Persistence, survival, vertical dispersion, and horizontal spread of the biocontrol agent, Penicillium oxalicum strain 212, in different soil types

The potential adverse effects of a biological control agent can be assessed from the knowledge on its environmental fate and behaviour. This study focuses on environmental fate and behaviour of Penicillium oxalicum Currie and Thom strain 212 (PO212), a promising biocontrol agent, after its application to three different soil substrates under different crop conditions in terms of the persistence, survival, vertical dispersion, and horizontal spread. Two different PO212 conidial formulations, one without any additives (F1) and one with additives (F2), were applied to the seedbeds of tomato plants seven days before their transplanting into three soil types: sterilized peat in an experimental glasshouse and the sandy loam. and the loamy sand soils in two commercial orchards. The size of the Penicillium spp. population in the substrate samples was quantified using the classical microbiological method of counting of number of colony-forming units on a semi-selective culture medium. The size of PO212 biomass in the samples was quantified by a specific quantitative real-time polymerase chain reaction. We found that PO212 had a very limited vertical dispersion and horizontal spread in the three soil substrates that were tested in the study. PO212 persisted in the natural soil substrates for at least one year at very low levels (0.45-61.2 ng dried PO212 biomass/g dry soil or 2.71-367.2 ng fresh PO212 biomass/g dry soil). Treatment influenced the horizontal spread of the PO212 biomass in the sterilized peat and sandy loam soils. We did not find significant increases in the size of indigenous Penicillium spp. population (10(2)-10(3) CFU/g dry soil) in the three soil substrates following application of the Fl or F2 conidial formulations. In the sandy loam soil of the orchard in the VO2009 field trial the Penicillium spp. population decreased at increasing depths. Although PO212 persists in the soil after its application, it does not proliferate. We conclude that PO212 is an effective and safe biocontrol agent to control soil-borne pathogens. Published by Elsevier B.V.