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First Report of Powdery Mildew Caused by Erysiphe quercicola on Cinnamomum camphora in Brazil

Dorneles, K. R., Dallagnol, L. J., Rivera, J. F.
Plant disease 2018 v.102 no.4 pp. 822
Cinnamomum camphora, DNA, DNA primers, Erysiphe, appressoria, camphor, computer software, conidia, conidiophores, defoliation, fungi, germ tube, greenhouses, inoculum, internal transcribed spacers, leaves, models, mycelium, necrosis, pathogen identification, pathogens, phylogeny, powdery mildew, relative humidity, seedlings, statistical analysis, temperature, Brazil
The camphor tree (Cinnamomum camphora [L.] J.) (Lauraceae) is used for industrial and pharmaceutical purposes, and is also an evergreen shade tree (Singh and Jawaid 2012). In 2016, intense defoliation and reduced seedling development was observed in camphor plants showing signs of powdery mildew in the municipality of Capão do Leão, Rio Grande do Sul, Brazil. White to gray rounded irregular patches, consisting of conidia and mycelia of the fungus were observed primarily on the adaxial surface of the leaves of camphor seedlings. When the disease was severe, the entire leaf surface was colonized by the pathogen, resulting in leaf necrosis and defoliation. For Koch’s postulates, five healthy seedlings were inoculated on their adaxial surface using an eyelash brush to place conidia on the leaf surface (10 to 15 conidia cm⁻²). Five noninoculated seedlings served as controls. Inoculated and noninoculated seedlings were kept in a greenhouse, but in a separate compartment, with relative humidity around 80% and temperature ranging from 20 to 30°C. Powdery mildew symptoms were observed only on inoculated plants 10 to 12 days after inoculation as sparse, white to gray rounded irregular patches similar to those observed on plants used as the inoculum source. Morphological characteristics and molecular phylogenetic analysis were used for pathogen identification. Mycelia were superficial with well-developed lobed appressoria and erect conidiophores producing conidia singly. Conidiophores were unbranched, cylindrical, 30 to 80 μm long (mean 56 μm), composed of a cylindrical foot cell 24 to 53 μm long (mean 34 μm), 4 to 6 μm wide (mean 6 μm), followed by one to two shorter cells. Conidia were ellipsoid-ovoid to subcylindrical, 26 to 36 μm long (mean 30 μm) and 10 to 19 μm wide (mean 15 μm), rugose outer wall when turgid, and without fibrosin bodies. Germ tubes were produced apically and ended in a lobed appressorium. Chasmothecia were not observed on sampled plants. DNA was extracted from conidia, conidiophores, and mycelium and used to amplify the ITS (ITS1-5.8s-ITS2) region using the ITS1-KYO2 e ITS4 (Kirschner and Liu 2014; Toju et al. 2012). The resulting sequence of ITS amplification (579 bp) was deposited (accession MF183968) in GenBank. BLASTn searches revealed similarity of 99 and 98% with Erysiphe quercicola and E. alphitoides, respectively. For molecular phylogenetic analysis, ITS sequences of Erysiphe species retrieved from GenBank were aligned using ClustalW. The sequences used were selected based on work done by Takamatsu et al. (2015), which separated the E. quercicola and E. alphitoides into two clades. The phylogenetic tree was constructed using the maximum likelihood (ML) method based on the Tamura-Nei model using MEGA6 software. E. glycines (AB015934) was used as outgroup taxon. Phylogenetic analysis indicates that Erysiphe from the camphor tree was placed in the clade (99% bootstrap support) that includes only species of E. quercicola. These data indicated the causal agent of powdery mildew on camphor in Brazil was E. quercicola. This disease was reported in Taiwan-China (Kirschner and Liu 2014), but to our knowledge, this is the first report of powdery mildew caused by E. quercicola on C. camphora in Brazil. Although the powdery mildew was not observed under field condition in Brazil, the disease reduced the development of seedlings in nursery.