Effect of cytoplasm on the agronomic performance of grain sorghum hybrids
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Hybrid sorghum [Sorghum bicolor (L.) Moench] seed production relies exclusively on cytoplasmic male sterility (CMS) systems and almost all hybrid sorghum seed is produced using the A1 CMS system. However, the reliance on a single CMS system increases the vulnerability of the crop to diseases and stresses that may attack that particular CMS system. Alternative CMS systems have been described and even used on a limited basis for hybrid seed production, but a direct comparison of the agronomic effects of different cytoplasms has not been possible because male-sterile lines with a common genetic background (and different cytoplasm) were not available. The recent development of isocytoplasmic A-lines allows more direct comparison of cytoplasmic effect on agronomic performance. The purpose of this study was to determine by means of a set of isocytoplasmic hybrids if cytoplasm per se influences agronomic performance. Twelve hybrid genotypes were created in three different cytoplasms (A1, A2, and A3 for a total of 36 hybrids), and they were evaluated for plant height, days to anthesis, and grain yield at Weslaco and College Station, TX, in 1998 and 1999. As expected, significant differences existed among hybrids for plant height, days to anthesis, and grain yield. Cytoplasm type had no effect on plant height and was of minimal practical effect on days to anthesis, but a significant reduction in yield was observed in A3 cytoplasm hybrids as compared with A1 and A2 cytoplasm hybrids. The specific reason for the reduced yield of A3 hybrids is not known, but seed set data indicated that it was not associated with fertility restoration. The results indicate that hybrids created in A2 cytoplasm yield comparably to the commonly used A1 cytoplasm and therefore, the A2 system will provide a suitable alternative for hybrid seed production should problems be encountered in the A1 CMS system.
