Assessment of genetic diversity, vernalization alleles, and heat tolerance markers in bread wheat lines under water stress conditions
Bread wheat is considered one of the most important crops in Egypt and worldwide and improving its productivity under water stress is a major breeding objective. This study aimed to evaluate advanced bread wheat lines under water stress and to characterize heat shock protein (HSP) and vernalization (Vrn) genes, as well as to assess genetic diversity and population structure among 19 lines using Start codon targeted (SCoT) markers. Analysis of variance revealed highly significant differences for all tested traits. Two lines (L3 and L14) recorded the lowest values for days to heading and reached maturity in a shorter period compared to the check cultivar. Seven lines (L27, L25, L20, L21, L5, L19, and L13) showed the highest grain yield. A weak relationship was observed between plant height and grain yield; however, high-yielding lines tended to be shorter. Spike number per plant showed the strongest positive correlation with grain yield (r = 0.77), indicating that it is the main determinant of yield. In addition, 1000-grain weight showed a weak positive correlation with grain yield (r = 0.11). In contrast, spike number and 1000-grain weight were weakly negatively correlated (r = -0.15). Furthermore, a single nucleotide polymorphism (SNP) marker for the HSP16.9 gene was utilized to assess heat tolerance in 19 wheat lines. All lines produced a single band of 197 bp, indicating a lack of allelic polymorphism at this locus among the evaluated genotypes. Furthermore, three gene-specific primers targeting Vrn genes (Vrn-A1b, Vrn-B1a, and Vrn-B1b) were used to characterize 19 wheat lines. All lines carried the dominant Vrn-A1b allele (147 bp), using primer Vrn-p2, indicating a spring growth habit and the ability to flower without a prolonged cold requirement. At the Vrn-B1a locus, 15 lines possessed the Vrn-B1a allele (709 bp), using primer Vrn-P5. Using the co-dominant marker Vrn-P7, one line (L10) exhibited the Vrn-B1a allele (215 bp), while 15 lines showed the dominant Vrn-B1b allele (252 bp). In addition, three lines (L5, L8, and L17) were heterozygous, displaying both 215 and 252 bp fragments. On the other hand, Jaccard’s genetic distance (GD) coefficient was employed to evaluate the genetic divergence among 19 wheat lines based on SCoT loci. The GD values ranged from 0.62 to 0.97. Therefore, the specific wheat genotypes possess valuable germplasm characteristics, making them excellent candidates for breeding programs focused on increasing grain yield and developing new, high-performing wheat varieties.