First Report of Pear Bitter Rot Caused by Colletotrichum fioriniae in France

Abstract : Bitter rot is a common disease mainly affecting apples (Malus domestica) worldwide, and resulting in considerable economic losses, but pears can also be affected (Ivic et al. 2013). Most of the reports refer to bitter rot of Chinese and Asian pears (Pyrus bretschneideri and P. pyrifolia) caused by C. acutatum sensu lato or C. fructicola (Jiang et al. 2014; Kim et al. 2007; Li et al. 2013). To our knowledge, the only report of bitter rot on European pears (P. communis) was done by Ivic et al. (2013) in Croatia and the causal agent was identified as C. fioriniae. In the last 4 to 5 years, anthracnose symptoms have been repeatedly observed on the pear cultivar Beurré Hardy in September during harvest in an orchard near Brest, France. Lesions were round, 1 to 4 cm in diameter, brown, and dry, with acervuli, producing orange spore masses in concentric rings. Two fungal isolates were obtained (in 2015 and 2016, respectively) from symptomatic pears by culturing necrotic tissue pieces on potato dextrose agar (PDA) at 25°C in the dark. Cultures were light gray, with cottony aerial mycelium becoming darker with age and reverse ranging from brownish pink to dark gray with black spots. Cultures have dark melanized structures similar to acervuli that oozed orange-colored conidia. Conidia were cylindrical to fusiform, pointed at one or both ends, and measured 10.0 to 14.0 μm × 3.0 to 3.5 μm. Both cultural and morphological characteristics were similar to those described for C. acutatum sensu lato (Damm et al. 2012). Total genomic DNA was extracted and the rDNA ITS region was amplified using universal primers ITS4 and ITS5 then sequenced. For both isolates (UBOCC-A-116033 and UBOCC-A-116034), resulting sequences were 100% identical to C. acutatum species complex sequences. Based on Damm et al. (2012), strains were further characterized by sequencing partial ACT, CHS-1, GAPDH, HIS3, and TUB2 genes (GenBank accession nos. KY344741–52). Multilocus phylogenetic analyses carried out with the obtained and reference sequences (Damm et al. 2012) revealed that both isolates clustered within C. fioriniae, as observed using BLAST; this result was consistent with their initial identification as belonging to the C. acutatum species complex. Koch’s postulates were performed on 10 ‘Comice’ pears for each isolate. Surface sterilized fruits were wound-inoculated with 20 μl of a conidial suspension (105 conidia ml–1). After 10 days incubation at 20°C, symptoms identical to those initially observed developed around the inoculation point, while controls inoculated with water remained symptomless. Fungal colonies reisolated from the lesions were morphologically similar to the original isolates. To our knowledge, this is the first report of pear bitter rot caused by C. fioriniae in France. Moreover, to date, bitter rot was not considered as a major problem for pear growing, but as pears are the eighth largest fruit crop in production yield worldwide, pear bitter rot caused by Colletotrichum species may become a major problem in the future and require further investigation.
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Submitted on : Tuesday, July 11, 2017 - 6:13:33 PM
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D. da Lio, R. Baroncelli, A. Weill, G. Le Floch, Patrice Nodet. First Report of Pear Bitter Rot Caused by Colletotrichum fioriniae in France. Plant Disease, American Phytopathological Society, 2017, 101 (7), pp.1319 - 1319. ⟨10.1094/PDIS-01-17-0129-PDN⟩. ⟨hal-01560665⟩



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