HomePlant DiseaseAhead of PrintFirst Report of Leaf Spot Caused by Alternaria alternata on Melissa officinalis in Italy PreviousNext DISEASE NOTE OPENOpen Access licenseFirst Report of Leaf Spot Caused by Alternaria alternata on Melissa officinalis in ItalyA. Garibaldi, D. Bertetti, G. Tabone, 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, G. TaboneCentre of Competence AGROINNOVA, University of Torino, 10095 Grugliasco, ItalySearch for more papers by this author, and M. L. Gullino†Corresponding author: M. L. Gullino; E-mail Address: [email protected]https://orcid.org/0000-0002-7706-1915Centre of Competence AGROINNOVA, University of Torino, 10095 Grugliasco, ItalySearch for more papers by this authorAffiliationsAuthors and Affiliations A. Garibaldi D. Bertetti G. Tabone M. L. Gullino † Centre of Competence AGROINNOVA, University of Torino, 10095 Grugliasco, Italy Published Online:18 May 2023https://doi.org/10.1094/PDIS-06-22-1360-PDNAboutSectionsPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat Lemon balm (Melissa officinalis), in the Lamiaceae family, is a perennial herbaceous species commonly used as an ornamental and aromatic plant for the lemon scent of the leaves. In Italy, the cultivation of lemon balm as an aromatic plant produces 72 tons of product per year (ISMEA 2013). During the summer of 2021, brown, irregularly shaped, necrotic spots, up to 2 to 3 mm in size, were observed on 40 6-month-old M. officinalis plants in a garden in Biella province (Northern Italy). The disease incidence was about 90%. Affected leaves were disinfected in sodium hypochlorite (1%) for 30 s and washed in sterile water. Small pieces of leaf tissue were taken from the margins of necrotic spots, plated on potato dextrose agar (PDA), and incubated at 25°C, obtaining slow-growing fungal colonies with greenish cottony mycelium after 7 days. Ten isolates from hyphal tips of these colonies were grown on PDA under a light/dark regime of 14 h/10 h. After about 10 days, colonies produced ovoid to obclavate conidia that were 18 to 45 × 9 to 20 (average 28 × 15) μm (n = 50). Conidia had one to five transverse and zero to five longitudinal or oblique septa. When present, beaks on the apical cells were 2 to 10 (average 4) μm long (n = 50). Based on these morphological characteristics, the fungus was identified as Alternaria sp. (Simmons 2007). The DNA of a representative isolate (coded 22/18) was extracted using the E.Z.N.A. Fungal DNA Mini Kit (Omega Bio-Tek, Darmstadt, Germany). A PCR reaction was performed using primers for the rpb2, tef1, and endoPG genomic regions (Woudenberg et al. 2015). Three sequences with 502 (rpb2), 240 (tef1), and 412 (endoPG) base pairs were obtained (GenBank accession nos. ON710882, ON710884, and ON710886). Using BLASTn, the rpb2 and tef1 sequences matched 99.4% (499/502 bp) and 100% (240/240 bp) to the CBS 916.96 of Alternaria alternata (KC584375; KC584634 respectively) and the endoPG sequence matched 100% (412/412 bp) to the CBS 117130 (KP124055). Pathogenicity testing was also performed with isolate 22/18. A mycelium and spore suspension in sterile deionized water containing 105 CFU/ml was obtained from fungal cultures grown on PDA using a sterile spreader and sprayed onto leaves of three healthy plants of M. officinalis (10 ml per plant). Three control plants were sprayed with sterile water. All plants were covered with moistened plastic bags for 7 days to maintain high relative humidity. Plants were kept in a shaded greenhouse at 18 to 25°C. Leaf spots appeared on inoculated plants about 8 days after the inoculation, then symptoms similar to those described above developed on inoculated leaves. A. alternata was reisolated and identified by the amplification of the rpb2, tef1, and endoPG genes (GenBank accession nos. ON710883, ON710885, and ON710887, respectively). No symptoms appeared on the control plants. The pathogenicity test was carried out twice with the same result. A. alternata has been previously reported on M. officinalis in Poland (Machowicz-Stefaniak et al. 2002). To our knowledge, this is the first report of A. alternata infecting M. officinalis in Italy. This disease is important because M. officinalis is a very common species and the production of aromatic plants from the Lamiaceae family is steadily increasing in Italy. A. alternata may be a seedborne pathogen (Rotem 1994), and this aspect should be investigated for A. alternata on M. officinalis.The author(s) declare no conflict of interest.
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Sep 18, 2023
Manuel Alfonso Patiño-Moscoso + 4
Open Access
