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Development of powdery mildew on cannabis leaves. (a) Initial infections are visible as white colonies on the upper surface of leaves. (b) Scanning electron microscopic image through a cross section of a diseased leaf showing powdery mildew mycelium growing over the surface of epidermal cells. The underlying cells of the epidermis and mesophyll layer, and the lower epidermis, can be seen in this section. (c) Abundant spore production from an older powdery mildew colony on the leaf surface.
Source publication
Powdery mildew on cannabis (Cannabis sativa L., marijuana), caused by Golovinomyces cichoracearum, reduces plant growth and overall quality. To investigate disease management options, biological, chemical and physical approaches were assessed. A mildew-susceptible strain, ‘Copenhagen Kush’, was grown indoors with continual exposure to mildew inocul...
Contexts in source publication
Context 1
... symptoms of powdery mildew infection on cannabis leaves were quite apparent as white mycelial growth and sporulation of the pathogen on the upper surface of leaves on plants in the growing room (Fig. 1a). Under the scanning electron microscope, a cross-section through a leaf showed mycelial growth on the epidermal surface ( Fig. 1b), and sporulation was abundant on the leaf surface (Fig. 1c). The production of spores in chains is a characteristic of the genus Golovinomyces ( Pépin et al. ...
Context 2
... symptoms of powdery mildew infection on cannabis leaves were quite apparent as white mycelial growth and sporulation of the pathogen on the upper surface of leaves on plants in the growing room (Fig. 1a). Under the scanning electron microscope, a cross-section through a leaf showed mycelial growth on the epidermal surface ( Fig. 1b), and sporulation was abundant on the leaf surface (Fig. 1c). The production of spores in chains is a characteristic of the genus Golovinomyces ( Pépin et al. ...
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... on cannabis leaves were quite apparent as white mycelial growth and sporulation of the pathogen on the upper surface of leaves on plants in the growing room (Fig. 1a). Under the scanning electron microscope, a cross-section through a leaf showed mycelial growth on the epidermal surface ( Fig. 1b), and sporulation was abundant on the leaf surface (Fig. 1c). The production of spores in chains is a characteristic of the genus Golovinomyces ( Pépin et al. ...
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... of leaves from plants receiving four applications of Regalia Maxx and grown in an indoor environment had mean chlorophyll a levels that were significantly (P < 0.05) higher than leaves from untreated plants, while there was no significant difference in chlorophyll b levels between treated and untreated plants (Fig. 10a). The chlorophyll a/ b ratios for untreated and Regalia Maxx treated plants were 0.8 and 1.4, respectively. On plants grown in the greenhouse, there were significant (P < 0.05) differences between the mean levels of both chlorophyll a and chlorophyll b in Regalia treated leaves compared to untreated leaves (Fig. 10b). The chlorophyll ...
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... treated and untreated plants (Fig. 10a). The chlorophyll a/ b ratios for untreated and Regalia Maxx treated plants were 0.8 and 1.4, respectively. On plants grown in the greenhouse, there were significant (P < 0.05) differences between the mean levels of both chlorophyll a and chlorophyll b in Regalia treated leaves compared to untreated leaves (Fig. 10b). The chlorophyll a/b ratios for untreated and Regalia Maxx treated plants were 2.67 and 2.61, respectively. The total chlorophyll content in leaves was about three-fold higher in plants grown in the greenhouse compared with the indoor environment, likely due to differences in light intensity levels and growing ...
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... disease scores for 12 cannabis strains are shown in Fig. 11a. Seven of the strains had significantly lower (P < 0.05) disease scores compared to the five highly susceptible strains, suggesting they were resistant to infection. A comparison of disease development on leaves selected from strains 'Space Queen', 'Pennywise', and 'Sweet Durga Mata' is shown in Fig. ...
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... for 12 cannabis strains are shown in Fig. 11a. Seven of the strains had significantly lower (P < 0.05) disease scores compared to the five highly susceptible strains, suggesting they were resistant to infection. A comparison of disease development on leaves selected from strains 'Space Queen', 'Pennywise', and 'Sweet Durga Mata' is shown in Fig. ...
Citations
... This strategy has been used to reduce root pathogen development on various crops [2]. On the foliage, exposure of plants to ultraviolet radiation, especially UV-C light, can suppress powdery mildew development [43]. Night-time exposure enhances pathogen susceptibility by limiting light-activated DNA repair mechanisms [44]. ...
... During this phase of crop development, care must be taken to avoid damage to inflorescence tissues and to avoid visual quality changes. Products including Agrotek vaporized sulfur ® , Regalia Maxx ® , Suffoil-X ® and Milstop ® are registered to reduce powdery mildew development [43]. Sulfur is applied via vaporizing pots, a method that ensures uniform dispersal and is commonly used on many other greenhouse crops [31] while the remainder are applied as sprays. ...
... Silicon is effective against various bacterial, fungal, and viral pathogens and can strengthen cell walls via silicon deposits and also induce plant defense responses [115,116]. Scott and Punja [43] reported that multiple weekly sprays of potassium silicate, Silamol ® , on vegetative cannabis plants significantly reduced powdery mildew development. In contrast, a single application showed no effect in the current study. ...
The increased cultivation of high THC-containing Cannabis sativa L. (cannabis), particularly in greenhouses, has resulted in a greater incidence of diseases and molds that can negatively affect the growth and quality of the crop. Among them, the most important diseases are root rots (Fusarium and Pythium spp.), Botrytis bud rot (Botrytis cinerea), powdery mildew (Golovinomyces ambrosiae), cannabis stunt disease (caused by Hop latent viroid), and a range of microbes that reduce post-harvest quality. An integrated management approach to reduce the impact of these diseases/microbes requires combining different approaches that target the reproduction, spread and survival of the associated pathogens, many of which can occur on the same plant simultaneously. These approaches will be discussed in the context of developing an integrated plan to manage the important pathogens of greenhouse-grown cannabis at different stages of plant development. These stages include maintenance of stock plants, propagation through cuttings, vegetative growth of plants, and flowering. The cultivation of cannabis genotypes with tolerance or resistance to various pathogens is a very important approach, followed by the maintenance of pathogen-free stock plants. When combined with cultural approaches (sanitation, management of irrigation, and monitoring for diseases) and environmental approaches (greenhouse climate modification), a significant reduction in pathogen development and spread can be achieved. The use of preventive applications of microbial biological control agents and reduced risk biorational products can also reduce disease development at all stages of production in jurisdictions where they are registered for use. The combined use of promising strategies for integrated disease management on cannabis plants during greenhouse production will be reviewed. Future areas for research are identified.
... The use of pesticides against PM in cannabis could have health risks for the consumer, and alternative methods include environmental control and applications of rhizobacteria promoting plant growth [14,15]. Currently, several products to manage PM in cannabis are available, like the bio-fungicide Regalia Maxx (an extract of giant knotweed) [15] and lacto-fermented products [15], such as Cyclone. ...
... The use of pesticides against PM in cannabis could have health risks for the consumer, and alternative methods include environmental control and applications of rhizobacteria promoting plant growth [14,15]. Currently, several products to manage PM in cannabis are available, like the bio-fungicide Regalia Maxx (an extract of giant knotweed) [15] and lacto-fermented products [15], such as Cyclone. Despite these pest management strategies, PM is still one of the most relevant biological diseases for cannabis, and the discovery and characterization of PM resistance genes is crucial for improving the cannabis industry in a sustainable way [10]. ...
Powdery mildew (PM) is one of the most common Cannabis sativa diseases. In spite of this, very few documented studies have characterized the resistance genes involved in PM defense mechanisms, or sources of natural genetic resistance in cannabis. The focus of the present work is on the two primary mechanisms for qualitative resistance against PM. The first is based on resistance (R) genes characterized by conserved nucleotide-binding site and/or leucine-rich repeat domains (NLRs). The second one involves susceptibility (S) genes, and particularly mildew resistance locus o (MLO) genes, whose loss-of-function mutations seem to be a reliable way to protect plants from PM infection. Cannabis defenses against PM are thus discussed, mainly detailing the strategies based on these two mechanisms. Emerging studies about this research topic are also reported and, based on the most significant results, a potential PM resistance model in cannabis plant–pathogen interactions is proposed. Finally, innovative approaches, based on the pyramiding of multiple R genes, as well as on genetic engineering and genome editing methods knocking out S genes, are discussed, to obtain durable PM-resistant cannabis cultivars with a broad-spectrum resistance range.
... Cannabis includes genotypes whose origins are geographically very different [28], and this genetic diversity leads us to believe the existence of naturally occurring genotypes characterised by resistance to specific pathogens. Indeed, among 12 Cannabis genotypes evaluated, it was found that seven displayed partial or complete resistance to PM [29]. Furthermore, a recent study provided insight on the variability of Cannabis cultivars on disease resistance and cannabinoid accumulation over the course of crop maturation [30]. ...
Cannabis (Cannabis sativa L.) is one of the earliest cultivated crops, valued for producing a broad spectrum of compounds used in medicinal products and being a source of food and fibre. Despite the availability of its genome sequences, few studies explore the molecular mechanisms involved in pathogen defense, and the underlying biological pathways are poorly defined in places. Here, we provide an overview of Cannabis defence responses against common pathogens, such as Golovinomyces spp., Fusarium spp., Botrytis cinerea and Pythium spp. For each of these pathogens, after a summary of their characteristics and symptoms, we explore studies identifying genes involved in Cannabis resistance mechanisms. Many studies focus on the potential involvement of disease resistance genes, while others refer to other plants however whose results may be of use for Cannabis research. Omics investigations allowing the identification of candidate defence genes are highlighted, and genome editing approaches to generate resistant Cannabis species based on CRISPR/Cas9 technology are discussed. According to the emerging results, a potential defence model including both immune and defence mechanisms in Cannabis plant-pathogen interactions is finally proposed. To our knowledge, this is the first review of the molecular mechanisms underlying pathogen resistance in Cannabis.
... A positive correlation between this pathway and induction of resistance against Botrytis cinerea was previously reported in apple fruits ) and table grapes (Xu et al. 2019). Daily short exposures of cannabis plants to UV-C light were shown to reduce powdery mildew development (Scott and Punja 2021). Extended exposure of plants to UV can result in physical damage to tissues from irradiation and may increase Botrytis cinerea infection prevalence by causing injured tissues for pathogen colonization. ...
Botrytis cinerea is a widespread necrotrophic plant pathogen that causes diseases on >1000 plant species, including vegetables and ornamental greenhouse crops. On cannabis (Cannabis sativ a L.), the pathogen is responsible for causing “bud rot”, a major disease affecting the inflorescences (compound flowers), as well as seedling damping-off and leaf blight under certain conditions. During greenhouse cultivation, Botrytis cinerea can destroy cannabis inflorescences rapidly under optimal relative humidity conditions (>70%) and moderate temperatures (17–24 °C). Little is currently known about the host–pathogen interactions of Botrytis cinerea on cannabis. Information gleaned from other hosts can provide valuable insights for comparative purposes to understand disease development, epidemiology, and pathogenicity of Botrytis cinerea on cannabis crops. This review describes the pathogenesis and host responses to Botrytis infection and assesses potential mechanisms involved in disease resistance. The effects of microclimatic and other environmental conditions on disease development, strategies for early disease detection using prediction models, and the application of biological control agents that can prevent Botrytis cinerea development on cannabis are discussed. Other potential disease management approaches to reduce the impact of Botrytis bud rot are also reviewed. Numerous opportunities for conducting additional research to better understand the cannabis–Botrytis cinerea interaction are identified.
... Schmidt) Nakai) extract can reduce powdery mildew development. 20,34 Integrated pest management (IPM) strategies may be further supplemented with biological control via carnivorous arthropods. 35 Cranshaw et al. 18 discussed the prevalence of numerous predaceous arthropod taxa in the USA, albeit in outdoor industrial hemp crops; the effects of medical Cannabis's resin-rich trichomes on the activity of natural enemies still requires investigation. ...
Owing to the expanding industry of medical Cannabis, we discuss recent milestones in RNA interference (RNAi)‐based crop protection research and development that are transferable to medical Cannabis cultivation. Recent and prospective increases in pest pressure in both indoor and outdoor Cannabis production systems, and the need for effective nonchemical pest control technologies (particularly crucial in the context of cultivating plants for medical purposes), are discussed. We support the idea that developing RNAi tactics towards protection of medical Cannabis could play a major role in maximizing success in this continuously expanding industry. However, there remain critical knowledge gaps, especially with regard to RNA pesticide biosafety from a human toxicological viewpoint, as a result of the medical context of Cannabis product use. Furthermore, efforts are needed to optimize transformation and micropropagation of Cannabis plants, examine cutting edge RNAi techniques for various Cannabis–pest scenarios, and investigate the combined application of RNAi‐ and biological control tactics in medical Cannabis cultivation. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.
... Besides, Pasini et al. (1997) reported that potassium salts of fatty acid fungicides may exhibit a phytotoxicity on some crops, but no phytotoxicity was observed for the fungicide on hemp in this study. R. sachalinensis and potassium silicate fungicides have exhibited efficacy against different types of powdery mildew on various crops in multiple studies (Dallagnol et al. 2012;Ghanmi et al. 2004;Kanto et al. 2007;Kim et al. 2002;Margaritopoulou et al. 2020;Menzies et al. 1991;Scott and Punja 2021;Shetty et al. 2012). Our findings further support these initial reports. ...
Powdery mildew is a common disease of hemp in greenhouses in Tennessee. Fungicide efficacy data can support the use or approval of new fungicides. Therefore, two greenhouse experiments were conducted to assess the efficacy of nine commercial fungicides against powdery mildew. 'BaOx2' or 'Sweetened' hemp cultivars, which are susceptible to powdery mildew, were inoculated with a conidial suspension one day before or one or seven days after the first fungicide application. Two additional fungicide applications were made at 7-day intervals by thoroughly spraying the plants using a hand-held sprayer. Control plants were sprayed with water only. Weekly disease incidence and severity ratings were done three times. Disease index (DI) and the Area Under the Disease Progress Curve were calculated. All the fungicides significantly reduced powdery mildew symptoms. Compared to the control plants, disease reductions ranged from 76% to 100%. Bonide sulfur, Luna Experience, and MilStop exhibited "excellent" efficacy, reducing disease by 96% to 100%. Cinnerate, Exile, Regalia, and Sil-Matrix exhibited "very good" efficacy, reducing disease by 86% to 95%. Defguard and Stargus exhibited "good" efficacy, reducing disease by 76% to 85%. Koch's postulates were performed with the PM isolate used in this study. The isolate recovered following inoculation was found to be identical to the original isolate used in the experiments. The isolate was identified as Golovinomyces ambrosiae based on ITS, IGS, and β-tubulin sequencing and phylogenetic analysis with nucleotide sequences from closely related species. These findings provide useful information for the control of hemp powdery mildew and further research.
... This will not cause the total crop loss but affects the end use quality. The use of fungicide to control powdery mildew accommodates with controversies in regard to its efficacy and consumer response (Scott and Punja 2021). Other management strategies like usage of strong UV lights (Scott and Punja 2021) and growth-promoting rhizobacteria ) are also limited, because it yet becomes most prominent disease in both field and green house condition. ...
... The use of fungicide to control powdery mildew accommodates with controversies in regard to its efficacy and consumer response (Scott and Punja 2021). Other management strategies like usage of strong UV lights (Scott and Punja 2021) and growth-promoting rhizobacteria ) are also limited, because it yet becomes most prominent disease in both field and green house condition. Thus, the genetic resistance will provide greater potential for the growth and sustainability of cannabis industry. ...
Cannabis is the most versatile species. Hemp and marijuana have been used for fibre, oil, medicinal and recreational purposes from millennia. Throughout the last century, the plant has been generally outlawed because of its psychotropic effects in many nations. In recent past, the studies on cannabis revealed the evidence of its high medicinal properties and its uses in treating life threatening diseases, which leads to the relaxation of legislation in many counties. Now, the genetic and genomics as well as the cannabis derived products enjoys renewed attention. In this chapter, the discussion was made on the advent of genomics and breeding strategies to improve various traits of cannabis. This will bring insights on future direction of cannabis breeding.
... However, the pathology underlying the different infections is poorly understood, and disease management programs have not been fully established [22]. The growers may apply inorganic agents, for example, potassium bicarbonate, hydrogen peroxide, boric acid, orthosilicic acid or synthetic fungicides such as fluopyram, to moderate or eradicate fungal pathogens [23]. To avoid using chemicals, natural products such as seaweed extract, plant growth-promoting bacteria, humic substances, and chitin/chitosan derivatives have been used to increase product yield and promote plant defense to combat pests and diseases in other crops [24,25]. ...
Background
Plant growth devices, for example, rhizoponics, rhizoboxes, and ecosystem fabrication (EcoFAB), have been developed to facilitate studies of plant root morphology and plant-microbe interactions in controlled laboratory settings. However, several of these designs are suitable only for studying small model plants such as Arabidopsis thaliana and Brachypodium distachyon and therefore require modification to be extended to larger plant species like crop plants. In addition, specific tools and technical skills needed for fabricating these devices may not be available to researchers. Hence, this study aimed to establish an alternative protocol to generate a larger, modular and reusable plant growth device based on different available resources.
Results
Root-TRAPR (Root-Transparent, Reusable, Affordable three-dimensional Printed Rhizo-hydroponic) system was successfully developed. It consists of two main parts, an internal root growth chamber and an external structural frame. The internal root growth chamber comprises a polydimethylsiloxane (PDMS) gasket, microscope slide and acrylic sheet, while the external frame is printed from a three-dimensional (3D) printer and secured with nylon screws. To test the efficiency and applicability of the system, industrial hemp ( Cannabis sativa ) was grown with or without exposure to chitosan, a well-known plant elicitor used for stimulating plant defense. Plant root morphology was detected in the system, and plant tissues were easily collected and processed to examine plant biological responses. Upon chitosan treatment, chitinase and peroxidase activities increased in root tissues (1.7- and 2.3-fold, respectively) and exudates (7.2- and 21.6-fold, respectively). In addition, root to shoot ratio of phytohormone contents were increased in response to chitosan. Within 2 weeks of observation, hemp plants exhibited dwarf growth in the Root-TRAPR system, easing plant handling and allowing increased replication under limited growing space.
Conclusion
The Root-TRAPR system facilitates the exploration of root morphology and root exudate of C. sativa under controlled conditions and at a smaller scale. The device is easy to fabricate and applicable for investigating plant responses toward elicitor challenge. In addition, this fabrication protocol is adaptable to study other plants and can be applied to investigate plant physiology in different biological contexts, such as plant responses against biotic and abiotic stresses.
... Neem oil as an alternate control agent has proven to be efficient, including for powdery mildew. The neem oil reduced powdery mildew severity in rose (Ramos et al., 2020), garden pea (Mishra et al., 2017) and in Cannabis sativa L. of over 50% (Scott and Punja, 2020). Spraying neem oil on C. sativa with powdery mildew was also efficient and the results did not differ statistically from that fluopyram treatment (Scott and Punja, 2020). ...
... The neem oil reduced powdery mildew severity in rose (Ramos et al., 2020), garden pea (Mishra et al., 2017) and in Cannabis sativa L. of over 50% (Scott and Punja, 2020). Spraying neem oil on C. sativa with powdery mildew was also efficient and the results did not differ statistically from that fluopyram treatment (Scott and Punja, 2020). ...
Purple ipe (Handroanthus impetiginosus) is an important tree species in Cerrado biome conservation and very popular at the landscaping and urban afforestation. However, its micropropagation is affected by pathogens, such as Oidium sp. The aim this study was evaluate the efficiency of seed treatments in the control of powdery mildew of purple ipe obtained by micropropagation. The symptoms were observed during in vitro germination, a Koch’s postulates were performed for confirm the pathogenicity, colonization of the pathogen on the leaves was analyzed in optical and scanning microscopes and a scale to evaluate severity was proposed. Two experiments were realized to powdery mildew control using a completely randomized design, with 30 replicates. First experiment: Seeds were treated with ethanol (Et), chlorothalonil + thiophanate-methyl (C+TM), and sodium hypochlorite (NaOCl); second experiment: Seeds were treated with Et, NaOCl, C+TM, and neem oil. Disease severity and area under the disease progress curve (AUDPC) were assessed in both experiments. Disease symptoms and typical pathogen structures were observed, and the pathogenicity was confirmed. The disease severity was reduced by 30.78% in 1.5% neem oil for 10 min when compared with C+TM for 15 min. We conclude that neem oil can be a strategy sustainable for the control of powdery mildew in purple ipe in tissue culture.
... Therefore, eliminating or reducing the oxygen can retard the fungal growth during storage [108]. As well as poor drying and storing under humid conditions, this can promote microbial growth and toxins like aflatoxin and mycotoxin-producing strains of Aspergillus [109][110][111], as well as powdery mildew, Botrytis [106,[112][113][114], Cladosporium cladosporioides [115], Alternaria alternate [112], Verticillium [106,116], Salmonella [117], Enterobacter, Streptococcus & Klebsiella [118]. However, the best solution is to store medicinal Cannabis at a water activity level below 0.3, and 11% w/w moisture content can activate microbial activity [59,107,113]. ...
... Therefore, eliminating or reducing the oxygen can retard the fungal growth during storage [108]. As well as poor drying and storing under humid conditions, this can promote microbial growth and toxins like aflatoxin and mycotoxin-producing strains of Aspergillus [109][110][111], as well as powdery mildew, Botrytis [106,[112][113][114], Cladosporium cladosporioides [115], Alternaria alternate [112], Verticillium [106,116], Salmonella [117], Enterobacter, Streptococcus & Klebsiella [118]. However, the best solution is to store medicinal Cannabis at a water activity level below 0.3, and 11% w/w moisture content can activate microbial activity [59,107,113]. ...
The traditional Cannabis plant as a medicinal crop has been explored for many thousands of years. The Cannabis industry is rapidly growing; therefore, optimising drying methods and producing high-quality medical products have been a hot topic in recent years. We systemically analysed the current literature and drew a critical summary of the drying methods implemented thus far to preserve the quality of bioactive compounds from medicinal Cannabis. Different drying techniques have been one of the focal points during the post-harvesting operations, as drying preserves these Cannabis products with increased shelf life. We followed or even highlighted the most popular methods used. Drying methods have advanced from traditional hot air and oven drying methods to microwave-assisted hot air drying or freeze-drying. In this review, traditional and modern drying technologies are reviewed. Each technology will have different pros and cons of its own. Moreover, this review outlines the quality of the Cannabis plant component harvested plays a major role in drying efficiency and preserving the chemical constituents. The emergence of medical Cannabis, and cannabinoid research requires optimal post-harvesting processes for different Cannabis strains. We proposed the most suitable method for drying medicinal Cannabis to produce consistent, reliable and potent medicinal Cannabis. In addition, drying temperature, rate of drying, mode and storage conditions after drying influenced the Cannabis component retention and quality
