Transient high temperatures during seed growth in narrow-leafed lupin (Lupinus angustifolius L.) I. High temperatures reduce seed weight

Abstract

Highly variable yields are a weakness of narrow-leafed lupins. Yield variability could be caused by many factors, including hot days during seed filling. This paper investigates the effects of 2 hot days at various stages of seed filling in L. angustifoliusL. cv. Merrit. Exposing adequately watered plants to a total of 6 h at 34, 36, or 38˚C, compared with 20˚C, over 2 consecutive days reduced weight per seed by 4, 8, or 12% at maturity, respectively. The 38˚C treatment, applied when seeds averaged 4% of their final weight, also caused 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, respectively). The reductions in weight per seed were not associated with reduced assimilate supply because: (a) neither photosynthesis nor leaf longevity were reduced by heat treatment; (b) competing inflorescences and branches were not allowed to develop; (c) the plants produced very large seeds for this cultivar (174-190 mg); and (d) leaves remained green well after the pods had matured. Seed N concentration decreased and fat concentration increased by small, although statistically significant, amounts in response to heat treatment at the last stage of seed development tested (57% of final weight per seed when treated) but not at earlier stages. This study indicates that hot days with pod temperatures as low as 34-36˚C during seed development can cause reductions in weight per seed, and hence yields, in narrow-leafed lupin crops.