The Interaction of Plant Growth Regulators and Vernalization on the Growth and Flowering of Cauliflower (Brassica oleracea var. botrytis)

Abstract

The growth and flowering response of a cold-requiring cauliflower (Brassica oleracea var. botrytis cv. '60 day') to a range of temperatures under 10 h photoperiod and to growth regulator application were investigated. Endogenous gibberellin A1 (GA1) concentrations were also assessed under these treatments. Flowering and growth of the inflorescence stalk were correlated with plant developmental stage at the time of a vernalizing cold treatment. Temperature and its duration also affected flowering and inflorescence development. The most effective temperature for inflorescence induction was 10 °C. Flowering did not occur in non-vernalized plants (25 °C) even though they had been treated with GA3. Application of GA3 promoted inflorescence stalk elongation greatly in vernalized plants (10 °C), but less so in partially vernalized plants (15 °C or 20 °C). Paclobutrazol (PP333) sprayed at the 8-9 leaf stage significantly suppressed inflorescence stalk length and slightly delayed flower bud formation and anthesis. Vernalization at 10 °C increased endogenous GA1 content in both leaves and the inflorescence stalk irrespective of GA3 or PP333 treatment. Application of GA3 tended to increase GA1 levels, while PP333 significantly reduce GA1, both irrespective of vernalization. Vernalization is an important factor for flowering, but not curd formation in this cauliflower cv. '60 day' and GA1 is likely a causal factor in inflorescence stalk elongation.