Interactions between Azotobacter chroococcum and vesicular‐arbuscular mycorrhiza and their effects on plant growth

B rown , M. E. & G arr , G. R. 1984 Interactions between Azotobacter chroo‐coccum and vesicular‐arbuscular mycorrhiza and their effects on plant growth. Journal of Applied Bacteriology 56 , 429–437. The effects of simultaneous inoculation of roots of lettuce seedlings with vesicular‐arbuscular endophytes and Azotobacter chroococcum are described. Endophytes alone increased yields of lettuce grown in partially sterilized P‐deficient soil, but not in the same unsterile soil. Dual inoculation with endophytes and Azotobacter in both soils produced larger plants than either inoculum alone. In another poorly structured unsterile soil with adequate P for plant growth, endophytes depressed yields of lettuce. There was no association between endophytes and Azotobacter . In none of the experiments did Azotobacter influence the level of endophyte infection in the roots; but numbers of Azotobacter on the root systems were decreased in the presence of the endophytes. Azotobacter alone always increased growth of young plants before the effects of the endophytes were observed.