Genetic analysis of seedling growth under cold temperature stress in grain sorghum

Planting of grain sorghum [Sorghum bicolor (L.) Moench] earlier in the season should contribute to a longer growing season and more effective utilization of late spring and early summer rainfall, but early planting is hindered by poor seedling vigor under cold temperature conditions. Sources of cold tolerance have been identified, but little is known about the inheritance of this trait. This study was conducted to determine combining ability for seedling growth characteristics under cold temperature conditions in generically diverse sorghum lines using a Design-II mating scheme. Parental lines and hybrids were evaluated under early and normal planting conditions in the field. The traits measured included emergence, emergence index, leaf number, vigor, and dry weight. Significant differences were observed among entries. Among hybrids, these differences were primarily due to effects of general combining ability. These results indicate that general combining ability is more important than specific combining ability in breeding for seedling vigor in sorghum. Heterosis had favorable effects on all seedling traits measured.