"A major issue with cannabis pathogens is that you sometimes don't see them until it's too late," says Veronica Codesido, Co‑founder and Manager of Cultivation of MIFCO Biosciences. In her presentation at Cannabis Business Europe, Veronica goes over some of the major cannabis pathogens, what growers should look out for, and how to prevent or control pathogens.
Antonio Sancho Lopez and Veronica Codesido Sampedro of MIFCO Biosciences
Fungi
So what are some of the most harmful cannabis pathogens? First of all, Veronica explains that harmful fungi species can cause serious problems for cannabis plants. "These fungi can infect the plants and cause diseases, leading to reduced growth, yield, and low quality of the final product. They can appear in the seeds, leaves, roots, stems, and flowers." Examples of pathogens affecting the roots are Fusarium, Pythium myriotylum, and Rhizoctonia.
Powdery mildew is an important fungus pathogen affecting the leaves. "This can affect plants at all stages of growth, and the symptoms can be seen on leaves, flowers, and occasionally on stems. The pathogen appears as white powdery patches. Infection may cause leaves to turn brown and drop prematurely, plants may also be stunned, with poor quality flowers."
Botrytis cinerea is a fungus pathogen affecting the buds. "Buds affected by botrytis initially appear soft and discolored. As symptoms progress, buds may turn crisp and brown. Under high humidity, the pathogen will produce grey mold. Most infections take place during the early fall and winter seasons, and only rarely during the warm summer months."
Bacteria
Plant pathogenic bacteria cause many different kinds of symptoms that include galls and overgrowths, wilts, leaf spots, specks and blights, soft rots, as well as scabs and cankers, Veronica explains. In contrast to viruses which are inside host cells, walled bacteria grow in the spaces between cells and do not invade them.
Viruses
Plant viruses can be transmitted by an assortment of vectors, through contact with an infected plant's sap, by a living organism, for example, insects and nematodes, and through pollen. "At the point when plant viruses are transferred between various plants, this is known as horizontal transmission, and when they are inherited from a parent, this is known as vertical transmission."
What are some of the most important viruses? "First of all, lettuce chlorosis virus, which leads to a failure to thrive. This failure is caused by the plant not being able to absorb as much sunlight as it would typically need, restricting its growth." Also, the tobacco mosaic virus is a major one. "Although there are no documented cases of TMV infecting cannabis, many growers suspect TMV in plants that develop a mosaic-like pattern of discoloration on the leaves."
According to Veronica, hop latent viroid is the smallest but worst cannabis pathogen." It's a big problem as it could be in your crop for generations without you knowing it. Symptoms are stunted growth, poor development of flowers, and poor rooting of clones. Also weaker stems, reduction of trichomes, and reduction in yield."
What is the solution?
How can growers prevent and control all those pathogens? Veronica shares some tips. "It's important to protect your plants from people and to sterilize surfaces, equipment, and planting media. You should also remove plant debris and sick plants. On top of testing regularly and replacing mother plants frequently, adequate distance should also be maintained between plants."
Veronica explains that meristem in vitro culture is a solution to clean your plants. "Tissue culture removes pathogens from contaminated strains, avoids degradation of strains, and ensures disease-free plants. In fact, a meristem culture is a tool for producing virus-free clones that can be further multiplied at a commercial scale to produce certified virus-free plants. This is because the apical dome region has no vascular connection to the developing procambium, leaf primordium, and axillary buds. This lack of vascular connection provides a basis for using the meristem for pathogen elimination, as viruses readily travel through the vascular system but do not efficiently transfer from cell to cell. Uninfected cells can be isolated from the meristematic dome."
For more information:
MIFCO Biosciences 
www.mifcobiosciences.com