This study aimed at investigating the efficacy of a PGPR strain, Bacillus subtilis 21-1 (BS21-1), under two different soil conditions for plant growth promotion and disease suppression. BS21-1 treatment significantly (P<0.05) promoted plant growth as measured by plant height and leaf width and increased the seed germination rate in organic soil (OS) compared with seed bed soil (SBS). In Chinese cabbage and lettuce, soft rot disease was reduced to 45 and 23.5 %, respectively, by BS21-1, and to 33 and 52.5 %, respectively, by benzo-(1,2,3)-thidiazole-7-carbothioic acid S-methyl ester (BTH) treatments in OS compared with SBS. These levels of disease suppression were greater than those found in the water-treated control upon pathogen challenge. There was a greater reduction of anthracnose lesions on the leaves of cucumber plants treated with BS21-1 and BTH in OS when compared with SBS. Botrytis rot disease in tomato caused by Botrytis cinerea was drastically reduced to 2 % in OS and 4 % in SBS by BS21-1 treatment. In the four plants studied, there was increased disease suppression in OS compared with SBS. Upon treatment with BS21-1, there was an increased expression of the PR-1a gene by β-gulcuronidase (GUS) activity in tobacco (Nicotiana tabacum L. cv. Xanthi-nc) plants in OS compared with SBS, which indicates a possible role of the SA pathway in BS21-1 mediated plant protection. Thus, the isolate BS21-1 could effectively be used as one of the biocontrol agents for disease suppression in four vegetable crops through systemic resistance and for plant growth promotion.
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