THE ROLE OF THE PROTEINASE VCP1 PRODUCED BY THE NEMATOPHAGOUS VERTICILLIUM-CHLAMYDOSPORIUM IN THE INFECTION PROCESS OF NEMATODE EGGS

The infection process of the nematophagous fungus Verticillium chlamyd osporium (isolate Vc10) was studied in two nematode species that diffe red in susceptibility according to standardized in vitro assays. After 14 d, V. chlamydosporium infected 9 and 80% of Globodera rostochiensi s and Meloidogyne incognita eggs, respectively. The purified proteinas e VCP1, from V. chlamydosporium, removed the protein coat from eggs of M. incognita but not of G. rostochiensis. VCP1 was more effective at hydrolysing proteins from M. incognita eggs than the related enzymes P rl and proteinase K, whereas the latter two were slightly more active against G. rostochiensis eggs than VCP1. Pretreatment of eggs with VCP 1 increased susceptibility to V. chlamydosporium from 80-100% in M. in cognita eggs and from 9 to 29% in G. rostochiensis eggs. These observa tions suggest that VCP1 is a host specificity-determining factor and a lso confirm it to be a pathogenicity determinant which works best in c oncert with other enzymes secreted by the actively growing fungus. Fun gal growth on the surface of eggs of both species was commensurate wit h the infection frequencies observed; growth was limited and fewer app ressoria were observed on eggs of G. rostochiensis compared with those of M. incognita. Eggs of M. incognita denatured by heat or killed wit h sodium azide, like eggs treated with VCP1, were more susceptible tha n untreated, healthy eggs. In contrast, heat and azide treatment of G. rostochiensis eggs did not increase the number of infections. Appress oria were observed on the eggs of both nematode species in all treatme nts, but the numbers and types varied greatly. On M. incognita, the do minant type was swollen and branched laterally from hyphae, while on G . rostochiensis lateral inconspicuous appressoria prevailed. Different iation of appressoria on live and dead nematode eggs showed that their production was not limited to the parasitic state of the fungus.