Physiology of growth and seed production in Lupinus angustifolius L. III. Effects of defoliation and lateral branch excision on dry matter and seed production at different growth temperatures

Abstract

Plants of Lupinus angustifolius cv. Unicrop were raised at 27/22 or 21/16¦C dayhight temperatures until flowering. They were then either grown on to maturity at these conditions or moved to the other regime. Branches were removed as they started to develop and leaves were removed at the start of flowering so that 0, 3, 6, 9, 12 upper leaves or all 21 leaves were retained. Conditions before flowering determined potential pod number. Defoliation treatments revealed that under favourably cool conditions all leaves contributed to seed yield but in treatments involving 27/22'C there was no seed yield response to more than about six leaves, emphasizing the significance of environmental conditions rather than current assimilate on pod set and other yield components. In another experiment, plants were raised to flowering at 27/22, 21/16 or 15/10¦C before flowering, when all were moved to 21/16¦C. Half the plants were allowed to develop branches and on the remainder branch buds were removed. Branch and stem growth appeared to provide severe competition for the development of the primary inflorescence. Though branching was much more pronounced in plants at 15/10¦C before flowering than in other treatments, vegetative development exceeded reproductive investment and harvest index was low under these conditions. It was suggested that there appears to be a need to develop and evaluate unbranched or less-branched lupin genotypes.