Effect of spore inoculum and agricultural practices on the vertical distribution of the biocontrol plant-growth-promoting bacterium Pasteuria penetrans and growth of Meloidogyne incognita-infected tomato

Abstract.

Three concentrations of Pasteuria spores applied to soil and some agricultural practices were evaluated for their effects on spore attachment to nematodes and biocontrol of Meloidogyne incognita on tomato in a microplot experiment. Applications of Pasteuria at concentrations of 5×10¹⁰ spores/m² increased tomato fruit yield per plant by 46% compared to non-Pasteuria treatments but also increased nematode densities in soil at harvest time. M. incognita juveniles recovered from plots where Pasteuria was applied at 5×10¹⁰ spores/m² showed greater spore attachment than those with application rates of 2.5×10⁹ spores/m² or 5×10⁹ spores/m². Pasteuria spores penetrated to 30–40 cm soil depth in a volcanic ash sandy soil after application of spore suspensions to the soil surface. Densities of over 2.5×10⁴ spores/g of soil were reached at 0–30 cm soil depth only when the application rate was 5×10¹⁰ spores/m², but at harvest and after fallow densities of about 2.5×10⁴ spores/g of soil were also reached in the top 10 cm of soil at 2.5×10⁹ and 5×10⁹ spores/m² application rates. Spore densities in soil decreased after 6 months of fallow when densities at harvest time were higher than 10⁵ spores/g of soil. Tillage and additional watering 2 days after spore application increased spore densities in soil at harvest throughout the soil depth (0–40 cm).