First Report of Pythium myriotylum Causing Damping off and Root Rot in Cannabis sativa in Florida
Year: 2025
Type: article
Abstract: In April of 2024, Cannabis sativa (L.) cuttings of 5 different cultivars (JUNK, GAR, SHOR, PBR, and ASNK) at indoor facilities in Mt. Dora and Homestead, FL were observed to have stunting, damping off, crown rot, and chlorosis. Of the 3,000 plants in the affected room, about 5-7% displayed the symptoms described. Pathogen identification was performed on 6 cuttings (cv. ASNK) from Homestead and 4 cuttings (cv. GAR and SHOR) from Mt. Dora. In a laminar flow hood, stems were surface sterilized in a 0.625% sodium hypochlorite solution for 2 min, rinsed in sterile deionized (DI) water, and cut into 1cm long segments. The segments were plated on both potato dextrose and V8 agar plates and incubated in the dark at 27°C for 48 hours. On V8 agar, dense aerial mycelia grew out from the stem segments. On PDA, the mycelium was fluffy and cotton-like, consistent with Pythium morphology (Kageyama, 2014). DNA from the mycelium was extracted using Quick DNA Fungal/Bacterial Kit (Zymo Research Irvine, CA, USA). The identities were confirmed with Internal Transcribed Spacer region (ITS) (Riit et al. 2016) sequences for two isolates which had 100% identity to P. myriotylum accession KX671096.1; and cytochrome oxidase subunit 1 (COI) (Robideau et al. 2011) sequences which had 99.69% identity to MT222351.1 using the BLASTn function of NCBI. The sequences were deposited into GenBank with accession nos. PQ143175 (ITS), PQ206192 (ITS), PQ206366 (COI), and PQ219680 (COI). A phylogenetic tree was constructed with MEGA software using concatenated ITS and COI sequences to show evolutionary relationships between these two P. myriotylum isolates and other Pythium/Globisporangium species. To prove pathogenicity, a pure culture of P. myriotylum was diced and transferred to 500 mL of V8 broth. A negative control was prepared using sterile V8 broth. The broths were placed on a rotary shaker and incubated at 150 rpm and 30°C for 72 hours. Light microscopy verified the presence of mycelial growth and motile zoospores in the inoculated broth and the absence of growth in the negative control. A total of 36 rockwool cubes were sterilized, 18 were soaked in the inoculated broth and 18 in the control broth for 30 minutes. Then, 36 cuttings were harvested from C. sativa plants (cv. CL1 and CL2), dipped in rooting gel (Clonex Rooting Gel, Growth Technology, Somerset, UK), and inserted into each rockwool cube. These cuttings were grown indoors in a humidity dome at 25°C under LED lights with an 18-hour photoperiod. After 6 days, infected clones exhibited damping off, wilting, and chlorosis. No symptoms were observed in the negative control plants. Crown sections of 5 symptomatic clones and 3 control clones were surface sterilized and plated onto V8 agar as previously described and incubated for 3 days at 27°C. Mycelial growth was observed from crown segments of inoculated plants and not from the control plants. Koch’s postulates were confirmed through re-isolation and amplification of the same ITS and COI regions from mycelial growth; sequences were identical to the originally isolated cultures. P. myriotylum has been previously described as causing disease symptoms in Cannabis (Punja, 2021). Since the cannabis industry currently relies on clonal propagation for cultivation and production, a P. myriotylum infection has the potential to cause economic damage. To our knowledge, this is the first report of P. myriotylum causing disease in Cannabis in Florida.
Source: Plant Disease
Authors: Ashley Brown, Eden Blit, Sydney Gerstenberg, Krista Say, Richard Philbrook
Language: English
Subfield: Plant Science
Domain: Life Sciences
Open Access status: bronze
OpenAlex ID: W4415105807