Single-Nucleotide Polymorphisms in Bmy1 Intron III Alleles Conferring the Genotypic Variations in β-Amylase Activity under Drought Stress between Tibetan Wild and Cultivated Barley

β-amylase activity is related to the polymorphisms of Bmy1 intron III; however, no attention has been given to such relationships under environmental stresses such as drought. In this study, 73 cultivated barley genotypes and 52 Tibetan wild barley accessions were used to test the association between Bmy1 gene intron III polymorphisms and β-amylase activity under drought stress. Our results showed that three alleles, Bmy1.a, Bmy1.b, and Bmy1.c, existed in the examined barley genotypes. Tibetan wild barley had a higher proportion of Bmy1.b, whereas cultivated barley showed a higher proportion of Bmy1.a. Impressively, barley genotypes with Bmy1.b showed a significant increase in β-amylase activity under drought stress, compared with those with Bmy1.a or Bmy1.c, indicating that the Bmy1.b allele might provide more chances for developing barley cultivars with higher β-amylase activity under water stress than both the Bmy1.a and Bmy1.c alleles. Furthermore, the Tibetan wild barley XZ147, belonging to the Bmy1.b allele type, showed significantly higher β-amylase activity than Triumph under drought stress. This might be the result of the unique amino acid substitution M527 or the amino acid composition of R115, D165, A233, S347, and M527 of XZ147.