Seed propagation and re-introduction of the U.S. federally endangered Hawaiian endemic, Platanthera holochila (Hbd.) Krzl. (Orchidaceae)

Abstract

Platanthera holochila (Hbd.) Krzl. [syn = Peristylus holochila (Hbd) N. Hallé] is the rarest of three orchids endemic to the Hawaiian Archipelago. As of 2011, 33 individual plants of this U.S. Federally endangered species remained on three islands with only one specimen known to occur on Kauai. This paper presents a summary of experiments aimed at cultivating this species from seed leading to the reintroduction of seedlings. We describe: 1) the mycorrhizal fungi acquired from P. holochila protocorms on Molokai, 2) the role of light vs. dark pretreatment on symbiotic seed germination using a mycorrhizal fungus from Florida, and 3) asymbiotic germination on three media (Murashige and Skoog, Knudson C, P723). Protocorms recovered in situ using seed packets yielded seven strains of a mycorrhizal fungus assignable to the anamorphic genus Epulorhiza Moore, but none of these strains prompted seed germination in vitro. Using the mycorrhizal fungus from Florida, no significant differences were detected between light pre-treatment vs. dark incubation on seed germination or development, but statistical differences were evident among two agar types tested. Seeds sown on acidified (pH 5.0) asymbiotic medium P723 (PhytoTechnology Labs) developed to the leaf-bearing stage 351 days after sowing and incubation in darkness at 16-19 C. Seedlings illuminated 451 days after sowing were eventually established on soil in a greenhouse (ex vitro). A total of 85 seedlings were promptly transported to Hawaii in March 2011. A minimum of 3.1 years is required for the propagation of P. holochila from seed using acidified asymbiotic medium P723.