Pollination Strategies of Some Perennial Weed Species

Abstract

Weeds have evolved a number of adaptations to thrive even under adverse conditions. One of the adaptations is their ability to set seeds even under pollination uncertain environments through autogamous self-pollination. Autogamous pollination which provides reproductive assurance (RA) is critical in annual weeds as they get only one chance to set seeds in their life; if they miss this chance their survival is threatened. In perennial weeds, however, RA through autogamous self-pollination is not so critical as they get repeated chances to set seeds; lack of seed set in some years does not affect their survival. There is very little information on pollination strategies of perennial weeds particularly of Indian species. To test this prediction, studies were carried out on five Indian perennial weeds — Cassia auriculata, Ipomoea obscura, Oxalis corniculata, Plumbago zeylanica and Dodonaea viscosa. Seed set in the populations of Ipomoea, Oxalis and Plumbago was exclusively dependent on autogamous pollination as they did not attract any pollinators and there was no difference in the extent of seed set in bagged and open-pollinated flowers. Autogamy was absent in Cassia; it depended exclusively on pollination by Xylocopa sp. Dodonaea depended on wind for pollen transfer. Thus, in agreement with the expectation, autogamy is not critical in perennial weed species and their pollination strategies vary from complete autogamy to obligate outbreeding, similar to non-weedy species.