Effect of commercially available rhizobacteria strains on growth and production of lettuce, tomato and pepper

Abstract

Seven microbial products of the genus Bacillus were evaluated under greenhouse and shadehouse conditions for efficacy on lettuce, tomato and pepper as plant growth promoters. Treatments were applied as a drench (10⁶ cfu ml¹) directly onto seedlings in composted pine bark growth medium. Variation in activity was observed between Bacillus preparations, and from one host to another. Three of the Bacillus preparations, Bacillus chitinosporus, B. uniflagellatus and B. subtilis significantly increased lettuce growth when seedlings were not supplemented with a nutrient source, NutriStart-AC (P < 0.001). Biostart® 2000 (a combination of B. chitinosporus, B. laterosporus and B. licheniformis) was the only microbial preparation to significantly increase seedling growth on tomato (P < 0.01) whereas B. uniflagellates and B. licheniformis were the only organisms to significantly increase fruit yield on pepper (P < 0.04 and P < 0.01 respectively). When seedlings were inoculated with bacteria and subsequently treated with a bacterial nutrient supplement, NutriStart-AC, B. chitinosporus (P < 0.001), B. uniflagellates (P < 0.02), B. laterosporus (P < 0.03), B. pumilus (P < 0.05) and Biostart® 2000 (P < 0.001) preparations all significantly promoted lettuce seedling growth. On tomato, all Bacillus preparations, with the exception of B. laterosporus, significantly increased seedling growth when NutriStart-AC was added as a supplement. However, only one preparation, Bacillus subtilis (P < 0.02) significantly increased pepper fruit yield when seedlings were supplemented with NutriStart-AC.