In greenhouse pathogenicity tests, diagnostic symptoms of the disease were not induced at inoculum levels below 103 conidia/gram of soil (Hao et al., 2009). At lower inoculum densities, the fungus did not compromise plant health and could not be recovered from stem tissue. Although FOV colonizes the vasculature of resistant cultivars, the infection is limited and may or may not result in obvious vascular discoloration (Hao et al., 2009).