Leaf-spot caused by Pseudocercospora lythracearum on Lagerstroemia indica in Brazil

Lagerstroemia indica (local name 'extremosa') is a small tree of the Lythraceae family, native to India and widely used as an urban ornamental tree in Brazil (Souza & Lorenzi, 2005). In December 2006, leaves of L. indica showing a necrotic leaf-spot disease were observed in many trees of an urban area (about 2 km²) in Volta Redonda (RJ-Brazil) (Fig. 1-2), causing severe defoliation. Leaf lesions were initially yellow and punctiform, becoming irregular, necrotic and confluent with age.

Ten symptomatic leaves were collected from an area of twenty trees, and a fungus was isolated directly on V8 juice agar. The fungus produced conidiophores, 3.0-3.5 x 7.0-25 µm, with inconspicuous scars and cylindro-obclavate conidia, 2.0-3.0 x 20-55 µm, with inconspicuous loci (Fig. 3). Based on these characteristics the fungus was identified as Pseudocercospora lythracearum (syn. Cercospora lythracearum). An isolate was deposited in the culture collection of the university (VIC 30465).

Mycelial plugs were taken from a 20-day old culture grown on V8 juice agar and placed on healthy L. indica leaves of different stages of development. The inoculated leaves were kept at 25°C, the first two days inside a moistened plastic bag. After 10 days, symptoms similar to the original field symptoms appeared and the fungus was reisolated from the leaf spots. The control leaves, on which V8 juice agar plugs were deposited, remained healthy.

In Brazil, only two diseases are known to occur on L. indica, a black mildew caused by Irenopsis lagerstroemiae (Mendes et al., 1998) and a powdery mildew caused by Erysiphe australiana (Liberato & Barreto, 2004). Pseudocercospora lythracearum is reported on L. indica and other Lagerstroemia species mainly from Asia (Brunei, China, Hong Kong, India, Japan, Korea, Myanmar, Philippines, Taiwan) and North America and Caribbean (USA, Panama, Trinidad and Tobago, Virgin Islands, Puerto Rico and Dominican Republic), and to a lesser extent from other continents (Bulgaria, Uganda, Mauritius and Papua New Guinea) (Crous & Braun, 2003).

This is the first report of leaf-spot on L. indica caused by P. lythracearum in Brazil and indeed in South America. Although very little information exists on the severity and importance of this disease, we believe that it may become a potential impediment to the use of L. indica in urban areas in Brazil, since it causes an undesirable premature leaf fall.