POD REMOVAL EFFECTS ON COWPEA GENOTYPES CONTRASTING IN MONOCARPIC SENESCENCE TRAITS

In grain legumes, the extent of leaf senescence during podding varies among genotypes and may also be modified by sink reduction, but few studies have compared these phenomena. In this study of delayed leaf senescence (DLS) in cowpea [Vigna unguiculata (L.) Walp.] field-grown populations of normally senescent (CBS and 1411) and DLS (7964 and 8517) genotypes were subjected to two treatments: removal of pods reaching color-break, and a nonpicked control. Picking increased leaf area duration more in normally senescent genotypes than in DLS genotypes during the reproductive phase. Pod removal changed the reproductive pattern of senescent genotypes from a monomodal to a bimodal distribution similar to that of nonpicked DLS genotypes. Picking had little influence on the number of pods produced during the first podset. Removing pods from CB5 progressively increased the ratio of photosynthetic source size to reproductive sink size during the first podset, relative to nonpicked CB5. During the same time, soluble sugar concentrations were maintained and starch accumulated in stems of picked CB5 and of nonpicked DLS genotypes, while these carbohydrates were depleted from stems of nonpicked CB5. Maintenance of stem carbohydrate concentrations was associated with greater plant survival of the first podset, which led to greater pod production during the second podset. Second-set pod production of picked CB5 and 1411 approached that of nonpicked DLS genotypes. We hypothesize that pod removal altered photoassimilate partitioning in normally senescent genotypes such that they phenotypically resembled nonpicked DLS genotypes.