Effects of Vrn-B1 and Ppd-D1 on developmental and agronomic traits in Rht5 dwarf plants of bread wheat

Preliminary evidence indicates that Rht5, a gibberellin-responsive (GAR) dwarfing gene, could reduce plant height without affecting coleoptile length and seedling vigour. However, Rht5 delayed ear emergence and anthesis, which would hinder its utilization in wheat improvement. To advance the flowering time of Rht5 dwarf plants, the dominant vernalization gene Vrn-B1 and the photoperiod-insensitive gene Ppd-D1 were introduced through two crosses between Ningchun45 (Vrn-B1) and Jinmai47 (Ppd-D1) with Marfed M (Rht5), respectively. Fifty-nine and 71 F2:3 and F3:4 homozygous lines from the first and the second cross were used to evaluate the effects of Vrn-B1 and Ppd-D1, respectively on the developmental and agronomic traits of Rht5 dwarf plants during two growing seasons in Yangling, Shaanxi, China. The results showed that Rht5 significantly reduced plant height (40.1% and 38.9%) but delayed the flowering time (14.0% and 4.8% in thermal time) in both populations. In general, Rht5 significantly decreased the spike length by 22.6% and 16.7, grain number by 14.5% and 11.5%, 1000-grain weight by 24.1% and 18.4%, and grain yield by 35.1% and 21.5% in the two populations, respectively. Vrn-B1 could not compensate for the negative effect of Rht5 on spike development and the flowering time and had no significant effect on plant height or other agronomic traits. However, Ppd-D1 was able to overcome the delaying effect of Rht5 on spike development by shortening the duration of the reproductive phase (double ridge stage-anthesis) and finally promoting earlier flowering (8.7% in thermal time) in Rht5 dwarf lines. Ppd-D1 also reduced plant height (10.0%), and the combination of Ppd-D1 and Rht5 produced even shorter plants (45.0%), achieving dwarf plants with higher lodging resistance. Additionally, Ppd-D1 increased the grain number (6.3% and 9.6%), 1000-grain weight (13.0% and 21.5%), plant yield (22.6% and 39.5%) and harvest index (31.1% and 49.6%) in both tall and dwarf plants, respectively. Clearly, the combination of Rht5 and Ppd-D1 had no negative effect on plant growth or grain yield, advanced spike development and the flowering time, and improved agronomic traits, which may be conducive to exploiting Rht5 for wheat improvement.