Biological control of Meloidogyne incognita by Trichoderma harzianum and Serratia marcescens and their related enzymatic changes in tomato roots

Abstract

Biological control against the root-knot nematode, Meloidogyne incognita was proven to occur in tomato, Solanum lycopersicom, soil-drenched with different isolates of Trichoderma harzianum and a commercial suspension of Serratia marcescens (Nemaless). The potential of such biocontrol agents to trigger plant defense response was discussed. Nematode reproduction in the presence of such possibly induced systemic resistance (ISR) elicitors was compared with that occurring on untreated plants and treated plants with the carbofuran nematicide. Dosages used were for carbofuran (1 mg ai/kg soil) and for S. marcescens (1 ~ 109 bacterium cells/ml water) 2 ml suspension/kg soil; three different T. harzianum isolates (f₁, f₃ and f₈) were separately added at 50 ~ 10Sup>8 CFU/kg soil. The possible ISR elicitors were tested on two tomato cultivars (Super Strain B and Alisa), which were inoculated with active juveniles (J2) of M. incognita, and plants were kept in a glasshouse. Indices of plant fitness (PFs) resulting from each treatment, which took into account various growth parameters were also determined. Carbofuran followed by S. marcescens and T. harzianum significantly decreased (P . 0.05) nematode development and reproduction when compared with the untreated controls. PF of cv. Alisa was higher than that of Super Strain B, and M. incognita reproduced better on the latter cultivar in all treatments. Polyphenol oxidase (PPO) and β-1,3-glucanase (GLUC) activities were detected in the roots of inoculated and uninoculated control tomato plants. Similar tests were carried out on inoculated plants treated with such ISR elicitors to search for possible enzyme activity changes as a result of resistance induction. Nematode infection did not cause any significant changes in GLUC activity, whilst PPO activity was enhanced in inoculated with respect to uninoculated roots. Treatments with ISR elicitors and carbofuran did not significantly change GLUC activity in both inoculated plants and uninoculated controls. While in the presence of the ISR elicitors, generally, PPO activity did not increase as a result of nematode infestation.

Key words: Enzymatic induction, root-knot nematode, nematode management, Serratia marcescens, Trichoderma harzianum, biological control, carbofuran, nematicide, polyphenol oxidase, β-1,3-glucanase, Solanum lycopersicum.