The Fungus that Poses as a Flower

Mummy berry disease coats blueberry leaves with sweet, sticky stains that smell like flowers, luring in passing insects to spread fungal spores.

Ben Andrew Henry
Jan 31, 2017

STOWAWAYS: Fungal pseudoflowers, in the form of a chalky white coating on leaves, lure in pollinators to spread pathogenic spores to neighboring plants. ANRO0002/WIKIMEDIA COMMONS; S. H. McArt et al., PLOS ONE, 11:e0165761, 2016


The paper
S. H. McArt et al., “Floral scent mimicry and vector-pathogen associations in a pseudoflower-inducing plant pathogen system,” PLOS ONE, 11:e0165761, 2016.

Unwanted company
Shriveled, sickly white berries are an unwelcome sight on any blueberry farm, symptoms of a crop-wasting infection called mummy berry disease. Researchers recently profiled the modus operandi of the fungus responsible, Monilinia vaccinii-corymbosi (Mvc), uncovering a previously unappreciated tactic for spreading its spores.

Faking it
The fungus starts off as an airborne spore riding on the breeze, waiting to land on a new leaf of a blueberry plant. There, the spore multiplies and exudes a sticky, sugary, fragrant, spore-laden film, which is called a pseudoflower for its ability to attract insects. Visiting pollinators carry the spores to real flowers, giving the fungus the opportunity to invade nascent fruits that eventually shrivel, fall to the ground, and crack open to release more spores to the wind.

Tools of the con
The adaptive role of the pseudoflower has not been clear, says Cornell University ecologist Scott McArt. Other fungal pseudoflowers fall into two categories: some mimic their host flower, while others form their own, unique kind of flower. To draw the distinction, McArt and his colleagues analyzed the volatile compounds responsible for the Mvc pseudoflower’s scent and discovered a close match to those released by actual blueberry flowers. “The degree of the mimicry is pretty extraordinary,” says University of Oregon ecologist Bitty Roy.

Aiding and abetting
A genetic analysis found Mvc fungal DNA on 56 percent of bees and wasps and 31 percent of flies captured, implicating them as spore vectors. But behavioral data on the preference for infected versus uninfected plants was equivocal, leaving the insects’ exact roles to be quantified in future field studies.