Crop Improvement Gains in Texas Rice Cultivars Released from 1944 to 1992.

Information on the contribution of plant breeding to changes in grain yield and agronomic traits is useful in optimizing selection gains and in estimating the breeding value of the germplasm used. This study was conducted to determine the contribution of crop improvement to changes in Texas rice cultivars during the 48 years since the release of Bluebonnet in 1944. Field experiments of 23 released cultivars were conducted in three environments, which included two plantings at the Texas AgriLife Research and Extension Center, Beaumont, TX, and one planting at the research station in Eagle Lake, TX. Replicated experimental plots were arranged in a split-plot design with nitrogen (N) levels (95 and 190 kg ha^-1 N) as whole plots and cultivars as subplots. Data on number of days to heading, plant height, whole and total milled rice percentages, and grain yield were determined and analyzed using ANOVA and LSD. Cultivar trait parameters were regressed against year of cultivar release in each N level to determine the direction and rate of change due to cultivar improvement. Significant variation among cultivars was found for all traits evaluated. N affected all traits except milled rice percentages. There was a significant decrease in number of days to heading and plant height of cultivars released since 1944. Both whole and total milled rice percentage increased at 0.06 and 0.03% yr^-1, respectively. There was a significant linear increase in the grain yield of rice cultivars released from 1944. The rate of increase due to the rice breeding was 42 and 26 kg yr^-1 for the 190 and 95 kg ha^-1 N treatments, respectively. The positive slope demonstrated the significant progress that rice breeding has achieved in increasing intrinsic cultivar yield potential regardless of fertilizer inputs and in developing cultivars that respond favorably to additional fertilizer inputs.