First Report of Diaporthe rudis Causing Fruit Rot of European Pears in the United States

HomePlant DiseaseVol. 103, No. 8First Report of Diaporthe rudis Causing Fruit Rot of European Pears in the United States PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Diaporthe rudis Causing Fruit Rot of European Pears in the United StatesA. N. KC and A. L. RasmussenA. N. KC†Corresponding author: A. N. KC; E-mail Address: achala.kc@oregonstate.eduhttp://orcid.org/0000-0003-1725-3242Oregon State University, Southern Oregon Research and Extension Center, Central Point, OR 97502 and A. L. RasmussenOregon State University, Southern Oregon Research and Extension Center, Central Point, OR 97502AffiliationsAuthors and Affiliations A. N. KC † A. L. Rasmussen Oregon State University, Southern Oregon Research and Extension Center, Central Point, OR 97502 Published Online:6 Jun 2019https://doi.org/10.1094/PDIS-12-18-2184-PDNAboutSections ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat Oregon is the second largest producer of European pears (Pyrus communis) in the United States. Fruit rots are major problems affecting the storage of European pears. In surveys conducted in 2017 and 2018 in southern Oregon, approximately 5% of fruits collected from picking bins in 10 orchards and 30% of fruits from cull bins at two packinghouses exhibited side rot symptoms. The symptoms appeared as brown spots on the fruit surface with water-soaked margins under the skin. The lesions progressed rapidly, and the entire fruit was covered with soft rot symptoms within 1 week at room temperature (21 ± 1°C). Fruits at an early stage of infection were surface disinfected by spraying with 75% ethanol and dried under a laminar flow hood. The margin of the lesions was cultured in half-strength potato dextrose agar (PDA) amended with streptomycin. Pure cultures of the pathogen were obtained by hyphal tipping followed by single-spore culture in full-strength PDA. Colonies on PDA started as white mycelium, which grew into white tufted aerial mycelium. Concentric rings of mycelium formed as colonies grew. The reverse side of the cultures was gray with embedded pycnidia, the diameter of which ranged from 439 to 888 µm (average 682 µm, n = 50). Alpha conidia, 4.6 to 7.8 × 1.7 to 3.5 µm (average 6.2 × 2.4 µm, n = 50), were abundant in culture, aseptate, hyaline, biguttulate, and tapering at one end. Beta conidia, average 27.8 × 3.6 µm (n = 20), were aseptate, slender to slightly curved. Gamma conidia, average 15.1 × 1.8 µm (n = 20) were aseptate and biguttulate. These morphological characteristics were similar to Diaporthe spp., anamorph: Phomopsis spp. (Udayanga et al. 2014). For confirmation, genomic DNA was extracted, and the internal transcribed spacer (ITS) and the elongation factor tef1 were sequenced (Guarnaccia and Crous 2017). The ITS and tef1 sequences (GenBank accession nos. MK131313 and MK183749, respectively) were 98 and 100% identical to Diaporthe rudis strain CPC 29658 (GenBank accession nos. MG281140 and MG281661, respectively). Pathogenicity of one isolate was tested on four replicates of fruits of European pear (cultivar Bosc), and the entire test was repeated. Fruits were surface disinfested with 75% ethanol and dried under a laminar flow hood. A sterilized nail head (5 × 5 mm) was used to create one wound per fruit. The wound was inoculated with 50 µl of conidial suspension (1 × 104 conidia/ml) and incubated under room temperature (21 ± 1°C and 12-h continuous light). As a control treatment, four fruits of European pear (cultivar Bosc) were wounded and inoculated with sterile water and incubated under the same conditions. After 1 week of incubation, 25% of inoculated fruits' surface was covered with water-soaked lesions around the inoculated site that increased to 75% in 2 weeks, and soft rot developed beneath the fruit skin. D. rudis was reisolated from the infected fruits, and the identity of D. rudis was confirmed by culture and conidial morphology, satisfying Koch's postulates. Control fruits remained symptomless. Species of Diaporthe are reported to cause rot in many fruit crops (Auger et al. 2013; Guarnaccia and Crous 2017), including European pear in Italy (Bertetti et al. 2018). To our knowledge, this is the first report of D. rudis causing fruit rot of European pears in the United States. Diaporthe spp. are important plant pathogens causing severe losses in fruit crops, and this report will assist in monitoring the severity of this pathogen in pear production regions of the United States.The author(s) declare no conflict of interest.References:Auger, J., et al. 2013. Plant Dis. 97:843. https://doi.org/10.1094/PDIS-10-12-0990-PDN Link, ISI, Google ScholarBertetti, D., et al. 2018. Plant Dis. 102:2651. https://doi.org/10.1094/PDIS-03-18-0499-PDN Link, ISI, Google ScholarGuarnaccia, V., and Crous, P. W. 2017. IMA Fungus 8:317. https://doi.org/10.5598/imafungus.2017.08.02.07 Crossref, ISI, Google ScholarUdayanga, D., et al. 2014. Persoonia 32:83. https://doi.org/10.3767/003158514X679984 Crossref, ISI, Google ScholarThe author(s) declare no conflict of interest.Funding: Funding was provided by Washington Tree Fruit Research Commission (grant no. PR-17-107).DetailsFiguresLiterature CitedRelated Vol. 103, No. 8 August 2019SubscribeISSN:0191-2917e-ISSN:1943-7692 DownloadCaptionPistachio fruit infected by Neofusicoccum mediterraneum (Moral et al.). Photo credit: T. J. Michailides. Leaf blight on Hosta ventricosa caused by Pseudomonas syringae pv. syringae (Liu et al.). Photo credit: Z. X. Liu. Metrics Article History Issue Date: 1 Aug 2019Published: 6 Jun 2019First Look: 16 Apr 2019Accepted: 7 Apr 2019 Pages: 2132-2132 Information© 2019 The American Phytopathological SocietyFundingWashington Tree Fruit Research CommissionGrant/Award Number: PR-17-107KeywordsEuropean pearDiaporthe rudispostharvest rotThe author(s) declare no conflict of interest.Cited byDiversity of Botryosphaeriaceae and Diaporthe Species Associated with Postharvest Apple Fruit Decay in SerbiaNina Vučković, Ivana Vico, Bojan Duduk, and Nataša Duduk16 March 2022 | Phytopathology®, Vol. 112, No. 4Occurrence of Diaporthe species in Eucalyptus globulus , Pinus pinaster and Quercus suber in Portugal27 January 2021 | Forest Pathology, Vol. 51, No. 2In-Season Monitoring of Postharvest Rot Pathogens on European Pears (Pyrus communis) in Southern Oregon and Subsequent Management StrategiesAchala N. KC and Ann L. 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