Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants
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| Authors: | Punja, ZK; Rodriguez, G |
| Year: | 2018 |
| Journal: | Can. J. Plant Pathol. 40 Article Link (DOI) |
| Title: | Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants |
| Abstract: | An increase in the cultivation of Cannabis sativa (cannabis or marijuana) plants in Canada is becoming associated with increased incidence and severity of various diseases, many of which have not been previously reported. In this study, hydroponically grown C. sativa plants were sampled over a 3-year period (2014-2017) to determine the prevalence of root pathogens. Following isolation, pathogenicity studies were conducted to establish the extent of disease symptoms caused by the recovered microbes. Root rot was found to be caused by two Pythium species - Pythium dissotocum Drechsler and P. myriotylum Drechsler. As well, two Fusarium species were recovered from diseased plants - Fusarium oxysporum Schlecht. emend. Snyder & Hansen and F. solani (Mart.) Sacc. Upon inoculation onto healthy plants, all isolates of Pythium spp. caused browning and a reduction in root mass, accompanied by stunting. Inoculation of plants with F. oxysporum caused browning of roots and crown rot infection, accompanied by pith and vascular discolouration, and in some cases wilting of plants, while root and crown infection was observed with F. solani. Phylogenetic analysis of internal transcribed spacer (ITS) and elongation factor 1 (EF-1) sequences revealed that the Fusarium species affecting cannabis plants shared 99-100% sequence homology with isolates causing stem rot and wilt in other hosts, including cumin and tomato, suggesting they were not uniquely adapted to cannabis. The potential for spread of F. oxysporum through the hydroponic system was confirmed by its detection in the recirculating nutrient solution. Furthermore, rooted cuttings obtained from commercial propagators were found to harbour Fusarium root infection that resulted in subsequent stunting, yellowing and occasional death of plants. This demonstrates the potential for long-distance spread of the pathogen. The two Pythium species recovered from cannabis plants have an extremely broad host range and are not unique to this host. An additional species, P. aphanidermatum (Edson) Fitzp., was recovered from diseased plants grown under greenhouse conditions in 2018. The management of these root pathogens on C. sativa will require the evaluation and implementation of sanitization methods, biological control agents, and chemical products adapted from greenhouse vegetable production practices. The use of pathogen-free propagation materials and identification of potential sources of disease resistance should also become a priority. |
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