A new study published in Scientific Reports has provided the first detailed transcriptomic picture of how cannabis plants respond to infection by Sclerotinia sclerotiorum, the fungal pathogen responsible for white mold disease. Using dual RNA sequencing, researchers simultaneously tracked gene expression changes in both the plant and the pathogen during the infection process, offering a level of molecular detail that was previously unavailable for this crop-disease interaction.
White mold has emerged as a significant concern for cannabis producers, particularly in greenhouse environments where the dense canopy and high humidity that cannabis requires also create ideal conditions for S. sclerotiorum. Understanding how the plant defends itself, and how the pathogen overcomes those defenses, opens new avenues for management.
How the Study Was Designed
Dual RNA sequencing is an approach that extracts RNA from infected tissue and sequences it all at once, capturing transcripts from both the host plant and the pathogen. Bioinformatic pipelines then separate the reads, mapping plant transcripts to the cannabis genome and pathogen transcripts to the S. sclerotiorum genome.
This allows researchers to see which plant defense genes are activated (or suppressed) during infection, and simultaneously which virulence genes the pathogen is deploying. The result is a dynamic picture of the molecular conversation between host and pathogen.
The study sampled infected cannabis stems at multiple time points after inoculation, tracking the progression from initial colonization through full lesion development.
Key Findings
The research identified several important themes in the cannabis response to Sclerotinia. Early in infection, the plant upregulated genes associated with pathogen recognition and signal transduction, including receptor-like kinases and WRKY transcription factors. These are part of the plant’s innate immune system, and their activation indicates that cannabis does detect and respond to Sclerotinia invasion.
However, the pathogen proved effective at overcoming these defenses. S. sclerotiorum deployed an arsenal of cell wall-degrading enzymes, oxalic acid biosynthesis genes, and effector proteins that suppressed host immunity. The study showed that certain plant defense pathways were initially activated but then suppressed as the infection progressed, suggesting that the pathogen actively manipulates host gene expression.
Genes associated with secondary metabolite production, including cannabinoid and terpene biosynthesis pathways, were also affected by infection. This is relevant for producers because it suggests that Sclerotinia infection may alter the chemical profile of surviving plant tissue, potentially affecting product quality even in plants that are not completely destroyed.
Practical Implications for Growers
While transcriptomics research does not directly translate into tomorrow’s management decisions, several practical implications emerge from this work.
First, the finding that cannabis does mount an immune response to Sclerotinia, even if it is ultimately overcome, suggests that genetic variation in defense gene expression could be exploited in breeding programs. Identifying genotypes with stronger or more sustained immune responses could lead to varieties with improved tolerance to white mold.
Second, the pathogen’s reliance on oxalic acid as a virulence factor has practical management relevance. Oxalic acid lowers the pH of host tissue, facilitating cell wall degradation and suppressing oxidative burst defenses. Management strategies that reduce oxalic acid’s effectiveness, including the biological control agent Coniothyrium minitans (marketed as Contans WG), target this specific vulnerability.
Third, the impact on secondary metabolite pathways reinforces why early detection and prevention are more valuable than tolerating some level of infection. Even if a plant survives Sclerotinia attack, the quality of the harvest may be compromised.
Detection and Monitoring
Effective Sclerotinia management starts with monitoring. The pathogen produces sclerotia, hard, black survival structures that persist in soil and on plant debris for years. Scouting for sclerotia in growing media and on the soil surface around production areas can reveal inoculum sources before they cause problems.
During the growing season, white cottony mycelial growth on stems and inflorescences is the hallmark symptom. Infections typically start at stem nodes or where canopy density creates persistent moisture. Environmental monitoring that tracks humidity and temperature within the canopy can help predict infection risk.
For broader pathogen monitoring programs, tools like AmplifyRP XRT platforms demonstrate the type of rapid molecular diagnostics that can be integrated into routine quality assurance programs. While specific Sclerotinia diagnostic kits may vary, maintaining a comprehensive pathogen testing program helps catch problems early.
Cannabis producers should also be testing for hop latent viroid as part of their routine monitoring, since HLVd-infected plants may be more susceptible to secondary infections including white mold due to their compromised vigor.
Integrating These Findings Into IPM
The transcriptomic data from this study will be most valuable when integrated into a comprehensive integrated pest management (IPM) framework. For cannabis white mold, this framework should include environmental management (reducing humidity, improving air circulation), biological controls (Coniothyrium minitans, Trichoderma species), cultural practices (pruning lower canopy to improve airflow, removing infected tissue promptly), and eventually genetic resistance as breeding programs advance.
The molecular insights from this research also open the door to more targeted screening tools. As the specific host-pathogen interactions are characterized at the gene level, diagnostic assays that detect active infection or predict disease susceptibility become possible. This is still in the future, but the foundational science is now in place.
For cannabis producers managing white mold today, the core principles remain prevention, early detection, and integrated management. This new research gives us a much deeper understanding of why those principles work at the molecular level, and it points the way toward more sophisticated management tools in the years ahead.
