The impact of terminal heat stress on yield and heat tolerance of bread wheat

In arid and semi-arid regions of the world bread wheat (Triticum aestivum L.) yield is highly limited due to late season heat stress, mostly occurring during the reproductive phase. Hence the current study was conducted to evaluate the effect of late season heat stress on grain yield and yield components of 20 spring bread wheat cultivars. For this purpose, a stripe block experiment including four sowing dates (6th of November, 6th of December, 5th of January and 4th of February) as vertical plots and 20 cultivars in horizontal plots was implemented with three replicates in North-East of Ahwaz, Khuzestan, Iran during 2007-2008 and 2008-2009 growing seasons. The results indicated that the main effect of year, sowing date, cultivar and interaction between sowing date and cultivar were significant for all studied traits. However, no significant interaction was found between year and other factors. Comparison of means showed that grain yield in the second year was higher than the first year. The maximum and minimum values (6.048 ton ha-1 and 1.754 ton ha-1) were obtained when seed sowing was performed on 6th of November and 4th of February, respectively. The maximum grain yield (5.019 ton ha-1) was related to Atila cultivar whereas the minimum yield (3.662 ton ha-1) was obtained from Inia 66 cultivar. In general, the maximum and minimum grain yields were produced by Atila cultivar sown on 6th of December and Seri82 and Roshan sown on 4th of February, respectively. The results suggest that Arvand, Vee/Nac, Atila and Baiat cultivars as heat tolerant cultivars and Roshan, Hamoon, Seri82, Star, Inia66 and Darab2 as susceptible cultivars may be used in heat tolerance studies.