Control of the root-knot nematode Meloidogyne javanica by the parasite Pasteuria penetrans as influenced by the initial nematode population densities.

The potential of Pasteuria penetrans for the biological control of Meloidogyne javanica on tomato plants was examined in a pot experiment. P. penetrans in dried powdered roots was applied at 11000 and 55 000 spores/cm 3 soil in pots inoculated with 420 or 4200 second stage juveniles. At 4 months after planting there was significantly less galling on plants grown in pots inoculated with 420 nematodes and 55 000 spores/cm 3 than in the unamended control pots. There was a 96% decrease in numbers of egg masses on these roots. The period of assessment had to be shortened because the control plants in the treatment with the higher nematode inoculum died prematurely curtailing further reproduction. Treatment with P. penetrans prevented premature senescence of the plants allowing nematode reproduction to continue. A significant interaction between P. penetrans density and nematode density was obtained on the number of juveniles in soil after the first crop. Where the nematode population was initially large (4200/pot), there were more juveniles in the treatments to which P. penetrans had been applied than in the untreated controls. However, where the nematode population was initially small (420/pot), there were more juveniles in the untreated control than in the treatment with the higher dose of P. penetrans. A second crop was grown in soil from the different treatments after either removing or incorporating the dried roots of the preceding crop. After 30 days, root galling and egg production were higher in pots initially inoculated with 420 nematodes. The effect of root incorporation on egg production was influenced by both nematode and P. penetrans level; greater numbers of eggs were produced on treatments with the initially higher levels. It is concluded that P. penetrans, deployed as a single control measure, may not give consistent or durable control, but that it may have a role in an integrated approach to nematode management.