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Title: SYMPTOM DEVELOPMENT, DETECTION, AND ELIMINATION OF VERTICILLIUM DAHLIAE IN MINT SHOOT CULTURES

Author
item WANG, NAN - OREGON STATE UNIV
item Reed, Barbara

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2002
Publication Date: 2/20/2003
Citation: WANG, N., REED, B.M. SYMPTOM DEVELOPMENT, DETECTION, AND ELIMINATION OF VERTICILLIUM DAHLIAE IN MINT SHOOT CULTURES. HORTSCIENCE. 2003. Vol. 38(1):67-70

Interpretive Summary: Fungal infections of plants can sometimes be symptomless and are passed unnoticed by vegetative propagation. This study was to determine if latent infections of Verticillium disease are possible in mint plants and tissue cultures. Roots were dipped in several concentrations of fungal spores and allowed to develop disease symptoms. Disease symptoms were proportional to the spore density. The disease verticillium was recovered from all inoculated plants but not from any of the control plants. Infected shoot cultures were stunted and 'Scotch Spearmint' stems split at higher inoculum concentrations. Peppermints had more severe disease symptoms than spearmints. We could produce fungus-free plants by excising shoot tips 3-5 mm long from either greenhouse or in vitro plants and growing them in tissue culture.

Technical Abstract: Roots of greenhouse-grown mint plants and in vitro-grown shoot cultures were inoculated Verticillium dahliae Kleb. conidial suspensions to study symptom development, detection, and elimination of the fungus. There were significant differences in the symptom expression of control and infected shoot cultures at all conidia concentrations for the four mint cultivars tested. Disease symptom ratings were proportional to the V. dahliae inoculum density. Infected shoot cultures were stunted when inoculated with 10 to the 3rd power or greater conidia/mL. V. dahliae was re-isolated from infected shoot cultures at all levels of inoculum, but not from any control cultures. Verticillium infections were easily detected by plating mint stems on potato dextrose agar. Shoot tips (0.5 to 15 mm) from infected in vitro and greenhouse-grown plants were isolated and screened for fungus. The most effective size for fungus elimination was 3-5 mm. Shoot tips from in-vitro infected spearmint cultivars at 10 to 2nd power and 10 to 3rd power conidia/mL were 100% Verticillium free, but only 42% of 'Black Mitcham' and 54% of 'Todd's Mitcham' peppermints. Shoot tips from infected greenhouse plants produced Verticillium-free cultures from 79% of 'Black Mitcham' and 90% of 'Todd's Mitcham' plants. These results indicate the utility of testing for Verticillium and the safety of micropropagated mint shoots for certified planting stock programs.