Abstract Simultaneous genetic improvements in grain yield and heat stress tolerance (HST) are necessary to avoid a fall in crop yields caused by global warming during the 21st century. Future food security depends on crop breeding solutions to this challenge, especially in developing countries where the need is greatest. We stochastically model a wheat breeding program during 60 years of rapid global warming based on rapid 2‐year cycles, with selection in early generations for HST, grain yield, disease resistance, and stem strength. In each cycle, breeding values were estimated by best linear unbiased prediction using all pedigree and phenotypic information (including selfing) back to the founders. We compared two methods of selection and mating design with similar costs. The first method was truncation selection for HST to match predicted increases in land temperatures followed by selection for an economic index composed of weighted estimated breeding values for each trait, followed by random pair‐wise mating among selections. The second method was optimal contributions selection ( OCS ) for the economic index with an overriding constraint to increase HST in each cycle to match global warming trends, and mating prescribed by OCS . Truncation selection caused a rapid loss of genetic diversity, and HST did not keep pace with global warming. Consequently, grain yield began to decline due to heat stress before 60 years. With OCS , HST matched global warming trends, the economic index almost tripled and grain yield nearly doubled during 60 years of global warming. OCS on an economic index, with a priority to meet HST, increased grain yields and avoided a major threat to global food security caused by global warming.
Rising temperatures or global warming will be detrimental for various crops. Moreover, because of increasing demand for lentil (Lens culinaris L.) grains, there is a need to broaden the adaptation of this crop into warmer climes. Hence, a study was conducted to evaluate the effects of high temperatures (>32/20oC) during reproductive growth on performance of lentil and to probe the mechanisms associated with reproductive failures. Three lentil genotypes, viz., LL699, LL931, and LL1122, were grown in pots at two sowing dates: (1) the normal sowing time (NS) in November so that day/night temperatures during the reproductive stage were below 32/20°C; and (2) late-sown (LS) in February so that temperatures during the reproductive stage were above 32/20°C. The plants were fully irrigated during both the sowing situations. In LS plants, the phenology was accelerated, leading to substantial reduction in biomass, flowers, and pods, accompanied by marked shortening of flowering period and podding duration, causing decreased seed yield. At the peak flowering stage (average temp. >32/23oC), the leaves of the LS plants had significantly lower relative leaf water content and lower stomatal conductance than NS plants at the same stage, indicating that the late sowing induced both water stress and heat stress. In LS plants, reproductive function was markedly reduced in all genotypes, causing increased pod abortion. The leaves of LS plants showed increased damage to membranes, chlorosis, decreased photochemical efficiency, with an associated reduction in sucrose synthesis and increase in its hydrolysis, compared with the NS plants. Heat stress, in combination with intermittent water stress during the reproductive phase in the LS plants, was extremely detrimental for all three lentil genotypes, with only minor differences among them. Controlled-environment studies, where the plants were subjected to high temperatures (33/15°C, 35/20°C) during reproductive growth, also validated the detrimental effects of heat stress on studied traits, similar to outdoor conditions.
Chickpea is the third major cool season grain legume crop in the world after dry bean and field pea. Chilling and freezing range temperatures in many of its production regions adversely affect chickpea production. This review provides a comprehensive account of the current information regarding the tolerance of chickpea to freezing and chilling range temperatures. The effect of freezing and chilling at the major phenological stages of chickpea growth are discussed, and its ability for acclimation and winter hardiness is reviewed. Response mechanisms to chilling and freezing are considered at the molecular, cellular, whole plant, and canopy levels. The genetics of tolerance to freezing in chickpea are outlined. Sources of resistance to both freezing and chilling from within the cultivated and wild Cicer genepools are compared and novel breeding technologies for the improvement of tolerance in chickpea are suggested. We also suggest future research be directed toward understanding the mechanisms involved in cold tolerance of chickpea at the physiological, biochemical, and molecular level. Further screening of both the cultivated and wild Cicer species is required in order to identify superior sources of tolerance, especially to chilling at the reproductive stages.
In order to determine the importance of awn photosynthesis on grain yield under terminal drought, six two-rowed cultivars of barley representing high yielding commercial releases from 1961 to 2006 were studied in a glasshouse experiment at CSIRO, Western Australia. The cultivars were grown with and without watering from anthesis. Detailed measurements of plant water status, awn, flag and penultimate leaf photosynthetic rate were made from anthesis. At final harvest, biomass, yield and yield components were measured. Awn net photosynthesis rate (Pn) was lower than penultimate and flag leaf and decreased gradually after anthesis. The rate of decreasing Pn was rapid under terminal drought. There was no difference in awn Pn among cultivars under well-watered conditions, but under terminal drought the awn Pn of barley cultivars Baudin and Clipper decreased faster than Vlaming, Gairdner and Stirling. Surface area of awns in each cultivar was higher than the flag and penultimate leaf. Thus, total awn photosynthesis under both well-watered and terminal drought conditions was higher than flag leaf photosynthesis. In Vlaming, total awn photosynthesis was higher than penultimate leaf photosynthesis. Grain yield of the cultivars Baudin, Covette and Gairdner was affected by terminal drought, but grain yield did not correlate with awn total photosynthesis. Under well-watered conditions awn Pn had a significant negative correlation with ear weight. We suggest that under terminal drought, higher awn area does not lead to higher grain yield because sink size may be the factor limiting grain yield in barley.
