Genetic gain in yield attributes of winter wheat in the great plains

Knowledge of changes associated with advances in crop productivity is essential for understanding yield-limiting factors and developing strategies for future improvement. Our objective was to identify plant traits associated with gains in grain yield of winter wheat (Triticum aestivum L.) in the Great Plains. Twelve landmark cultivars and one experimental line were compared with 'Turkey' (introduced 1873) at Hutchinson (Clark-Ost complex soil) and Manhattan (Reading silt loam soil), KS. during 1996-1997 and 1998-1999. Agronomic traits, leaf rust infection (caused by Puccinia recondita Rob. ex Desm. f. sp. tritici), and grain yield and its components were measured. Grain yields ranged from 2718 kg ha(-1) for Turkey to 4987 kg ha(-1) for the experimental line, with mean genetic gains of 0.16% per year for early genotypes and 0.63% per year for recent genotypes. Kernel number per unit of soil area had the highest phenotypic correlation with grain yield and contributed most to its genetic gain. Gains in spike numbers per unit of soil area and above-ground biomass also contributed significantly to higher yields of some genotypes. Significant genetic changes over time and correlations with grain yield were observed for early heading, decreased height, and reduced lodging and leaf rust but not for kernel weight. Our results suggested that yield components that form during vegetative phases (spike numbers per unit of soil area and kernels per spike) when conditions for growth are generally favorable are more amenable to genetic improvement than kernel weight, which forms during maturation when moisture and temperature are often unfavorable.