Expanded Range of Cylindrocladium colhounii in the United States

Abstract

Plant pathologists in Florida and Oregon have recently found Cylindrocladium colhounii for the first time on two new ornamental plant species. Brown, pinpoint leaf spots were observed on Callistemon rigidus (stiff bottlebrush) in a Florida nursery. C. colhounii was isolated consistently from these lesions. To confirm Koch's postulates, 25 ml of aconidial suspension at 96,000 conidia per ml was used to spray a 38.1-cm branch of C. rigidus. Plants were maintained in a moist chamber at room temperature (25 ± 2°C). Symptoms appeared within 3 days, and included brown, pinpoint spots (1 mm or less) occurring on both leaf surfaces, sunken blotches, and blight. The fungus was consistently reisolated from symptomatic tissue. In Oregon, the first detection of C. colhounii was from leaf spots on Gaultheria procumbens (wintergreen) in a nursery. No proof of pathogenicity was done in Oregon on G. procumbens. C. colhounii has now been reported on 14 host genera in 10 families from Australia, India, Mauritius, South Africa, and the U.S. (FL, HI, LA, NC, OR, SC) (1-4).