Responses of Sitka spruce callus to challenge with wood decay fungi

In dual cultures Sitka spruce callus inhibited the growth of several decay and mycorrhizal fungi. This effect was influenced by the quantities of plant growth regulators in the tissue culture medium: higher levels of auxin increased the inhibition, though this effect was partially suppressed by cyto‐kinins. Two compounds with antifungal activity were found in methanol extracts of callus. One of these was soluble in chloroform and present in small quantities in relation to its antifungal activity. The second, present in larger quantities, remained in the aqueous phase on partitioning, but was recovered into ethyl acetate after saturation with NaCl. The structural and histochemical responses of callus to direct application of fungal inoculum were also examined. Reactions were similar with all fungi used; cells adjacent to the inoculum became necrotic and their walls thickened. Groups of cells close to this zone became suberized. Also, an amorphous gel impregnated with phloroglucinol‐HCl reactive material was secreted into intercellular spaces around the necrotic region. Hyphae grew into the gel matrix, but did not penetrate the suberized tissues.