Fruit Abscission in Cowpea,Vigna unguiculata(L.) Walp

One of the hypotheses proposed for the abscission of flowers and fruits from the cowpea was that the oldest fruits at raceme 1 on the peduncle monopolize the mobile nutrients available to the whole inflorescence. Consequently, the distal young fruits and flowers starve, abort, and are shed. This hypothesis was tested through autoradiographic studies of the distribution of 14C-assimilates on the cowpea inflorescence and the comparative growth of ovaries from persisting and abscising open flowers and young fruits. 14C-asaimilates were distributed to the fruits at raceme 1 and to flower buds, open flowers, and young fruits distal to raceme 1. Therefore, the hypothesis that the fruits at raceme 1 monopolize the mobile assimilates cannot be maintained. At the time of opening the persisting flowers of raceme 1 had heavier ovaries than the aborting flowers of raceme 3 although both types of flowers were visually alike. During the initial 12 h following opening, the difference in ovary size was maintained and often accentuated. The ovary of the persisting flower increased in both fresh and dry weights. The growth of the ovary of the aborting flower was variable; the fresh weight often decreased, although it also increased in some experiments; the dry weight remained unchanged or decreased or increased remarkably. The availability of nutrients was considered to be of secondary importance in the chain of events leading to fruit abscission. Other internal factors which may control vital processes related to embryo development appear to be of primary, underlying importance.