Harnessing the biocontrol potential of Bacillus amyloliquefaciens for the management of root knot nematode and bacterial wilt complex in Capsicum annuum var grossum

Abstract

Capsicum (Capsicum annuum var. grossum) is a popular vegetable crop extensively newlinecultivated for its commercial value and economical importance in India. Meloidogyne newlineincognita, the southern root knot nematode, is the most common nematode pest hampering newlinethe production of capsicum upto 12.85% under protected cultivation. It causes severe root newlinedamage and facilitates easy entry of other microbial pathogens causing disease complexes. newlineAlthough synthetic nematicidal chemicals are widely used for nematode management, newlinefrequent use of these chemicals endangers the environment and biotic life. Biological control newlineagents have gained importance as an environment friendly alternative to chemical pesticides newlinedue to its ability to antagonize the nematodes and other pathogens. Among several beneficial newlinerhizobacteria, Bacillus spp. are unique in their antagonizing activity and have commercial newlineimportance. newline newlineKeeping this in view, the present investigation was carried out to evaluate the anti- newlinenematode and anti-microbial activity of native isolate of Bacillus amyloliquefaciens IIHR newline newlineBA 2 against M. incognita and a multitude of soil borne phytopathogenic fungi and bacteria. newlineUnder in vitro, B. amyloliquefaciens IIHR BA 2 culture filtrates exhibited higher nematcidal newlineactivity in terms of suppressing egg hatching and causing mortality of M. incognita juveniles newlinein 72 h. In dual cultures, it caused significant reduction in growth of pathogenic microbe s newlineviz., Sclerotinia sclerotiorum, Fusarium oxysporum, Phytophthora capsici, Rhizoctonia newlinesolani and Ralstonia solanacearum. Various antibiotic genes like iturin (A, C and D), newlinesurfactin, bacilycin (BacAB and BacD), nematicidal purL gene and two protease genes viz., newlinealkaline protease and neutral protease were detected in its genome. Bioassays on its newlineantibiotic crude extracts also revealed significantly greater mortality and lesser egg hatching newlineof M. incognita and higher inhibition in growth of the pathogenic microbes. Three terpenoid newlinevolatile organic compounds were detected higher in concentration viz., Limonene, and#945;-Pinene newlineand Carvone and synthetic compounds of these three volatiles caused juvenile mortality. newlineLiquid carrier based formulations developed for B. amyloliquefaciens IIHR BA 2 amended newlinewith different additives survived up to 12 months in the formulation I and showed higher newlinecolony count compared to formulation II and III. In pot culture trials, liquid formulation I newlineshowed enhanced capsicum growth, decreased nematode population and root gall index and newline newlinereduced R. solanacearum wilt incidence in all treated capsicum plants compared to untreated newlinecontrol. Biochemical analysis revealed relatively greater expression of defense enzymes viz., newlinepolyphenol oxidase, peroxidase, catalase, superoxide dismutase, phenylalanine ammonia newlinelyase and total phenols in B. amyloliquefaciens IIHR BA 2 treated capsicum along with newlineinoculation of M. incognita and R. solanacearum, under pot culture condition. In field newlineconditions, application of B. amyloliquefaciens IIHR BA 2 enriched vermicompost at 5t/ha newlineeffectively colonized the capsicum roots and caused significant reduction in nematode newlinepopulation and R. solanacearum disease incidence together with enhanced yield compared newlineto untreated control. Hence the results of present investigation proved that newlineB. amyloliquefaciens IIHR BA 2 possesses promising biocontrol potential with multiple newlinemechanism of action against nematode wilt complex in capsicum. newline