Infection of Second Stage Juveniles of Potato Cyst Nematodes By the Nematophagous Fungus Hirsutella Rhossiliensis in Dutch Potato Fields

Abstract

The infection of second stage juveniles of potato cyst nematodes (PCN) by fungal parasites was studied in populations extracted from soil by centrifugal flotation. Soil was collected from five experimental plots which had annual crops of potatoes for at least nine years. The percentage of fungus-infected juveniles ranged from 10 to 60%. After 12 weekly additions of Globodera pallida juveniles, the percentage of infected individuals increased to 45-90%. The endoparasitic nematophagous fungus Hirsutella rhossiliensis was the only fungal parasite found. The fungal infection of juveniles of PCN was also studied in soil samples from 20 fields in a starch potato growing area in northeastern Netherlands where potatoes are intensively grown (once every two years). Infection by H. rhossiliensis was observed in 17 of the 20 field populations of free-living juveniles, with an average infection percentage of 15%. After 12 weekly additions of G. pallida juveniles, the average infection percentage increased to 25% and extended to 100% of the samples. Again H. rhossiliensis was the predominant parasite. In a laboratory experiment most of the juveniles added to pasteurized soil at weekly intervals were recovered after 12 weeks when H. rhossiliensis was not present but few were recovered when H. rhossiliensis was present, probably because of the rapid disintegration of infected juveniles. Detached conidia of H. rhossiliensis did not adhere to the juvenile cuticle on agar plates, but newly formed conidia, attached to conidiophores, adhered to and infected juveniles. The possible role of H. rhossiliensis in the biological control of potato cyst nematodes and other plant parasitic nematodes is discussed.