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First Report of Monilinia fructicola Causing Brown Rot on Stored Japanese Plum Fruit in Chile

In autumn 2013, fruit of Japanese plum (Prunus salicina) cvs. Angelino and Black Kat developed an unusual brown and soft rot after 2 months in cold storage (0°C) on nearly 1% of the fruit. Fruit showed small, circular, light brown spots that eventually destroyed the entire fruit. Small sporodochia appeared on the fruit surface. Fruit was harvested from orchards located near San Francisco de Mostazal (33°59′ S, 70°41′ W), Chile. Small pieces of diseased tissue were selected from margins of lesions of surface disinfected (96% ethanol) fruit (n = 7) and placed on acidified potato dextrose agar (PDA) plates for 5 days at 20°C. Light brown colonies with even margins and concentric rings of spores were obtained. The conidia of five isolates were one-celled, hyaline, lemon-shaped, (min. 10.7) 14.9 ± 1.5 (max. 18.6) × (min. 8.1) 9.4 ± 0.8 (max. 10.8) μm (n = 30), and borne in branched monilioid chains. This fungus was identified as Monilinia fructicola (G. Winter) Honey (1). Identification was confirmed by amplifying and sequencing the ribosomal ITS1-5.8S-ITS2 region using ITS1 and ITS4 primers (3). BLAST analysis of Chilean plum isolates (GenBank Accession Nos. KF148610 and KF148611) were 99 to 100% identical to isolates of M. fructicola originating from the United States (DQ314727 and HQ846966, respectively) and 100% identical to the first Chilean isolate (JN001480) found in nectarines originating from California at the supermarkets in Santiago in June 2009. Koch's postulates were fulfilled by reproducing brown rot symptoms on mature wounded Japanese plums cv. Angelino (n = 8) inoculated with 10 μl of a conidial suspension (10⁵ conidia/ml) or with a mycelium plug (5-mm diameter). After 2 days in humid chambers (>80% relative humidity) at 25°C, all inoculated fruit developed brown rot symptoms with necrotic lesion means of 15.8 and 21.5 mm in diameter in fruit inoculated with conidia and mycelium, respectively. Non-inoculated control fruit remained healthy. Re-isolations were performed on PDA and the presence of M. fructicola was morphologically confirmed in 100% of the symptomatic fruits. To our knowledge, this is the first report demonstrating the presence of M. fructicola causing brown rot in stored Japanese plums in Chile after its first interception in 2009 in Chile, suggesting that this pathogen has been established in the field. Currently, M. fructicola is a quarantine organism under official control, restricted to Prunus orchards between Santiago and Nancagua in central Chile (2).

References: (1) EPPO. EPPO Bull. 39:337, 2009. (2) Servicio Agrícola y Ganadero, SAG, Ministerio de Agricultura, Gobierno de Chile. www.sag.cl, accessed 15 November 2013. (3) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. M. A. Innis et al., eds. Academic Press, NY, 1990.