Disease Note.

First Report of Leaf Spots and Stem Lesions on Common Periwinkle Caused by Colletotrichum gloeosporioides. . M C. Koelsch, Department of Horticulture and Landscape Architecture Oklahoma State University, Stillwater 74078 . J. C. Cole, Department of Horticulture and Landscape Architecture and S. L. von Broembsen, Department of Plant Pathology, Oklahoma State University, Stillwater 74078 . Plant Dis. 79:83. Accepted for publication 14 November 1994. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-0083B.

Disease symptoms including leaf spots, stem lesions and stem dieback have been observed each summer since 1990 on common periwinkle (Vinca minor L.) and less commonly on cv. Bowles in Oklahoma nurserles and landscapes. Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. in Penz. was consistently isolated from leaf spots with concentric rings and stem lesions. The maximum diameter of leaf spots was approximately 1 cm while stem lesions completely encircled the stems in some cases. In growth chamber tests, leaves on 25-30-cm-long stems of common periwinkle and Bowles periwinkle were inoculated with C. gloeosporioides by applying a spore solution (1.3 ? 104 ml-1) with a hand mist sprayer until runoff. The stems were placed in 250-ml flasks containing 150 ml of water and incubated in the dark at 29 C with 90% relative humidity for 17 hr. Thereafter a 14-hr photoperiod (151 ?mol m-2 s-1 light intensity) with 90% relative humidity was imposed for 10 days. Approximately 50% of the leaf area became necrotic in common periwinkle while only isolated leaf and stem lesions appeared on Bowles periwinkle. This differential response has also been observed in the field and may indicate some resistance in Bowles. No symptoms appeared on controls sprayed with sterile water. Koch’s postulates were completed by reisolating C. gloeosporioides from inoculated leaves of both Vinca types. This is the first known report of C. gloeosporioides on this host in Oklahoma.