DIFFERENTIAL RESPONSES TO DEFOLIATION OF GRAIN-SORGHUM YIELD COMPONENTS AND YIELD-RELATED TRAITS

Leaf removal can significantly reduce yield of grain sorghum [Sorghum bicolor (L.) Moench]. Genotype X defoliation interactions for yield have been reported in other crops, but limited information is available in sorghum. This study was conducted on eight sorghum hybrids to evaluate hybrid responses of yield components and grainfill traits to N application and post-anthesis defoliation. A factorial arrangement of three defoliation levels and three N fertilization rates was used in experiments conducted in five Nebraska and Kansas environments. Defoliation treatments (0, 50, and 100%) were applied at 10 d post anthesis. Removal of 50 and 100% of the leaves caused curvilinear reductions in all measured traits. Significant N effects were not observed in all environments. Defoliation X N interactions did not occur for the traits studied. Genotype X defoliation interactions occurred for grain yield, seed weight, seed number, duration of grain fill, and rate of grain fill, indicating that hybrids did not respond the same to defoliation treatments. Hybrids with higher seed number and longer preanthesis period maintained higher grain yields with defoliation. Responses of seed number to N application were similar for all hybrids. Genotype X defoliation X environment interactions were observed for all traits. Environmental interactions need to be considered when using defoliation to differentiate among hybrids in their components of yield and the relationships of these traits to grain yield.