Field ecology of the ochratoxin A-producing Penicillium verrucosum: Survival and resource colonisation in soil

A field experiment was conducted to elucidate the survival of P. verrucosum in infested bulk soil (T1) and infested soil with waste grain (T2). The in fested soil and reference soil (T3) was filled into steel cylinders, which were buried and sampled 13 times during a period from October 1994 to March 1996. The abundance of P. verrucosum and indigenous soil fungi were assess ed by dilution plating on a selective and diagnostic medium (DYSG). Kernel infection was examined in T2. According to our results, P. verrucosum seems well adapted to survival in arable soil and little affected by indigenous fungi. During the first autumn and winter the grain caused a proliferation of P. verrucosum while its abundance in bulk soil was more constant except for a decrease in February 95, which is ascribed to frost/thaw alternations . In T2, P. verrucosum initially infected more than 50% of the kernels but during the first few months it was ousted by other fungi. A hypothesis rega rding waste grain as the natural niche for the fungus in the field was ther efore partly rejected. A gradual decrease in the abundance of P. verrucosum in soil during spring, a die-off in the dry summer and a proliferation dur ing the second winter were found in both T1 and T2. Our results cannot prov ide the reason for the increase during the second winter. On an overall bas is, however, they show that P. verrucosum can survive in the field, prolife rate on soil organic matter and probably become an integral part of the soi l ecosystem. This may constitute a risk of grain contamination when given a ppropriate environmental conditions.