| Suppression of plant-parasitic nematodes with microbial agents is an alternative or supplemental management tactic that is receiving increased interest among nematologists. One nematode antagonist, the endospore-forming bacterium Pasteuria penetrans, has shown great potential in suppressing field populations of several plant-parasitic nematodes throughout the world. This obligate parasite of mainly root-knot nematodes, Meloidogyne spp., was studied for its potential to suppress M. arenaria on peanut, and M. incognita and M. javanica on tobacco. The objectives were to monitor the population densities of the root-knot nematode and P. penetrans in peanut microplots and in a naturally infested tobacco field, to develop a suppressive-soil test that allows the determination of the role of P. penetrans in nematode-suppressive soils, and to evaluate the effect of cultural practices, such as crop rotation, autumn cover crops, resistance and fertilizer regimes on the abundance of P. penetrans. Within 4 years after inoculation or contamination by P. penetrans, M. arenaria was nearly eliminated from microplot soil, and peanut yields were similar to that of the nematode free control. The P. penetrans-infested soil remained suppressive to M. arenaria for 3 years. Similar results were observed in a tobacco field. After 4 years of tobacco monoculture, a mixed population of M. incognita, M. javanica, and M. arenaria was suppressed to non-damaging levels. Two P. penetrans isolates were more pathogenic to M. incognita than to M. javanica. Inorganic nitrogen fertilizer rates and host resistance to M. incognita had inconsistent effects on the endospore build-up, which was favored by cultivation of susceptible cover crops. A microwave radiation treatment of 3 minutes/kg of soil containing 6% to 7% water reduced the fungal population in soil samples without impairing attachment of P. penetrans endospores to nematode juveniles. This treatment allowed the separation of nematode suppression by fungi from that caused by P. penetrans. Nematode suppressiveness in microplot and field soil was preserved after microwave and air-drying treatments, but not after soil was autoclaved. The bacterial parasite, P. penetrans, was identified as the main contributor to the suppressiveness of the microplot and the field soil. |
