Autecological studies on Audouinia capitata (Bruniaceae). 3. Pollination biology

Abstract

Flower production in Audouinia capitata is highest during the first post-fire season. Self-pollinated flowers produced a mean of only 0.8% fruits bearing seeds. This seed set was increased 17-fold by natural insect-mediated cross-pollination. Hand cross-pollination induced an approximately 5-fold increase in seed set when compared to natural cross-pollination. Germination and initial pollen tube growth are normal following self- as well as cross-pollination. Selfing, however, is characterized by abnormal pollen tube growth at the stylar base, resulting in cessation of growth except in the case of occasional pollen tubes. By one week after cross-pollination, pollen tubes have penetrated the egg apparatus. Average in vitro germination of pollen and frequencies of small underdeveloped microspores in 20 populations varied from 2.5 to 28.4% and from 2.0 to 23.7%, respectively, with large interplant variations within populations in both germination (0 – 79.6%) and underdeveloped microspores (0 – 61.0%). The prevalence of non-viable pollen and insufficient insect-mediated transfer of pollen between the plants which have an insignificant ability to produce seed following self-pollination, are limiting factors in reproduction.