Fluazaindolizine mitigates plant-parasitic nematode activity at sublethal dosages

Plant-parasitic nematodes are significant pests for many crops with considerable economic impact worldwide. Alternatives to highly toxic soil fumigants and nematicides are urgently sought after. Fluazaindolizine is a fluorinated nematicide with a novel, unknown mode-of-action and very low mammalian toxicity. The current research investigated the early responses of several plant-parasitic nematode species to the compound by in vitro mortality and parasitism trials with nematode-susceptible host plants. After a 72-h in vitro exposure time, fluazaindolizine exhibited the most potent toxic activity against the second-stage juveniles (J2) of Meloidogyne incognita and Tylenchulus semipenetrans with LC 50 values of 177.14 and 355.2 mg L −1 , respectively. Pratylenchus brachyurus , J2 of the Heterodera schachtii , and eggs of M. incognita were considerably less sensitive to the nematicide. The fitness of M. incognita J2 was strongly affected when exposed to various concentrations of fluazaindolizine for 12 h before inoculation of cucumber seedlings in soilless seed pouches. The lowest level of 5 mg L −1 reduced root galling, egg mass production, and the number of eggs to about 25% compared to the water control. In another bioassay, H. schachtii J2 were exposed to fluazaindolizine at 100 and 200 mg L −1 for 72 h before used to infest soil with 3-day-old radish seedlings. About 39.8% and 59.6%, respectively, fewer J2 invaded the roots compared to the control. In conclusion, the tested nematode species varied considerably in their in vitro mortality following fluazaindolizine exposure. However, the bioassays demonstrated that parasitism was already severely impacted at non-lethal concentrations and short-term exposure to the nematicide.