First Report of Curvularia richardiae Causing Leaf Blight on Richardia brasiliensis in Brazil
Authors: Lisboa W. S. , Duarte L. L. , Barreto R. W. 
Published: June 2014

Richardia brasiliensis (Rubiaceae), also known as white eye or ‘poaia-branca’ in Brazil, is an important agricultural weed in the tropics (2). Relatively little is known about diseases affecting this species. In March 2013, all of the plants of this weed species invading an orchid plantation in Nova Friburgo (State of Rio de Janeiro) and a private orchard at Viçosa (State of Minas Gerais) in Brazil were found to bear intense leaf blight symptoms. Lesions were circular to elliptical, 1.4 to 10.5 mm in diameter, grayish to pale brown, and coalesced leading to necrosis of large areas of the leaves. Leaf samples were collected, dried in a plant press, and representative specimens deposited in the local herbarium at the Universidade Federal de Viçosa (Accession Nos. VIC 39759 and VIC 39760). A fungus found in association with diseased tissues was isolated by directly transferring conidia from infected leaves onto PDA plates, and two isolates were deposited in a local culture collection (COAD Accession Nos. 1335 and 1443). Conidia were removed from infected leaves using a scalpel, and mounted in lactophenol and lactofuchsin for observation with a light microscope (Olympus BX 51). Conidiophores were epiphylous, isolated, subcylindrical, straight to slightly curved, 97.5 to 170.0 × 5.0 to 8.0 μm, 2 to 6 septate, unbranched, pale brown and paler towards the apex, and smooth. Conidia were straight to slightly curved, pyriform to obovoid, 35.5 to 43.5 × 12.5 to 25.0 μm, with the apex rounded and the base subacute, 1 to 3 distoseptate, the subterminal cell often dark brown and larger than the other cells (sometimes leading to the distortion and curving of conidia); the other cells were golden brown and the conidia were smooth. The morphology of the fungus on R. brasiliensis was equivalent to that described for Curvularia richardiae (1). Genomic DNA was extracted from a 7-day-old pure culture of both isolates, and the large subunit (LSU) region of ribosomal DNA (rDNA) was amplified with the primers LR0R/LR5 (3). The resulting sequences were deposited in GenBank (KF880800 and KF880801). A BLASTn search revealed 99% similarity of the two isolates from Brazil with the LSU sequence of an isolate of Cochiobolus geniculatus (JN941528). Three healthy, 10-cm-tall R. brasiliensis plants were inoculated with a conidial suspension (1 × 106 conidia/ml) of isolate COAD 1335 until runoff, and the plants kept for 2 days in a dew chamber at 26 ± 3°C. Additionally, two plants were sprayed with distilled water and kept under the same conditions. Six days after inoculation, symptoms appeared on all inoculated plants that were similar to symptoms on plants in the field. Non-treated control plants remained healthy. C. richardiae was isolated from the lesions on inoculated plants. Although there is an incomplete record of a Curvularia sp. associated with seeds of R. brasiliensis in Brazil (4), that record included no description of the fungus or information on a disease caused on the plants. This is the first report of C. richardiae causing a disease on R. brasiliensis in Brazil. Although the fungus was first described in Australia (1), C. richardiae is most likely a native from the neotropics, as is the host plant, R. brasiliensis. The fungus was probably introduced accidentally into Australia on the weedy host but has remained unnoticed in the native range until now.

References: (1) J. L. Alcorn. Trans. Brit. Mycol. Soc. 56:155, 1971. (2) R. R. Rosseto et al. Planta Daninha 15:25, 1997. (3) R. Vilgalys et al. J. Bacteriol. 172:4239, 1990. (4) C. Yamashita et al. Fitopatol. Bras. 13:122, 1988.