The use of and research on medical cannabis (MC) is becoming more common, yet there are still many challenges regarding plant diseases of this crop. For example, there is a lack of formal and professional knowledge regarding fungi that infect MC plants, and practical and effective methods for managing the casual agents of disease are limited. The purpose of this study was to identify foliar, stem, and soilborne pathogens affecting MC under commercial cultivation in Israel. The predominant major foliage pathogens were identified as Alternaria alternata and Botrytis cinerea, while the common stem and soilborne pathogens were identified as Fusarium oxysporum and F. solani. Other important fungi that were isolated from foliage were those producing various mycotoxins that can directly harm patients, such as Aspergillus spp. and Penicillium spp. The sampling and characterization of potential pathogenic fungi were conducted from infected MC plant parts that exhibited various disease symptoms. Koch postulates were conducted by inoculating healthy MC tissues and intact plants with fungi isolated from infected commercially cultivated symptomatic plants. In this study, we report on the major and most common plant pathogens of MC found in Israel, and determine the seasonal outbreak of each fungus.

Background: The use of medical cannabis (MC) in the medical field has been expanding over the last decade, as more therapeutic beneficial properties of MC are discovered, ranging from general analgesics to anti-inflammatory and anti-bacterial treatments. Together with the intensified utilization of MC, concerns regarding the safety of usage, especially in immunocompromised patients, have arisen. Similar to other plants, MC may be infected by fungal plant pathogens (molds) that sporulate in the tissues while other fungal spores (nonpathogenic) may be present at high concentrations in MC inflorescences, causing a health hazard when inhaled. Since MC is not grown under sterile conditions, it is crucial to evaluate current available methods for reduction of molds in inflorescences that will not damage the active compounds. Three different sterilization methods of inflorescences were examined in this research; gamma irradiation, beta irradiation (e-beam) and cold plasma to determine their efficacy in reduction of fungal colony forming units (CFUs) in vivo. Methods: The examined methods were evaluated for decontamination of both uninoculated and artificially inoculated Botrytis cinerea MC inflorescences, by assessing total yeast and mold (TYM) CFU levels per g plant tissue.In addition, e-beam treatment was also tested on naturally infected commercial MC inflorescences. Results: All tested methods significantly reduced TYM CFUs at the tested dosages. Gamma irradiation reduced CFU levels by approximately 6-and 4.5-log fold, in uninoculated and artificially inoculated B. cinerea MC inflorescences, respectively. The effective dosage for elimination of 50% (ED 50 )TYM CFU of uninoculated MC inflorescence treated with e-beam was calculated as 3.6 KGy. In naturally infected commercial MC inflorescences, e-beam treatments reduced TYM CFU levels by approximately 5-log-fold. A 10 min exposure to cold plasma treatment resulted in 5log-fold reduction in TYM CFU levels in both uninoculated and artificially inoculated B. cinerea MC inflorescences. Conclusions: Although gamma irradiation was very effective in reducing TYM CFU levels, it is the most expensive and complicated method for MC sterilization. Both e-beam and cold plasma treatments have greater potential since they are cheaper and simpler to apply, and are equally effective for MC sterilization.

Medical cannabis (MC) production is a rapidly expanding industry. Over the past ten years, many additional phytocannabinoids have been discovered and used for different purposes. MC was reported beneficial for the treatment of a variety of clinical conditions such as analgesia, multiple sclerosis, spinal cord injuries, Tourette's syndrome, epilepsy, glaucoma, Parkinson disease and more. Yet, there is still a major lack of research and knowledge related to MC plant diseases, both at the pre- and postharvest stages. Many of the fungi that infect MC, such as Aspergillus and Penicillium spp., are capable of producing mycotoxins that are carcinogenic, or otherwise harmful when consumed, and especially by those patients who suffer from a weakened immune system, causing invasive contamination in humans. Therefore, there are strict limits regarding the permitted levels of fungal colony forming units (CFU) in commercial MC inflorescences. Furthermore, the strict regulation on pesticide appliance application in MC cultivation exacerbates the problem. In order to meet the permitted CFU limit levels, there is a need for pesticide-free postharvest treatments relying on natural non-chemical methods. Thus, a decontamination approach is required that will not damage or significantly alter the chemical composition of the plant product. In this research, a new method for sterilization of MC inflorescences for reduction of fungal contaminantstes was assessed, without affecting the composition of plant secondary metabolites. Inflorescences were exposed to short pulses of steam (10, 15 and 20 s exposure) and CFU levels and plant chemical compositions, pre- and post-treatment, were evaluated. Steam treatments were very effective in reducing fungal colonization to below detection limits. The effect of these treatments on terpene profiles was minor, resulting mainly in the detection of certain terpenes that were not present in the untreated control. Steaming decreased cannabinoid concentrations as the treatment prolonged, although insignificantly. These results indicate that the steam sterilization method at the tested exposure periods was very effective in reducing CFU levels while preserving the initial molecular biochemical composition of the treated inflorescences.