توصيفگر ها :
گندم نان , تنش گرما , عملكرد دانه , شاخص تحمل به تنش , فتوسنتز , كيفيت دانه , نقشهيابي ارتباطي
چكيده انگليسي :
Heat stress during the grain-filling period is the main abiotic stress factor limiting grain yield and quality in wheat (Triticum aestivum L.). In this study, 64 wheat genotypes including 60 genotypes CIMMYT's core germplasm (CIMCOG 1-60) panel and four cultivars (Kohdasht, Zagros, Karim and Dehdasht) were exposed to heat stress during reproduction phase caused by delayed sowing. A lattice 8×8 design replicated twice within each of two growing seasons was used. The results of combined ANOVA showed that the effect of stress was significant for all pheno-morphological and yield traits, except for flag leaf width and area traits. Heat stress significantly accelerated the phenological development of the plant and shortened the growing season of wheat by reducing days to heading, days to pollination, days to physiological maturity, days to flag leaf senescence. Peduncle length, plant height and spike-related traits including number of spikes/m2, number of spikelet/spike, spike length and number of grain/spike were significantly decreased due to heat stress. Heat stress caused a significant decrease in 1000 grain weight (27.63%). Grain yield of genotypes exposed to heat stress decreased by 57.08% on average. Genotypes no. 2, 3, 5, 6, 11, 16, 17 and 28 were identified as heat-tolerant genotypes and genotypes no. 9, 13, 19, 34, 38, 40, 44, 49 and 58 as heat-sensitive genotypes. Results of photosynthetic gas exchange and chlorophyll fluorescence were subjected to combined analysis of variance, which revealed significant differences in gas exchange parameters, and maximum quantum efficiency PSII photochemistry (Fv/Fm) among the genotypes between the normal and heat stress conditions and genotype × stress interactions. Exposure to heat stress resulted in significant decreases in net CO2 assimilation rate, stomatal conductance, transpiration rate, intrinsic water use efficiency, instantaneous water use efficiency and Fv/Fm ratio, while it increased sub‐stomatal CO2 concentration. Moreover, grain yield was found to be strongly correlated with sub‐stomatal CO2 concentration, Fv/Fm, and net CO2 assimilation rate. Path coefficient analysis and stepwise multiple regression revealed that greater improvements will be achieved in sub‐stomatal CO2 concentration and Fv/Fm by increasing yield and net CO2 assimilation rate performance when wheat is bred for tolerance to heat stress than those achieved by breeders under normal growing condition. Heat stress caused a significant decrease in starch content, ratio of amylose to amylopectin and grain moisture content and increased protein content, flour water absorption, Zeleny sedimentation, ash content, lipid content, bread volume, wet gluten content, dry gluten content and gluten index. Heat tolerant genotypes were superior in terms of grain yield, 1000 grain weight, starch content, amylose to amylopectin ratio and grain moisture content. While sensitive genotypes contained higher protein content, bread volume, gluten index and amylopectin content. A comprehensive genome-wide association study was conducted using whole genome SNP genotyping platform (35K Axiom® arrays) and applying general linear model and mixed linear model. A total of 383 and 342 SNPs at P ≤0.001 were found associated with the traits in normal and heat stress conditions, respectively. The highest density of marker-trait association (MTA) was observed on the B genome and the lowest on the D genome. Among MTAs, many SNPs were identified at similar positions on specific chromosomes, indicating possible QTLs controlling this trait. Several markers showed pleiotropic effects for many traits in normal and heat stressed conditions. Hereby, a total 39 and 43 SNPs with pleiotropic effects were found on the chromosomes of the three genomes under normal and heat stress conditions, respectively.
