Predominance of flowers and newly formed pods in reproductive abscission of Lupinus angustifolius L

Abstract

The stage of development at which reproductive organs abscised on the main inflorescence of Lupinus angustifolius L. plants was studied in field plot trials which incorporated site, sowing date, density and cultivar treatments. The average number of pods on the main inflorescence at final harvest ranged over 1.8 to 8.4, the Reproductive Index (number of seeds per gram total above-ground dry weight, excluding seeds) varied from 3.1 to 7.6, and the Harvest Index from 0.17 to 0.50. Four stages at which abscission occurred were identified (flower [ovaries 7-8 mm long], pl [pods 9-10 mm], p2 [pods 11-13 mm], p3 [pods 14-27 mm long]) and used to assess reproductive development on a week by week basis. In all treatments, losses of flowers and pl pods accounted for 92% or more of total reproductive abscission and, of this, the majority was due to flower abscission. The number of abscised pl pods was relatively stable across treatments, but the number of p2 and p3 pods which abscised varied markedly with sowing date, possibly indicating a relationship with changes in environmental conditions. Examination of ovaries following cryosectioning and fluorescence microscopy showed that pollination of ovules occurred with a similarly high frequency in flowers destined to abscise (77%) compared with those destined to form pods (88%). The difference was due to a 50% probability of pollination of the fifth ovule in ovaries of flowers forming pods and only a 25% probability in those which abscised. The data are discussed in relation to the likely physiological basis for the regulation of reproductive abscission in the species.