Exploration of genetic variation for heat tolerance in wheat: a global core collection and EMS mutagenesis approach

Abstract

Wheat, one of the world's most important crops, faces unprecedented challenges as climatic variability increases and finite resources such as soil and water degrade. Although wheat occupies the largest total harvested area among cereals, its total productivity remains the lowest due to abiotic stress-induced losses. The main challenge for breeders lies in developing wheat cultivars that can sustain or boost their productivity amidst stressful conditions. To address this challenge, screening methods at various developmental stages are needed to evaluate wheat lines under heat stress. Screening was conducted under controlled conditions in growth chambers at the seedling stage under a continuous heat stress of 40°C for four days and at all developmental stages under a continuous diurnal heat stress of 35/28°C (day/night) temperatures for the entire life cycle. To evaluate existing and novel genetic variation for heat tolerance, both screens utilized a global germplasm collection and an EMS (ethyl methanesulfonate) population using Montana cultivars MT Sidney and Dagmar. The goal was to identify and leverage genetic diversity in heat tolerance for eventual development of Montana-adapted, heat tolerant wheat varieties. The seedling stage screen of the germplasm collection revealed 51 heat tolerant wheat lines, three of which exhibited repetitive tolerance. Using the same germplasm collection, the full lifecycle screen revealed 27 heat tolerant wheat lines that maintained vegetative, reproductive, and post-reproductive growth and development under diurnal heat stress conditions. Four of these lines correlated with the seedling stage screen and thus may exhibit tolerance under heat stress conditions from seedling stage all the way until senescence. Mutagenesis revealed ten MT Sidney M2 lines that outperformed all controls during the seedling stress screen. Additionally, five Dagmar M2 lines maintained vegetative, reproductive, and post-reproductive tolerance under full lifecycle heat stress conditions. Because both MT Sidney and Dagmar M2 lines exhibited better heat tolerance than their respective controls, some sort of heat response advantage was likely conferred via EMS mutagenesis. This study emphasizes the importance of germplasm material for identifying abiotic stress tolerance using various screening methods. Mutagenesis techniques are also pivotal for the development of abiotic stress tolerant crops.