Sensitivity to fluensulfone of inactivated Meloidogyne spp. second‐stage juveniles

Abstract

BACKGROUND: Nonfumigant nematicide efficacy is affected by several factors, such as nematode species and environmental conditions. However, the influence of nematodes' physiological status on nematicide efficacy is unknown. Inactive nematodes, such as those in quiescence or dormancy, seem to be more tolerant to nematicides than active ones. Second-stage juveniles of Meloidogyne species were inactivated by low temperatures and reversible nematicides before and during exposure to fluensulfone. The sensitivity of inactive juveniles to fluensulfone the nematicide was compared to that of active juveniles by EC 50 (median effective concentration) for juvenile immobilization and root gall reduction.RESULTS: Inactivating Meloidogyne hapla and Meloidogyne javanica juveniles at 5°C increased the EC 50 (median effective concentration) of fluensulfone for immobilization of and root galling by Meloidogyne spp. 3.6 to 9.5 times. When the exposure temperature was decreased from 25 to 15°C, EC 50 for M. javanica root gall reduction after 24 and 48 h exposure increased 3.1 and 4.9 times, respectively, whereas for M. hapla, it increased 2.3 and 2.0 times, respectively. Juveniles of M. javanica and M. incognita immobilized by fenamiphos were as sensitive to fluensulfone as active juveniles based on the number of root galls. However, juveniles of these species immobilized by fluopyram were more tolerant to fluensulfone than untreated active juveniles. An interaction of fluopyram and fluensulfone activities is suggested. CONCLUSION: Changes in the sensitivity of inactive Meloidogyne spp. juveniles to fluensulfone depend on the inactivation method. Fluensulfone could be better applied when nematodes are active in the soil.

From Old-Generation to Next-Generation Nematicides

“…In in-vitro experiments using lettuce seedlings in Pluronic Gel, Meloidogyne incognita J2 exposed to fluensulfone at 4.0 mg L −1 for 17 h, followed by rinsing in water, were mobile at inoculation, but they were not attracted to lettuce seedling roots, and did not infect the seedlings [71]. Similar results were obtained in experiments in which the number of root galls was highly reduced by the exposure of Meloidogyne J2 to fluensulfone, followed by rinsing in water, although the J2 were motile at inoculation [69].…”

“…Fluensulfone may kill G. pallida via metabolic impairment. M. javanica J2 that were temporarily inactivated by fluopyram were less sensitive to fluensulfone than untreated active J2 [69]. The results suggest that the target site for fluensulfone in the nematode may be related to that of fluopyram, which is a succinate dehydrogenase inhibitor (SDHI) [18,19].…”

“…Interestingly, even when second-stage juveniles (J2) of Meloidogyne spp. were motile after exposure to fluensulfone, followed by rinsing in water, the J2 gradually lost their motility and infectivity [69][70][71]. In the case of Meloidogyne hapla, for example, after exposing the J2 to fluensulfone at 1.0 mg L −1 for 24 h, followed by rinsing in water, more than 90% of them were motile at rinsing, but more than 80% of them became immobilized 48 h later in water [69].…”

“…The feature that most distinguishes fluensulfone from old-generation nematicides is the irreversibility of its nematicidal activity; in other words, the compound kills nematodes by irreversible paralysis [70,71]. However, it affects and paralyzes nematodes much more slowly than organophosphates [69] or fluopyram [71]. Interestingly, even when second-stage juveniles (J2) of Meloidogyne spp.…”

“…were motile after exposure to fluensulfone, followed by rinsing in water, the J2 gradually lost their motility and infectivity [69][70][71]. In the case of Meloidogyne hapla, for example, after exposing the J2 to fluensulfone at 1.0 mg L −1 for 24 h, followed by rinsing in water, more than 90% of them were motile at rinsing, but more than 80% of them became immobilized 48 h later in water [69]. In in-vitro experiments using lettuce seedlings in Pluronic Gel, Meloidogyne incognita J2 exposed to fluensulfone at 4.0 mg L −1 for 17 h, followed by rinsing in water, were mobile at inoculation, but they were not attracted to lettuce seedling roots, and did not infect the seedlings [71].…”