Transient high temperatures during seed growth in narrow-leafed lupin (Lupinus angustifolius L.) II. Injuriously high pod temperatures are likely in Western Australia

Studies under controlled environment conditions indicate that transient high temperatures (34{38 - C) during grain fllling can signiflcantly reduce weight per seed in narrow-leafed lupin (Lupinus angustifolius L.). This study has shown that on average, lupin pods reach temperatures about 3{5 - C higher than the maximum daily air temperature during seed fllling under fleld cropping conditions. These difierences do not appear to be markedly in∞uenced by the amount of radiation intercepted by the canopy, stage of pod development, or position of the pods in the canopy, but ∞uctuate more as a result of difierences in radiation intensity, wind speed, and water availability. Trickle irrigation reduced the difierence between pod and air temperature by about 2 - C. Lupin species with larger pods (L. cosentinii and L. atlanticus) reached higher maximum daily temperatures than those of L. angustifolius. Long-term meteorological data indicate that air temperatures during seed fllling of lupins in Western Australia are likely to exceed 30 - C and will occasionally exceed 35 - C. In lupin-growing areas of Western Australia, pod temperatures exceeding 33{35 - C can be expected about 1 year in every 3, and more rarely (about 1 in 10 years), pod temperatures exceeding 38{40 - C can be expected. These transient high temperatures are likely to increase signiflcantly the year to year variation in yields of lupin grain. Additional keywords: heat stress, yield variability, probabilities of high temperatures, grain legumes, fleld pea (Pisum sativum), faba bean (Vicia faba).