Interactions between the Steinernema feltiae–Xenorhabdus bovienii Insect Pathogen Complex and the Root-Knot Nematode Meloidogyne incognita

The interactions between a plant-parasitic nematode, Meloidogyne incognita, and an entomopathogenic nematode, Steinernema feltiae, and its associated symbiotic bacterium, Xenorhabdus bovienii, are described. Our objective was to determine the manner in which the presence of the S. feltiae–X. bovienii nematode–bacterium complex affected infectivity and reproduction of M. incognita in tomato roots (cv. Rutgers). Tests demonstrated that a common application rate of S. feltiae for insect control, 2.5 billion/ha (scaled to our laboratory and greenhouse tests), significantly decreased M. incognita galling, egg production, and egg hatch rate. Two time course experiments were conducted against M. incognita with rates of S. feltiae that corresponded to the effective concentrations. In the first time course experiment, M. incognita and S. feltiae were applied the same day to tomato seedlings in sand. Twelve plants were assessed destructively each week for 6 weeks after inoculation with the two nematode species. Neither M. incognita penetration rate nor developmental rate was affected by S. feltiae application. Egg production per plant and egg hatch rate were significantly reduced in the treated plants. However, the number of eggs per egg mass in treatment plants was not different from that in control plants. The average number of galls per plant 6 weeks after the initial inoculation was lower in the treated plants than in the control plants. In the second time course experiment, the same rate of S. feltiae was applied to sand in which plants already infected with M. incognita had been transplanted. Development of nematodes inside the root was not affected by S. feltiae in the sand. Galling 6 weeks after the application was again less in the treatment than in the control plants. The presence of the S. feltiae–X. bovienii complex at a density that reflects the recommended field application rate had suppressive effects on M. incognita in these laboratory trials. Our data show that S. feltiae applications decrease M. incognita galling, egg production per plant, and egg hatch but not individual female egg production.