First Report of “Black Spot” of Basil Incited by Colletotrichum gloeosporioides in Italy. M. L. Gullino, .VA.P.R.A. - Patologia Vegetale, Via Giuria 15, 10126 Torino, Italy. A. Garibaldi, and G. Minuto. DI.VA.P.R.A. - Patologia Vegetale, Via Giuria 15, 10126 Torino, Italy. Plant Dis. 79:539. Accepted for publication 3 April 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-0539D.
Basil (Ocimum basilicum L.) is a very important crop for fresh consumption and processing on the Riviera Ligure (Northern Italy), covering approximately 60 hectares under greenhouse. During the past few years, a severe outbreak of a new foliar disease was noticed by growers in that region of Italy in most greenhouses cultivated with basil. Black spot symptoms were observed on both leaves and stems. On leaves, lesions appeared as either circular or irregular shaped necrotic spots which often expanded and coalesced. Older lesions appeared desiccated with shredded tissue at the lesion center. On the stems, lesions were observed that girdled the stem. Early stem attacks may lead to plant death that can also be caused by other basil pathogens including Rhizoctonia solani or Fusarium tabacinum. The causal agent, consistently isolated from infected plants, has been identified as Colletotrichum gloeosporioides Penz. & Sacc. in Penz. (Glomerella cingulata (Stoneman) Spauld & H. Schrenk). (Identification confirmed by R. A. Samson, Centraalbureau voor Schimmelcultures, Baarn, The Netherlands, personnal communication.) The teleomorph stage of the pathogen was never observed Koch’s postulates were completed by inoculating healthy basil plants, maintained in a growth chamber at 20 to 22°C, kept after inoculation covered with plastic bags for 12 hr, and by reisolating the pathogen from infected leaves. The first black spot symptoms were observed 5 to 6 days after inoculation. The disease is favored by high relative humidity leading to long periods of leaf wetting, and temperatures of 15 to 200C it is particularly severe in crops grown at a very high density. Its control is difficult, since very few chemicals are registered for use on basil. This is the first report of this disease in Italy. Similar attacks caused by Colletotrichum sp. were described in Florida (1).Reference: (1) S. A. Alfieri, Jr., et al. Index Plant Dis. Flor. Bull. 11, 1984.