Germination of orchid seeds

Abstract

Bernard (1909) accidentally discovered that fungi are important for the germination of orchid seeds. It appears that orchids live in a symbiotic relationship with fungi, from the moment of germination. Symbiosis is the association of two organisms, to their mutual advantage. The symbiotic relationship between fungus and a root is known as a mycorrhiza; which literally means fungus-root. It was already established around 1900 that the hyphae (fungal threads) penetrate the protocorms and the roots of the plant and are ‘digested’ possibly making nutrients and other materials available to the orchids. It has been established that there are two different types of host cells in orchids; subepidermal host cells, in which the fungus can remain untouched and ‘healthy’, and more deeply lying host cells, in which the fungus is ‘digested’ into an amorphous mass (Hadley, 1975; Harley, 1969). The most important fungi that have symbiotic relationships with orchids are from the genus Rhizoctonia Since in the early days (1900-1910), it was thought that orchids could only germinate in vitro in the presence of a fungus, only symbiotic germination or orchids was carried out. It was supposed that germinating and juvenile orchids were heterotrophic, and were reliant on the fungi for the supply of materials; the main reason for this assumption was the small amount of food reserve found in the orchid seeds.