Whether blended into a smoothie, served as an ice cream topping, or accompanied by a pinch of sugar, strawberries are a worldwide fan favorite fruit. No matter the season, strawberries can be found at local farmers markets or in grocery stores and are notorious for their bright red color, fresh smell, and sweet, juicy taste. But, the next time you grab a container of strawberries from the local grocery store, think about the intensive agricultural methods and the associated pesticides involved in growing close to 10 million tons annually of this delicious fruit.
Every year, the Environmental Working Group creates the “Dirty Dozen,” a list of foods with the highest pesticide residue1 . Believe it or not, your beloved strawberries are at the top of that list! The U.S. Department of Agriculture tested produce samples from different fruits and vegetables and found that strawberries and spinach contained the highest amounts of pesticide residues2 . Strawberries specifically tested positive for 20(!) different pesticides2 .
The pest that is inflicting damage on your much-loved strawberries is the airborne fungus Botrytis cinerea, otherwise known as the cause of gray mold growth on numerous crops1 . Unlike strawberry farmers, vineyard owners welcome this fungus due to its ability to dry grapes on their clusters in order to create spectacular dessert wines1 . But due to the crop yield damage that B. cinerea typically causes, there is a world-wide push for improved cultivation solutions.
While a possible solution to B. cinerea is the application of fungicides, an alternative approach involving a mutualistic symbiosis between strawberries and bumblebees has emerged1 . In order to study this relationship, 16S rRNA gene analysis was conducted on microbial communities taken from pollen and flowers found on strawberries1 . The existence of gray mold disease was inversely correlated with the presence of Streptomyces, which exhibited strong antifungal activity against B. cinerea1 . This Streptomyces strain is also able to colonize the gut of bumblebees1 . Therefore, bees are able to transport the Streptomyces bacterium from strawberry plant to strawberry plant, thus spreading the antifungal activity against B. cinerea. In addition, Streptomyces strains have been shown to reduce B. cinerea incidence when sprayed on strawberries in a greenhouse. Only 12% of the sprayed plants were infected versus the 31% of the control plants1 . The Streptomyces bacterium carried by the bees also reduced the disease occurrence from 42% in the control versus 12% when treated with the bacterium1 . The most surprising fact from this study was that the Streptomyces strain was able to protect the pollinator bees against entomopathogenic bacteria including Paenibacillus larvae and Serratia marcescens. Thus, there is this mutualistic relationship between strawberries and bees that protects both from dangerous pathogens.
Even though conscious efforts are being made to decrease the fungal activity that is damaging strawberry cultivation, it is important for you, as consumers, to know about the food that you are eating. It is important to not only eat healthy foods, but also to understand the relationship between pesticide exposures and short- and long-term health effects.
References:
1. Zambrano, M. (2019) Strawberry Fields Forever. [online] Small Things Considered. Available at https://schaechter.asmblog.org/schaechter/2019/10/strawberry-fields-forever.html [Accessed 8 Jan. 2020].
2. Park, A. (2018) Strawberries Top the ‘Dirty Dozen’ List of Fruits and Vegetables with the Most Pesticides. TIME: Diet/Nutrition Available at https://time.com/5234787/dirty-dozen-pesticides/.
