Leaf Spot and Stem Blight Caused by Botrytis cinerea on Poinsettia in Argentina

Poinsettia (Euphorbia pulcherrima Will. ex. Klotzsch) is a worldwide potted or landscape ornamental plant that belongs to the Euphorbiaceae family. During 2003 and 2004, several symptoms were observed on poinsettia potted plants in nurseries and crops near Buenos Aires. Symptoms included irregular, brown, water-soaked spots on adult plants and leaf spots that extended causing stem blight in seedlings. Small pieces of diseased tissues were surface disinfected for 2 min in 2% sodium hypochlorite, plated on 2% potato dextrose agar (PDA), and incubated at 22°C for 48 h. Dense, whitish mycelia developed on PDA and then turned gray when asexual structures were formed. The fungus conidia were ellipsoid, hyaline, nonseptate, and were formed on botryose heads. The pathogenicity test was carried out on 10 plants using a conidial suspension (2 × 10⁶ spores per ml) that was sprayed on leaves with and without injuries. All plants were incubated in a moist chamber at 22 ± 2°C for 48 h and then maintained in a greenhouse. After 3 days, symptoms similar to the original were observed on the inoculated plants. Control plants sprayed with distilled water remained symptomless. Koch's postulates were confirmed by reisolating the same fungus from diseased plants. In accordance with conidial and cultural characteristics, the pathogen was identified as Botrytis cinerea Pers: Fr. (1). To our knowledge, this is the first report of B. cinerea causing leaf spot and stem rot on poinsettia in Buenos Aires, Argentina. Reference: (1) M. V. Ellis and J. M. Waller. No. 431 in: Descriptions of Pathogenic Fungi and Bacteria. CMI, Kew, Surrey, UK, 1974.