THE SURVIVAL OF INFECTIVE HYPHAE OF VESICULAR-ARBUSCULAR MYCORRHIZAL FUNGI IN DRY SOIL - AN INTERACTION WITH SPORULATION

Contrary to previous evidence, the hyphae of a vesicular-arbuscular (VA) mycorrhizal fungus, Acaulospora laevis Gerd. and Trappe, did not remain infective in soil for a length of time, and at a level of dryness, equivalent to that occurring in seasonally-dry field soils. A possible interaction between the survival of hyphae and the timing of sporulation was therefore examined in a second experiment. We tested the hypothesis that hyphae of A. laevis and Scutellospora calospora (Nicolson and Gerdemann) Walker and Sanders, will only remain infective in dry soil if sporulation has not commenced. The capacity of the hyphae of A. laevis to remain infective, in undisturbed soil that had been allowed to dry, depended on the stage of the life cycle reached at the time of the onset of drying. If sporulation had commenced, then infectivity quickly declined as the soil dried. In contrast, infective hyphae of S. calospora survived for at least 11 wk, regardless of the timing of the commencement of drying of the soil in relation to sporulation. Quantifying entry points was an important measure for assessing the survival of infective hyphae, complementing the measure of total mycorrhiza formation by the test plants.