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

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. Blomproduksie is hoër in die eerste seisoen na vuur as op latere stadiums. Selfbestuiwing het gemiddeld 0.8% vrugte met sade tot gevolg gehad. Hierdie saadset kon 17-voudig verhoog word deur natuurlike kruisbestuiwing deur insekte. Hand-kruisbestuiwing in vergelyking met natuurlike kruisbestuiwing, het ongeveer ’n vyfvoudige verhoging in saadset geïnduseer. Ontkieming en aanvanklike stuifmeelbuisgroei is normaal na self- sowel as kruisbestuiwing. In die geval van selfbestuiwing kom abnormale stuifmeelbuisgroei egter by die basis van die styl voor, wat lei tot staking van verdere groei met die uitsondering van enkele buise. Een week na kruisbestuiwing kan stuifmeelbuise in die eierapparate waargeneem word. Gemiddelde in vitro-ontkieming en die frekwensie van klein, onderontwikkelde mikrospore in 20 bevolkings het respektiewelik van 2.5 tot 28.4% en van 2.0 tot 23.7% gewissel, met groot tussenplant-variasies in beide ontkieming (0 – 79.6%) en onderontwikkelde mikrospore (0 – 61.0%). Die algemene voorkoms van nie-kiemkragtige stuifmeel en onvoldoende insek-kruisbestuiwing in ’n spesie met ’n baie beperkte vermoë tot saadvorming na selfbestuiwing, word as beperkendefaktore in voortplanting beskou.