Emergence of suppression of root-knot nematodes in sweet potato cropping systems treated with Pasteuria penetrans

Abstract

Reproduction of root-knot nematodes and plant damage to the sweet potato cropping system treated with Pasteuria penetrans, a parasitic bacterium of nematodes, were examined in a field plot test. Bacterial cultures were applied to nematode-infested soil at a concentration of 7 x 109 endospores/9 m2 plot, and sweet potato cropping systems were conducted during an eight-year period. In a consecutive cropping system with Kokei 14, a susceptible cultivar, significantly higher density of the P penetrans endospores was observed in the soil at the end of the fourth year. In this system, population densities of the second-stage juvenile of Meloidogyne spp. in the soil had been lower than in the system without bacterial application since the third year. In this system, a yield of marketable storage root was obtained comparable to that treated with 1,3-dichloropropene (92% a.i., 201/10 a) fumigation in the fifth and sixth year. In a rotational cropping system using Beniotome, a cultivar which has resistance, suppressive effects of P. penetrans application emerged in the sixth and eighth year.