Plant growth-promoting rhizobacterial mediated protection of tomato in the field against cucumber mosaic virus and its vector Aphis gossypii

Abstract

Studies evaluated the effect of rhizobacterial interactions on a virus under natural conditions of high levels of vector–virus pressure on tomato plants. The rhizobacterium Bacillus subtilis was isolated from the rhizosphere soil of healthy tomato plant and the strain is referred to as BS3A25. The BS3A25 treatment of seeds significantly enhanced tomato seed germination rates to 99% compared to the control seeds at 78%. Combination of both seed and foliar spray treatments significantly protected the plants from cucumber mosaic virus (CMV) and also significantly enhanced plant growth. Strain BS3A25 possesses many positive traits such as phosphate solubilization ability, ACC utilization as the sole source of nitrogen and production of significantly higher concentrations of indoles, IAA and the cytokinin, IPA. The growth parameters of the aphid Aphis gossypii Glover such as development time, time from birth to adult (t_D) and prereproduction time (t_d) were longer, whereas the relative growth rate (RGR) and intrinsic rate of natural increase (r_m), were found to be lower in the BS3A25 supernatant treatment compared to commercial insecticide imidacloprid treatment. Noticeably, the present study recorded higher activity of phenylalanine ammonia lyase, Peroxidase, total phenols, and polyphenol oxidase in plants treated with BS3A25 generating the speculation of induced defence responses in plants. The results obtained in the field study showed that treatment by BS3A25 formulation as seed and foliar treatment proved highly effective in reducing the aphid population and CMV incidence compared to a commercially available insecticide. The highest cost:benefit ratio (1:2.5) was obtained in BS3A25 formulation treatment followed by imidacloprid (1:2.0) and control plants (1:1.4). These constitute an important step towards the production of BS3A25 as a commercially-available induced resistance agent.

Keywords:

• cucumber mosaic virus
• Bacillus subtilis
• Aphis gossypii
• imidacloprid
• field study

Acknowledgements

The first author gratefully acknowledges the financial support of Council of Scientific and Industrial Research (CSIR), Government of India and is obliged to Dr. Thavamani D. Palanisamy, The secretary, and Dr. S.S. Sudha, Head, Department of Microbiology, Dr. N.G.P. Arts and Science College, Coimbatore, India, for their encouragement and support.