Is Regulation of Mating Within Branches Possible in Wild Radish (Raphanus sativus L.)?

Abstract

Non-random mating can affect the success of a plant's offspring by altering the identity and diversity of pollen donors that sire the seeds. Wild radish is known to discriminate among pollen donors within fruits and to selectively fill those fruits which have been multiply sired. In this study, the order of pollinations was varied along branches in order to test whether these plants also regulate mating by differential filling of fruits sired by pollen donors that are locally common or locally rare on branches. Overall, fruits sired by pollen donors that were locally rare had larger individual seeds and larger total weights of seeds per fruit, but the responses of the five maternal families studied were quite heterogeneous. Some families showed no response. One family showed increased size of fruits sired by a rare pollen donor, but the result was not due to the process we were testing. In that case, one donor was a poor donor and fruits of the better donor were large when rare because they had little competition for resources. Only one of the five families showed selective filling of fruits with rare genotypes. This process acts to allocate resources where offspring diversity is highest and it acts in the same direction as selective filling of multiply sired fruits. The result was very strong in the family where it occurred. While this process, like other characters in wild radish, is highly variable, the data show that regulation of mating at the level of the branch can operate in the same direction as regulation of mating within fruits. Key-words: Mate choice, non-random mating, pollen donor effects, Raphanus sativus, resource allocation, seed paternity