The relationship between the Rht₁ and Rht₂ dwarfing genes and grain weight in Triticum aestivum L. spring wheat

The study was carried out in the first year on samples of random F₅ lines, uniform in height and in heading date, of three crosses between semi dwarf spring wheat cultivars (Triticum aestivum L.), differing in grain weight and in their Rht gene. In the second year only the progenies of the early heading F₅ lines were studied. All the material was grown in the absence of lodging. The culm-length genotypes of the different lines were identified by test crosses and by a seedling GA response test. No differences in grain weight were found between the two semi dwarf genotypes (Rht₁Rht₁rht₂rht₂ and rht₁rht₁Rht₂Rht₂). The tall genotype (rht₁rht₁rht₂rht₂) was significantly higher in grain weight than the two semi dwarf genotyes and the grain weight of these genotypes exceeded markedly the grain weight of the dwarf genotype (Rht₁Rht₁Rht₂Rht₂). These genotypic effects were independent of differences in plant height, heading date or number of grains per spike.