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On October 17th, marijuana (Cannabis) —a widely distributed plant in tropical and temperate regions— was legalized in Canada, becoming one of the few countries where recreational consumption, use for medical purposes and its cultivation are legal. Of course, there are still restrictions on the use of plants, but without doubt the opportunities to expand knowledge about marijuana are many. Precisely at the beginning of this year, the University of Saskatchewan, in Canada, hired the young researcher Robert Laprairie as part of the College of Pharmacy and Nutrition, to develop research related to the cannabinoid receptors, one of the active compounds of great importance in marijuana, demonstrating the growing interest in the plant and the products that are obtained from it. This university has also been a pioneer in other research concerning Cannabis, such as the study of its genome and genes involved in the synthesis of cannabinoids1, but nevertheless, there is an area of vital importance that has been forgotten in Canada and other countries where marijuana is legal or decriminalized: phytopathology.
The production in large quantities of any crop involves the arrival of pests and diseases and therefore losses in yield. In this area, Canada has experience given that the extensive production of canola in the Prairie provinces was seriously affected by the appearance of the clubroot disease. That is why, in view of the anticipated extensive production of marijuana, a coherent and effective phytopathological strategy is essential. But what is known about the pathogens and diseases affecting marijuana? —Almost nothing.
In 2000, the book “Hemp Diseases and Pests, Management and Biological Control” was published by the CABI publishing house2, but despite the publication date and the attractive title for the reader, this book uses very general information and studies of the early century as references, without counting the fact that hemp (also derived from Cannabis sativa) is not marijuana, despite sharing many common characteristics.
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There is an area of vital importance that has been forgotten in Canada and other countries where marijuana is legal or decriminalized: phytopathology
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Among the pathogens identified affecting Cannabis sp., up to 13 species of fungi —such as Phomopsis ganjae, Schiffnerula cannabis and Septoria neocannabine-, were identified in the United States during a 12-year study investigating the Cannabis-fungus association3. In addition, pathogenic members of the Bacteria domain have also been identified affecting Cannabis sp., like Xanthomonas campestris pv. cannabis in Romania and Japan4, and phytoplasmas causing the disease known as witches’ broom in plants of India5 and Iran6. One of the very few studies found in the literature referring to plant pathogens affecting marijuana in Canada was made in the province of British Columbia, which identified pathogens affecting the roots (Pythium dissotocum and Fusarium oxysporum), bulbs (Botrytis cinerea) and leaves(Golovinomyces cichoracearum) of the plants.
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Although cannabis can basically grow anywhere (just remember it is called “weed”), there are strains that have been identified as more suitable for tropical environments. In Latin America, marijuana has been decriminalized in several countries, mainly for recreational use, a change that although is important, is not enough to grow the plant as an extensive crop. Uruguay, in 2013, become the first country legalizing marijuana in the world, and to this day, there are no publications about local phytopathological studies. Very healthy plants or lack of interest by plant pathologists? Is still the plant a taboo?
To date, nothing is known about the mechanisms involved in the Cannabis-pathogen interaction, there is no specific diagnostic method for a rapid and efficient detection of plant pathogens affecting marijuana and no studies have been carried out on the epidemiology and/or vectors that could be involved in the spread of diseases. The doors have opened to marijuana research and plant pathologists were ready! Just a few days before “legalization day”, in October, the Canadian Journal of Plant Pathology published two papers describing pathogens that affect marijuana’s root and crown7, as well as its flower and foliage8. I am completely sure that a lot more of research is coming in this area, and who knows, maybe in a few years I´ll switch from canola to marijuana phytopathology.
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Department of Biology, University of Saskatchewan
Saskatoon, SK, Canada
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Images
Marijuana leaves in Petri dish. Photograph by author.
Research Crop - U.Miss. Photo by NIDA(NIH) (U.S. Government Works)
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References
1Van Bakel, et al. (2011). The draft genome and transcriptome of Cannabis sativa. Genome biology, 12(10), R102.
2McPartland, J. M., et al. (2000). Hemp diseases and pests: management and biological control: an advanced treatise. CABI.
3McPartland, J. M. & Cubeta, M. A. (1997). New species, combinations, host associations and location records of fungi associated with hemp (Cannabis sativa). Mycological Research, 101(7), 853–857.
4Netsu et al. (2014). Bacterial leaf spot of hemp caused by Xanthomonas campestris pv. cannabis in Japan. Journal of General Plant Pathology, 80(2), 164-168.
5Raj, S. K., et al. (2008). ‘Candidatus Phytoplasma asteris’ (group 16SrI) associated with a witches’broom disease of Cannabis sativa in India. Plant pathology, 57(6), 1173-1173.
6Sichani, F. V. et al. (2011). Characterization of Stolbur (16SrXII) group Phytoplasma associated with Cannabis sativa witches’-broom disease in Iran. Plant Pathology Journal, 10(4), 161-167.
7Punja, Z. K., et al. (2018). Root and crown rot pathogens causing wilt symptoms on field-grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology, DOI: 10.1080/07060661.2018.1535470
8Punja, Z. K. (2018). Flower and foliage-infecting pathogens of marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology, DOI: 10.1080/07060661.2018.1535467