Studies on the Flowering of Thlaspi arvense L. II. A Comparative Study of Early- and Late-Flowering Strains

Abstract

A comparison of genetically distinct early- and late-flowering strains of stinkweed (Thlaspi arvense L.) showed that, when seedlings of each type were planted in the field at monthly intervals, differences in their rate of flowering were correlated with the planting date. Seedlings which emerged naturally in the spring all showed the early-flowering phenotype, but those emerging during the summer comprised both the early-flowering strain, which flowered within a few weeks, and the late-flowering strain, which remained vegetative until the end of the season. The two strains were readily distinguished by characteristic differences in leaf shape. Experiments conducted under controlled conditions indicated that the differences in their flowering behavior could be attributed mainly to temperature effects. These experiments showed that increasing either the day or night temperature accelerated flowering and reduced leaf number of the early-flowering genotype but delayed flowering and increased leaf number of plants of the late-flowering strain. Vernalization (2 C for 2-4 wk) also induced earlier flowering of the late-flowering strain. Germination of freshly harvested seed of both strains was 95%-100% at a 12-h 10-25-C temperature alternation and was strongly promoted by exposure to light. A constant 25-C temperature discriminated between the two genotypes, giving about 45% germination of the early-flowering plants while completely preventing germination of the late-flowering strain.