Viruses and diseases have been wreaking havoc on the plant kingdom for centuries. With the advent of modern day agriculture, these pesky infections have been hosting, mutating, and growing more pervasively, especially with large scale agriculture and monocrop systems. Plant viruses and diseases such as latent bacterial or fungal pathogens can drastically impact overall plant health, yield, and vigor. To the eye, symptoms can be masked or camouflaged as falsely diagnosed nutrient deficiency, insect damage, or environmental stress. Often, growers don’t know they have infected hemp plants until it’s too late.
With the explosion of hemp cultivation across the country, we are beginning to see a host of viruses and viroids present in fields and indoor facilities. This is due to viral transmission. Analogous to how mammalian viruses are transmitted, plant viruses can be vectored in a secondary organism (such as an insect or bacterium) or be passed on by direct manual transfer. Transmission of virus can occur from insects such as fungus gnats or aphids but the most effective virus transmitters are actually humans. Poor sanitation, subpar stock management, or simply lack of knowledge pertaining to virus can all lead to plant virus transmission on a large scale.
Let’s run through a scenario. Say we are standing in a greenhouse at a cloning facility and there is one plant that has a virus or latent fungal infection (such as botrytis), and an employee is cutting the stock plants for vegetative propagation (cloning). Unfortunately, neither of these diseases have manifested any symptoms yet so we can’t tell which plants are infected and which ones are clean. We watch this employee trim and prepare the cuttings, moving from one stock plant to the next with the same pair of clippers without any standard operating procedure for sterilizing the clippers and her hands (hopefully she is wearing gloves). Due to the lack of sanitation and the highly adaptable virus and fungal pathogen, these diseases spread with ease through the stock plant population. These pathogens are mechanically transmitted from the dirty clippers into the open wound created by the employee’s dirty clippers. Now, not only are the stock plants potentially infected, but the same clippers were used to cut the clones that will now be delivered to the customer’s field in 4-5 weeks, meaning they have a high probability of also being infected.
But what about hemp seeds, can they also carry virus? The answer is an assured yes – we have seen multiple fields from seed with a range of viral infections. Some of these viruses appear to be aesthetic with mottling and yellowing of the leaves (and slightly decreased vigor), but other viruses become rampant into flower and affect bud development and yield. Just like vegetative propagation, seeds can get virus from using infected parent lines when breeding hemp seed.
The question becomes: how do you germinate, propagate, breed, and grow non-diseased plant material? The answer lies in testing and treatment. To determine if plants are “clean,” candidate plants need to be virus indexed and pathogen tested. This process can begin with a serological test, such as an Elisa Kit, which uses antibodies in a “lock and key” process to detect the presence of virus. More specific molecular diagnostic tools such as PCR and RT-PCR (Polymerase Chain Reaction and Reverse Transcription PCR) can be used for further testing to better detect and test for specific viruses, viroids, bacteria, and fungi. If a candidate plant has positive results of infection, the candidate can either be disposed of or remediated with treatments such as thermotherapy in tissue culture.
The saying is true, “bad in, bad out.” Once the plant is in your field, you can’t fix or cure a disease. It’s important to start with clean, tested stock to ensure the downstream clones or seed will perform to their full potential. With the burgeoning hemp industry, we will continue to see the rapid spread of disease not only across fields but also stock facilities and seed producers. It’s important to work with companies who understand these challenges and have protocols in place to virus index and pathogen index stock material – both for clonal propagation and seed production. It’s also important to note that even if you start with clean plants, virus can travel among fields through vectors such as insects. To learn about one such virus in citrus, click here.
Deciding on hemp plants for your field is one of the most important decisions you will make as a hemp farmer. After all, the plants you grow are the actual product (and potential profit) you will be either selling to a processor or vertically integrating into your own end product company. This decision needs to go beyond “which varieties do I grow?” to “are these plants or seeds healthy stock and how do I ensure this?” Ask lots of questions, do your due diligence, and make sure you are working with a trusted supplier. Not all hemp seeds or clones are created equal!