Introduction

The project at Kew is concerned primarily with the symbiotic method of raising European orchids from seed. However, asymbiotic sowings have occasionally been made for direct comparison of the relative effectiveness of the two methods, and in an attempt to raise seedlings where the symbiotic method has proved unsuccessful. This paper describes a comparison between asymbiotic and symbiotic germination of three species of Orchis, for which both methods were successful. In addition, the effective asymbiotic methods for germination of rare British species, where symbiotic methods have failed, and the germination response of three orchid species from each of the genera Orchis, Ophrys, Dactylorhiza and Serapias to nine vigorous and eight less vigorous orchid symbionts are reported. The pattern of orchid/fungus compatibility is also discussed in relation to the raising of seedlings beyond initial germination stages, and the routinely used orchid/fungus combinations for bulk propagation of certain species are recorded and illustrated.

Materials and methods

All sowings were made on to agar-based media in Petri dishes using aseptic techniques (Muir 1987). For symbiotic germination the media used were Modified Oats Medium (O3) (Clements et al. 1986) and G4 – a modification of O3, using 1.2 gdm–3 amylopectin in place of the oats, on the recommendation of P. Milon (Laboratoire de Recherches Horticoles, 78570 Chanteloup-les-Vignes, Paris). The media of Harvais (1973), Mead & Bulard (1975), Norstog (1973) and Curtis (1936) were used for asymbiotic germination.