Induction of plant defense response against root-knot nematode Meloidogyne javanica in tomato by Trichoderma harzianum BI

The biocontrol activity of T. harzianum BI on root-knot nematode M. javanica and its ability to induce some biochemical defense responses on tomato were investigated. The roots of tomato seedlings were inoculated with suspension (106 conidia/ml) of the antagonistic fungus and 2000 second-stage juveniles (J2) per plant. Enzymatic activity of peroxidase, polyphenol oxidase and levels of phenolic compounds were measured on days1 to 8 after inoculation. In addition to significant reductions in disease incidence and the number of nematode galls on the roots of plants in green house, T. harzianum BI increased the death percent of second stage juveniles (J2), and at the same time decreased the percent of egg hatch in the laboratory assays. It also increased peroxidase and polyphenol oxidase activities that reached their maximum levels 4 days after nematode inoculation. The highest level of phenolic compounds was observed on the 5th day after nematode inoculation in treatments of T.harzianum BIand nematode compared with control. The ability of T. harzianum BIto increase activities of peroxidase, polyphenol oxidase and levels of phenolic compounds and plant defense induction may be some of the mechanisms responsible for its biocontrol activity.