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

Paul D. Mihalyov,Andrea R. Garfinkel

doi:10.3389/fagro.2021.720215

Paul D. Mihalyov, Andrea R. Garfinkel

Open Access

https://doi.org/10.3389/fagro.2021.720215

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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.

Highlights

IntroductionFollowing the passage of the 2014 and 2018 Farm Bills that federally legalized the cultivation of hemp-type cannabis, there are more than 100,000 acres grown across the United States (Olson et al, 2020)
Emerging nutraceutical markets have driven increased agricultural interest in Cannabis sativa (2n = 2X = 20), commonly known as hemp or marijuana, due to its suite of secondary metabolites including the cannabinoids tetrahydrocannabinolic acid (THCA) and cannabidiolic acid (CBDA)
Since G. spadiceus has recently been determined to be synonymous with G. ambrosiae (Qiu et al, 2020), we identify the causal organism of disease as the latter species

Summary

Introduction

Following the passage of the 2014 and 2018 Farm Bills that federally legalized the cultivation of hemp-type cannabis, there are more than 100,000 acres grown across the United States (Olson et al, 2020). While traditionally bred plant varieties take multiple years to develop, the sudden onset and continued growth of cannabinoid demand has prompted the need for rapid structuring of hemp population genetics suitable for commercial cultivation. Among the many research focuses deserving attention, one such priority should be identifying genetic markers linked to naturally occurring disease resistance, thereby accelerating the development of varieties which are less dependent on the use of pesticides in disease management. We address the widespread need for collaborative germplasm improvement strategies by outlining the fastest route (single-cross) for mapping genetic resistance to powdery mildew, one of the most prevalent fungal diseases in cannabis

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