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Genetic diversity in a collection of 70 bread wheat ( Triticum aestivum) genotypes was studied using 73 microsatellite [simple sequence repeat (SSR)] loci evenly spaced on wheat chromosomes. A total of 592 alleles with an average of 8.53 allele/locus were detected, of which 185 (31.25%) occurred only in a specific group of genotypes. A set of SSR markers consisted of 22 loci with polymorphic information content values of 0.80 or higher were selected for rapid fingerprinting of many genotypes. Average of gene diversity was 0.74 ± 0.017, and significant difference between observed and maximum theoretical values of gene diversity in the analysed SSR loci was obtained using a paired t-test. Genetic distance-based clustering methods including unweighted pair group method with arithmetic average and neighbour joining (NJ) were used for grouping of genotypes. The resulted dendrogram based on NJ and number of differences coefficient hinted of the existence of three groups. This grouping was in agreement with the pedigree information and confirmed by high within-group bootstrap value. A comparatively higher genetic diversity in the studied wheat collection as revealed by presence of high allelic diversity and large number of specific alleles could be utilised in development of new cultivars with desired characteristics. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]