ENDOMYCORRHIZAL COLONIZATION OF GLASSHOUSE-GROWN WHEAT AS INFLUENCED BY FERTILIZER SALTS WHEN BANDED OR SOIL-MIXED

Seven different species from 3 genera of common vesicular-arbuscular mycorrhizal (VAM) fungi differed in the extent of their root colonization and in their effect on growth of winter wheat when applied in combination with different forms of N (NH4+ vs. NO3-) and fertilizer anions (Cl-, SO42-, NO3-), treatments that influence other soil fungi such as the take-all disease organism, Gaeumannomyces graminis tritici. Banded fertilizer salts, singly and in combinations, were more inhibitory to root colonization by most VAM species than were incorporated salts. NO3- N salts were more inhibitory to both wheat growth and VAM development than were NH4+ N salts. Two Glomus species, G. clarum and G. fasciculatum, appeared to be salt tolerant, developing abundant vesicles, hyphae, and colonizations to near 50% in the presence of incorporated (NH4)2SO4 or NH4Cl. However, colonizations often were not indicative of growth responses; e.g., colonizations of 10% by Gigaspora gilmorei or 20 to 40% by Glomus species often depressed growth, whereas 5 to 10% colonization by Acaulospora spinosa in the presence of NH4Cl + KCl stimulated growth significantly. The effect of Cl- (with NH4+) in suppressing the pathogenic take-all fungus did not occur with symbiotic VAM fungi. The results indicate the relative effectiveness of certain species in tolerating liberal fertilization as well as their potential for stimulating or depressing plant growth. [Other VAM fungi studied were Gigaspora margarita, G. gigantea and A. trappei.].