Germination and Seedling Cold Tolerance in Sorghum

Early planting of sorghum [Sorghum bicolor(L.) Moench] hybrids in temperate agriculture confers numerous advantages but requires genetic variation, both in lines and in parental effects for germination and seedling tolerance to low soil temperatures. The objectives of this study were to examine genetic variation among 12 diverse sorghum lines and their hybrids with two testers for their relative ability to germinate and emerge at low soil temperatures. Rate of germination, final germination level, and rate of shoot growth were measured under normal and constant cold temperature conditions (20–30°C in a greenhouse and 15°C in a growth chamber, respectively) as well as in an early planted field. Two early maturing lines, PI550666 and PI550597 (from Russia), appear to be better sources of germplasm than Shan Qui Red (from China) for germination and early seedling cold tolerance because of fewer undesirable characteristics. There were significant differences among genotypes under normal temperature conditions for both total germination percentage and rate of early shoot growth, whereas no significant differences were found in cold conditions. Of the two testers (female parents), N123A generally showed a negative combining ability for rate of germination in cold conditions, whereas crosses with tester N250A tended to be substantially better than the male parent. Selection for germination cold tolerance in seed parents will be more effective than in male parents. Though only inferred by this research, it is likely that differences in combining ability exist between seed parents for germination cold tolerance.