Genetic progress in stem lodging resistance of the dominant wheat cultivars adapted to Yellow-Huai River Valleys Winter Wheat Zone in China since 1964

Analysis of genetic progress for lodging-related traits provides important information for further improvement of lodging resistance. Forty winter wheat cultivars widely grown in the Yellow-Huai River Valleys Winter Wheat Zone (YHWZ) of China during the period of 1964-2015 were evaluated for several lodging-related traits in three cropping seasons. Plant height, height at center of gravity, length of the basal second internode, and lodging index decreased significantly in this period, and the average annual genetic gains for these traits were -0.50 cm or -0.62%, -0.27 cm or -0.60%, -0.06 cm or -0.63%, and -0.01 or -0.94%, respectively. Different from other traits, stem strength showed a significant increasing trend with the breeding period, and the annual genetic gains were 0.03 N or 0.05%. Correlation analysis showed that lodging index was positively correlated with plant height, height at center of gravity, and length of the basal second internode, but negatively correlated with stem strength. Meanwhile, significantly positive correlations were observed between plant height, height at center of gravity, and length of the basal first and second internodes. By comparison with the wild types, dwarfing genes had significant effects on all lodging-related traits studied except for length of the basal first internode and stem strength. Principle component analysis demonstrated that plant height and stem strength were the most important factors influencing lodging resistance. Clustering analysis based on the first two principle components further indicated the targets of wheat lodging-resistant breeding have changed from reducing plant height to strengthening stem strength over the breeding periods. This study indicates that the increase of stem strength is vital to improve lodging resistance in this region under the high-yielding condition when plant height is in an optimal range.