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First report of brown rot on peach, nectarine, cherry and plum fruits caused by Monilinia fructicola in Bulgaria

Journal Contribution - Journal Article

Field surveys in the region of Plovdiv within a small mixed orchard of peach and nectarine trees in the summer of 2017 revealed symptoms and signs of brown rot attended by numerous, slightly greyish conidial pustules on the surface of unripe and mature fruits. Similar symptoms and signs were found also in the summer of 2018 on cherry and plum fruits in two additional orchards in the same region. The putative Monilinia species (Ogawa et al. 1995) was isolated by transferring conidia from naturally infected fruits of these four Prunus species to potato dextrose agar (PDA). After 24 to 48 h of incubation at 25°C, germinated conidia were transferred to PDA, and a week later, greyish-beige colonies with consecutively forming concentric rings of sporodochia appeared. The tufts from the diseased plant tissues and colonies in culture consisted of branched monilioid chains, hyaline conidiophores, and one-celled, lemon-shaped conidia and measured 19.5 (15.0 to 25.0) × 13.7 (10.0 to 16.7) μm. Pathogenicity of three randomly selected isolates obtained from each of these four stone fruit hosts was demonstrated twice by inoculating surface-sterilized (96% ethanol) mature peach, nectarine, cherry, plum, apricot, apple, pear, and medlar fruits and immature almond fruits in three replicates. Using a sterile cork borer (diameter = 5 mm), shallow holes were made into the fruit, and mycelial plugs (5 mm) from 5-day-old fungal cultures were inserted into the wounds; sterile PDA plugs were used as a negative control. In the first test, the inoculated sites were covered with transparent adhesive tape. Fruits were incubated at room temperature (20 to 25°C) in sterilized plastic boxes. Necrotic lesions were observed after 3 to 4 days of incubation only on the fruits in which mycelium plugs were inserted. Subsequently, a varying number of conidial tufts were registered on the fruits of all species. The potential pathogen was reisolated from all inoculated samples but not the negative controls. The DNA of isolates obtained from peach (seven isolates), cherry (five pieces), nectarine (two pieces), and plum (two pieces) was extracted using the Nucleospin Plant II kit (Macherey-Nagel) and later on was used for a PCR reaction with ITS1 and ITS4 primers (White et al. 1990). For each isolate, a single amplicon was obtained. These amplicons were gel-purified and sequenced in both directions using the same primers used for PCR. All obtained sequences were identical, and the consensus sequence was subsequently used in a BLAST search. It was 100% identical to exclusively Monilia fructicola sequences, including CBS isolates CBS 165.24, CBS 228.72, CBS 329.35, and CBS 127259. The internal transcribed spacer sequence of the first isolate from peach was submitted to GenBank (accession no. MN453261). Based on the symptoms and the pathogen’s characteristics obtained, it can be concluded that M. fructicola (Winter) Honey (anamorph M. fructicola Batra) is the causal agent of the observed brown rot on peach, nectarine, cherry, and plum fruits. To our knowledge, this is the first report of M. fructicola in Bulgaria, and the local fruit growers should also pay attention to this expanding in Europe (Hrustić et al. 2015; Poniatowska et al. 2013), because it is a broad-host-range Monilinia species.
Journal: Plant Disease
Issue: 5
Volume: 104
Publication year:2019
Accessibility:Open