Difference in toxicity and physiological response of Meloidogyne incognita to sub-lethal doses of post-plant nematicides

Authors: WRAM, CATHERINE - Oregon State University; Zasada, Inga

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2019
Publication Date: 4/24/2019
Citation: Wram, C.L., Zasada, I.A. 2019. Difference in toxicity and physiological response of Meloidogyne incognita to sub-lethal doses of post-plant nematicides. Phytopathology. 109(9):1605-1613. https://doi.org/10.1094/PHYTO-11-18-0420-R.
DOI: https://doi.org/10.1094/PHYTO-11-18-0420-R

Interpretive Summary: Plant-parasitic nematodes are microscopic soil worms that attack the roots of plants and cause significant yield loss. Farmers lack reliable methods to reduce the impact of nematodes on plant productivity. In recent years, there have been three new nematicides, chemicals that kill nematodes, that have become available for us by growers to manage plant-parasitic nematodes in a diversity of crop production systems. This research was conducted to evaluate these new nematicides side-by-side for effects on nematode viability, mobility, and ability to reproduce on a plant. Results indicate that the dose required to kill nematodes varies greatly among the nematicides. Some of the nematicides caused irreversible damage to nematodes; in other words, when the chemical was removed the nematodes still died. Only one of the nematicides was identified that could reduce hatch of nematode eggs. Those nematicides that killed mobile nematodes were also very effective at reducing the number of nematodes that could feed and reproduce on a plant host. These findings will help guide growers in the proper use of new nematicides to reduce the impact of nematodes on crop productivity. Understanding how plant-parasitic nematodes respond to nematicides is a step forward in the proper stewardship of these nematicides.

Technical Abstract: Meloidogyne species are one of the most important groups of plant-parasitic nematodes globally due to their ability to damage most cultivated plants. Although widespread and economically important, there are few control measures to combat these nematodes. New nematicides have been discovered which have the potential to be widely utilized for the management of plant-parasitic nematodes. In this study, the post-plant nematicides oxamyl (Vydate), fluazaindolizine (Salibro), fluensulfone (Nimitz), and fluopyram (Velum), were evaluated to understand how sub-lethal doses affect fecundity and mobility of Meloidogyne incognita second stage juveniles (J2). Using a microwell assay system, dose-response curves for each nematicide were established for M. incognita J2. Velum was the most toxic nematicide, with effective doses up to 230 times lower than that of other nematicides. The other nematicides had predicted doses resulting in 50% morality of the population (LD50) of 89.4, 131.7, and 180.6 PPM for oxamyl, fluensolfone, and fluazaindolizine, respectively. The 24-hour LD50 of each nematicide was then used in both mobility and infectivity assays. The mobility and viability of M. incognita J2 exposed to LD50 doses of fluazaindolizine and fluensulfone were significantly reduced, with nematodes initially being mobile but eventually dying. Whereas, mobility of M. incognita J2 exposed to LD50 doses of fluopyram and oxamyl were not different from a water control. In a pot assay, M. incognita J2 exposed to a LD50 doses of fluazaindolizine, oxamyl, and fluensulfone were unable to reproduce on tomato with reproduction factors (RF = final population density/initial population density) of 0 to 0.03. Fluopyram did not reduce reproduction of M. incognita with a RF of 38.7 (+4.5), which was similar to the water control (RF = 46.3 (+4.6). This study is the first comprehensive evaluation of M. incognita mortality, motility, and fecundity after exposure to the traditionally nematicide, oxamyl, as well as three new nematicides, fluazaindolizine, fluopyram, and fluensulfone.