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First Report of Powdery Mildew Caused by Golovinomyces sp. on Plantago australis in Brazil

The plantain Plantago australis Lam. (Plantaginaceae) is a herbaceous species native to southern Brazil that is known for the analgesic, antibiotic, and anti-inflammatory properties of its leaf extracts (2). Powdery mildew was observed on wild P. australis plants in the cities of Tapejara, Jari, and Santa Maria (State of Rio Grande do Sul, Brazil) during the summer of 2011. Affected plants were more often observed in shaded areas. Signs included sparse to abundant white powdery masses of conidia and mycelium on pseudo-petioles and leaves, mostly on the adaxial surface. Severely affected plants (≥80% of foliar area affected) had small chlorotic leaves and reduced size compared to healthy ones. Mycelia were superficial and presented nipple-shaped appressoria. Conidiophores were often curved at the base, unbranched, cylindrical, 81 to 125 μm long (average 97.3 ± 14.9 μm) and composed of a cylindrical foot cell 52 to 73 μm long (average 65.4 ± 7.5 μm) and 9 to 14 μm wide (average 11.6 ± 1.5 μm) followed by one to two shorter cells 17 to 29 μm long (average 23.4 ± 3.6 μm). Conidia were produced in chains of up to eight cells, did not contain fibrosin bodies, ranged from ellipsoid-ovoid to subcylindrical, and measured 24 to 35 μm long (average 30.5 ± 3.7 μm) and 12 to 19 μm wide (average 15.8 ± 1.7 μm). Germ tubes were produced apically (reticuloidium type). Chasmothecia were not observed on sampled leaves. Genomic DNA was extracted from conidia, conidiophores, and mycelium and used to amplify the internal transcribed spacer (ITS) (ITS1-5.8s-ITS2) region using the ITS1 and ITS4 primers. The resulting sequence (558 bp) was deposited under accession number JX312220 in GenBank. Searches with the BLASTn algorithm revealed similarity of 100% with Golovinomyces orontii (Castagne) V.P. Heluta 1988 from Veronica arvensis L. (AB077652.1) (3), 99% with G. orontii from Galium spurium L. and Galium aparine L. (AB430818.1 and AB430813.1) (2) and 99% with G. sordidus (L. Junell) V.P. Heluta 1988 from P. lanceolata L. (AB077665.1) (3). Based on morphological characteristics and sequence analysis of the ITS region, the fungus was identified as belonging to Golovinomyces sp. To fulfill Koch's postulates, five cultivated plants of P. australis with four to five expanded leaves were inoculated by dusting conidia (10 to 15 conidia cm^–2) on their leaves. Inoculated and non-inoculated control plants were kept in a greenhouse at 27 ± 5°C and relative humidity of 80 ± 15%. Powdery mildew symptoms identical to those of wild plants were observed 8 to 10 days after in inoculated plants. Although G. sordidus was previously reported on P. australis subsp. hirtella in Argentina and on several species of Plantago in others world regions (1), to our knowledge, Golovinomyces sp. has not been previously reported as a pathogen of P. australis in Brazil. Although the economic impact of the disease is limited, the reduction in plant size and leaves affects biomass production used in the extraction of pharmaceutical compounds.

References: (1) U. Braun and R. T. A. Cook. Taxonomic Manual of the Erysiphales (Powdery Mildews), CBS Biodiversity Series 11, 2012. (2) G. C. Sousa et al. J. Ethnopharmacol. 90:135, 2004. (3) S. Takamatsu et al. Mycol. Res. 113:117, 2009.