Factors Affecting Vesicular-Arbuscular Mycorrhizal Development and Growth of Cotton

SUMMARY

The influence of inoculum level, soil fertility, soil temperature, and cotton cultivar on vesicular-arbuscular mycorrhizal development and plant growth were determined. In a phosphorus-deficient soil, inoculum levels of either 200 or 400 azygospores of Gigaspora margarita per plant significantly stimulated cotton growth, whereas rates of 10, 50, and 100 spores per plant had little or no effect. In a soil deficient in nitrogen and phosphorus, G. margarita increased plant growth only when sufficient nitrogen was added, but the mycorrhizal growth response was not as great as when both nitrogen and superphosphate were added to non-mycorrhizal plants. When phosphorus was deficient in the soil mix, mycorrhizal plants consistently had a higher content of this element in the foliage than did nonmycorrhizal cotton. Addition of superphosphate (25 μg or more of P/g of soil) to a soil containing 10 μg/g of phosphorus produced a growth increase at least equal to the growth response induced by G. margarita or Glomus etunicatus, and rates of 50 and 150 μg/g suppressed root infection. Maximum mycorrhizal development by G. margarita and subsequent cotton growth stimulation occurred at 30 and 24 C and was slight or absent at 19 or 14 C. Growth stimulation of five cotton cultivars inoculated with G. margarita varied considerably; Coker 310 and Stoneville 213 responded best, Acala 1517–70 and Deltapine 16 were marginally influenced, and Paymaster 909 was relatively unaffected.