Biological control of root-knot nematode on sugarcane in soil naturally or artificially infested with Pasteuria penetrans

Soil was collected from a sugarcane field where most of the second-stage juveniles of root-knot nematode (Meloidogyne javanica) were encumbered with endospores of Pasteuria penetrans. A pot experiment was established to determine whether the bacterium was present at levels capable of reducing populations of the nematode. Endospores of the bacterium were eliminated by autoclaving the soil and then eggs of Meloidogyne javanica were inoculated into Pasteuria-free and naturally-infested soil. When the experiment was harvested 19 and 37 weeks later, the root-knot nematode population was respectively 96 and 99% lower in the naturally-infested field soil, indicating that this soil was highly suppressive to the nematode. Pasteuria penetrans was also mass-produced on its nematode host and a further experiment was set up to determine the effect of endospore concentration in soil on multiplication of root-knot nematode. Sugarcane was grown in pasteurised sand containing 0, 6000, 12,000, 24,000 and 50,000 endospores/g soil and treatment effects were assessed after 6, 13 and 20 months. The results showed that regardless of harvest time, the severity of root galling and the number of nematode eggs produced per plant decreased as the endospore concentration increased. The lowest endospore concentration significantly reduced the number of eggs per plant at all three harvest times while the highest concentration reduced egg numbers by 96, 88 and 81% at 6, 13 and 20 months, respectively. These results suggest that when high endospore concentrations are continually maintained in the root zone, P. penetrans will markedly reduce populations of root-knot nematode, a particularly important pest of sugarcane.