RESUMO
Root-knot nematodes (RKN) are one of the most harmful soil-borne plant pathogens in the world. Actinobacteria are known phytopathogen control agents. The aim of this study was to select soil actinobacteria with control potential against the RKN (Meloidogyne javanica) in tomato plants and to determine mechanisms of action. Ten isolates were tested and a significant reduction was observed in the number of M. javanica eggs, and galls 46 days after infestation with the nematode. The results could be explained by the combination of different mechanisms including parasitism and induction of plant defense response. The M. javanica eggs were parasited by all isolates tested. Some isolates reduced the penetration of juveniles into the roots. Other isolates using the split-root method were able to induce systemic defenses in tomato plants. The 4L isolate was selected for analysis of the expression of the plant defense genes TomLoxA, ACCO, PR1, and RBOH1. In plants treated with 4L isolate and M. javanica, there was a significant increase in the number of TomLoxA and ACCO gene transcripts. In plants treated only with M. javanica, only the expression of the RBOH1 and PR1 genes was induced in the first hours after infection. The isolates were identified using 16S rRNA gene sequencing as Streptomyces sp. (1A, 3F, 4L, 6O, 8S, 9T, and 10U), Kribbella sp. (5N), Kitasatospora sp. (2AE), and Lentzea sp. (7P). The efficacy of isolates from the Kitasatospora, Kribbella, and Lentzea genera was reported for the first time, and the efficacy of Streptomyces genus isolates for controlling M. javanica was confirmed. All the isolates tested in this study were efficient against RKN. This study provides the opportunity to investigate bacterial genera that have not yet been explored in the control of M. javanica in tomatoes and other crops.