Rich allelic variations of Viviparous-1A and their associations with seed dormancy/pre-harvest sprouting of common wheat

The allelic variations of Vp-1B have been confirmed to have close association with seed dormancy (SD) and pre-harvest sprouting (PHS) of Chinese wheat in previous research, but little was known regarding whether the alleles of two other orthologs of Vp1 on 3AL (Vp-1A) and 3DL (Vp-1D) are also present and related to these traits. In view of this, 11 primer pairs flanking the whole sequences of these two orthologs were designed to investigate their allelic variations. The results identified six alleles of Vp-1A using the primer pair A17-19 among 81 wheat cultivars and advanced lines, which were designated as Vp-1Aa, Vp-1Ab, Vp-1Ac, Vp-1Ad, Vp-1Ae, and Vp-1Af. Except for Vp-1Ac, the other five alleles were proven novel, but no allelic variation was found in Vp-1D. On sequence analysis of alleles of Vp-1A, five deletions were observed, all occurring in the same region holding many TTC repeats. Of the six alleles detected in this study, four (Vp-1Aa, Vp-1Ac, Vp-1Ae, and Vp-1Af) were generally distributed in varieties exhibiting higher average germination index (GI, range 0.46–0.56) and spike sprouting (SS, range 39.6–49.4%); however, the alleles Vp-1Ab and Vp-1Ad were distributed in genotypes carrying higher SD (GI 0.19–0.26) and stronger PHS resistance (SS 12.3–17.2%). On Spearman correlation analysis, the allele Vp-1Ab had significantly negative correlation with GI (−0.479) and SS (−0.542) at the 0.01 level, and the three alleles Vp-1Aa, Vp-1Ac, and Vp-1Ae had significantly positive correlation with GI [0.311 (0.05 level), 0.401 (0.01 level), and 0.294 (0.05 level)] and SS [0.283 (0.05 level), 0.309 (0.05 level), and 0.266 (0.05 level)]. The other alleles, including Vp-1Ad and Vp-1Af, also exhibited correlation, albeit not significant, with these two traits. This negative correlation showed that Vp-1Ab helped to improve SD and PHS tolerance, but Vp-1Aa, Vp-1Ac, and Vp-1Ae appeared to exert the opposite effect. To further confirm the association between alleles of Vp-1A and the two traits, a recombinant inbred line (RIL) population with 157 lines was genotyped using the primer pair A17-19, developed from the cross between Wanxianbaimaizi (Vp-1Ab) and Jing411 (Vp-1Ac). General linear model analysis indicated that variation in Vp-1A had a significant (P < 0.001) association with the two traits, explaining 23.4% of the variation in GI and 16.7% of the variation in SS in the population across three crop seasons.