Rht1 and Rht2 Semidwarf Genes Effect on Hybrid Vigor and Agronomic Traits of Wheat

Abstract

The ‘Norin 10’ dwarfing genes, Rhtl and Rht2, have been an effective source of stature control in commercial cultivars of hexaploid wheat (Triticum aestivum L.). Various and conflicting studies have reported on the yield effects associated with these genes. The present study was undertaken to examine pleiotropic effects on yield and yield related characters in inbreds and F1 hybrids near‐isogenic for Rht1 and Rht2. Isogenic series for six diverse cultivars at three levels of dwarfing; tall (no Rht alleles), semidwarf (2 Rht alleles), and double‐dwarf (4 Rht alleles) were intercrossed in all possible combinations within each dwarfing level, without reciprocals, to construct three near‐isogenic series of 15 F1 hybrids. Parents and hybrids were grown in replicated field trials in each of two locations for two years. Mean grain yield of all genotypes declined significantly as a linear function of the number of Rht genes. Negative effects of Rht were a consequence of significantly reduced kernel weights that were not offset by other yield components. Midparent heterosis for one measure of yield was greatest for tall hybrids (14%), followed by semidwarfs (10%), and double‐dwarfs (2%). The Norin 10 Rht alleles appear to limit the expression of hybrid vigor.