Botrytis cinerea, out of all the fungi on the planet, is the one that keeps farmers awake at night. This gruesome fungus is omnivorous. The fungus will happily eat hundreds of plant species, although it prefers soft fruits such as grapes. It covers everything with a thick layer of mold. If you have ever put a tub of strawberries in the fridge for too long only to return to find them looking gray-green, it is likely that one of the Botrytis spores floating through the air made its permanent home in your dessert.
Botrytis is a problem for the food industry. A spoiled dessert can be a real pain. Each year, this single species of fungus causes at least $10 Billion in crop damage. The figure could be as high as $100 trillion according to some estimates. It is so problematic that plant pathologists ranked it second in the most important plant fungal disease. This can only be described by TIME magazine's "Most Influential Persons" list. Magnaporthe Oryzae, a fungus that destroys rice fields around the world, took the top spot.
Mark Singleton is the head of plant health and animal health at GreenLight Biosciences in Massachusetts. He's working on a new type of sprays to protect farmers from Botrytis and other pests. There are many downsides to existing pesticides and fungicides. They can cause environmental damage and buildup, and can also lead to resistance in pests and weeds. Singleton is trying to find a solution. Singleton's starting point is RNA, a molecule that is similar to DNA and is one of the most fundamental building blocks of human life.
The new generation of pesticides is built on a cell trick that goes back over a billion years. It was discovered by the last common ancestor, which includes animals, plants, fungi and protists. Cells were able to destroy the genetic material of pathogens like viruses at some point in their history. We don't know when exactly. A cell will hack up double-stranded DNA (dsRNA), which is the genetic code used by viruses to reproduce themselves. These dsRNA chunks are tiny wanted posters. The cell's molecular cells pick up these dsRNA fragments and use them to search for matching messenger RNA (mRNA). These molecules are used by the cell to convert genetic instructions into protein. The cell will be able to stop the molecular bad guys from getting chopped up before they can begin being made into proteins.
Two scientists were awarded the Nobel Prize in Physiology or Medicine 2006 for their discovery of RNA interference (RNAi). This discovery sparked an international race to create new tools. Scientists quickly realized that you could insert dsRNA into any pesky pathogen, such as a particularly irritating fungus. This would instruct the pathogen's cells not to make crucial proteins and destroy its mRNA. They could also switch off pathogen genes at will. "We are just going in there looking at the orchestral of genes and proteins and we're silence the violins. "That's all that we do," Michael Helmstetter, chair at RNAissance Ag (another startup attempting to bring RNA crop-sprays to market), said.
A few RNA sprays have already been developed. RNAissance Ag is currently working on a spray to target the diamondback moth. This pest has an insatiable appetite and has developed some resistance to common pesticides. The Environmental Protection Agency is currently evaluating a GreenLight Biosciences RNA spray that targets the Colorado potato beetle. The company expects to make a decision about that spray in the middle of 2022. It is also developing a Botrytis spray and a Varroa mite spray to combat the widespread insect that infects honeybees. GreenLight has completed initial laboratory tests and is now testing the Botrytis spray against grapes in California as well as strawberries in Italy. Singleton said that they are interested in finding out how the spray sticks to plants, and how it compares with chemical fungicides.
The potential benefits of RNA crop sprays over chemical-based pesticides are significant. The problem of environmental buildup is reduced by microbes that can quickly break down RNA in soil. Because RNA sprays target specific genes, there is a lower chance of other organisms getting caught in the crossfire. Clauvis N.T. Taning, a postdoctoral researcher at Ghent University, Belgium, believes that even two closely related species can have enough genetic differences to be able to create RNA sprays that target one bug and leave the rest.
