First Report of Leaf Spots Caused by Alternaria arborescens on Symphyotrichum novi-belgii in Italy

Abstract

HomePlant DiseaseVol. 104, No. 1First Report of Leaf Spots Caused by Alternaria arborescens on Symphyotrichum novi-belgii in Italy PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Leaf Spots Caused by Alternaria arborescens on Symphyotrichum novi-belgii in ItalyA. Garibaldi, D. Bertetti, S. Matić, I. Luongo, and M. L. GullinoA. GaribaldiCentre of Competence AGROINNOVA, University of Torino, 10095 Grugliasco, ItalySearch for more papers by this author, D. BertettiCentre of Competence AGROINNOVA, University of Torino, 10095 Grugliasco, ItalySearch for more papers by this author, S. MatićCentre of Competence AGROINNOVA, University of Torino, 10095 Grugliasco, ItalySearch for more papers by this author, I. LuongoDISAFA, University of Torino, 10095 Grugliasco, ItalySearch for more papers by this author, and M. L. Gullino†Corresponding author: M. L. Gullino; E-mail Address: marialodovica.gullino@unito.ithttp://orcid.org/0000-0002-7706-1915Centre of Competence AGROINNOVA, University of Torino, 10095 Grugliasco, ItalyDISAFA, University of Torino, 10095 Grugliasco, ItalySearch for more papers by this author AffiliationsAuthors and Affiliations A. Garibaldi1 D. Bertetti1 S. Matić1 I. Luongo2 M. L. Gullino1 2 † 1Centre of Competence AGROINNOVA, University of Torino, 10095 Grugliasco, Italy 2DISAFA, University of Torino, 10095 Grugliasco, Italy Published Online:11 Nov 2019https://doi.org/10.1094/PDIS-07-19-1474-PDNAboutSectionsSupplemental ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat Traditional Michaelmas daisy (Symphyotrichum novi-belgii, earlier Aster novi-belgii), Compositae family, is an herbaceous, perennial plant producing rose-purple flowers, grown in gardens as well as for cut flower production. During the spring of 2019, leaf spots were observed on leaves of 10-month-old potted plants of S. novi-belgii growing in a nursery at Agroinnova Centre (Torino, northern Italy). Ten of 30 plants were affected. The disease was also observed on 10 of 100 plants growing in a private garden located in Biella province (northern Italy). Necrotic areas were irregular, light brown spots, surrounded by a dark halo, 0.5 to 5.0 mm in size. The affected plants lost their ornamental value. Affected leaves were washed with sterile water and dried. Then, small pieces of tissue were taken from the margins of the necrotic areas and plated on potato dextrose agar, at temperatures ranging from 20 to 25°C under a light/dark regime of 16 h/8 h. Dark green fungal colonies were obtained that produced branched conidiophores with chains of ovoid to ellipsoid, tan to brown conidia. Conidia had one to five transverse septa and zero (rarely one to two) longitudinal or oblique septa and measured 11 to 45 × 6 to 17 µm (average 26 × 11 µm) (n = 50). These morphological characteristics indicated that the fungus isolated from S. novi-belgii was an Alternaria sp. (Simmons 2007). The fungal DNA from one isolate was extracted using the E.Z.N.A. Fungal DNA Mini Kit (Omega Bio-Tek, Darmstadt, Germany), and a PCR reaction was performed using the internal transcribed spacer (ITS) (White et al. 1990), the rpb2, the endoPG, the Alt a 1, and the OPA10-2 primers (Woudenberg et al. 2015). Sequences with 549 bp (ITS), 809 bp (rpb2), 464 bp (endoPG), 498 bp (Alt a 1), and 702 bp (OPA10-2) (GenBank accession nos. MN183754, MN185003, MN185001, MN185002, and MN185004, respectively) were obtained. A BLASTn analysis of these sequences showed the highest identity with Alternaria arborescens. The identities with the reference strain CBS 102605 of A. arborescens were 100% for ITS, 99.74% for rpb2, 99.57% for endoPG, 99.15% for Alt a 1, and 99.68% for OPA10-2 (accession nos. AF347033, KC584377, KP124712, AY563303, and AY295028, respectively). In the pathogenicity test, a spore suspension of 1.0 × 105 CFU/ml was obtained from a culture of the isolate used for molecular analysis and sprayed onto leaves of three healthy plants of S. novi-belgii. Three control plants were treated with sterile water. All plants were maintained at high relative humidity in plastic bags for 7 days, at temperatures ranging from 18 to 25°C. About 10 days after the inoculation, the first leaf necrosis appeared, only on inoculated plants. A. arborescens was reisolated from symptomatic leaves. Control plants remained symptomless. Alternaria zinniae is recorded on several hosts belonging to the Asteraceae family, including the Aster genus (David 1991). To our knowledge, this is the first report of A. arborescens affecting S. novi-belgii in Italy, or anywhere in the world. This disease could become important because of the increasing use of S. novi-belgii both in the landscape and in cut flower production.The author(s) declare no conflict of interest.