First Report of a New Leaf Spot Disease of Ctenanthe Caused by Pyricularia oryzae. A. C. Pappas, University of Thessaly, School of Agriculture Crop & Animal Production, Laboratory of Plant Pathology, Pedion Areos, 383 34 Volos. Irene Vloutoglou, Benaki Phytopathological Institute, 145 61 Kiphissia, Greece. Plant Dis. 80:463. Accepted for publication 22 January 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0463B.
In June 1995, an unusual spotting was observed on the foliage of young plants of Ctenanthe oppenheimiana (E. Morr.) K. Schum. and C. setosa Eichl. 'Greystar', imported to Greece from the Netherlands, but originally from Brazil. The primary symptoms of the disease on partially unfolded leaves were round to slightly irregular pinpoint spots, 1 to 3 mm in diameter. White, necrotic centers surrounded by zonate, well-defined, narrow, water-soaked brown-yellow halos were observed with transmitted light. On older leaves the spots were white and necrotic and scattered over the leaf surface. Frequently they coalesced to form extended necrotic areas on the margins, resembling Phytotoxicity. Pyricularia oryzae was consistently isolated, on potato dextrose agar. The fungus had simple, long, pale brown conidiophores (100 to 125 µm). bearing al their tips single, subhyaline, three-celled, pyriform conidia (18 to 32 x 7 to 12 µm) on sympodial points growing in succession. Conidia were attached al the broader end with a distinct protruding hilum (C. V. Subramanian, 1968, C.M.I. Descriptions of Pathogenic Fungi and Bacteria No. 169, Kew, England). To complete Koch's postulates, polled plants of C. oppenheimiana and C. selosa were inoculated by placing five drops of a conidial suspension (50,000/ml) on the lower surfaces of leaves. Following inoculation, the plants were covered with moist polyethylene bags and incubated at 24 to 30°C with a photoperiod of 12 h. Four to 5 days later whitish lesions with yellow halos covered with the characteristic fructifications of the fungus appeared at the points of inoculation. Control plants, inoculated with water drops and maintained under the same conditions, remained symptomless. This is the first report of a leaf spot disease of plants of the family Marantaceae caused by Pyricularia oryzae.