Viability testing of orchid seed and the promotion of colouration and germination

This study reports the ability of Fusarium to induce orchid seed colouratio n and germination. The in vitro bioassay germination test, using a Fusarium isolate from the protocorm of Cypripedium reginae, was compared with stand ard chemical procedures of triphenyl tetrazolium chloride (TTC) and acid fu chsin (AC) for testing seed viability. With Cypripedium reginae, Cypripediu m parviflorum and Platanthera grandiflora, the efficiency of the bioassay w as similar to that of the TTC and AC procedures. However, the bioassay was more appropriate for estimating embryo viability after a prolonged seed pre treatment (more than 2 h) in 10% sodium hypochlorite, a surface sterilant o ften used to enhance germination of terrestrial species. We also obtained i n vitro Cypripedium reginae seed germination induction and protocorm format ion by the same Fusarium isolate. This is the first confirmation of Bernard 's early reports that orchid fusaria could stimulate seed germination (Bern ard N. 1990. Revue Generale de Botanique 12: 108-120). However. the importa nce of the non-mycorrhizal Fusarium fungus in promoting germination seems t o be relatively minor compared to that of specific Rhizoctonia orchid mycor rhizas. Our results are discussed in light of the current North American st rategy on orchid conservation methods which proposes the use of symbiotic g ermination. (C) 2000 Annals of Botany Company.