongly positively correlated to the image data, through L*, a* and b*, and average pixel count per “eye,” respectively. Conclusions Quality testing involving human sensory panels within a breeding program is time consuming, costly and can be impractical for the selection of superior lines from large numbers of selection candidates to the next stage. Objective tests such as imaging analysis can be used at earlier stages in the breeding program which would allow breeding lines with suitable injera quality to be progressed. This would result in new sorghum varieties with fresh injera quality similar too or better than tef. Significance and novelty A new image analysis program compliments chemical analysis for early screening of sorghums for injera, saving time and costs.

Water scarcity can limit sorghum (Sorghum bicolor (L.) Moench) production in dryland agriculture, but increased whole-plant transpiration efficiency (TEwp, biomass production per unit of water transpired) can enhance grain yield in such conditions. The objectives of this study were to quantify variation in TEwp for 27 sorghum genotypes and explore the linkages of this variation to responses of the underpinning leaf-level processes to environmental conditions. Individual plants were grown in large lysimeters in two well-watered experiments. Whole-plant transpiration per unit of green leaf area (TGLA) was monitored continuously and stomatal conductance and maximum photosynthetic capacity were measured during sunny conditions on recently expanded leaves. Leaf chlorophyll measurements of the upper five leaves of the main shoot were conducted during early grain filling. TEwp was determined at harvest. The results showed that diurnal patterns in TGLA were determined by vapour pressure deficit (VPD) and by the response of whole-plant conductance to radiation and VPD. Significant genotypic variation in the response of TGLA to VPD occurred and was related to genotypic differences in stomatal conductance. However, variation in TGLA explained only part of the variation in TEwp, with some of the residual variation explained by leaf chlorophyll readings, which were a reflection of photosynthetic capacity. Genotypes with different genetic background often differed in TEwp, TGLA and leaf chlorophyll, indicating potential differences in photosynthetic capacity among these groups. Observed differences in TEwp and its component traits can affect adaptation to drought stress.

Drought and heat stress are increasingly important abiotic limitations to productivity of sorghum. Here, we use long-term simulations to quantify the importance of transpiration rates to drought adaptation and the importance of threshold temperatures and tolerance above the threshold for adaptation of seed set to heat stress. Simulations were parameterised using results of detailed physiological studies. The importance of transpiration rates to drought adaption was studied by comparing productivity of maize and 3dwarf sorghum. These crops have similar transpiration efficiency but contrasting transpiration rates per unit green leaf area (TGLA), which was captured through differences in RUE. Results showed that the greater TGLA of maize reduced productivity under drought stress, but increased productivity in well-watered conditions, indicating a trade-off between yield potential and drought adaptation. The increased water use of maize associated with higher yield potential could negatively affect carry-over of soil water in a cropping systems context. Simulations for sorghum productivity under heat stress, using long-term weather records for six locations across the Australian sorghum belt, showed that the most common incidence of heat stress around anthesis was the occurrence of individual days with maximum temperatures of 36–38 °C. Because these temperatures were near the threshold that limits seed set, increased temperature thresholds generally minimised yield reductions. However, predicted temperature increases in coming decades justify additional selection for increased tolerance above the threshold. As manipulating sowing dates did not reduce risks of heat stress around anthesis, genetic improvement provides the best prospect to mitigate adverse effects on grain yield.

Well-designed agricultural decision support tools (DS) equip farmers with a rapid, easy way to compare multiple scenarios as well as the influence of different management strategies on crop production. One such tool, CropARM (http://www.armonline.com.au) assists users in establishing a framework of risk, with simulations incorporating climate scenarios and management actions, such as fertiliser rates, sowing time, row spacing, and irrigation regimes. When used in conjunction with soil and climate characteristics, biophysical model-based DS tools provide information that complements farmer experience and helps establish a framework for risk management given local climate characteristics. In this study, we used the APSIM model to provide the simulation data necessary to expand CropARM for new management conditions and environments in southern Australia. Prior to this work being undertaken, no CropARM data was available for Tasmania and no sites in CropARM allowed users to compare rainfed and irrigated wheat crops. This study collated data from 27 plots across ten sites in Tasmania, from the period 1981 to 2011, under both rainfed and irrigated conditions. APSIM was parameterised with these field observations and the subsequent scenario simulations were used to populate CropARM. Wheat cultivars used in the parameterisation of APSIM include Brennan, Isis, Mackeller, Revenue, Tennant (winter types) and Kellalac (spring type). The validation showed reliable model parameterisation, with an r2 value of close to 1, which is considered satisfactory. 670,680 simulations were undertaken and incorporated within the CropARM database for wheat cropping systems across Tasmania. With regularly updated climate streams, the free online framework provided by CropARM gives users the ability to assess downside risks associated with several different crop management alternatives, and by simultaneously comparing multiple scenarios, users can select management options that are likely to adh

High temperatures across the Australian sorghum belt can reduce sorghum yields, but genotypic differences in heat tolerance could mitigate these yield losses. The objectives of this study were to quantify occurrences of high temperatures around anthesis of sorghum, determine their yield impacts, and assess the potential for management and genetics to minimise any adverse effects. Long term weather records for six locations across the Australian sorghum belt were used to quantify the probability of high temperature occurrence. These records were then used in a simulation study with the APSIM-sorghum model. The model was adapted to capture high temperature effects on grain yield for five hypothetical genotypes that differed in temperature threshold for effects on seed set and in tolerance to temperatures above that threshold. Results showed that the most common incidence of heat stress around anthesis was the occurrence of individual days with maximum temperatures between 36–38° C. Because these temperatures were near the threshold limiting seed set in tolerant genotypes, an increased temperature threshold generally minimised adverse yield effects. However, 1–5 °C predicted temperature increases in coming decades will justify additional selection for increased tolerance above the threshold. Manipulation of sowing dates did not reduce risks of heat stress around anthesis, unless sowing was extremely late. Hence, genetic improvement provides the best prospect to mitigate heat stress effects on grain yield.