Determination of molecular diversity of wheat types with different tolerances against boron toxicity with ssr markers

To feed an estimated 9 billion population by 2050, crop production needs to be doubled. However, the existing crops yield is not enough to meet this demand. Wheat (Triticum aestivum) is one of the most important cereal crops whose production is restricted by climate change and different biotic and abiotic stresses. Boron toxicity in soil is a critical abiotic stress condition reducing wheat productivity especially in arid and semi-arid regions of the world. Thus, there is a need to develop boron toxicity tolerant wheat varieties via breeding programs that can be grown in high boron affected regions. Nevertheless, genetic base of elite germplasm has been decreased due to modern wheat breeding especially during the Green Revolution. Wheat genetic resources including wild relatives, landraces, and neglected wheat species may possess specific alleles that can be exploited to enhance boron toxicity tolerance in modern cultivars. However, in order to utilize them efficiently in the breeding programs, it is necessary to analyze their genetic diversity and group them according to their molecular profiles so that breeders can choose genetically diverse and complementary parents with different tolerance levels for crossing programs. As per the available literature, very few studies have been conducted to assess the genetic variation of boron toxicity tolerant or susceptible wheat genetic resources including both wild and cultivated wheat genotypes using simple sequence repeats (SSR) markers. Thus, filling the research gap, in this thesis study using 12 SSR markers, we evaluated the genetic polymorphism of 83 primitive, wild, and modern wheat genotypes with varying boron toxicity tolerance levels that were identified under the scope of the TÜBİTAK project (No.119O455). The obtained results showed notable genetic diversity in root and shoot biomass of studied genotypes under toxic boron treatment. A significant high genotypic variation of 62.3% was observed in shoot dry weight of the genotypes as compared to root dry weight that showed significant but lower variation of 30.0%. B toxicity had more suppressive effect on roots as compared to shoots. A total of 8 genotypes belonging to eight different Triticum species showed positive increases in both root and shoot dry weight under B toxicity confirming their tolerance to high boron. In SSR analysis, while the polymorphism information content (PIC) of each SSR marker ranged from 0.936 to 0.991 with an average value of 0.968 on examining total number of alleles, assessment of only frequent alleles revealed that polymorphism information content (PIC) of each SSR marker ranged from 0.66 to 0.97 with an average value of 0.858. Not only the selection of appropriate primers, but also the presence of diverged species in the experiment was responsible for obtaining high polymorphism in the genotypes. These findings suggest that boron toxicity adaptation is variable among the studied wheat genetic resources. The genotypes from contrasting clusters can be selected for hybridization that could help in evolution of better segregants for improving high boron tolerance in wheat. The genotypes used in this study with variable boron tolerances can be directly used by the breeders in pre-breeding or breeding programs based on the genetic distances identified between them that will consequently strengthen the ongoing breeding efforts.