First Report of Hainesia lythri Causing Leaf Spots of Paeonia suffruticosa in China.

Abstract

Tree peony (Paeonia suffruticosa) is known as "the king of flowers" for its beautiful and showy flowers. It is regarded as the symbol flower of China and is cultivated throughout the country. During the summer of 2006, a leaf spot was observed on tree peony cultivated in the Zhengzhou area of Henan Province, and in 2007, the leaf spot was observed in the Luoyang area. In some gardens, the leaf spot affected more than 50% of the plants. Early symptoms appeared as small, round, water-soaked lesions on the leaves. Lesions expanded into 5 to 35-mm-diameter spots that were circular or irregular, brown to dark brown, with pale brown margins. Later, the center of some lesions dropped out. Signs of the suspected pathogen were usually seen on the leaf spots after an abundant rainfall. Lesions contained numerous, pale brown, cupulate conidiomata with salmon-colored spore masses. Conidiophores (70 × 1 to 2 μm) were hyaline, branched, septate, and filiform. Conidia (5.5 to 7.5 × 1.5 to 2 μm) were hyaline, aseptate, and cymbiform to allantoid. The pathogen was identified as Hainesia lythri on the basis of the morphology. This fungus infects a wide variety of hosts including P. suffruticosa, Acer pseudoplatanus, Calluna sp., Dissotis paucistellata, Epilobium angustifolium, and Eucalyptus saligna (3). The fungus was isolated on potato dextrose agar (PDA) medium using conidia from conidiomata found on symptomatic leaf tissue; the fungus produced gray-to-brown colonies. Pathogenicity was tested by inoculating 10 leaves on one 5-year-old tree with a mycelia plug from the colony (0.5 cm in diameter); leaves inoculated with plugs of PDA medium served as controls. Inoculated leaves were covered with plastic for 24 h to maintain high relative humidity and incubated at 25 to 28°C. After 5 days, 100% of the inoculated leaves showed symptoms identical to those observed on leaves from P. suffruticosa infected in the field while controls remained symptom free. Reisolation of the fungus from lesions on inoculated leaves confirmed that the causal agent was H. lythri. Thus, we concluded that H. lythri is the causal agent of leaf spots of P. suffruticosa. To our knowledge, this is the first report of H. lythri infecting P. suffruticosa in China. H. lythri has been previously reported on Paeonia in Japan and Korea (1,2).