INHIBITION OF HYPHAL GROWTH OF A VESICULAR-ARBUSCULAR MYCORRHIZAL CONTAINING SODIUM-CHLORIDE OF INFECTION FROM FUNGUS IN SOIL LIMITS THE SPREAD SPORES

The hyphal growth of some vesicular-arbuscular (VA) mycorrhizal fungi is inhibited by increasing concentrations of NaCl in soil, and this ma y influence the formation of mycorrhizas. Our objective was to examine the effect of NaCl on the distance that hyphae of a VA mycorrhizal fu ngus, Gigaspora decipiens Hall and Abbott can grow through soil and in fect roots of a known host plant, Trifolium resupinatum. L. cv. Kyambr o. An experimental procedure was developed to enable the effect of NaC l on the pre-symbiotic growth of hyphae of a VA mycorrhizal fungus to be studied separately from other phases of the life-cycle. Roots 1 cm from the spores were infected after 15d in soils moistened with 0 or 7 5 mM NaCl, indicating that the initial hyphal growth was not inhibited in soil moistened with 75 mM NaCl. With time, hyphal growth became in creasingly inhibited by NaCl, as roots 2.5 cm from the spores were not infected after 26 d in soil moistened with 75 mM NaCl, bur were infec ted in soil without NaCl added. In soil moistened with 150mM NaCl, roo ts 1cm from the spores were infected after 26 d, but roots 2 cm from t he spores were not infected after 36 d. Increasing concentrations of N aCl inhibited either the hyphal growth or the infectivity of G. decipi ens hyphae after they had grown through soil. The latter may be unlike ly, because the infectivity of G. decipiens hyphae placed directly ont o the roots was not affected by NaCl. Increasing concentrations of NaC l also inhibited the spread of infection after the initial infection h ad occurred, and this is probably due to NaCl in the soil inhibiting h yphal growth as well as possibly affecting the supply of carbohydrates from the plant to the fungus. (C) 1998 Elsevier Science Ltd. All righ ts reserved.