Effectiveness of Entomopathogenic Nematode-Induced Systemic Resistance against Pests and Pathogens of Tobacco and Soybeans in Tennessee

Entomopathogenic nematodes (EPNs) Steinernema and Heterorhabditis are currently used as biological control agents in multiple cropping systems. EPNs also have been shown to induce resistance in some treated plant species, such as tomatoes and hostas. Recent studies where EPNs are applied to the soil have shown reduction in the number of plant parasitic nematodes and foliar nematodes. Other studies have also shown reduction in development of above-ground chewing and sucking insect pests as well as a pathogen. However, the mechanisms that cause these reductions are poorly understood. This research hypothesized that EPNs could induce resistance in tobacco and soybean plants. This hypothesis was tested by conducting a field study on tobacco against naturally-occurring pests and pathogens and a greenhouse study on tobacco and soybean to determine the development of the chewing pest Helicoverpa zea (corn earworm). In both studies larval cadavers of greater wax moth (Galleria mellonella) infected by Steinernema carpocapsae were applied to the soil around plant roots while control treatments of freeze-killed wax moth cadavers were applied in the same manner. Actigard 50WG, with a mode of action that induces resistance in plants, was used as a soil treatment in both studies as a positive control. In the field study, incidences of pest and disease damage on selected leaves and the number of insects on each soil-treated plant were recorded over a five-week period before the tobacco was topped. In the greenhouse study, larvae were exposed to plants 5, 10, or 15 days after treatment (DAT) and then weighed every 48 hrs. Results of both studies showed no evidence of an EPN-induced resistance effect against a chewing pest in the greenhouse setting or against pest damage in the field. EPN soil treatments also did not differ from control treatments in the tobacco field in controlling plant disease or the number of insects on the plants. More research is necessary to better understand the mechanisms involved in the phenomenon of EPNinduced resistance and its effect on different plant species