Email: pk.bhati@cgiar.org

Terminal heat stress which occurs during the reproductive phase causes significant loss of crop yield in wheat round the world. It has been well documented in wheat, causing morphophysiological alterations, biochemical disruptions, and reduction of genetic potential. Combined with the consequences of climate change, we must ensure that farmers across the world are equipped to overcome the negative impact of heat stress. To address the issue of terminal heat stress, a new partnership between BISA-ICAR-NBPGR was initiated in 2020 for germplasm characterization and trait discovery in wheat using precision phenotyping and genotyping approaches for improving climate resilience, productivity and nutritional quality.

The main goal of this partnership was to develop, evaluate and disseminate wheat germplasm in which grain yield is sustained not compromised too much under heat stress. A set of 3200 diverse lines including newly developed CIMMYT advanced lines, landraces, primitive and traditional cultivar, wild and Indian varieties were evaluated to extreme heat under field conditions. These lines were evaluated for grain yield under optimum and heat stress condition for two years (2020-21 and 2021-22) with two replications at three different locations in BISA India: Ludhiana, Jabalpur and Pusa. Genomic data was also used to discard nonperforming lines.

A set of 560 heat tolerant entries were selected based on two years data of 3200 lines. These selected 560 entries were again planted at the three sites of BISA. The planting was done in replicated standard plots (3.02m2) for yield and yield-related parameters under optimum (early November) and heat stressed (Late December) conditions. About 20 traits were recorded at each BISA site and more than 80,000 data points were recorded digitally in one year of testing. The yield of the optimum sown trial at Ludhiana ranged from 3.41 to 7.78 t/ha while under heat stress it was 2.26 to 7.34 t/ha.

Similarly, the optimum and heat-sown trials yield at Jabalpur ranged from 4.44 to 8.18 and 3.65 to 6.21 t/ha respectively. The plot yield at Samastipur, Bihar under normal sown conditions ranged from 2.29 to 7.58 t/ha while it was 1.09 to 4.69 t/ha under heat stress. The effect of heat stress on the mean grain yield of genotypes was significant in each of the three zones but was highest (2.4 t/ha) in the northeast plain zone (Samastipur) and lowest (1.0 t/ha) in the northwest plain zone (Ludhiana). In the central zone (Jabalpur) the average yield decline was 1.8 t/ha. 

Based on heat susceptibility index (HSI), 162 heat tolerant lines were identified. Most (128) of them were from Ludhiana, while about 32 were from Jabalpur. At Samastipur, only 2 lines were able to express heat tolerance. These lines have been provided to national partners for either direct release or use in their breeding program.