Assessing the relationship between endosperm type and grain yield potential in sorghum (Sorghum bicolor L. Moench).

Sorghum hybrids with waxy endosperm (either homozygous or heterozygous waxy) have lower grain yield potential compared to non-waxy endosperm hybrids. The cause of this yield reduction is not known. From a genetic perspective, the yield reduction could be due to pleiotrophy or genetic linkage between the wx locus and other loci that influence grain yield. The specific cause of the relationship is important because an effective breeding program can alleviate the problem if it is due to linkage. The objective of this study was to determine whether linkage or pleiotrophy is causing the negative relationship between grain yield and waxy endosperm. From each of two F2 breeding populations segregating for waxy endosperm, between 40 and 50 inbred lines were derived, with equal numbers of waxy and non-waxy endosperm lines. No selection for yield was practiced during the development of these lines. The lines from these two populations and a set of testcross hybrids (derived from one population) were evaluated in four environments in Texas from 1998 to 2000. Across all tests and environments, the combined yield of the waxy genotypes was 17% lower than non-waxy genotypes. While yields were lower in waxy genotypes, analysis of the individual inbred lines and hybrids revealed that several waxy inbred lines were not statistically different from the best non-waxy inbreds. These results imply that selection of high yielding waxy genotypes is possible, but a significant breeding emphasis on their development is required to effectively identify those genotypes.