The combination of Bacillus amyloliquefaciens and Purpureocillium lilacinum in the control of Meloidogyne enterolobii

Abstract

Nowadays, numerous microorganisms have been identified as effective agents against plant-parasitic nematodes (PPNs) when applied individually. However, under field conditions, the combination of biocontrol agents is a desirable strategy to improve control efficacy against soil-borne pathogens. Since, as different biogents species possess different mechanisms, the combination of strains is an alternative to improve the biocontrol effects. The present study aimed to investigate in planta the efficacy of the association of two commercial bionematicides against M. enterolobii. Here, the combination of Purpureocillium lilacinum strain PL251 (PL) and Bacillus amyloliquefaciens strains D747 (Ba) simultaneously inoculated on cucumber roots, in Florida (USA) soil, significantly reduced (p<0.05) the number of eggs per gram of roots (84%) and gall index compared to negative control. Contrasting with the mixture, the application of each microorganism alone didn’t show any difference to the negative control. In in vitro assays, the combined cell-free supernatants cultures of these microorganisms were also effectiveness on increasing Meloidogyne enterolobii second-stage juvenile (J2) toxicity and inhibit the eggs hatching. Also in in vitro assays, the chemotaxis of M. enterolobii J2 showed to be repellent to both microorganisms. M. enterolobii (J2) repellence was also obtained when root exudates of cucumber were simultaneously inoculated with both microorganisms. On the other side, the exudate of cucumber roots free of those microorganisms was highly attractive to the J2. Despite the notable toxicity of Ba's volatile organic compounds (VOCs) to M. enterolobii J2 compared to the control, the impact of VOCs from Ba alone was significantly more pronounced (P<0.05) when the combined microorganisms were examined. Hence, the enhanced nematode control observed in in vivo experiments is substantiated by the combined impact of the mixture.