VA MYCORRHIZAL SPORES FROM 3 SPECIES OF ACAULOSPORA - GERMINATION, LONGEVITY AND HYPHAL GROWTH

The spores of three species of Acaulospora were examined to compare their rate of germination, the effect of long term storage on their viability, their tolerance to disturbance, and the length of hyphae they produced. The rate of germination of Acaulospora laevis was initially slower than that of the other two species but all species reached maximum germination after 21 d incubation. For each fungus only a small proportion of spores stored for 2 months in dry pot culture soil germinated. After storage for 4-6 months most spores germinated indicating that dormancy, which was most marked in A. laevis, was overcome. Spores were then germinable for many months. The larger spore of A. laevis produced greater hyphal length per spore and was more sensitive to physical disturbance than the smaller spores of Acaulospora trappei and Acaulospora sp. (WUM 18-1). None of the three fungi were able to colonize living roots when dead mycorrhizal root pieces were used as an inoculum source. A technique to allow the distinction between newly formed spores and those present in the original inoculum was developed.