Genetic evaluation of commercial bread wheat (Triticum aestivum L.) cultivars for duration and rate of grain filling under normal and heat stress conditions

Grain filling period and grain filling rate are among the traits that affect plant response to heat stress. Our knowledge about the the status of these traits in Iranian commercial bread wheat cultivars under normal and heat stress conditions is so rare if not available. The purpose of this study was to evaluate grain filling duration and grain filling rate of Iranian commercial bread wheat cultivars and to study genetic diversity under normal and heat stress of the earth's hottest places, Ahvaz condition.

The experiments were conducted during 2017 and 2018 under normal (optimal planting date) and terminal heat stress (delayed cultivation) conditions on 33 commercial bread wheat cultivars including: Kaz (international heat tolerant), Montana (international heat sensitive), two other international cultivars, weebill and babax and 29 commercial varieties in Iran, namely Roshan, Arvand, Ghods, Flat, Hirmand, Alvand, Verinac, Zagros, Kavir, Chamran, Marvdasht, Shiraz, Dez, Pishtaz, Hamoon, Bam, Sistan, Neyshabur, Sepahan, Arta, Bahar, Arg, Pars, Aflak, Chamran 2, Mehregan, Shosh, Barat and Khalil. The experiment was conducted as a randomized complete block design with three replications at the experimental field of Shahid Chamran University of Ahvaz.

The results of combined analysis showed significant differences (P≤0.01) between genotypes, environment (heat stress) and also genotype-environment interaction for grain yield, grain filling duration and grain filling rate. In general, grain yield and grain filling period of cultivars were significantly reduced under stress condition compared to non-stress condition. However, grain filling rate decreased in most cultivars and almost increased in tolerant cultivars such as kaz. Results of principal component analysis showed that Hamoon, Kaz, Chamran 2, Arvand, Chamran, Falat, Verinac, Alvand, Mehregan and Shosh had high yield and yield stability under heat stress condition. The coefficient of genotypic and phenotypic variation for different traits indicated significant variation for all traits. In addition, significant heritability and genetic improvement were estimated for grain filling rate. This trait showed a high correlation with grain yield under both stress and non-stress conditions.

Among the commercial bread wheat varieties Chamran 2, Shoush and Alvand showed considerable heat tolerance compared to the international heat tolerant cultivar, Kaz. Grain filling rate was identified as an important trait in optimal response of plants to terminal heat stress. The results showed good genetic variation among commercial bread wheat varieties for grain filling rate. This trait can be used to identify and enhance heat tolerant varieties in breeding programs.