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

This study reports the ability of Fusarium to induce orchid seed colouration and germination. The in vitro bioassay germination test, using a Fusarium isolate from the protocorm of Cypripedium reginae, was compared with standard chemical procedures of triphenyl tetrazolium chloride (TTC) and acid fuchsin (AC) for testing seed viability. With Cypripedium reginae, Cypripedium parviflorum and Platanthera grandiflora, the efficiency of the bioassay was similar to that of the TTC and AC procedures. However, the bioassay was more appropriate for estimating embryo viability after a prolonged seed pretreatment (more than 2 h) in 10% sodium hypochlorite, a surface sterilant often used to enhance germination of terrestrial species. We also obtained in vitro Cypripedium reginae seed germination induction and protocorm formation by the same Fusarium isolate. This is the first confirmation of Bernard's early reports that orchid fusaria could stimulate seed germination (Bernard N. 1990. Revue Generale de Botanique 12: 108-120). However. the importance of the non-mycorrhizal Fusarium fungus in promoting germination seems to be relatively minor compared to that of specific Rhizoctonia orchid mycorrhizas. Our results are discussed in light of the current North American strategy on orchid conservation methods which proposes the use of symbiotic germination. (C) 2000 Annals of Botany Company.