Genetic Improvement in Agronomic Traits of Hard Red Winter Wheat Cultivars 1919 to 1987

Periodic evaluation of genetic improvement of crop cultivars is useful, both as a demonstration of the importance of plant breeding to the public and as a way of identifying traits or target environments that may require increased efforts by breeders. Evaluation of cultivars from different eras in a common environment is the most direct of the several methods that have been used to estimate breeding progress. Thirty‐five hard red winter wheat ( Triticum aestivum L. em. Thell.) cultivars introduced or released between ca. 1874 and 1987 were evaluated in experiments at three locations in Kansas during 1986 and 1987 (three other cultivars were evaluated only in 1987) to estimate genetic progress achieved by hard red winter wheat breeding programs. Linear regression of cultivar means on years of release showed increases of 16.2 kg ha −1 yr −1 in grain yield, 0.4 kg m −3 yr −1 in volume weight, and 0.04 g yr −1 in thousand‐kernel weight. Days to heading and plant height decreased at rates of −0.1 d yr −1 and −0.5 cm yr −1 , respectively. There were also significant increases over time in lodging resistance. There was no significant change in biomass yield over time. Rates of genetic improvement varied significantly across evaluation environments, with the greatest gain in grain yield (1.4% of the experiment mean per year) estimated in an epidemic of stem and leaf rust (caused by Puccinia graminis Pers. f. sp. tritici Eriks. & Henn., and P. recondita Rob. ex. Desm. f. sp. tritici , respectively). Moderate gain per year (0.6%) was estimated in the most highly productive environment, lower gain (0.4%) was found under drought stress, and there was no gain when evaluation was conducted under an epidemic of tan spot (caused by Helminthosporium tritici‐ repentis Died.), a foliar disease. High levels of resistance to H. tritici‐repentis had not been incorporated into hard red winter wheat cultivars. No evidence of a yield plateau was found for hard red winter wheat cultivars evaluated under a range of environmental conditions in Kansas.