First Report of <i>Pythium ultimum</i> Crown and Root Rot of Industrial Hemp in the United States

HomePlant DiseaseVol. 102, No. 10First Report of Pythium ultimum Crown and Root Rot of Industrial Hemp in the United States PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Pythium ultimum Crown and Root Rot of Industrial Hemp in the United StatesJ. Beckerman, J. Stone, G. Ruhl, and T. CreswellJ. Beckerman†Corresponding author: J. Beckerman; E-mail: E-mail Address: [email protected]http://orcid.org/0000-0003-2063-8362, J. Stone, G. Ruhl, and T. CreswellAffiliationsAuthors and Affiliations J. Beckerman † J. Stone , Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907 G. Ruhl T. Creswell , Purdue Plant and Pest Diagnostic Laboratory, Purdue University, West Lafayette, IN 47907. Published Online:8 Aug 2018https://doi.org/10.1094/PDIS-12-17-1999-PDNAboutSections ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat During June 2016, root rot symptoms were observed on industrial hemp (Cannabis sativa cv. 'Canda'), in research plots in Lafayette, IN. Rainfall in Indiana during June (127.8 mm) of 2016 was similar to previous averages of 116.1, although a severe rainfall event on 4 June (47.2 mm), 2 days after planting, resulted in physical crusting of the soil surface. Symptom development first appeared 14 days after sowing with temperatures ranging from 25 to 30°C. Affected plants were stunted with chlorotic leaves. Most of the symptomatic plants simply persisted in stunted growth. A sampling of 12 symptomatic plants was removed from the soil, and brown, water-soaked root lesions were observed. Plants were rinsed in tap water to remove soil debris and then 1 to 2 in. was clipped from the bottom of each seedling root to use on Pythium selective medium. Half the seedlings were plated directly onto quarter-strength potato dextrose agar (PDA), and half were surface sterilized in 1% sodium hypochlorite and plated on quarter-strength PDA, and on a medium selective for oomycetes containing pimaricin, ampicillin, rifampicin, and pentachloronitrobenzene. Plates were incubated at 22°C in the dark (Masago 1977). Isolates were grown on V8 medium (V8 vegetable mix, 300 g; agar, 15 g; CaCO3, 1.5 g; and distilled water, 1 liter); light microscopy revealed morphological characters consistent with Pythium ultimum and included spherical, terminal sporangia, along with intercalary sporangia (Watanabe 2002). Isolates were grown and DNA extracted with the Qiagen DNeasy Plant Mini Kit (Valencia, CA). Polymerase chain reaction (PCR) was performed using the primers ITS1/ITS4 to amplify the internal transcribed spacer (ITS) region of rDNA of a single isolate. BLAST analysis (Altschul et al. 1997) identified 9 of 20 isolates as P. ultimum; a 734-bp segment showed 100% homology with the sequence of P. ultimum (GenBank accession nos. MF115493.1, KJ744319.1, and others). The nucleotide sequence has been assigned GenBank accession number MG720851. Pathogenicity tests were performed using 20 seeds per pot sown in three 1-liter trays filled with a steam-disinfested soil (Metromix, SunGro Horticulture, Agawam, MA). Plants were fertilized 1 day before inoculation with the equivalent of 0.9 g of ammoniacal nitrogen to simulate field fertility levels of 150 lb N/acre. Plants were inoculated 14 days after sowing (postemergent) with sterilized hemp kernels or quarter-strength PDA colonized with two isolates of P. ultimum. Infested and control inoculum was placed in rows 5 mm from plants. Trays were replicated three times for both control and inoculated treatments. Plants were kept in a greenhouse at 25°C. The first symptoms developed 1 week after the artificial inoculation. After 42 days, 80 to 100% of plants were infected at 25°C. Control plants remained healthy, with 100% of the seedlings emerging and remaining uninfected. This experiment was repeated 5 days later, with symptoms first developing within the first week postinoculation. P. ultimum was consistently reisolated from the lesions, and PCR was performed to confirm identification owing to a loss of morphological characteristics. To our knowledge, this is the first report of Pythium root rot of C. sativa caused by P. ultimum in the United States. This disease may increase in incidence and severity in early spring plantings under cool conditions, in low-lying or flood-prone regions (McPartland 1996), or when physical crusting of the soil has occurred after high-intensity rainfall.References:Altschul, S. F., et al. 1997. Nucleic Acids Res. 25:3389. https://doi.org/10.1093/nar/25.17.3389 Crossref, ISI, Google ScholarMasago, H. 1977. Phytopathology 67:425. https://doi.org/10.1094/Phyto-67-425 Crossref, ISI, Google ScholarMcPartland, J. M. 1996. J. Int. Hemp Assoc. 3:19. Google ScholarWatanabe, T. 2002. Pictorial Atlas of Soil and Seed Fungi. CRC Press, Boca Raton, FL. https://doi.org/10.1201/9781420040821 Crossref, Google ScholarFunding: Funding was provided by Purdue University (Purdue University AgSeed Award 2016).DetailsFiguresLiterature CitedRelated Vol. 102, No. 10 October 2018SubscribeISSN:0191-2917e-ISSN:1943-7692 Metrics Article History Issue Date: 28 Sep 2018Published: 8 Aug 2018First Look: 26 Apr 2018Accepted: 21 Apr 2018 Pages: 2045-2045 Information© 2018 The American Phytopathological SocietyFundingPurdue UniversityGrant/Award Number: Purdue University AgSeed Award 2016Cited byIdentification and Characterization of Bacteria-Derived Antibiotics for the Biological Control of Pea Aphanomyces Root Rot8 August 2022 | Microorganisms, Vol. 10, No. 8An Overview of Pathogens Associated with Biotic Stresses in Hemp Crops in Oregon, 2019 to 2020H. M. Rivedal, C. N. Funke, and K. E. 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