Development of an in vitro axillary bud propagation system for slash pine (Pinus elliottii, Engelm.)

Excised zygotic embryos of slash pine were cultured on hormone containing media for the production of adventitious buds. Seven culture media were tested for bud production and nutritional support of the embryos. Media selection had significant effects upon embryo vigor and adventitious budding. In general, bud production was low and buds were difficult to elongate. Adventitious bud production was abandoned for an in vitro axillary bud system. Hypocotylary explants of young seedlings of slash pine were dipped for 45 seconds in a hormone containing solution and cultured on basal media containing charcoal. A mean of 6.23 axillary buds per open-pollinated seedling explant was produced in 29 days. Elongation of the axillary buds into shoots was rapid compared to the elongation of adventitious buds. Elongated axillary shoots and hypocotylary explants were retreated to expand the number of clones. Seed from a 3 male by 5 female factorial cross were used to assess genotype influence on axillary bud production in vitro. Four of the 15 crosses produced progeny with greater mean response than the progeny of open-pollinated crossings. All four outstanding responders were progeny of one male. An In vitro rooting protocol for axillary shoots was developed. Seventy-four percent rooting of axillary shoots from progeny of open-pollinated trees was obtained when cultured on hormonal medium for 13 days. Axillary shoots from controlled cross progeny were utilized to assess genetic influence on rooting in vitro. Ninety-three percent rooting of seedling explants was obtained via treatment with Pseudomonas vesicularis. Rooting of axillary shoots through bacterial treatment was less frequent, achieving 31.6 percent.