First report of leaf spot of Salvia elegans caused by Alternaria alternata in Italy

Abstract

Salvia elegans (pineapple sage) is a perennial plant belonging to the Lamiaceae family. This plant produces fruit-scented leaves and red inflorescences and is used for mixed plantings in borders in parks and gardens. During the summer of 2017, chlorosis and irregular brown necrosis were observed on the margins and blades of leaves of 6- to 8-month-old plants growing in a private garden located in Biella Province (northern Italy). Affected leaves dropped prematurely. A fungus producing greenish colonies showing light and dark concentric rings was isolated from affected tissues on potato dextrose agar (PDA). The isolates, grown for 15 days on potato carrot agar (PCA) (Simmons 2007), with 14/10 h light/dark, produced olivaceous, roughened, ovoid to obclavate conidia measuring 9 to 31 × 6 to 13 (avg. 17 × 8) µm (n = 50). Conidia were multicellular, with 1 to 5 transverse and 0 to 2 longitudinal septa. The beak was 2 to 5 (avg. 3) µm long or absent. On the basis of these morphological characteristics, the fungus was identified as Alternaria sp. (Simmons 2007). DNA was extracted from one isolate and a PCR reaction was performed using primers ITS1/ITS4 (White et al. 1990) to amplify the internal transcribed spacer (ITS) region of rDNA. The obtained ITS sequence was not able to differentiate the species of Alternaria. Therefore, the portion of the histone 3 gene was amplified with the primers H31a (5′-ACTAAGCAGACCGCCCGCAGG-3′) and H31b (5′-GCGGGCGAGCTGGATGTCCTT-3′) (Glass and Donaldson 1995) and sequenced. A BLASTn search of the 423-bp sequence (GenBank accession no. MG213850) showed 100% similarity with A. alternata (KF280540). A pathogenicity test was performed by inoculating leaves of three healthy plants of S. elegans with plugs of hyphae taken from a pure culture of one isolate of the fungus grown on PDA. Controls were treated with PDA without the inoculum. Plants were kept in sealed plastic bags for 7 days and then removed. The first symptoms of necrosis developed about 10 days after inoculation. Control leaves did not develop symptoms. A. alternata was reisolated from 10 leaves of symptomatic plants and a sequence from one reisolate was rechecked and confirmed the identity. A. alternata has been reported on other species of Salvia including S. officinalis and S. guaranitica (Kameniecki et al. 2013) in Argentina, and on S. officinalis, S. nemorosa, and S. farinacea in Poland and Japan. To our knowledge, this is the first report of A. alternata on S. elegans in Italy. Although the importance of this disease is currently limited, the expanding use of S. elegans for landscaping may result in increased Alternaria leaf spot.