A Guide to Cannabis Virology: From the Virome Investigation to the Development of Viral Biotechnological Tools

Abstract

Cannabis sativa cultivation is experiencing a period of renewed interest due to the new opportunities for its use in different sectors including food, techno-industrial, construction, pharmaceutical and medical, cosmetics, and textiles. Moreover, its properties as a carbon sequestrator and soil improver make it suitable for sustainable agriculture and climate change mitigation strategies. The increase in cannabis cultivation is generating conditions for the spread of new pathogens. While cannabis fungal and bacterial diseases are better known and characterized, viral infections have historically been less investigated. Many viral infection reports on cannabis have recently been released, highlighting the increasing threat and spread of known and unknown viruses. However, the available information on these pathogens is still incomplete and fragmentary, and it is therefore useful to organize it into a single structured document to provide guidance to growers, breeders, and academic researchers. This review aims to present the historical excursus of cannabis virology, from the pioneering descriptions of virus-like symptoms in the 1940s/50s to the most recent high-throughput sequencing reports. Each of these viruses detected in cannabis will be categorized with an increasing degree of threat according to its potential risk to the crop. Lastly, the development of viral vectors for functional genetics studies will be described, revealing how cannabis virology is evolving not only for the characterization of its virome but also for the development of biotechnological tools for the genetic improvement of this crop.

Challenges to Cannabis sativa Production from Pathogens and Microbes—The Role of Molecular Diagnostics and Bioinformatics

“…Therefore, while the diagnostic assays described in this study provide confirmation of pathogen presence, their causation or involvement in symptom expression remains to be confirmed. In previous experimental inoculations conducted on hemp plants by Keglar and Sparr [ 27 ] (summarized by Miotti et al [ 28 ]), it was reported that a number of mechanically transmitted viruses could cause mosaic and mottling symptoms on leaves, including AMV, CMV, potato viruses X and Y, and arabis mosaic virus. None of these viruses were identified in this study on cannabis, while AMV was detected in hemp plants in 2020.…”

“…BCTV exists as phylogenetically different strains and is reported to affect hemp grown in Colorado, Arizona, Nevada, Oregon, Washington, and California [ 3 , 34 , 35 , 36 , 37 , 39 , 41 ]. The virus has an extremely wide host range and is considered to be a pathogen that poses a significant threat to this crop [ 28 ]. Additional research is likely to identify more viruses and phytoplasmas occurring on both cannabis and hemp, particularly where these crops are grown in close proximity to nonhemp crops that can provide a source of inoculum for spread to cannabis and hemp plants, in addition to the presence of insect vectors that can transmit these pathogens.…”

“…An extensive review of the potential impact of viruses/viroid on cannabis and hemp (historical and current) has been recently published by Miotti et al [ 28 ]. Some potential aphid-transmissible viruses that can infect cannabis and hemp plants under artificial inoculation conditions, but have not yet become widespread under commercial conditions, include AMV, CMV, and PVY [ 28 , 63 ]. Viruses vectored by thrips which can also pose a threat include Tobacco streak virus and Tomato spotted wilt virus [ 28 ].…”

“…Some potential aphid-transmissible viruses that can infect cannabis and hemp plants under artificial inoculation conditions, but have not yet become widespread under commercial conditions, include AMV, CMV, and PVY [ 28 , 63 ]. Viruses vectored by thrips which can also pose a threat include Tobacco streak virus and Tomato spotted wilt virus [ 28 ]. Many of these emerging viruses are potentially also seed-borne [ 28 ].…”

“…Viruses vectored by thrips which can also pose a threat include Tobacco streak virus and Tomato spotted wilt virus [ 28 ]. Many of these emerging viruses are potentially also seed-borne [ 28 ]. These observations suggest that cannabis and hemp crops are susceptible to a range of viruses, and that the insect-vectored pathogens appear to have the greatest potential to cause damage under widespread cultivation conditions, with mechanically transmitted pathogens less so.…”