Mutualistic interaction of rhizobacteria with arbuscular mycorrhizal fungi and its antagonistic effect on Fusarium oxysporum in Carica papaya seedlings

There are numerous studies evaluating biocontrol of root rot by using the antagonistic effects of either arbuscular mycorrhizal fungi (AMF) or rhizobacteria, but usually independently. Fewer studies, although growing in number, report on evaluating the effectiveness of concurrent fungi–bacteria inoculation in combating root rot; and furthermore, there are none to date reported with papaya. In this study, an indigenous Pseudomonas sp. (PPV3) was isolated from roots of papaya (Carica papaya L. cv. Maradol) and used with an AMF complex (MTZ01) consisting of four fungi Glomus intraradices, Glomus mosseae, Glomus etunicatum and Gigaspora albida to inoculate roots of papaya in order to determine their antagonistic effects against Fusarium oxysporum, individually and in combination. It was found that with inoculation with PPV3 and MTZ01 protection was highest (85%) and had reduced disease (10%) as well as reducing F. oxysporum colonization in papaya seedlings. Inoculations with MTZ01 or PPV3 showed an efficacy of 54 and 60%, with a level of disease severity of the 38 and 22%, respectively. The combination of the AMF complex (MTZ01) with rhizobacterial Pseudomonas sp. (PPV3) modified the effects of F. oxysporum and provided increased protection for C. papaya than either acting alone. These results suggest that rhizobacteria and arbuscular mycorrhizal fungi acting together formed a mutualistic relationship that enhances disease control against F. oxysporum and stimulates growth in C. papaya.

► We isolated indigenous rhizobacteria from roots of papaya (Carica papaya). ► First report of biocontrol using both rhizobacteria and mycorrhiza in papaya. ► Biocontrol of root rot was improved with mycorrhiza in papaya. ► Biocontrol of root rot was better with rhizobacteria in papaya. ► Biocontrol of root rot was best with rhizobacteria and mycorrhiza in papaya.