Studies to Improve Wheat for High Temperature Stress Areas

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Heat stress is one of major limitations in wheat (Triticum aestivum L.) productivity in arid, semiarid, tropical and semi tropical regions of world. Wheat is grown as winter cereal crop in subtropical countries like India. The crop experiences chronic high temperature at most of phenological stages of growth. A detailed understanding of genetic variation and mechanisms of heat tolerance in wheat would facilitate development of intrinsically thermotolerant genotypes. To understand thermotolerance of currently grown wheat varieties, studies on physiological assays at seedling stage, canopy temperature depression (CTD), dry matter translocation (DMT) were carried out along with estimation of field performance. Seedling screening assays identified varieties showing thermotolerance at seedling stage and showed association with high temperature tolerance at adult plant stage. Advanced generation selections were developed from the crosses involving these genotypes, which showed yield advantage over standard check in rod row trials at three different locations. The thousand-kernel weight for these selections ranged from 47.7 to 50.1g with average increase of 13% over the parental mean at Pune location. Studies on an alternative dwarfing gene Rht8, known to reduce plant height by 10 percent without significant reduction in yield under high temperature was also undertaken. Genotypic and phenotypic analysis of 92 genotypes confirmed the absence of Rht8 gene in the cultivated varieties of India. Rht8 gene was transferred to tall genotypes viz. Ajantha and MP3054 from donor Chuan Mai18. Studies on canopy temperature depression on a set of varieties in complementation with dry matter translocation established that cooler canopies with a longer grain-filling period of 40-42 days after ear emergence showed advantage under continual heat stress throughout growth period. Further research is in continuation to dissect and understand the genetic basis to variation in heat stress tolerance exhibited by different varieties.