UV Light and Plant “Sunscreen”
Plants can produce many different types of “sunscreens”. Some of these sunscreens are physical, like trichomes, and some of them are chemical, like anthocyanins and beta-carotene. Trichomes are hair-like outgrowths found on the epidermis (skin) of many species of plants. Trichomes are reflective and can shield the plant from harmful UV rays. For this reason, UV radiation can increase the trichome density. Since THC is produced and stored in cannabis trichomes, UV light also increases THC content. If you want to learn more, we have a whole article dedicated to trichomes. Growers can use this response to their advantage by providing cannabis plants with small amounts of UV light to encourage their plants to grow more and larger trichomes.
The second type of “sunscreen” is chemical sunscreen. UV-A light increases anthocyanin content while UV-B light increases the amount of lycopene, beta-carotene, glycosides, and hydroxycinnamic acid derivatives3–5. While these sciency-sounding chemicals can act as sunscreens, they also play other roles. For example, anthocyanins give many plants a red-purple-blue color (think of blueberries and raspberries). Beta-carotene gives plants an orange color (think of carrots and yams). And many glycosides are responsible for giving our foods flavor and smell (think of wine!) Growers can capitalize on these plant responses to make vegetables look, smell, and taste better. For example, applying UV-A light to tomato fruits enhances the smell, acidity, and overall flavor of the ripe tomatoes6!
UV Light Reduces Fungal Growth
UV light can alter the DNA of all organisms – plants, humans, animals, and even fungi. Organisms exposed to UV light on a regular basis develop mechanisms for preventing and treating DNA damage, such as “sunscreens” and DNA repair enzymes. Some fungal pathogens have reduced or lost activity of these DNA repair enzymes10. Upon exposure to UV light, some fungal pathogens will accumulate so much DNA damage that they are incapable of reproducing and spreading. As growers, we can use this to our advantage, as plants are often the victims of fungal attack! For example, treating rose plants with a couple of hours of UV-B light reduces powdery mildew (PM) infection by up to 90%12! Researchers found that UV light prevented PM spores from germinating and surviving12. And it’s not just in roses: UV-B light also reduces the severity of PM in both strawberry and rosemary – by up to 99% compared to untreated controls11! UV-B light is effective against other types of fungal pathogens, such as Botrytis (Grey Mould)13, which commonly affects cannabis plants. UV light, particularly UV-B light can cause DNA damage to many organisms, including fungi. As growers, we can use UV-B light to our advantage to reduce the spread and severity of fungal invasions on cannabis plants.