| Abstract: | Cauliflower (Brassica oleracea L. botrytis) and broccoli (Brassicaoleracea L. italica) plants were grown in large pots in growthchambers for a range of temperatures (mean air temperaturesfrom 7.0-25.3 C) and irradi-ances (from 9.3-50.8 mol m–2d–1 or 4.7-25.4 MJ m–2 d–1). The extinctioncoefficient for PAR decreased with plant size reaching a valueof 0.55 in cauliflower and 0.45 in broccoli at plant leaf areasof 0.235 m2 and 0.227 m2, respectively. The leaf area expansionrate was unaffected by irradiance when compared at identicalleaf surface temperatures. The response of expansion rate tosurface temperature was fitted to a broken stick model witha base temperature of –0.7C and an optimum temperatureof 21.0C. The radiation conversion coefficient increased withair temperature below 13.8C and remained constant above this.The estimated radiation conversion coefficient above 13.8Cand for a PPFD of 20 mol m–2 d–1 was 0.77 g mol–1in cauliflower and 0.87 g mol–1 in broccoli. The radiationconversion coefficient declined with increasing irradiance levelfrom a maximum of 1.89 g mol–1 at near nil irradiancein cauliflower. Key words: Leaf area, dry matter, radiation use efficiency, extinction coefficient |
