Reproductive biology aspects of two species of the genus Gavilea (Orchidaceae, Chloraeinae) in populations from Central Chile

Resumo

The extent to which plants depend on pollinators for outcross pollen transportation is a key issue in plant reproductive ecology. We evaluated the putative breeding system, floral display, and natural pollination in two Southern Cone of South American orchids, Gavilea araucana and G. venosa, by performing four hand pollination trials (agamospermy, autogamy, geitonogamy, and xenogamy tests) and by counting each flower and fruit produced by plants in natural conditions. Fruit set differed significantly depending on the origin of pollen as well as on the presence of a pollen vector. None of these species produced fruits by the agamospermy tests, therefore indicating that they require the presence of pollen on the stigmas for fruit setting. By contrast, only G. araucana was capable of fruit setting following the autogamy test, therefore demostrating that this orchid needs not depend on pollinators for fruit set. Furthermore, G. araucana and G. venosa produced 100% fruits by geitonogamy and by xenogamy, thereby indicating that both plants are totally self-compatible. The mean number of flowers per plant was 2.1 times higher in G. venosa with respect to G. araucana; however, natural fruiting success was 28.8% and 98.9%, respectively. Furthermore, while the increase in fruiting success significantly and positively correlated with an increase in floral display in G. araucana, in G. venosa these variables were unrelated. Certainly, further studies concerning the reproductive strategies in orchids of southern South America are of great importance.