Studies on the Flowering of Thlaspi arvense L. III. The Influence of Vernalization Under Natural and Controlled Conditions

Abstract

Field observations on the flowering of early-flowering (EF) and late-flowering (LF) strains of stinkweed (Thlaspi arvense L.) showed that all of the spring-germinating population had the EF phenotype. Their progeny, however, when grown under controlled conditions, were predominantly of the LF strain, indicating that expression of the LF genotype had been prevented by natural vernalization in the field. Approximately 10%-20% of the parent plants had progeny in which both strains were represented and provided a measure of the extent to which crossing between the two strains may occur. Cotyledon-stage seedlings, planted in the field in October, showed no difference in winter survival and flowered concurrently in the spring, expression of the LF genotype having been completely eliminated. Vernalization of seeds of the LF strain for 6 wk at 2 C had the greatest effect when started 48 or 96 h after the start of germination; vernalization at earlier or later stages of development was much less effective. With only 2 wk of vernalization flowering occurred first on lateral shoots, but with a 4-wk treatment most plants flowered first at the main shoot apex. The appearance of a flower first on a lateral branch was correlated with the developmental stage at vernalization and was associated with a delay in flowering at the apex of the main shoot.