Bacillus thuringiensis regulates Chinese cabbage growth beyond growth promotion

Seventy-seven Bacillus thuringiensis (Bt) strains, isolated from diverse resources had been investigated for their regulation on plant growth. Chinese cabbage was selected as tested plant. Height, fresh weight and number of leaves of the seedlings were measured after 30 days cultivation. Of the 77 Bt strains, 32 strains promoted the growth while 28 strains inhibited Chinese cabbage production, indicating that Bt regulates Chinese cabbage growth beyond growth promotion Interestingly, Bt plant-growth promoting strains BRC-CWS5, BRC-SFR2, BRC-SFR6 and HQ20 produced indole-3-acetic acid (IAA) in LB liquid media supplementing with tryptophan but they were not able to soluble phosphate. The results suggested that IAA production and phosphate-solubilizing ability may not be universal mechanisms for plant-growth-promoting Bt strains. Our data implied that both good effects (insecticidal spectrum, plant growth promotion etc.) and potential adverse effects (plant growth inhibition etc.) should be considered when choosing a new Bt strain for production.