Disease Development on Lisianthus Following Aerial Transmission of Fusarium avenaceum by Adult Shore Flies, Fungus Gnats, and Moth Flies

Abstract

Fusarium crown and stem rot of lisianthus (Eustoma grandiflorum), caused by Fusarium avenaceum, is a destructive disease in California. The pathogen produces large masses of orangecolored macroconidia on stem lesions that extend up to 35 cm in length from the soil surface. Populations of macroconidia (97% viability) range from 1.1 × 108 to 1.9 × 108 per cm of infected stem tissue. An aboveground life stage for a soilborne pathogen could serve as a source for acquisition and aerial dissemination by adult shore flies, fungus gnats, and moth flies. Our results provide evidence that these three insects are attracted to and readily acquire (either externally and/or internally) macroconidia of F. avenaceum produced on naturally infected lisianthus stems and then disseminate acquired macroconidia to healthy plants, which subsequently died, or to an abiotic substrate (Komada's medium, KM). The high percentage of transmission, as evidenced by both the number of KM plates colonized by the pathogen (up to 68.5% within 18 h) and the number of plants infected (75% within 4 days), reflects the efficiency of these insects as vectors.