Growth and pathogenicity of six isolates of Corynespora cassiicola (Berk. & Curt.) Wei

Abstract

Corynespora cassiicola, the causal agent of Corynespora leaf spot on tobacco in Nigeria, was isolated from a stand of symptomatic flue-cured tobacco in Virginia. The Virginia isolate of C. cassiicola was compared to five other isolates of the fungus to determine relative morphology, growth rate, and pathogenicity on several cultivars of tobacco and selected plant species. Macro- and microscopic differences were noted in colonies of the six isolates, including differences in colony appearance, spore color, and secondary conidial formation. The Virginia isolate (VI) of C. cassiicola was found to be extremely slow growing relative to the other isolates. All isolates tested were found to have limited host ranges. Isolate CC3 from cucumber was pathogenic on nine of the plant species examined, while isolate ATCC 16718 from azalea attacked none. The Virginia isolate was pathogenic on three species but had no effect on the tobacco cultivars tested. The data from growth studies and pathogenicity tests indicate that the Virginia isolate of C. cassiicola poses no threat to tobacco production in Virginia. The possibility exists, however, that this fungus is a wound pathogen, and is currently going undetected in the field.