Exploiting the Rht portfolio for hybrid wheat breeding.

KEY MESSAGE: The portfolio of available Reduced height loci (Rht-B1, Rht-D1, and Rht24) can be exploited for hybrid wheat breeding to achieve the desired heights in the female and male parents, as well as in the hybrids, without adverse effects on other traits relevant for hybrid seed production. Plant height is an important trait in wheat line breeding, but is of even greater importance in hybrid wheat breeding. Here, the height of the female and male parental lines must be controlled and adjusted relative to each other to maximize hybrid seed production. In addition, the height of the resulting hybrids must be fine-tuned to meet the specific requirements of the farmers in the target regions. Moreover, this must be achieved without adversely impacting traits relevant for hybrid seed production. In this study, we explored Reduced height (Rht) loci effective in elite wheat and exploited their utilization for hybrid wheat breeding. We performed association mapping in a panel of 1705 wheat hybrids and their 225 parental lines, which besides the Rht-B1 and Rht-D1 loci revealed Rht24 as a major QTL for plant height. Furthermore, we found that the Rht-1 loci also reduce anther extrusion and thus cross-pollination ability, whereas Rht24 appeared to have no adverse effect on this trait. Our results suggest different haplotypes of the three Rht loci to be used in the female or male pool of a hybrid breeding program, but also show that in general, plant height is a quantitative trait controlled by numerous small-effect QTL. Consequently, marker-assisted selection for the major Rht loci must be complemented by phenotypic selection to achieve the desired height in the female and male parents as well as in the wheat hybrids.