Blossom blight of Japanese plum (Prunus salicina), nectarine (P. persica var. nectarina), and sweet cherry (P. avium) was observed in commercial orchards in central Chile in 2012. Disease prevalence of 8% and 1% were estimated in 2012 and 2013, respectively. Early symptoms appeared as small pale-brown necrotic lesions on the petals that eventually affected the entire flowers. White and cottony fungal colonies were consistently isolated on potato dextrose agar acidified with 0.5 ml/liter of 92% lactic acid (APDA), incubated for 5 days at 20°C. Black spherical to elongated sclerotia of 2.5 to 4.2 × 2.8 to 5.3 mm (n = 60) were formed on APDA. This fungus was tentatively identified as Sclerotinia sclerotiorum (Lib.) de Bary. The identity of the fungus was confirmed by BLAST analysis of the internal transcribed spacer (ITS) region (GenBank Accession Nos. KF148604 to KF148609) of rDNA, amplified with PCR primers ITS1/ITS4 (3), demonstrating a 99 to 100% similarity with the reference S. sclerotiorum strains (EU082466 and JX307092). The pathogenicity was studied in detached flowers of ‘Larry Ann’ Japanese plum, ‘Summer Bright’ nectarine, and ‘Bing’ sweet cherry that were inoculated with a mycelial suspension (106 fragments/ml) of six isolates of S. sclerotiorum and incubated for 5 days at 20°C in humid chambers (>80% relative humidity). Inoculated flowers developed a light brown petal necrosis that eventually comprised the entire flower. The same S. sclerotiorum isolates were inoculated in mature fruits of ‘Larry Ann’ Japanese plum, ‘Summer Bright’ nectarine, and ‘Staccato’ sweet cherry. Surface disinfected (1% NaOCl for 1 min) fruits were inoculated by placing a mycelium plug (4 mm in diameter) into a wound made with a sterile scalpel and incubated for 3 days at 20°C in humid chambers. Symptoms consisted on light brown soft lesions that varied from 8.7 to 46.5 mm in diameter. A superficial white and cottony septated mycelium was also obtained. An equal number of non-inoculated flowers and wounded but non-inoculated fruits remained healthy. S. sclerotiorum was re-isolated from 100% of the artificially inoculated flowers and fruits, completing Koch's postulates. S. sclerotiorum was reported causing shoot blight on apricot (P. armeniaca), lemon tree (Citrus limon), and table grapes (Vitis vinifera) in Chile (1,2), and to our knowledge, this is the first report of S. sclerotiorum associated with blossom blight in Japanese plum, nectarine, and sweet cherry in Chile.
References: (1) R. Acuña. Compendio de Bacterias y Hongos de Frutales y Vides en Chile. Servicio Agrícola y Ganadero, Santiago, Chile, 2010. (2) B. A. Latorre and M. J. Guerrero. Plant Dis. 85:1122, 2001. (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, San Diego, CA, 1990.
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