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In order to study the tolerance of wheat accessions of National Plant Gene Bank of Iran to heat stress, during the crop years of 2014 to 2019 for five consecutive years, each year 256 accessions with 3 control cultivars (Chamran-Chamran2-Aflak ) were cultivated in an augmented experimental design at the Agricultural and Natural Resources Research Center of Khuzestan (under normal and heat stress conditions) and in 400 hectare farm of Karaj (in normal conditions). Every year, 256 accessions were regenerated and multiplied in Karaj and the next year, the regenerated accessions were planted in Ahwaz in two planting dates: the beginning of December (suitable planting date as normal conditions) and the second half of January (late planting date to face plants heat stress in different stages of growth and development ,especially at the stages of spikelet emergence, pollination and grain filling period). In Ahvaz experiment, spike length, 100-grain weight, plant height, number of grains per spike, number of spikelets per spike, number of florets per spikelet, days to heading, days to maturity, grain filling duration, grain weight of five spikes from main stems were evaluated and in Karaj experiment, in addition to the traits evaluated in Ahvaz, traits such as awl condition, Glume color, Glume Hairness, Stem Thickness and number of nodes per stem were also evaluated according to IPGRI (International Plant Genetic Resources Institute) descriptor. Heat tolerance index was calculated using Yp as grain weight of five spikes under normal conditions and Ys as grain weight of five spikes under heat stress conditions. Among the 256 accessions studied in the 2014-2015 crop year, 235 accessions were bread wheat and 19 accessions were durum wheat. Considering stress tolerance index and yield under normal and stress conditions, accessions of 12811, 12889, 12695, 12661 and 12703 from bread wheat and accessions of 12876, 12875 and 12872 from durum wheat were identified as heat tolerant accessions. In the 2015-2016 crop year, out of 256 accessions studied, 240 accessions were bread wheat and 14 accessions were durum wheat. Considering stress tolerance index and yield under normal and stress conditions, accessions of 13013, 13037, 13005, 13087 and 13010 from bread wheat and accessions of 12938, 12944 and 12937 from durum wheat were identified as heat tolerant ones. Among the 256 accessions studied in the 2016-2017 crop year, 237 accession were related to bread wheat and 15 accessions were related to durum wheat. Considering stress tolerance index and yield under normal and stress conditions, accessions of 13318, 13408, 13319 and 13320 from bread wheat and accessions of 13501 and 13281 from durum wheat were identified as tolerant accessions. In the 2017-2018 crop year, out of 256 accessions investigated, 208 accessions were bread wheat and 35 accessions were durum wheat. Considering stress tolerance index and yield under normal and stress conditions, accessions of 13726, 13765, 13807, 13836, 13799 and 13785 from bread wheat and accessions of 13784, 13757 and 13786 from durum wheat were identified as tolerant ones. Among the 256 accessions studied in the 2018-2019 crop year, 213 accessions were related to bread wheat and 40 accessions were related to durum wheat. Considering stress tolerance indexes and yield under normal and stress conditions, accessions of 14388, 15131, 14315, 14307 and 14386 from bread wheat and accessions of 14467, 14443 and 14290 from durum wheat were identified as tolerant ones.
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