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First Report of Colletotrichum fructicola Causing Bitter Rot of Pear (Pyrus bretschneideri) in China

Pyrus bretschneideri cv. Dangshansuli is the most important commercial Asiatic pear cultivar worldwide. In recent years, a fruit rot disease of unknown etiology have caused considerable fresh market losses in the ‘Dangshansuli’ production operations in Dangshan county, Anhui Province, China. Fresh market losses typically range from 60 to 90% and in 2008 were estimated at US$150 million. Symptomatic mature ‘Dangshansuli’ pears were collected from an orchard in Dangshan County in February 2008. A thin section (about 1 mm³) of symptomatic tissue was sterilized in a bleach and placed on potato dextrose agar (PDA) medium for isolation. From all fruit, a single fungus was recovered displaying gray-white dense aerial mycelium. Identical fungi were isolated from six additional symptomatic ‘Dangshansuli’ pears collected from other orchards in the county. Pathogenicity tests using one isolate (DS-0) were conducted in triplicate by placing 4 mm diameter discs from 7-day-old PDA plates onto the mature ‘Dangshansuli’ pear fruit that were incubated in an incubator at 25°C with a 12-h photoperiod for 30 days. An equal number of noncolonized PDA inoculations were included as a control. Isolate DS-0 caused symptoms similar to those in the field within 7 days and complete collapse of cortical tissues within 30 days. No symptoms were observed on control fruit. Round brownish lesions with a diameter of about 3 cm on inoculated fruit was populated by sunken, rotiform acervuli on which numerous, colorless, oblong single cell shape conidia with width/length of 6 × 20 μm were produced. A comparison of morphology and sequence analysis of the ribosomal internal transcribed spacer (ITS) regions in pre- and post-inoculation cultures from inoculated fruit confirmed the presence DS-0. To further characterize DS-0, aliquots of extracted genomic DNA from the fungus were subjected to PCR amplification and sequencing of seven gene regions from the ITS, actin (ACT), β-tubulin 2 (TUB2), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), manganese-superoxide dismutase (SOD2), chitin synthase (CHS-1), and calmodulin (CAL), using the primers listed by Weir et al (4), except for the primer pair of ITS1 (5′-TCCGTAGGTGAACCTGCGG-3′) and ITS4 (5′-TCCTCCGCTTATTGATATGC-3′) for ITS amplification, and SODglo2-R (5′-TAGTACGCGTGCTCGGACAT-3′) and SODglo2-R (5′-TAGTACGCGTGCTCGGACAT-3′) for TBU2 amplification. Two or three clones of PCR products of each gene were sequenced and compared (GenBank Accession Nos. KC410780 to KC410786) to published data at http://www.cbs.knaw.nl/colletotrichum. The result indicated that DS-0 shared the highest similarity of 99.91% with Colletotrichum fructicola, corroborating numerous reports of Colletotrichum spp. causing bitter rot of pear on P. pyrifolia (1,2,3,4). C. fructicola was only recently reported as causing bitter rot of P. pyrifolia (4) and to our knowledge, this is the first report of C. fructicola causing bitter rot of P. bretschneideri, which will help producers select the best management practices for this devastating disease.

References: (1) P. F. Cannon et al. Stud. Mycol. 73:181, 2012. (2) N. Tashiro et al. J. Gen. Plant Pathol. 78:221, 2012. (3) G. K. Wan et al. Mycobiology 35:238, 2007. (4) B. S. Weir et al. Stud. Mycol. 73:115, 2012.