Repeated applications of Penicillium oxalicum prolongs biocontrol of fusarium wilt of tomato plants

The suppression of fusarium wilt of tomato achieved by Penicillium oxalicum (PO) applied one or several times (up to four) was assessed during three glasshouse experiments. The first application of PO (10⁶ conidia g^-1 substrate) to the growing substrate (peat and vermiculite, 1 : 1, v : v) was performed prior to its infestation with Fusarium oxysporum f. sp. lycopersici (FOL) (10⁴–10⁶ chlamydospores g^-1). Repeated applications of PO prolonged the duration of control of fusarium wilt especially when disease incidence was high. The timing of repeated applications of PO did not affect the efficacy of the control. Disease reduction was not associated with a decrease in density of FOL in the rhizosphere, irrespective of the number of applications of PO. Density of PO in the tomato rhizosphere was higher when repeated applications were made. No relationship was observed between reduction of disease and high densities of PO. Reasons for a longer disease reduction in tomato plants following several applications with PO are discussed.