The mating system of Sesbania sesban (L.) Merr. (Leguminosae)

The mating system of Sesbania sesban was studied using one natural population and two cultivated populations. A large number of progeny (600) was assayed from each population for one polymorphic locus of Malate dehydrogenase (Mdh). The level of out-crossing in the studied populations ranged from 40–100%. The genotype frequencies were in agreement with those of the Hardy-Weinberg expected genotype proportions as in randomly mating populations at P < 0.05. The floral structure and the pollen shedding behaviour of the flowers of S. sesban could favour cross-pollination and/or self-pollination depending on the circumstances. Self-pollination usually occurs late in the flowering period when pollinators fail to visit the flowers. Such a “delayed selfing” facilitates out-crossing in the presence of appropriate pollinators under natural conditions, but confers a selective advantage where pollinators are limiting. The results indicated that S. sesban could be self-fertilized in the absence of pollinators or could out-cross with other heterozygous individuals in the neighboring population when suitable pollinators are available. S. sesban exhibits “facultative xenogamy” or “delayed selfing” and is a mixed mating species. Key words/phrases: Allozymes, delayed selfing, Hardy-Weinberg equilib rium, malate dehydrogenase, mixed mating system SINET: Ethiopian Journal of Science Vol.25(2) 2002: 177-190