PATHOGENICITY OF 3 FUSARIUM SPECIES ASSOCIATED WITH ASPARAGUS DECLINE IN SOUTH-AFRICA

Isolations were made from crown, root, and stem lesions of symptomatic U.C. 157 F2 asparagus plants and from soil debris sampled in a declining asparagus field. Fusarium oxysporum, F. proliferatum, and to a lesser extent F. solani were the three dominant fungi isolated. Isolates of each species were evaluated for pathogenicity by inoculating U.C. 157 F2 plants in a greenhouse assay and an in vitro agar-test-tube assay. All three Fusarium spp. were pathogenic to asparagus, although they differed significantly in their disease-causing ability. In an in vitro assay, F. proliferatum isolates had a mean disease rating class of 4 compared with a class 3 for F. oxysporum and 2 for F. solani, on a scale of 1-5. Significant differences between F. proliferatum isolates were also detected. The high frequency of isolation and virulence of both F. oxysporum and F. proliferatum indicate that both species are important pathogens associated with asparagus decline in South Africa.