Effects of temperature and irradiance on vegetative growth of cauliflower (Brassica oleracea L. botrytis) and broccoli (Brassica oleracea L. italica)

Abstract

Cauliflower (Brassica oleracea L. botrytis) and broccoli (Brassica oleracea L. italica) plants were grown in large pots in growth chambers for a range of temperatures (mean air temperatures from 7.0-25.3°C) and irradiances (from 9.3-50.8 mol m-2 d-1 or 4.7-25.4 MJ m-2 d-1). The extinction coefficient for PAR decreased with plant size reaching a value of 0.55 in cauliflower and 0.45 in broccoli at plant leaf areas of 0.235 m2 and 0.227 m2, respectively. The leaf area expansion rate was unaffected by irradiance when compared at identical leaf surface temperatures. The response of expansion rate to surface temperature was fitted to a broken stick model with a base temperature of -0.7°C and an optimum temperature of 21.0°C. The radiation conversion coefficient increased with air temperature below 13.8°C and remained constant above this. The estimated radiation conversion coefficient above 13.8°C and for a PPFD of 20 mol m-2 d-1 was 0.77 g mol-1 in cauliflower and 0.87 g mol-1 in broccoli. The radiation conversion coefficient declined with increasing irradiance level from a maximum of 1.89 g mol-1 at near nil irradiance in cauliflower.