1996/09/01 by Susan M. Carthew, Robert J. Whelan, David J. Ayre
Agricultural and Biological Sciences · Biochemistry, Genetics and Molecular Biology · Environmental Science · #Ecology and Vegetation Dynamics Studies #Plant Reproductive Biology #Plant and animal studies
paper · doi:10.1086/297382
openalex publication_date 1996/09/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/06/11
Several features of the phenology and reproductive biology of members of the genus Banksia indicate that these plants either have a high level of mate choice or are obligate outcrossers, with many flowers being functionally male or sterile. These species produce many inflorescences with vast numbers of flowers, yet seed-set is typically very low. Most species studied appear to have at least limited self-compatibility and outcrossing rates close to one. Despite this, pollinators normally deposit a large amount of self-pollen on stigmas. In this study, we used experimental pollinations to test for evidence of preferential outcrossing within populations of Banksia spinulosa and Banksia ericifolia. Our allozyme analysis of progeny arrays indicates that the studied populations of both B. spinulosa from a prior study and B. ericifolia as determined for 27 plants in this study are highly outcrossed. Results from pollinations using applications of self- and cross-pollen and mixtures of the two indicated that, at the early prezygotic stage, all treatments had an equal potential to produce seed. This contrasts with the observation of almost no pollen tube growth from the autogamy treatment conducted on B. spinulosa. Seed-set from experimental treatments was low for both species, and only one inflorescence from each species produced seed after self-pollination. This indicated that self-pollen may be inhibited at some later stage, but self-fertilization is possible. However, small sample sizes meant that there were no significant differences in seed-set between treatments. When mixtures of self- and cross-pollen were applied to stigmas, the genetic composition of resulting seeds showed that most progeny were derived from outcrossing events. This preferential outcrossing may occur via a recessive lethal system. Moreover, the results provide an explanation for the observed discrepancy between the high outcrossing rates obtained for both species and observations that pollinators are likely to transfer large amounts of self-pollen.