Characterization of D-genome diversity for tolerance to boron toxicity in synthetic hexaploid wheat and in silico analysis of candidate genes

Abstract

Boron toxicity is one of the most important environmental stresses prevailing globally, which limits grain production. In wheat, tolerance to boron toxicity has been manipulated around the Bo1 locus on 7BL chromosome. However, there is a need to identify new diversity in other Triticeae to broaden the germplasm base for genetic improvement and greater tolerance durability. Among these resources, Aegilops tauschii (2n = 2x = 14; DD) accessions have demonstrated significant outputs with their contribution of novel alleles for various biotic and abiotic stresses influencing traits that add value to wheat improvement. This study demonstrates the performance of 45 D-genome synthetic hexaploids wheats (SHWs) derived from a durum cultivar ‘Decoy’ for their tolerance to boron toxicity at seedling plus adult stages and validates their diversity at the molecular level. The root and shoot growth suppression as percentage of control was taken as the selection criteria for boron toxicity tolerance. Analysis of variance (ANOVA) exhibited ample variability (at P = 0.0001) among genotypes, treatments, and their interaction. Among 45 SHWs analyzed, 11 were found tolerant at the seedling stage, while 12 were found tolerant during adult plant screening. The different tolerant accessions at seedling and adult plant revealed that the tolerant mechanism was different at both stages. Genetic diversity was investigated using SSR marker specific to chromosome 7D. A total of 38 alleles were amplified with a mean value of 3.8 alleles per marker. Analysis of molecular variance (AMOVA) further established significant genetic diversity among different clusters. The potential genomic regions underlying tolerance to boron toxicity were also highlighted by searching sequences of cereal boron tolerance genes in wheat-specific databases. The wheat genome survey sequence and the draft genome sequence of Ae. tauschii proved to be useful genomic resources that identified five different chromosomal regions highly similar to the available boron tolerant genes in cereals. Conclusively, tolerance to boron toxicity in SHWs, genetic variability among the tolerant accessions based on SSRs, and availability of orthologous copies of boron tolerance genes make SHWs as potent genetic resources for wheat improvement against boron toxicity.