Contribution of Azospirillum brasilense Cd to growth of tomato seedlings is not through nitrogen fixation

Abstract

A wild type and a site-directed mutant strain (Nif−) of Azospirillum brasilense Cd, totally deficient in N2-fixation capability, were used to evaluate if improvement in tomato seedling growth is due to the N2-fixation process. The mutant (Nif−) exhibited several physiological, ecological, and antigenic features similar to the parental strain. When inoculated onto tomato seeds, the significant positive effects of the A. brasilense Nif− on seedling growth under greenhouse conditions in artificial medium were similar to that of the wild-type strain. It is concluded that the contribution of A. brasilense Cd to the improvement of tomato seedling growth is not through N2-fixation.