Investigating the Inhibitory Effect of Some Plant Crude Extracts against Root-Knot Nematode (Meloidogyne javanica) in Cucumber Plant

Some plant extracts contain elicitors for inducing systemic resistances in treated plants like the lavender extract, whose protective effects against pathogen proved to be by activating the SAR systemic defense pathway. In this study, plant crude extracts including Azadirachta indica (neem), Tagetes erecta (marigold), Thymus daenensis (thymus), and Carum carvi (caraway) were used to control Root-Knot Nematode (RNK) Meloidogyne javanica in cucumber. First, the effect of these extracts on egg hatching and juvenile mortality was investigated, then, the effect of plant extracts on characters such as numbers of egg masses, nematode galls, and eggs per plant root was evaluated under greenhouse conditions. In the third part of this study, the effect of plant extracts on Polyphenol Oxidase (PPO), Peroxidase (POX), Catalase (CAT), Phenylalanine Ammonia-Lyase (PAL) and β(1,3) Glucanase (β-1, 3-Glu) enzyme activities was studied. Finally, the expression level of three stress enzymes genes including CAT, PPO, and β-1, 3-Glu β-1, 3-glu was evaluated by Real-time RT-PCR method. Results showed that, on the second day after treatment, 500 and 2,500 ppm concentrations of aqueous neem extract inhibited 64.79 and 73.48% of eggs hatching, respectively. In the greenhouse conditions, the four studied plant extracts (neem, marigold, Thymus, and caraway) at 1,500 ppm concentration significantly suppressed the development and reproduction of M. javanica terms of eggs/plant root, egg-masses, numbers of galls, nematode population in soil and, consequently, enhanced growth of the plants. In addition to the activity of the enzymes, the expression levels of these defense enzymes were also increased by the use of plant extracts.