Target Spot of Catharanthus roseus Caused by Corynespora cassiicola. R. J. McGovern, University of Florida-IFAS, Southwest Florida Research and Education Center, Immokalee 33934. Plant Dis. 78:830. Accepted for publication 11 April 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0830E.
Numerous leaf spots and severe defoliation were observed in all Catharanthus roseus (L.) G. Don (Madagascar periwinkle) plants in a landscape site in west central Florida. Leaf spots first appeared as small (1-2 mm) necrotic lesions most often associated with margins of leaves of all ages. As spots enlarged, they turned brown, became round to oblong (6.45 x 2 cm), and assumed a targetlike appearance. Eventually entire affected leaves turned yellow, then brown, and dropped prematurely. Hyphae and conidia of Corynespora cassiicola (Berk. & M.A. Curtis) C.T. Wei were detected in symptomatic leaf tissue, and the fungus was consistently isolated from lesion margins on acidified PDA following disinfestation. Fungal conidia were olivaceous, obclavate to cylindrical, straight or curved, 40-190 Μm long, 8-22 ?m thick, 5-7 ?m wide at the truncate base, and had 4-16 pseudosepta. A 3-wk-old culture of C. cassiicola from periwinkle was comminuted in 500 ml of sterile, deionized water, and atomized on four periwinkle plants, which were enclosed in moist chambers. Inoculated plants and an equal number of noninoculated controls were incubated at constant day and night temperatures of 28 and 20 C, using a 14-hr photoperiod. Leaf spots and defoliation identical to those observed in landscape plants appeared on all inoculated plants 7-10 days following inoculation, and C. cassiicola was reisolated from symptomatic tissue. This is the first report of infection of Madagascar periwinkle by C. cassiicola