Acalypha wilkesiana (Euphorbiaceae), common names copperleaf or Jacob's coat (in Brazil, crista-de-peru), is a popular ornamental native from the Pacific islands. It is widely used in gardens in Brazil (4). In January 2012, a group of diseased A. wilkesiana was found in a nursery at the municipality of Itaboraí (state of Rio de Janeiro, Brazil). Later, another group of individuals of the same plant species bearing identical disease symptoms were found in a botanic garden in the city of Rio de Janeiro (Jardim Botânico do Rio de Janeiro). Diseased plants had intense leaf blight. Such leaves dropped over healthy leaves of the same or other plants and necrosis was hence initiated on such leaves. Inflorescences were also affected by blight and after becoming necrotic a dieback of supporting stems also resulted. Abundant grayish sporulation was easily observed over necrotic tissues. Samples were collected, dried in a plant press, and representative specimens were deposited in the herbarium at the Universidade Federal de Viçosa. These were from Itaboraí (VIC 31822) and from Rio de Janeiro (VIC 31931). Structures were mounted in lactophenol for observation under a microscope and isolated in pure culture on PCA plates. Isolates were deposited in the culture collection of the Universidade Federal de Viçosa with accession numbers of COAD 1112 and COAD 1108, respectively. The fungus had the following morphology: conidiophores cylindrical, up to 1,200 μm branching dicotomously at mid-length in broad angles and then branching secondarily, light brown; conidiogenous cells ampulliform, terminal, denticulate; conidia globose, 6 to 11 μm diam, subhyaline to pale brown, smooth. This combination of features is typical of Amphobotrys ricini (2), a common pathogen of castor bean (1) and several other members of the Euphorbiaceae. DNA was extracted from each isolate growing in pure culture and ITS sequences were generated and deposited in GenBank under the accession numbers JX961613 (COAD 1108) and JX961614 (COAD 1112). These were compared by BLASTn with other entries in GenBank, and the closest match for both isolates was A. ricini (JF433374) with 97% nucleotide homology (over 97% query coverage) for COAD 1112 and 98% nucleotide homology (over 98% query coverage) for COAD 1112. Pathogenicity of the isolate from A. wilkesiana was demonstrated through brush inoculation of a conidial suspension (3 × 106 conidia. mL–1) onto healthy leaves of a A. wilkesiana individual followed by its transfer to a humid chamber for 48 h. Symptoms appeared after 3 days of inoculation and sporulation appeared over necrotic tissues after 10 days. Despite the importance of A. ricini as a plant pathogen, little has been investigated on its taxonomy with molecular tools. Although morphology and host-association are the basis for the delimitation of A. ricini, our preliminary results for ITS sequences suggest that this species may include cryptic taxa that are not properly discriminated on a morphological and pathological basis. This report follows other novel reports of A. ricini on ornamental Euphorbiaceae in Brazil (3) and, to our knowledge, represents the first report of A. ricini on A. wilkesiana worldwide.
References: (1) G. H. Godfrey. J. Agric. Res. 23:679, 1923. (2) G. L. Hennebert. Persoonia 7:183, 1973. (3) B. V. Lima et al. Australas. Plant Dis. Notes 3:5, 2008. (4) H. Lorenzi and H. M. Souza. Plantas Ornamentais no Brasil - Arbustivas, Herbáceas e Trepadeiras. Nova Odessa: Instituto Plantarum, 1999.