Gray mold, also known as Botrytis cinerea, is a scourge to more than 200 agricultural and ornamental plant species, including staples such as tomatoes, strawberries, snap and lima beans, cabbage, lettuce and endive, peas, peppers and potatoes.

Gray mold envelops its target in a velvety vise, releasing a toxin that poisons the host plants’ cells, eventually causing the plant to die, according to a new release.

So far, the only way to eliminate the pathogen is to spray plants with fungicides, which can be costly.

Now Brown University chemist David Cane, working with researchers in France and Spain, has figured out how the fungus’s deadly toxin is made and how it might be disarmed naturally.

The scientists have identified the set of genes that manufactures the toxin and, in particular, the central gene the fungus uses for this production.

They also have shown that shutting off this gene by interrupting the fungus’s DNA completely shuts down toxic production, removing the special weapon the mold uses to kill and invade target plant cells.

“It’s a big step to being able to disarm this toxin naturally through a combination of DNA sequencing and chemistry,” says Cane, who's based in Providence, R.I.

The researchers, led by French scientist Muriel Viaud, started by determining the complete DNA sequence for Botrytis cinerea.

Working with Spanish organic chemist Isidro Collado, the scientists focused on the chemical agent — botrydial — that gray mold uses to overwhelm host plants.
From among the roughly 9,000 genes present in gray mold, the researchers identified a cluster of five genes that is responsible for producing botrydial. They then sought to learn how this cluster manufactures the chemical agent and which of the genes was the mastermind.

The culprit is an enzyme called a sesquiterpene cyclase, Cane’s laboratory found.

In laboratory tests, Cane and the team introduced a mutant gene that deleted the sesquiterpene cyclase enzyme, which completely eliminted toxin production.

“This means that if you can inhibit the enzyme from this pathway, you can eliminate this toxin,” Cane says.

The team now is working on a similar procedure to tackle a strain of Botrytis cinerea that is able to produce both botrydial and a second toxin that it uses to attack its plant targets.

To subscribe to the print version of The Grower, click here.