Procedure for establishing sheathing mycorrhizas on tree seedlings

A simple procedure is described where seedlings emerging from surface sterilised seeds (of Betula pendula, B. pubescens, Pinus contorta and Picea sitchensis) were grown axenically in a peat/vermiculite mixture which had been previously inoculated, and incubated, with sheating mycorrhizal fungi (including Hebeloma sacchariolens, Paxillus involutus and Amanita muscaria). Mostly, seedlings were grown in split polystyrene tubes (50 mm tall x 13 mm internal diameter) which were arranged 140 150 per tray, the trays being covered with transparent propagator lids so forming a unit that could be sealed and sterilised before use with gamma radiation. With the formation of sheating mycorrhizas after about 7 weeks the sterility of the container was broken to enable seedlings to be hardened off prior to transplanting. Roots of Betula pendula seedlings grown in tubes were smaller, as judged by numbers of 'fragments', than those of plants which were not 'restricted'. 'Tubing' increased: (a) the proportion of root fragments with mycorrhizas; and (b) the sizes of individual mycorrhizas. The sizes of the 'tubing' effects differed with different isolates of A. muscaria, so suggesting, because of the sensitivity of the system, that environmental and genotypic factors must be carefully controlled.