Pollination biology and breeding systems in the terrestrial orchid Bletilla striata

Abstract

The levels of fruit set in different habitats (three inland populations vs. three coastal populations) and the breeding system in the terrestrial orchid Bletilla striata were examined in two groups of populations in Haenam-gun, Jollanam-do Province in southern Korea. In total inland populations (mean fruit set=13.3%) showed about eight-fold higher fruit set per plant than the coastal populations (1.6%), probably due to mild climatic conditions in the inland populations during the flowering period. Honey bee workers Apis mellifera were observed in the inland populations, but no visitors were found in the coastal populations. However, a great increase in fruit set was achieved by hand-pollination: the percentage of fruit set through artificial self-pollination and geitonogamous pollination were close to 90%, indicating that B. striata is self-compatible. Agamospermy and spontaneous autogamy (automatic self-pollination) were not detected in this study. These indicate that pollinia vectors are essential for achieving fruit set in natural populations of B. striata. Except in one inland population examined in 2001, there was no significant correlation between the patch size per population and the average percentage of fruit set, which might reflect deception-pollination of B. striata and/or paucity of pollinators. Overall levels of fruit sets within and among patches in each population were homogeneous during a two-year period.