Sink Characteristics of Reproductive Organs of Dwarf Bean in Relation to Likelihood of Abscission

Abstract

In common with other grain legumes, dwarf bean (Phaseolus vulgaris L.) exhibits premature abscission of reproductive organs and concomitant reduction in harvestable yield potential. This problem was investigated by mapping 14C‐photosynthate partitioning to individual buds, flowers, and pods of dwarf bean plants growing in a controlled‐ environment cabinet. Experimental plants bore a single raceme for which probabilities of abscission at each reproductive site were determined beforehand with a separate batch of plants. Reproductive organs at proximal sites on the raceme had low probabilities of abscission and always received greater proportions of 14C‐photosynthate than did reproductive organs at distal sites with high abscission probabilities. The activity of reproductive organs as sinks in relation to their developmental stage and position on the raceme was also examined. Sink activity of reproductive organs was determined in this study as the percentage of total 14C‐activity imported by reproductive organs per dry weight of the organ expressed as a percentage of total dry weight of reproductive organs. Sink activities of reproductive organs could be ranked in the order buds > pods > flowers. Most importantly, it was clear that pods likely to abscise had reduced sink activity when at both the flower and bud stages compared with those likely to be retained. It is proposed that loss of sink activity by reproductive organs is a key event leading to their eventual abscission and an essential feature of the mechanism whereby pod number is controlled in grain legumes.