Sick Mold

DEADLY FUZZ: Sclerotinia sclerotiorum forms a complex hyphal tissue called sclerotia coating a kidney bean plant (Phaseolus vulgaria).RASBAK/WIKIMEDIA COMMONSThe paper
X. Yu et al., “Extracellular transmission of a DNA mycovirus and its use as a natural fungicide,” PNAS, 110:1452-57, 2013.

The disease
The white mold caused by Sclerotinia sclerotiorum looks like a harmless cotton ball, but the fuzz can massacre more than 400 species of plants, including rapeseed, soybean, bean, potato, and carrot. S.sclerotiorum is estimated to cause upwards of $200 million in crop damage per year in the U.S., but an effective treatment is still out of reach.

The catch
Plant pathologists have fought similar fungal pathogens—most notably chestnut blight—using fungi-attacking viruses called mycoviruses. But scientists thought that mycoviruses couldn’t survive outside a fungal host, making it tricky to use them as fungicides—until now. Recently, Daohong Jiang, at the Huazhong Agricultural University in Wuhan, China, and colleagues found a mycovirus that has the ability to infect as “free particles,” outside of its host mold, which would make the antifungal viruses more useful to farmers.

The spread
Jiang and colleagues identified a DNA mycovirus that infects S. sclerotiorum, called SsHADV-1, which they suspected would be an efficient spreader due to its aggressive infection rate. They extracted the virus from infected mold and swabbed it directly onto plant leaves. They then inoculated the leaves with S. sclerotiorum and found that the mold became infected when it crept into the areas treated with the mycovirus.

The message
The research suggests these freely infecting mycoviruses could reveal strategies “for modifying other viruses that could be used for biocontrols,” says Donald Nuss of the University of Maryland, who was not involved in the study. Nuss says the finding could be applied in human infections, such as toenail fungus, as well.