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

Abstract

Studies under controlled environment conditions indicate that transient high temperatures (34-38˚C) during grain filling can significantly 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 filling under field cropping conditions. These differences do not appear to be markedly influenced by the amount of radiation intercepted by the canopy, stage of pod development, or position of the pods in the canopy, but fluctuate more as a result of differences in radiation intensity, wind speed, and water availability. Trickle irrigation reduced the difference 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 filling 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 significantly the year to year variation in yields of lupin grain.