An analysis of the improvements in yield and yield related-components of winter wheat cultivars in the Southern Great Plains from 1971-2008

Twenty-eight semi-dwarf winter wheat cultivars released and grown in the Southern Great Plains in the period 1971 to 2008 were evaluated for genetic progress in grain yield and associated changes for eight yield-related components i.e., grain yield, thousand kernel weight, kernels per spike, kernels per square meter, harvest index, biomass per fertile tiller, spikes per square meter and quality. Cultivars were evaluated in four locations: two locations in Oklahoma and two locations in Kansas in 2010 and 2011 crop growing seasons, following the procedure of a split plot design with three replications. Level of fungicide treatment was the main plot and cultivars were the subplot. In all locations, there was no significant difference between fungicide treated and untreated plots. Cultivars were significantly different for all traits included in this study indicating considerable amount of variation among cultivars for each character. A significant yield increase of 12.27 kg/ha/year was recorded across all locations. Of the yield components, kernels per square meter and kernels per spike showed significant progress across locations and years, while thousand kernel weight declined over the years. Harvest index and biomass per productive tiller showed no significant change. The association study between grain yield and yield related components revealed that kernels per square meter and kernels per spike had a significant contribution on the genetic gain in grain yield. Thousand kernel weight showed a significant negative correlation with kernels per square meter and kernels per spike. Trend analysis revealed that even though harvest index and biomass showed little change, a linear trend was significant. Linear and quadratic trends were significant for kernels per square meter, kernels per spike, and thousand kernel weight. These results indicated that kernels per square meter and kernels per spike perhaps approached the leveling off, and thousand kernel weight started to decline. The negative association between individual kernel weight and kernel number per unit area indicated that any further yield improvement via kernel number will make individual kernel weight smaller. Modern cultivars included in this study have high kernel number per unit area and high grain yield, but have inferior kernel weight when compared with the older cultivars.