First Report of Fusarium oxysporum Causing Fusarium Root Rot on Yacon Potatoes in Brazil

Abstract

HomePlant DiseaseVol. 101, No. 4First Report of Fusarium oxysporum Causing Fusarium Root Rot on Yacon Potatoes in Brazil PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Fusarium oxysporum Causing Fusarium Root Rot on Yacon Potatoes in BrazilW. B. Moraes, R. F. de Mendonça, V. V. Schwan, F. L. de Oliveira, C. H. P. Venturin, F. B. Souza-Sobreira, and T. C. B. SoaresW. B. MoraesSearch for more papers by this author, R. F. de MendonçaSearch for more papers by this author, V. V. SchwanSearch for more papers by this author, F. L. de OliveiraSearch for more papers by this author, C. H. P. VenturinSearch for more papers by this author, F. B. Souza-SobreiraSearch for more papers by this author, and T. C. B. SoaresSearch for more papers by this authorAffiliationsAuthors and Affiliations W. B. Moraes R. F. de Mendonça V. V. Schwan F. L. de Oliveira C. H. P. Venturin , Department of Plant Production, UFES, 29500-000 Alegre-ES, Brazil F. B. Souza-Sobreira , Graduate Program in Genetics and Breeding, Center for Agricultural Sciences and Engineering, UFES T. C. B. Soares , Department of Pharmacy and Nutrition, UFES, 29500-000 Alegre-ES, Brazil. Published Online:8 Feb 2017https://doi.org/10.1094/PDIS-04-16-0493-PDNAboutSections ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat Production of yacon potato (Smallanthus sonchifolius) has raised interest worldwide because its tuberous root is considered a functional food with health-beneficial compounds (Gusso et al. 2015; Ojansivu et al. 2011). There is information available on diseases in yacon. Fusarium root rot is among the main plant diseases, and it occurs in different phenological stages of various crop plants. Its symptoms in yacon appeared in November 2014 when plants were 6 months old and with 70% of their life cycle completed, increasing gradually. They included yellowing, damping-off, and rot of rhizophores and tuberous roots. After 5 weeks, 80% of the plants in the area exhibited symptoms. In the following month, 60% mortality was observed in the study area, the city of Alegre-ES-Brazil (20°45′49″S, 41°31′59″W). Symptomatic tuberous roots were cut into small pieces and surface-sterilized with 70% alcohol and 1% sodium hypochlorite, dried, and plated in potato dextrose agar (PDA) culture media. After isolation, the Petri dishes (9 cm) were incubated at 25°C until the fungus filled the plate. A single spore from a single isolate was picked up to obtain a monosporic culture of the fungus using the carnation leaf agar culture medium for fungus identification based on its spore characteristics and colony morphology on PDA (Marasas et al. 2006). Macroconidia were canoe-shaped with 2 to 5 septa and measured 24.4 to 34.0 × 5.2 to 7.6 μm. Oval, unicellular microconidia developed on short monophialides, and measured 8.4 to 17.6 × 6.4 to 7.6 μm. The colony on PDA was cottony and its pigmentation varied from purple to whitish. Petri dishes containing monosporic colonies were reisolated and after 4 days of incubation at 25°C, a suspension of 1.6 × 106 conidia/ml was prepared for inoculation into three healthy potatoes. The suspension was injected with a syringe through holes made by a piercer. Three noninoculated yacon potatoes were maintained under the same conditions, serving as the control. The inoculated and noninoculated potatoes were allocated in plastic pots covered with a polyethylene film under a 12-h photoperiod at 25°C. Only the inoculated potatoes showed the same symptoms as those of the diseased potatoes. For molecular identification, Invitrogen Platinum Taq DNA Polymerase was used to amplify the TEF-1 α gene region, using ef1 and ef2 primers. PCR was conducted according to the manufacturer’s specification. The PCR product generated was submitted for DNA sequencing to Myleus biotechnology using the Sanger methodology-ABI 3130/3130 XL (Applied Biosystems). The nucleotide BLAST NCBI allowed querying the sequences against the database, resulting in 99% sequence identity with Fusarium oxysporum (GenBank accession no. KC622308.1). The fungus was reisolated from the diseased potatoes, and was identified as F. oxysporum based on its morphological characteristics, genetic analysis, and pathogenicity test, fulfilling Koch’s postulates. To the best of our knowledge, this is the first confirmed report of Fusarium root rot in yacon in Brazil.