Analysis of the effect of cold stratification on the germination response to light and alternating temperatures using selected seed populations of Ranunculus sceleratus L.

Abstract

From a single population of achenes (seeds) of Ranunculus sceleratus L. sub-populations were selected on the basis of the sensitivity of individuals to an increasing number of daily light/temperature shift cycles. Each cycle comprised a 4 h pulse of red light followed by a 4 h temperature shift from 16 to 31 °C. Selection for low dormancy (NND and ND) and high dormancy (D and DD) populations resulted in a > 5-fold difference in the number of cycles required for 50% germination. Despite a shift in the mean level of dormancy the distributions of sensitivity (slopes of dose-response curves) were similar in all four selected populations. Differential effects of cold stratification on the germination response to light and alternating temperatures were related to the depth of primary dormancy. The proportion of individuals that responded positively to the dormancy breaking effects of cold stratification followed the trend DD < D < ND < NND. In high dormancy populations (D and DD) the rate and uniformity of germination of some individuals was reduced by cold stratification, indicating a dormancy inducing effect. Over the range 2 to 11 °C the effectiveness of dormancy release or dormancy induction was inversely related to temperature. The effects of cold stratification on the expression of dormancy in R. sceleratus are discussed in relation to a reproductive strategy involving winter and summer annual behaviour. © 1989 Oxford University Press.