Occurrence of a population of the root-knot nematode, Meloidogyne incognita, with low sensitivity to two major nematicides, fosthiazate and fluopyram, in Japan.

Abstract

Background: The root-knot nematode (RKN), Meloidogyne incognita, affects food production globally and nematicides, such as fosthiazate and fluopyram, are frequently used in Japan to control damage caused by RKN. In aboveground pests, the emergence of a population with developed resistance is frequently found after the continuous use of the same pesticides; however, there are few studies on changes in the sensitivity of plant-parasitic nematodes, including RKN, to nematicides.

Results: We compared the sensitivity of two populations of M. incognita to fosthiazate and fluopyram, one population with a history of exposure to fosthiazate and 1,3-dichloropropene (Ibaraki population) and the other without nematicide use for decades (Aichi population). A concentration of fosthiazate and fluopyram causing 50% mortality at 24 h post-treatment (LC₅₀) was markedly higher in the Ibaraki population (5.4 and 2.3 mg L^-1) than in the Aichi population (0.024 and 0.011 mg L^-1 in fosthiazate and fluopyram, respectively), indicating the low sensitivity of the Ibaraki population to fosthiazate and fluopyram. Experiments using different enzyme inhibitors indicated the involvement of acetylcholinesterase (AChE), which is the target of fosthiazate, and glutathione S-transferase (GST), a typical enzyme related to detoxification, in the low sensitivity mechanism. The activity of AChE was 33-fold higher in the Ibaraki population than in the Aichi population and there were many differences in their nucleotide sequences. In addition, the gene expression level of GST was 239-fold higher in the Ibaraki population than in the Aichi population.

Conclusion: These results revealed differences in the sensitivity to nematicides among RKN populations. Two factors were identified as related to the mechanism of low sensitivity in the Ibaraki population. This is the first report showing the difference in the sensitivity to fluopyram between populations of M. incognita. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.