Introduction

Although epiphytic orchids have been grown routinely from seed for more than sixty years using the asymbiotic method developed by Knudson (1922), relatively little interest has been attached to techniques for the storage of such seed. This is surprising, especially in view of the rapid loss of many orchid habitats, and in particular the loss of tropical moist forest, with the imminent threat of extinction of a large number of orchid species in the wild (Myers 1979, 1980; Koopowitz & Kaye 1983; Hagsater & Stewart 1986; Koopowitz 1986; Stewart 1986). Knudson (1934) indicated the desirability of storing seed to insure against either failure to germinate or the accidental loss of seedlings. The development of such techniques would also allow an assessment of the commercial merits and potential of a particular cross while still retaining a proportion of the seed.

The cryopreservation of seed shows considerable potential. Thus seeds of Encyclia vitellinum have been stored at a temperature of –40°C for 35 days without loss of viability (Koopowitz & Ward 1984). Svihla & Osterman (1943) reported that Cattleya hybrid seed survived freezing at –78°C, and Ito (1965) successfully stored seeds of Dendrobium nobile and Cattleya hybrids for periods of up to 465 days at –79°C. Pritchard (1984; 1985) reported that seeds of a number of terrestrial and epiphytic species with seed moisture contents below 14% were not damaged by storage in liquid nitrogen (–196°C).