Four seed-quality measures in orchids with different pollination systems

Abstract

The number of seeds is an indicator of plant fitness. We compared four quality measures – seed number, abortion, viability and germination. To test as wide a span of seed variability as possible, we cross-pollinated and self-pollinated one nectarless and one nectar-rewarding orchid species, assuming that nectariferous species should be more adapted to geitonogamous selfing than the cheating one and that seed quality should reflect that. Seed number for both species was lowest in selfed fruits. Viability and germination did not show any difference in deceptive Orchis militaris treatments, but the trend was different in rewarding Platanthera bifolia. Seed number and seed abortion correlated well as did viability and germination in vitro. This shows that these two stages are controlled by different mechanisms. Therefore, seed number or seed abortion rate alone cannot be proxies for reproductive output.