Honeybush (Cyclopia spp.) pollen viability and surface morphology

Abstract

Genotypes of Cyclopia, used to produce honeybush tea, are being improved through selective breeding for suitability in large-scale cultivation and consistent flavour/aroma qualities. Though high levels of natural fecundity have been reported in honeybush species, attempts at controlled crosses have hitherto resulted in virtually no seed set. While investigating this problem, it was found that many basic questions regarding the specific reproductive physiology of the genus have not been answered. Studies were undertaken to provide the necessary data about sexual reproduction in honeybush species, in support of existing breeding programmes. This paper presents data concerning pollen viability in relation to flower bud stage, storage and pollen surface morphology of C. longifolia, C. maculata and C. subternata. Pollen anthesis and viability (measured as in vitro pollen germination percentage - PGP11Pollen germination percentage) were linked to visual stages of flower bud development. Pollen samples, dried and stored for 540 days at -18 °C, were tested for PGP at intervals (7, 30, 90, 180, 365, 540 days) during the storage period. While there was an overall decrease in PGP over storage time, four genotypes did not have any significant decrease in PGP over time. The effect of media sucrose content (MSC22Media sucrose content) (0–25%) on in vitro PGP of honeybush pollen was tested and differences in response were observed between species. Pollen surface morphology was investigated using FE-SEM microscopy and no consistent differences in shape or surface ornamentation were observed between the species, though differences in grain size were observed.