Genetic relatedness among developing seeds and intra fruit seed abortion in Dalbergia sissoo (Fabaceae)

Dalbergia sissoo, a wind-dispersed tropical tree, exhibits high intrafruit seed abortion. Of the four to five ovules in the flower, generally one and occasionally two or three develop to maturity. It has been proposed that th e seed abortion is a consequence of intense sibling competition for materna l resources and that this competition occurs as an inverse function of the genetic relatedness among the developing seeds. Accordingly, developing see ds compete intensely when they are genetically less related but tend to dev elop together when genetically more related. We tested this hypothesis by c omparing the genetic similarity among the pairs of seeds developing within a pod with that among (a) random pairs from the pool of all seeds, (b) rand om pairs from single-seeded pods, and (c) random pairs from two-seeded pods , using both randomly amplified polymorphic DNA (RAPD) and isozymes in five trees. We found that the pairs of seeds developing within a pod are geneti cally more similar than any random pairs of seeds in a tree. Thus the forma tion of two-seeded pods appear to be associated with increased genetic rela tedness among the developing seeds. We discuss the results in the context o f possible fitness advantages and then discuss the possible mechanisms that promote tolerance among related seeds.