Abstract
SummaryIn asymbiotic cultures Orchis (Dactylorchis) purpurella seed germinated freely on deionized water agar and on defined and undefined media. Germination was enhanced by prolonged sterilization periods and high temperatures but was inhibited by light. Asymbiotic protocorms never attained the photosynthetic stage except on undefined media.Several Rhizoctonia solani strains enhanced seed germination at low temperatures. The further development of the relationship between host and endophyte varied with the strain; two pathogenic isolates from tomato and rice were strongly symbiotic to protocorms while other strains although stimulating growth ultimately became parasitic.Symbiosis was most stable at low temperatures but with any one strain there was a general pattern of infection in which nutrient depletion in the protocorm was often followed by parasitism. Drip feeding with carbohydrate delayed parasitism but in some conditions led to intense growth of the fungus. It is suggested that a careful balance of nutrients is important in the maintenance of a stable relationship between host and endophyte. The significance of this is discussed in relation to conditions in nature.
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