Nematicidal Potential of Thymol against Meloidogyne javanica (Treub) Chitwood.

Root-knot nematodes (RKN; Meloidogyne spp.) are obligatory endoparasites with worldwide distribution which cause severe damage to agricultural crops. The present study aimed to define the nematicidal activity of thymol on different life stages of the root-knot nematode Meloidogyne javanica (Treub) Chitwood, at concentrations of 37.5-1000 µL/L. This study is the first to report the effect of thymol on egg differentiation and also its vapor and sublethal concentration activities. A mortality of greater than 90% of M. javanica second-stage juveniles (J2s) occurred after 96 h of exposure at a concentration of 500 µL/L. At this concentration, thymol inhibited 59.7% of nematode hatching. In addition, the use of thymol at sublethal concentrations reduced the number of females per gram in tomato roots in a pot test, as well as inhibiting egg differentiation. On the contrary, no nematostatic effects were observed in paralysis bioassays. The results presented here indicate that the use of thymol may show its potential as a source of a new sustainable nematicidal product.

Compatibility of fluazaindolizine and oxamyl with Pasteuria penetrans on spore attachment to juveniles of Meloidogyne javanica and M. incognita.

Fluazaindolizine is a novel sulfonamide nematicide that is the active ingredient (a.i.) of Salibro™, a.i. Reklemel™. Its compatibility with Pasteuria penetrans, a bacterial parasite of root-knot nematodes (Meloidogyne spp.), was investigated in populations of M. javanica and M. incognita. Spores of a single P. penetrans isolate (Pp 3) or a blend of six isolates were incubated in the suspensions of fluazaindolizine (SalibroTM 500SC, at 5, 50, and 250 ppm a.i.) and oxamyl (Vydate™ 10 L, 10% (a.i.) at 25 and 50 ppm a.i.) for 1, 7, and 21 days; controls were incubated in water. Thereafter, the suspensions were washed through a cellulose filter (3 µm) so as to remove the nematicide, and the spores retained on the filter were suspended in water. Juveniles (J2) were exposed in these spore suspensions in Petri dishes and the number of attached spores was recorded. Neither fluazaindolizine nor oxamyl, at all the tested dosages, had any negative effect on the rate of spore attachment. The spore encumbered J2 from some experiments were used to infect tomatoes. Females without egg masses were extracted from the roots after 50 days and checked for eggs in ovaries and mature spores of P. penetrans. Despite no mature spores present in the females, there was evidence of a low percentage of infection in a few treatments. A possible explanation is that since the bacterium had been kept stored in the form of dried roots for a long period, its ability to infect nematodes was decreased.Fluazaindolizine is a novel sulfonamide nematicide that is the active ingredient (a.i.) of Salibro™, a.i. Reklemel™. Its compatibility with Pasteuria penetrans, a bacterial parasite of root-knot nematodes (Meloidogyne spp.), was investigated in populations of M. javanica and M. incognita. Spores of a single P. penetrans isolate (Pp 3) or a blend of six isolates were incubated in the suspensions of fluazaindolizine (SalibroTM 500SC, at 5, 50, and 250 ppm a.i.) and oxamyl (Vydate™ 10 L, 10% (a.i.) at 25 and 50 ppm a.i.) for 1, 7, and 21 days; controls were incubated in water. Thereafter, the suspensions were washed through a cellulose filter (3 µm) so as to remove the nematicide, and the spores retained on the filter were suspended in water. Juveniles (J2) were exposed in these spore suspensions in Petri dishes and the number of attached spores was recorded. Neither fluazaindolizine nor oxamyl, at all the tested dosages, had any negative effect on the rate of spore attachment. The spore encumbered J2 from some experiments were used to infect tomatoes. Females without egg masses were extracted from the roots after 50 days and checked for eggs in ovaries and mature spores of P. penetrans. Despite no mature spores present in the females, there was evidence of a low percentage of infection in a few treatments. A possible explanation is that since the bacterium had been kept stored in the form of dried roots for a long period, its ability to infect nematodes was decreased.

The Use of Essential Oil and Hydrosol Extracted from Satureja hellenica for the Control of Meloidogyne incognita and M. javanica.

Essential oil (EO) and hydrosol (HL) isolated from an indigenous plant species Satureja hellenica were evaluated against Meloidogyne incognita and M. javanica. Particularly, the activity of extracts on a second stage juvenile's (J2s) motility, the hatching of J2s from eggs, egg differentiation and the effect on J2s in soil were tested. A paralysis of 100% of the J2s of both species was recorded after 96 h of immersion in the essential oil, at a dose of 2000 µL/L. At the same dose, the percentage of paralyzed J2s after 48 h of immersion was more than 80%, for both Meloidogyne species. The use of hydrosol has shown encouraging results only in the dilution of 50%, where for both Meloidogyne species tested, the percentage of paralyzed J2s was more than 70% after 48 h of immersion, while the percentage was increased to 90% after 96 h of immersion. Egg differentiation was ceased after immersion, either in EO or HL. However, this decrease in egg differentiation was evident only at higher concentrations of EO and at the highest HL dilution (0.5 v/v). The hatching of M. incognita J2s was decreasing as the dose was increasing. The lowest numbers of hatched J2s were recorded at the doses of 2000 and 4000 µL/L. A clear reduction in M. javanica J2s hatching was observed as the dose was increased to 250 µL/L, a fact constantly observed as the dose was increasing up to 4000 µL/L. Lower numbers of nematodes were recorded in roots grown in infested soil after the application of EO or HL at the highest doses. The EO of S. hellenica is characterized by the presence of p-cymene (27.46%) and carvacrol (23.25%), and in a lesser extent of other constituents, such as borneol (6.79%), carvacrol methylether (6.77%), γ-terpinene (4.63%) and 4-terpineol (3.65%). Carvacrol was the major constituent found in the HL (50.12%), followed by borneol and 4-terpineol (20.42 and 6.72%, respectively).

The potential of eugenol as a nematicidal agent against Meloidogyne javanica (Treub) Chitwood.

Root-knot nematodes (RKN; Meloidogyne spp.) are the most destructive plant parasites in vegetable production and their control is very challenging. This study aimed to define the nematicidal activity of eugenol on different life stages at 33.75 to 1,000 ppm doses against the root-knot nematode Meloidogyne javanica (Treub) Chitwood, 1949. This work is the first to report the effect of eugenol on egg differentiation and its vapor and sublethal doses activities. Second-stage juveniles (J2) were dead (99.5-100%) after 48 hr of exposure at a dose of 500 ppm. At this concentration, eugenol inhibited more than 70% nematode hatching. Additionally, the use of eugenol at sublethal doses reduced the number of females per gram in tomato roots in a pot test, and also inhibited egg differentiation. To the contrary, no nematostatic effects were observed in nematode motility bioassays. The phenolic monoterpenoid eugenol described herein merits further study as potential nematicide against the rootknot nematode Meloidogyne javanica.