First Report of Crown Rot Caused by Phytopythium helicoides on Strawberry in the Americas

Abstract

HomePlant DiseaseVol. 103, No. 10First Report of Crown Rot Caused by Phytopythium helicoides on Strawberry in the Americas PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Crown Rot Caused by Phytopythium helicoides on Strawberry in the AmericasM. V. Marin, T. Seijo, J. Mertely, and N. A. PeresM. V. Marinhttp://orcid.org/0000-0002-5190-6983University of Florida, Wimauma, FL 33598Search for more papers by this author, T. SeijoUniversity of Florida, Wimauma, FL 33598Search for more papers by this author, J. MertelyUniversity of Florida, Wimauma, FL 33598Search for more papers by this author, and N. A. Peres†Corresponding author: N. A. Peres; E-mail Address: [email protected]University of Florida, Wimauma, FL 33598Search for more papers by this authorAffiliationsAuthors and Affiliations M. V. Marin T. Seijo J. Mertely N. A. Peres † University of Florida, Wimauma, FL 33598 Published Online:15 Aug 2019https://doi.org/10.1094/PDIS-03-19-0658-PDNAboutSectionsSupplemental ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat During the 2018 to 2019 growing season (October to April), a crown rot causing up to 50% mortality on ‘Florida Radiance’ strawberry (Fragaria × ananassa) was observed in six commercial farms in Florida. The wilted and collapsing plants had symptoms of reddish-brown to dark brown discoloration in the crown. A Pythium-like organism was consistently isolated from symptomatic crowns on the selective medium P5ARP (Erwin and Ribeiro 1996). Three isolates were selected and produced rapidly growing colonies with average radial growth rates at room temperature of 144, 148, and 165 mm/day on PDA, P5ARP, and V8 agar, respectively. Papillate sporangia were produced on 2-week-old V8 agar plugs placed in sterile pond water for 24 h. The sporangia were borne on irregularly branched sporangiophores and were 25 to 39 μm wide (average = 37 μm; n = 25) and 22 to 43 μm long (average = 31 μm; n = 25). Chlamydospores were observed on P5ARP after 1 week and measured 17 to 26 μm (average = 19 μm; n = 25) in diameter. Sexual structures were not observed. DNA was extracted from the same three isolates using a FastDNA kit (MP Biomedicals, Solon, OH), and the ribosomal internal transcribed spacer (ITS) regions 1 and 2, cytochrome oxidase I gene (cox I), and cytochrome oxidase II gene (cox II) were amplified and sequenced using primer pairs ITS4/ITS6 (White et al. 1990), FM35/FM59, and FM66/FM58 (Martin 2000), respectively. Sequences were deposited in GenBank as accession numbers MK630215 to MK630217, MK636714 to MK636716, and MK636711 to MK636713, for ITS, cox I, and cox II, respectively. A BLAST query of the sequences matched Phytopythium helicoides, with 99 to 100% identity (GenBank accession nos. HQ643382.1, KT258906.1, and AB257273.1 for ITS, cox I, and cox II, respectively). To complete Koch’s postulates, isolates were grown for 10 days in the dark at 30°C on twice-autoclaved brown rice. Seven 2-week-old ‘Florida Radiance’ transplants in 1-liter pots were inoculated by placing 10 g of colonized rice from a single isolate next to each plant. After inoculation, pots were saturated with water for 24 h to induce zoospore production. After 15 days, each isolate produced wilting or collapse of at least six out of seven inoculated plants, whereas noninoculated controls remained healthy. The pathogen was reisolated from symptomatic plants and confirmed to be P. helicoides by morphological characteristics. Pathogenicity tests were repeated once. Root and stem rot in miniature rose, Chrysanthemum, and Kalanchoe, and strawberry crown rot caused by P. helicoides have been reported in Japan (Chen et al. 2016; Ishiguro et al. 2014). In the United States, the pathogen causes root rot in pistachio (Fichtner et al. 2016). To our knowledge, this is the first report of P. helicoides causing crown rot of strawberry in the Americas. Future work is needed to assess the epidemiology, cultivar response, fungicide sensitivity, and disease management of this possible new emerging pathogen of strawberry.The author(s) declare no conflict of interest.