Better understanding epidemiology of Panama disease of banana

Abstract

This study involved traditional and molecular methods to track the movement of Fusarium oxysporum f.sp. cubense (Foc) in the vascular system of banana. Traditional studies were conducted in the field using naturally-infected Lady finger banana plants, and molecular studies are currently being conducted at UQ using banana plants artificially-inoculated with GFP-transformed Foc isolates in the glasshouse.

Panama disease is a polycyclic disease where inoculum causing infection is produced in individual plants infected during the course of the epidemic. This field study clearly demonstrated that the sap produced in such plants will be contaminated with Foc, and will contribute to epidemic build-up if allowed to contaminate the soil. Thus, sap as a source of inoculum is very important when managing disease containment.

The study also suggested that the laticifers are not colonised by Foc and that when a pseudostem is cut, the sap from the laticifers is contaminated by inoculum from severed vascular strands and/or associated necrotic tissues. It is difficult to separate these tissues, but results suggest that mycelial fragments may come from severed vascular strands or xylem fluid, and microconidia from necrotic cells adjacent to the vascular bundles.

It is anticipated that GFP-transformed isolates being used in the experiment at UQ will provide more definitive evidence on the systemic infection process of Foc in banana. It will determine whether movement in the vascular tissue is via mycelial growth or microconidia, and may explain why the incubation and latent periods for the disease are often so long.

Chemical intervention to reduce inoculum levels may be possible but will require much more detailed research.

The production of a volatile chemical (bicyclo(4,2,0) octa-1, 3, 5-triene) detected in this study by race 4 strains of Foc in culture is interesting and presents the opportunity for detection of disease by “sniffer” dogs before external disease symptoms are produced. Whether this chemical is produced in infected plants is yet to be determined.