Causes of infertility in the endangered Australian endemic plant Borya mirabilis (Boryaceae)

Abstract

Borya mirabilis Churchill (Boryaceae, Asparagales) is a herbaceous perennial and one of Australia’s most endangered plants. Only one population of four colonies remains, on a rock ledge in the Grampians (Gariwerd) National Park in Victoria, Australia. The reasons why B. mirabilis flowers freely but does not set seed were investigated. Borya mirabilis had a greater proportion of floral abnormalities than other, fertile Borya species. The pollen was often mis-shapen, with ≤ 1% pollen tube formation, but the ovules showed no structural dissimilarity from other, fertile Borya species. The flowers offered a nectar reward and many insects visited the pollen-bearing flowers in the field. Artificial cross-pollination resulted in the first recorded seed for this species. Borya mirabilis has ~66 chromosomes, relative to the diploid number of ~26 in Borya constricta Churchill, strongly suggesting that B. mirabilis is polyploid. Only 4–7% genetic diversity was found within the remaining B. mirabilis field population using 25/60 RAPD primers that showed heterogeneity. An ex-situ nursery collection was found not to contain all genotypes. Recommendations for the conservation of B. mirabilis include capturing all the known genetic diversity in cloned plants in preference over further attempts to produce seed.