ESTIMATING THE VIABILITY OF VESICULAR-ARBUSCULAR MYCORRHIZAE FUNGAL SPORES USING TETRAZOLIUM SALTS AS VITAL STAINS

The tetrazolium salts -dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazoli um bromide and ophenyl)-3-(p-nitrophenyl)-5-phenyl-2H-tetrazolium chlo ride were evaluated as viral stains for estimating the viability of fu ngal spores of Glomus mosseae and Glomus clarum. Respiring fungal spor es accumulated tetrazolium bromide-formazan and tetrazolium chloride-f ormazan in the cytoplasm as a visually distinct color reaction. Estima tes, however, of fungal spore viability based on tetrazolium bromide s taining were inconsistent with viability estimates based on a bioassay using single spores of G. clarum. Inconsistencies were due largely to the ambiguous interpretation of the significance of black spores. In contrast, color reactions in tetrazolium chloride were relatively stab le and consistent with bioassay estimates of viability. Generally, inc ubation in 1 mg ml(-1) tetrazolium chloride for 48 to 72 h was suffici ent to ensure maximum color reaction. Viable spores were distinguishab le from those which were unable to colonize a host plant on the basis of the intensity of color reaction in tetrazolium chloride. We conclud e that tetrazolium chloride staining can be used as a rapid indicator of vesicular-arbuscular mycorrhizae fungal spore viability.