Cardinal temperatures and vernalisation requirements for a selection of vegetables for seed production

Abstract

The cardinal temperatures and vernalisation requirements for a selection of vegetables for seed production were studied. Experiment one assessed the rate of germination (1/days) of selected vegetable species over a range of 5-40 °C, in order to calculate the cardinal (base, optimum and maximum) temperatures for germination. The cardinal temperatures for carrot and red beet were 0.1, 30.9 and 40.7 °C, and 4.2, 35.9 and 44.4 °C respectively. Experiment two examined the vernalisation response of imbibed cabbage, carrot and red beet seeds, plus perennial ryegrass as a comparison over duration treatments of 0-12 weeks at 4 °C. Red beet and ryegrass had positive vernalisation responses with anthesis occurring in plants from the 4-12 week durations in red beet, and all durations in ryegrass. The number of days to anthesis and the final number of main stem leaves did not differ significantly (P = 0.143 and P = 0.323 respectively) among vernalisation durations in red beet, but did differ significantly in ryegrass (P <0.001 and P = 0.004 respectively). The number of days to anthesis decreased by 3.6 days for every one week increase in vernalisation duration. The same pattern was observed for main stem leaf number in ryegrass, with a decrease of 0.1 leaves for every one week increase in vernalisation duration. This response is likely to be attributed to perennial ryegrass having a lower base temperature (1.1 °C) than the vernalisation treatment (4 °C), leading to continued development towards anthesis throughout the vernalisation period. Red beet had a base temperature of 4.6 °C, so may not have experienced development towards reproduction, or may have reached vernalisation saturation at ≤ 4 weeks, resulting in a minimum number of leaves produced for all durations. There is potential for the sowing date of red beet to be changed to spring for successfully vernalised seeds, which would reduce the expenses of weed, pest and disease control and give opportunity of other land uses over the winter period.