Microbial-based products and papaya-derived compounds against root-knot nematodes

Abstract

Plant-parasitic nematodes are one of the limiting factors in agricultural productivity. Their management can be achieved using chemical formulations, biological agents, and plant extracts. The objectives of this study were: i) to investigate the efficacy of the combination of two commercial bionematicides, Purpureocilliumlilacinum strain PL251 (PL) and Bacillus amyloliquefaciens strain D747 (Ba), against Meloidogyne enterolobii, in vivo in cucumber plants and in vitro in different life stages of the nematode and ii) to evaluate the nematicidal potential of papaya latex and papain in controlling Meloidogyne javanica at different nematode life stages and to verify the induction of resistance by both compounds in tomato roots. The combined application of P. lilacinum strain PL251 (PL) and B. amyloliquefaciens strain D747 (Ba) on cucumber roots significantly reduced (p<0.05) the number of eggs per gram of roots by 84% and the gall index compared to the negative control, while each microorganism alone did not show a significant effect. In vitro assays demonstrated that the combined cell-free culture supernatants of PL and Ba increased the toxicity of the second-stage juveniles (J2) of M. enterolobii and inhibited egg hatching. Additionally, root exudates from cucumber plants inoculated with both microorganisms were repellent to J2s, unlike the exudates from non-inoculated roots. Volatile organic compounds (VOCs) from Ba were notably toxic to J2s, however, volatiles from both combined microorganisms demonstrated greater toxicity (P<0.05). Assays using papaya latex and papain showed 100% nematode mortality at a 1% concentration and reduced J2 hatching by an average of 45% in the first experiment, with reductions of 39% and 61.9% at concentrations of 1.5% and 3%, respectively, in the second experiment. Nematode infectivity and reproduction were significantly reduced in both experiments. Treatment with 3.5% papain resulted in a 72% reduction in J2 mortality and significantly reduced juvenile hatching and nematode reproduction. Both papaya latex and papain were effective in activating the tomato's defense system. In summary, both tested controls were effective in the sustainable management of plant-parasitic nematodes, contributing to safer agricultural practices.