Suppression of Meloidogyne incognita by co-application of chitin and Streptomyces nigrescens (AMV1033)

ABSTRACT Root-knot nematodes, Meloidogyne spp., are among the most polyphagous and ubiquitous plant-parasitic nematodes. Among other management strategies, organic soil amendments and biological control agents are proposed. In this study, potential synergistic benefits of co-application of chitin and Streptomyces nigrescens (AMV1033) against M. incognita were determined. Hypothetically, chitinolytic activity of these microbes deteriorates nematode eggshells reducing nematode numbers. Additional chitin could enhance actinobacteria activity for nematode suppression. In in vitro and greenhouse bioassays, suppressive capacities of M. incognita by chitin amendment at 50 mg/g of soil (chitin-low) and at 500 mg/g of soil (chitin-high; only tested in the greenhouse), Streptomyces nigrescens (AMV1033) and the co-application of AMV1033 with the two chitin rates were tested. After four weeks of in vitro egg incubation, the number of extractable second-stage juveniles (J2s) was significantly reduced after co-application of chitin-low plus AMV1033, and less so after sole application of AMV1033. In a similar 2-week in vitro assay with M. incognita egg masses, the numbers of J2s were similarly reduced after the same treatments. In a watermelon greenhouse bioassay with M. incognita, root infection was decreased after co-application of AMV1033 plus chitin-high or chitin-low compared to the non-treated control. After these treatments, plants grew similarly as in the control, whereas sole chitin-high addition led to severe plant damage. Some amelioration of phytotoxicity of chitin-high by the co-application of AMV1033 was found. The results of the study demonstrated the potential to enhance suppression of M. incognita by S. nigrescens by co-application of chitin.