Effects of allelic variation at Rht - B1 and Rht - D1 on grain yield and agronomic traits of southern US soft red winter wheat

Semi dwarfism in hexaploid wheat ( Triticum aestivum L.) is primarily governed by two loci, Rht - B1 and Rht - D1 . Cultivars adapted to the soft red winter wheat growing region of southeastern USA are predominantly Rht - D1b genotypes but report no significant grain yield advantage over Rht - B1b semi dwarfing cultivars. The objective of this study was to determine the effect of allelic variation at Rht - B1 and Rht - D1 on plant height, grain yield and additional yield components in a doubled haploid population consisting of 35 semi dwarfs with Rht - B1b , 50 semi dwarfs with Rht - D1b , eight wild type lines, and two lines with dwarfing alleles at both loci. Rht loci significantly affected plant height, with double dwarfs shorter than both single gene semi dwarfs and wild types. Rht - D1b semi dwarfs were significantly shorter than their Rht - B1b counterparts. Rht loci also had a significant effect on grain yield, with Rht - D1b lines having higher mean grain yield (4.03 t ha −1 ) compared to Rht - B1b (3.83 t ha −1 ) and wild type (3.49 t ha −1 ) lines. A significant interaction between Rht loci and site-year was detected only for thousand kernel weight, indicating that the advantage of Rht - D1b over the other haplotypes was consistent across environments. Overall, their higher grain yield was due in part to higher thousand kernel weight that contributed to higher kernel weight spike −1 and likely influenced by a shorter stature. The results of this study will aid breeders in choice of semi dwarfing alleles for adaptation to the soft wheat growing region of the southern USA.