Measurement of the viability of arbuscular-mycorrhizal fungi using three different stains; relation to growth and metabolic activities of soybean plants

Histochemical staining of alkaline phosphatase (ALP) and succinate dehydrog enase (SDH) activities in four arbuscular mycorrhizal fungi (Glomus intrara dices, G. fasciculatum, G. monosporum and G. mosseae) and their relation to growth and metabolic activities of soybean plants were investigated in a g reenhouse experiment. In general, mycorrhizal inoculation significantly inc reased the growth responses, phosphorus and nitrogen contents, acid and alk aline phosphatases as well as total soluble protein of soybean compared to non-mycorrhizal plants. Stimulation was related to the viability of each my corrhizal fungus. The localization of succinate dehydrogenase (as a vital s tain of metabolically active fungus) and alkaline phosphatase activity (as a potential marker of efficiency of the symbiosis) in the arbuscular mycorr hizal fungi were variable. The activity appeared in young arbuscles and int ercellular hyphae, whereas the collapsed arbuscules were inactive. The hist ochemical staining results demonstrated that the activity of alkaline phosp hatase fungi was lower than succinate dehydrogenase. The use of nitroblue t etrazolium chloride as a vital stain for SDH activity showed that all mycor rhizal infection revealed by trypan blue staining was not physiologically a ctive. Thus, the possible utilization of these enzymes to assess the activi ty of mycorrhizal fungi and its relation with effectively for plant growth and mineral contents is discussed.