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In the summer-autumn 2019 plants of Salvia involucrata (Lamiaceae family) grown in a private garden near Biella (northern Italy), showed light-brown leaf spots that progressively enlarged causing the fall of the leaves. The disease affected 20% of the plants. From the margins of the necrotic tissues olivaceous fungal colonies were isolated with a frequency of 90%. The fungus grown on PDA produced dark-brown, ovoid or ellipsoid conidia, with 1 to 3 transverse and 0 to 1 longitudinal septa. They measured 8.7 to 36.9 (average 19.1) × 4.5 to 12.4 (average 8.4) μm (n = 50) and some of them showed a light or brown short beak, 1.5 to 5.6 (average 3.6) μm. On the basis of these morphological characteristics the fungus was identified as Alternaria sp. (Simmons 2007). From the DNA of the isolate coded 19/47 a PCR was carried out for ITS, rpb2, endoPG and OPA 10–2 region (Woudenberg et al. 2015) (GenBank accession Nos. MN622996; MN615843; MN615842; MN615844, respectively). A BLASTn analysis exhibited 100% identity with the ex-type CBS 916.96 of Alternaria alternata in ITS, and OPA10–2 (AF347031, KP124632, respectively), and 99% identity in rpb2, and endoPG regions (KC584375, JQ811978, respectively). Three repeated pathogenicity tests (three plants/test) were carried out on plants of S. involucrata. Leaves were sprayed with a water suspension (5 ml/plant) at a concentration of 105 conidia/ml. Three plants inoculated with deionized water served as control. The plants, covered with plastic transparent bags for 5 days, were maintained in a greenhouse at 20–25 °C. Leaf spots were observed on inoculated plants and A. alternata was re-isolated with a frequency of 90% while the controls showed no symptoms. A. alternata was reported on several species of sage (Farr and Rossman 2020). This is the first report of A. alternata on S. involucrata in Italy as well as elsewhere.
References
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Garibaldi, A., Tabone, G., Matić, S. et al. First report of Alternaria alternata causing leaf spot on Salvia involucrata in Italy. J Plant Pathol 102, 1279 (2020). https://doi.org/10.1007/s42161-020-00560-z
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DOI: https://doi.org/10.1007/s42161-020-00560-z