Comparative in vitro seed germination and seedling development in tropical and temperate epiphytic and temperate terrestrial orchids

Abstract

Ex situ conservation of orchid seeds requires the application of modern biotechnology to determine seed quality and to optimise in vitro regeneration. The nutrient requirements for germination and seedling growth in vitro can be species-specific and influenced by life history traits and habitats. Therefore, this study aimed to explore in vitro seed germination and subsequent seedling development of selected tropical and temperate epiphytic and terrestrial orchids on different growth media. Seeds of three epiphytic orchids [Dendrobium strebloceras (tropical), D. lineale (tropical) and D. cunninghamii (temperate)] were sown on four different media supplemented with 2% sucrose: (1) Murashige and Skoog (MS); (2) Vacin and Went (VW); (3) Norstog; and (4) water agar. In addition, D. strebloceras seed were sown on the media above supplemented with 3% sucrose and half-strength MS supplemented with either 2% or 3% sucrose. Seed germination of three temperate terrestrial orchids (Gastrodia cunninghamii, Pterostylis banksii and Thelymitra nervosa) was assessed on media (1–4) but with VW replaced by terrestrial orchid medium-BM1. Whilst all epiphytic orchids germinated on all media tested, the best seedling development for the two tropical species was on full or half-strength MS media. The temperate epiphyte D. cunninghamii germinated best on Norstog medium but did not develop further. Norstog and BM1 media supported germination and seedling development better in P. banksii and T. nervosa. This study concludes that temperate terrestrial P. banksii and T. nervosa need more excating media (Norstog and BM1 media) for seed germination and subsequent seedling development compared to tropical epiphytic species D. strebloceras and D. lineale. Optimising these nutrient requirements in vitro will underpin successful ex situ conservation of orchid species. Seeds of tropical epiphytic orchids, D. strebloceras and D.linelae require a less stringent nutrient medium for in vitro germination and seedling development compared to temperate terrestrial orchids P. banksii and T. nervosa. Understanding the differences in nutrient requirements for germination and subsequent seedling development underpins successful ex situ conservation of orchids.