Dark Heart Nursery identifies new pathogen, creates patent-pending process for testing and eliminating cannabis "dudding".



Research Started in 2017, with 31 Varietals Cured To Date

Project Lead Dr. Jeremy Warren Joins Dark Heart Nursery as Director of Plant Health

OAKLAND, Calif., (March 4, 2019) — Dark Heart Nursery (DHN) proudly announced today that it is the first organization to positively identify hop latent viroid (HpLVd), previously identified as Putative Cannabis Infectious Agent (PCIA), as the cause of “dudding” in cannabis. Since 2018, DHN has also been successfully testing for and eliminating HpLVd through a patent-pending clean plant process.

On the heels of this groundbreaking completed research, the company has also announced that project lead Dr. Jeremy Warren has officially joined DHN as Director of Plant Health.


“The positive identification of the HpLVd pathogen and our patent-pending clean plant process to test for and eliminate it represents a significant advance towards keeping cannabis crops healthy and supporting long-term business growth for cultivators,” said Dan Grace, Founder and President of Dark Heart Nursery. “With Dr. Warren at the helm, we are incredibly excited to now offer diagnostic and curative services for HpLVd to licensed cannabis businesses in California, as well as continue our research in identifying and eradicating additional cannabis-infecting pathogens.”


“Dudding” is a colloquial name for a variety of symptoms, which include loss of vigor, stunting, reduction in yield, reduction in potency and changes in morphology. The syndrome was codified in 2017 by Dr. Rick Crum who first coined the phrase “Putative Cannabis Infectious Agent” (PCIA) to describe it. In 2015, Dr. Crum reported that as many as 35% of observed plants showed PCIA symptoms.


In 2017, Dark Heart Nursery began working with Dr. Warren to determine the cause of PCIA.  Symptomatic and asymptomatic plants were collected, and next-generation RNA sequencing was performed to determine a probable cause of the disease. After analysis of the results in November 2017, it was determined that Hop latent viroid (HpLVd) was the most likely candidate pathogen. A genetic test was then developed to aid in differentiating healthy plants from infected plants.


“It is important to note that finding a potential pathogen within a plant was only the first step in determining if the pathogen is indeed causing the disease in question,” said Dr. Warren. “To demonstrate causality, healthy plants were inoculated with an infectious clone of HpLVd to confirm that the developed symptoms were consistent with PCIA. Our team monitored these infected plants, as well as controlled (healthy) plants for three months to track symptom development. After this time, it was apparent that the HpLVd-infected plants were showing symptoms consistent with PCIA, such as yellowing of leaves, malformed leaves, and stunted growth. These results confirmed that HpLVd is causing PCIA symptoms in cannabis.”



In 2014, DHN established the cannabis industry’s first tissue culture laboratory. Among other areas of research, this lab has focused on the development of clean plant protocols through which cannabis can be cured of pathogens and cataloged for later use. Under the leadership of Research Manager Will Roberts, the company developed a patent-pending clean process, which is capable of reliably eliminating HpLVd from infected specimens. For the last year, Dr. Warren’s discovery and subsequent diagnostic tests have allowed DHN’s lab team to reliably and demonstrably eliminate HpLVd. To date, 31 varietals have been cured of the disease.



Dark Heart Nursery is one of California’s oldest and most respected cannabis nurseries. Based in Oakland, California, the company employs 63 staff members at three locations and focuses on producing ultra-high-quality pest and disease-free plants. Dark Heart Nursery also invests substantially in research, plant genetics and pathology to ensure its customers are always afforded the best chance of success. For more information visit darkheartnursery.com


Dark Heart Nursery is now offering diagnostic and curative services for HpLVd to licensed cannabis businesses throughout California. It is likely that there are other unidentified pathogens which infect cannabis; DHN’s team is available to identify suspect pathogens on a contract basis. DHN’s team is also available for general consulting engagements. Interested parties should contact Melanie Nash at melanie@darkheartnursery.com.



Dr. Jeremy Warren received his B.S. degree in biochemistry from the University of California at Davis in 2000 and his Ph.D. in Plant Pathology from the University of California at Davis in 2015. He pursued postdoctoral research at the University of California at Davis and has over 20 years of experience in the field of plant pathology. He recently accepted a position at Dark Heart Nursery as Director of Plant Health.



Will Roberts has a B.S in Soil Science from Humboldt State University and a M.S. in Environmental Management from the University of San Francisco. He has over a decade of agricultural research experience and has been with Dark Heart Nursery since 2012, including nearly five years of experience in cannabis tissue culture.



Hop latent viroid (HpLVd) was first characterized in Humulus lupulus (hop) plants (Putcha et al. 1988). The initial research suggested it was a minor pathogen in hops; however, recent research has shown that infection with HpLVd can have a significant impact on yields and secondary metabolite production (Adams et al. 1991, Barabra et al. 1990, Matousek 1994). These yield and metabolite impacts seem to be even more pronounced in cannabis. If plants are showing symptoms of HpLVd infection, there are a few actions to consider. Always remove infected plants from the growing area to prevent spread. HpLVd, like many viroids, has been shown to be primarily mechanically transmitted, so strong nursery sanitation protocols are necessary when pruning and processing plants. The secondary means of HpLVd transmission are not yet fully understood. However, other viroids in the Cocadviroid genus have been shown to be pollen and seed transmissible. This suggests that HpLVd may also be transmitted in a similar manner, but further study is required. Insect transmission of viroids is also still being studied. Cannabis plants can be carriers for HpLVd without showing any outward symptoms of the disease. For this reason, it is important to test all the plants in a mother block for HpLVd infection and to purchase clean plant materials whenever possible. Although the company’s work did not include any hemp varietals, it is highly likely that HpLVd also impacts that crop.



A.N. Adams, D.J. Barbara, A. MortonEffects of hop latent viroid on weight and quality of the cones of the hop cultivar Wye Challenger

Ann. Appl. Biol., 118 (1991), pp. 126-127


D.J. Barbara, A. Morton, A.N. Adams, C.P. GreenSome effects of hop latent viroid on two cultivars of hop (Humulus lupulus) in the UK

Ann. Appl. Biol., 117 (1990), pp. 359-366


  1. Matoušek, L. Trnĕná, P. Svoboda, P. RůžkováAnalysis of hop latent viroid (HLVd) in commercial hop clones in Czech Republic

Rostlinná výroba, 40 (1994), pp. 973-983


  1. Puchta, K. Ramm, H.L. SängerThe molecular structure of hop latent viroid (HLV), a new viroid occurring world-wide in hops

Nucleic Acids Res., 16 (1988), pp. 4197-4216

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