Discovery and Genetic Mapping of PM1, a Powdery Mildew Resistance Gene in Cannabis sativa L.

Abstract

Powdery mildew is among the most common diseases of both hemp- and marijuana-type cultivated Cannabis sativa. Despite its prevalence, no documented studies have characterized sources of natural genetic resistance in this pathosystem. Here we provide evidence for the first resistance (R) gene in C. sativa, represented by a single dominant locus that confers complete resistance to an isolate of the powdery mildew pathogen Golovinomyces ambrosiae, found in the Pacific Northwest of the United States. Linkage mapping with nearly 10,000 single nucleotide polymorphism (SNP) markers revealed that this R gene (designated PM1) is located on the distal end of the long arm of one of the largest chromosomes in the C. sativa genome. According to reference whole genome sequences and Sanger sequencing, the marker was tentatively placed in a cluster of R genes of the nucleotide-binding site (NBS) and leucine-rich repeat (LRR) protein type. PM1's dominant behavior, qualitative penetrance, and a co-segregating qPCR marker to track its inheritance were confirmed in two separate genetic backgrounds totaling 185 recombinant F1 plants. The goal of this study is to provide a foundation for the discovery and characterization of additional sources of genetic resistance to pathogens that infect C. sativa.

Integrated Management of Pathogens and Microbes on <em>Cannabis sativa</em> L. (Cannabis) under Greenhouse Conditions

“…The utility of disease-tolerant genotypes that may have been developed through selective breeding and genotype screening is an important aspect of IDM for stock plants. Diseasetolerant genotypes of cannabis have been identified for a number of pathogens, including root rot (Fusarium oxysporum) [23], powdery mildew (Golovinomyces ambrosiae) [10][11][12]32], leaf blight (Neofusicoccum parvum) [33], and bud rot (B. cinerea) [34,35] (Figure 8). Recent research suggests that specific defense genes may play a role in certain host-pathogen interactions, leading to a resistant phenotype [11][12][13]36].…”

“…Diseasetolerant genotypes of cannabis have been identified for a number of pathogens, including root rot (Fusarium oxysporum) [23], powdery mildew (Golovinomyces ambrosiae) [10][11][12]32], leaf blight (Neofusicoccum parvum) [33], and bud rot (B. cinerea) [34,35] (Figure 8). Recent research suggests that specific defense genes may play a role in certain host-pathogen interactions, leading to a resistant phenotype [11][12][13]36]. The impact of cannabis genotype on disease development at the flowering stage will be discussed later in this review.…”

“…Consequently, some high-yielding genotypes frequently show high susceptibility to various pathogens, as will be illustrated in this review. Fortunately, the broad genetic variation that currently exists among cannabis genotypes has led to the identification of resistance in various genotypes to specific pathogens, such as powdery mildew [6,[10][11][12]. The mechanisms underlying this resistance are currently under investigation [13].…”

Hemp Genome Editing—Challenges and Opportunities

“…Targeting resistance (R) and susceptibility (S) genes are one way to increase a plant's resistance. A recent study has identified a powdery mildew resistance (R) gene in a Cannabis sativa cultivar, designated PM1, that confers resistance to the pathogen Golovinomyces ambrosiae (Mihalyov and Garfinkel, 2021). Improving food quality of seed and seed oil is also possible.…”

Genome-Wide Characterization of the MLO Gene Family in Cannabis sativa Reveals Two Genes as Strong Candidates for Powdery Mildew Susceptibility

“…Since a similar situation has been observed between hop (Humulus lupulus, the closest relative of cannabis) and Podosphaera macularis (Henning et al, 2011), it is likely that such gene-for-gene interactions exist between cannabis and PM. Indeed, the first gene conferring complete resistance to an isolate of PM has recently been identified in cannabis (Mihalyov and Garfinkel, 2021). In grapevine, resistance is usually considered polygenic, and there appears to be a diverse range of responses to invasion by Erysiphe necator, from penetration resistance to the induction of plant cell death (Feechan et al, 2011).…”