TRANSIENT HIGH-TEMPERATURES DURING SEED GROWTH IN NARROW-LEAFED LUPIN(LUPINUS-ANGUSTIFOLIUS L.) .1. HIGH-TEMPERATURES REDUCE SEED WEIGHT

Highly variable yields are a weakness of narrow-leafed lupins. Yield v ariability could be caused by many factors, including hot days during seed filling. This paper investigates the effects of 2 hot days at var ious stages of seed filling in L. angustifolius L. cv. Merrit. Exposin g adequately watered plants to a total of 6h at 34, 36, or 38 degrees C, compared with 20 degrees C, over 2 consecutive days reduced weight per seed by 4, 8, or 12% at maturity, respectively. The 38 degrees C t reatment, applied when seeds averaged 4% of their final weight, also c aused significant seed abortion. High temperatures reduced weight per seed at all stages of seed growth, except when seeds were <5-12 mg dry weight (3 and 6% of final seed dry weight, Expts 1 and 2, respectivel y). The reductions in weight per seed were not associated with reduced assimilate supply because: (a) neither photosynthesis nor leaf longev ity were reduced by heat treatment; (b) competing inflorescences and b ranches were not allowed to develop; (c) the plants produced very larg e seeds for this cultivar (174-190 mg); and (d) leaves remained green well after the pods had matured. Seed N concentration decreased and fa t concentration increased by small, although statistically significant , amounts in response to heat treatment at the last stage of seed deve lopment tested (57% of final weight per seed when treated) but not at earlier stages. This study indicates that hot days with pod temperatur es as low as 34-36 degrees C during seed development can cause reducti ons in weight per seed, and hence yields, in narrow-leafed lupin crops .