Reproductive success in a reintroduced population of a critically endangered shrub, Symonanthus bancroftii (Solanaceae)

Abstract

Symonanthus bancroftii is a critically endangered dioecious shrub, with only one male and one female plant known in the wild. Micropropagated, clonal plants of the male and female parents were hand-pollinated. Seed was germinated in sterile culture and a subsequent daughter (F1) seedling was multiplied in vitro. Micropropagated plants of the original parents and daughter were reintroduced to a natural habitat site. We detail the first study of pollination biology and reproductive success in this extremely rare species. Floral morphology, flowering phenology, pollen viability, female receptivity and fruit set of reintroduced plants of S. bancroftii were investigated. Flower viability of S. bancroftii shows a 25-day maximum for male flowers, whereas non-pollinated female flowers remain viable for a maximum of 38 days (female parent) and 41 days (daughter), respectively. Flowering of reintroduced male and female plants overlaps from mid-June to early November. Pollen remained viable for at least 8 days after anther dehiscence. Maximum stigma longevity recorded was 28 days (female parent) and 39 days (daughter) and maximum ovule longevity varied from 13 days (female parent) to 28 days (daughter). The mean percentage of flowers setting fruit was 39 ± 13% for female parent plants and 48 ± 4% for daughter plants. Empirical reproductive success measures for male–daughter crosses generally exceeded those of the original parent crosses. The reproductive success of S. bancroftii so soon after reintroduction of plants is a positive sign indicating that rapid accumulation of a soil seedbank is feasible and is thus an important first step towards successful establishment of self-sustaining populations of this critically endangered species.