Temperature effects on germination of Trifolium balansae and T. resupinatum with special reference to high-temperature dormancy

Abstract

The effect of temperature on germination of the annual pasture legumes Trifolium balansae and T. resupinaturn was investigated. Seed of T. resupinatum lines SA 12240, SA 14433 (from South Australia), C1Z1Res-B, CPI (Commonwealth Plant Introduction number) 026202-3, CPI 026205-2, CPI 027376-2, SA 14433 (from Western Australia), SA 18904, SA 18922, SA 19851 and CPI 045887-2 and cvv. Kyambro and Maral and T. balansae cv. Paradana and lines CPI 045856-1, CPI 045856-4 and AZ 2326 was germinated at 10, 15, 20, 25, 30 and 35¦C. T. subterraneum cv. Junee was included for comparison. It was found that germination in all lines except Maral was reduced at 35¦C, whereas at 30¦C germination was reduced significantly in all lines except Maral, ClZlRes-B, CPI 026202-3, CPI 026205-2, CPI 027376-2, SA 19851 and CPI 045887-2. Germination at 35OC in T. resupinaturn was related to thousand seed weight with the equation: Germination = -31.19+92-39 thousand seed weight (r2 = 0.76). In order to determine the mechanism responsible for the failure of seed to germinate at temperatures above 25¦C, seed of T. resupinatum lines SA 12240 and SA 14433 and Maral and T. balansae cv. Paradana was allowed to germinate at temperatures of 25, 30, 35, 40, 45 and 50¦C for 8 h, 1, 2, 5 and 10 days after which they were placed at 15¦ C for 10 days. It was found that temperatures in the 30-40¦C temperature range inhibited germination in all lines except Maral, but the same seed germinated readily when placed at 15¦C. This seed was considered to possess an enforced high-temperature dormancy. Seed of all lines exposed to 45 and 50¦C for longer than 8 h died, but at 8 h final germination was unaffected. It was concluded that high-temperature dormancy could play a role in preventing seed from germinating in the case of a false break. It was proposed that lines should be screened for high-temperature dormancy.