First Report of Sclerotinia Crown Rot Caused by Sclerotinia minor on Hemp

Abstract

HomePlant DiseaseVol. 103, No. 7First Report of Sclerotinia Crown Rot Caused by Sclerotinia minor on Hemp PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Sclerotinia Crown Rot Caused by Sclerotinia minor on HempS. T. Koike, H. Stanghellini, S. J. Mauzey, and A. BurkhardtS. T. Koike†Corresponding author: S. T. Koike; E-mail Address: SKoike@trical.comhttp://orcid.org/0000-0002-3184-3778TriCal Diagnostics, Gilroy, CA 95020Search for more papers by this author, H. StanghelliniTriCal Diagnostics, Gilroy, CA 95020Search for more papers by this author, S. J. MauzeyTriCal Diagnostics, Gilroy, CA 95020Search for more papers by this author, and A. BurkhardtTriCal Diagnostics, Gilroy, CA 95020Search for more papers by this authorAffiliationsAuthors and Affiliations S. T. Koike † H. Stanghellini S. J. Mauzey A. Burkhardt TriCal Diagnostics, Gilroy, CA 95020 Published Online:16 May 2019https://doi.org/10.1094/PDIS-01-19-0088-PDNAboutSectionsSupplemental ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat In summer 2018, commercial field grown hemp (Cannabis sativa L.) plants in San Benito County, CA, showed signs of a disease. Leaves initially wilted and turned dark green. Foliage eventually dried up completely. The base of the plant crown in contact with soil supported the growth of white to gray mycelium and small (0.5 to 3 mm diameter), irregularly shaped, black sclerotia. Crown tissue beneath the epidermis was necrotic. However, plant roots appeared symptomless. To estimate disease incidence, eight replicates of 100 plants each were assessed for collapse symptoms and sclerotia on plant crowns. Overall disease incidence was limited and was approximately 1%. To test for pathogens, symptomatic crown pieces were surface sterilized in 0.006% NaOCl for 2 min and plated on acidified (2 ml of 25% lactic acid/liter) corn meal agar. After 2 to 3 days, rapidly growing, colorless, appressed mycelium emerged from crown pieces. Mycelial transfers to potato dextrose agar (PDA) plates resulted in white to gray colonies that produced profuse numbers of black sclerotia typical of Sclerotinia minor (Koike et al. 2007). Sclerotia that were removed from the collected field plants, dipped in ethanol, rinsed, and plated on acidified PDA resulted in colonies that again appeared typical of S. minor. To test for pathogenicity, four isolates were grown on PDA until sclerotia were fully developed and surface mycelium was dry. For each isolate, 10 sclerotia were removed from the PDA plates and placed adjacent to the crowns of eight 2-month-old potted hemp plants approximately 1 cm below the soil surface. The sclerotia were then covered lightly with potting medium. Plants were maintained under ambient light and a daytime temperature range of 19 to 24°C. After 2 weeks, leaves of inoculated plants began to wilt and crown tissue was necrotic. Isolation from symptomatic crowns resulted in colonies that morphologically and molecularly were identical to the original isolates. Control plants, inoculated with sterile sand, developed no foliar or crown symptoms. For species identification, DNA was extracted using the DNAeasy Plant kit (Qiagen) from mycelium scraped from the surfaces of 21-day-old cultures of both the original and postinoculation isolates. DNA was amplified and sequenced using the ITS1 and ITS4 primers for the internal transcribed spacer region. Using the NCBI nucleotide BLAST, original (MK356550) and postinoculation (MK356551) isolates matched S. minor (KC836493.1) with 100% query cover and 100% identity. Based on these molecular and morphological data, the isolates were identified as S. minor Jagger. This is the first report of a crown rot disease on hemp caused by S. minor, which we designate as Sclerotinia crown rot. Hemp is known to be a host of Sclerotinia sclerotiorum (Lib.) de Bary, which causes hemp canker disease on crowns and stems (McPartland 1996).The author(s) declare no conflict of interest.