Floral characterization and pollen germination protocol for Castanea crenata Siebold & Zucc

Abstract

Chestnuts have staminate (male) and androgynous (hermaphrodite) flowers in the same individual. The male flowers are grouped into unisexual catkins, while the female flowers are located at the base of male inflorescences. There is divergence in the functionality of pollen grains among chestnut species. As this species requires cross-pollination, germination tests are essential in breeding programs. The objective of this study was to comparatively evaluate pollen viability as a function of the type of flower using colorimetric assays, to develop a culture medium protocol for in vitro pollen germination and characterize the floral morphology of the Japanese chestnut (C. crenata). Eleven Japanese chestnut cultivars were evaluated for characterization and description of the floral morphology, pollen viability by staining, and in vitro germination with determination of the percentage of viability regarding the type of inflorescence (staminate x androgynous). In addition, a culture medium was established to induce germination of chestnut pollen and determination of the percentage of in vitro pollen germination, as well as quantification of the number of anthers per flower and pollen grains per anther and per flower for all cultivars. There was no difference in pollen viability between androgynous and staminate catkins. The culture medium containing 6 g L−1 of agar, 46.5 g L−1 of sucrose, and 460.23 mg L−1 of boric acid in the absence of calcium nitrate, pH 5.25, promoted the best conditions for in vitro pollen germination. Cultivars with the highest percentage of viability recorded the lowest amounts of pollen per anther and per flower. This characteristic may influence the number of flowers necessary for extraction of anthers in crosses and the success of hybridization in the field.