['To test the biocontrol potential of Penicillium oxalicum, a biocontrol agent against fungal diseases and against the potato cyst nematodes (PCNs), Globodera pallida and Globodera rostochiensis.', "We tested the effect of P.\xa0oxalicum on the nematode cysts under laboratory conditions or in soil microcosms. A reduction in the rate of G.\xa0pallida juveniles hatching by P.\xa0oxalicum was observed when root diffusates from the 'Monalisa' and the 'Désirée' potato cultivar were used (98·6 and 74·1% reduction, respectively). However, the rate of G.\xa0pallida juveniles hatching was not significantly reduced when root diffusates from the 'San Pedro' tomato cultivar were used. Penicillium oxalicum also significantly reduced the ability of the G.\xa0rostochiensis juveniles to hatch (30·9% reduction) when root diffusates of the 'Désirée' potato cultivars were used. Penicillium oxalicum treatment of the soil significantly reduced the number of G.\xa0pallida cysts that were recovered from the soil of each pot that contained the 'Désirée' potato cultivar."] Does penicillium oxalicum reduce the number of cysts and juveniles of potato cyst nematodes?