Studies on the Flowering of Thlaspi arvense L. I. The Influence of some Environmental and Genetic Factors

Abstract

When seedlings of Thlaspi arvense were grown in the greenhouse, some flowered within 30-50 days while others grew as leafy rosettes for 90-150 days before flowering occurred. The early-flowering plants produced only early-flowering progeny, whereas the late-flowering plants had progeny of both types. Experiments under controlled conditions (16-hr days at 15 C) confirmed these results and also showed that seed from summer annuals produced only early-flowering plants while in the progeny from winter annuals both types were represented. The existence of genetically distinct early- and late-flowering strains is indicated by these results, but their phenotypic expression under field conditions and their relation to the summer and winter annual habit require further investigation. Seedlings of the early-flowering strain were grown at photoperiods of 8 and 16 hr combined factorially with nitrogen levels of 5.25 and 210 ppm. Flowering occurred under both day lengths but was significantly accelerated by the longer photoperiod. Increasing the nitrogen supply delayed flowering under long days but promoted it under short days. The number of leaves produced prior to flowering was increased to a similar extent either by increasing the nitrogen supply or by reducing the day length. This result and the additional observation that short-day effects could be simulated by reducing the light intensity suggest that for this species the C/N ratio may be significantly involved in the mechanism of flowering control.