The 5 Creepiest Ways Plant Diseases Mutate Flowers

By Elizabeth Preston | February 25, 2014 10:10 am

Lychnis_viscaria0

Pretty blossoms aren’t immune to the body-morphing, plague-spreading powers of a good microbe. Some of the flowers you admire on a spring day might only be blooming, for example, because they’re hostages of a disease. Plant diseases can’t scatter in sneeze droplets like a human virus can. But they can change the look and behavior of their hosts to make sure they travel as widely—and dangerously—as possible.

1. Replacing pollen with disease bombs

In a new review of flower diseases (title: “Arranging the bouquet of disease”), Scott McArt of the University of Massachusetts at Amherst and his colleagues examined the ways that infectious microbes can alter their host plants. One such microbe is a fungus called Microbotryum violaceum, which infects plants in the carnation family.

Plants are infected with the fungus when pollinating insects visit, carrying spores another infected plant has dusted onto their bodies. The fungus burrows down into the new plant, finds the site of developing pollen, and destroys it. Then it replaces the flower’s packets of pollen with its own spores.

2. Growing fake flowers

Another fungus, called “mummyberry,” infects blueberry plants and turns their fruits into pale, shriveled carcasses. But it doesn’t stop there. Infected shoots of the plant grow grayish spots at their tips that reflect UV light, smell like flowers, and leak sugary liquid. Pollinators that are attracted to these “pseudoflowers” will pick up more infectious spores on their bodies.

3. Impersonating a neighbor

When yet another fungus infects Drummond’s rockcress, a North American wildflower, that plant produces pseudoflowers too. But instead of “blooming” when a healthy plant’s flowers do, these pseudoflowers emerge at the same time that a similar-looking ranunculus species blooms. Infected rockcress plants that are growing close to ranunculus flowers receive more visits from pollinating insects—which add up to more opportunities for the disease to spread.

4. Luring bees and birds with sweets

Plants that are weakened by fighting a disease sometimes produce smaller flowers and less nectar than usual. But several kinds of fungus can make plants grow pseudoflowers that have lots of artificial nectar, tempting their pollinators. Once an insect visitor arrives, it will find that this sugary liquid is spread over the surface of the pseudoflower, instead of concentrated in one spot like a real flower’s nectar. This means the insect has to crawl all over the place to get its reward—staying in contact with the pseudoflower for even longer.

These false flowers may smell like their host’s real flowers. They may even mimic the smell of insect pheromones. Hitching a ride to a new host is how a disease survives, so attracting insects (and getting them to linger) is crucial to the fungus.

5. Forcing a host to stay open all the time

When the fungus M. violaceum infects Viscaria vulgaris, the sticky catchfly (pictured above), the plant’s flowers open earlier than usual and stay open for longer. This attracts extra pollinating insects, which then carry the disease away and spread it elsewhere. (Later in the flowering season, when insects are more experienced, they seem to avoid infected blooms.) In a Mexican flowering shrub called Moussonia deppeana, infection by another fungus makes flowers stay open for two days longer than healthy flowers. This leads to increased visits from that flower’s pollinators, hummingbirds. In general, the authors write, infections make plants produce more flowers.

But plants have ways of fighting back. Reducing the size and scent of their flowers can lower their odds of infection. So can growing smaller, less attention-grabbing blooms. Of course, shrinking flowers too much would keep a plant from getting pollinated at all. So blossoms must strike a balance: attracting the attention of their pollinators while avoiding attention that will kill them.


Image: Viscaria vulgaris by Kurt Stüber (via Wikipedia)

McArt SH, Koch H, Irwin RE, & Adler LS (2014). Arranging the bouquet of disease: floral traits and the transmission of plant and animal pathogens. Ecology letters PMID: 24528408

  • epreston8

    Thanks to Malcolm Campbell for pointing out that the title of this piece could be misleading, because geneticists use “mutate” strictly to mean “change the DNA of.” Here I’m using it in the more casual sense of “transform (in a freaky way).” The fungi in the story are only changing the flowers superficially, not (as far as I know) altering their genes. –EP

  • usarian

    >>”But plants have ways of fighting back. Reducing the size and scent of their flowers can lower their odds of infection. So can growing smaller, less attention-grabbing blooms”

    Pet Peeve #37 – personification of evolutionary processes. Flowers do not CHOOSE to “fight back”, it’s that there are a large number of flowers and the ones that coincidentally happen to fall into this optimum size zone statistically fail to receive as many visits.

    You may as well be saying stones can fight back against the plague of children skipping them across lakes by being jagged and uneven.

    • Defiant

      I had the same thought…however…if you have enough pet peeves for a list of at LEAST 37 items…I think you should switch to decaf…
      (joke)

    • David Mowers

      Can they not? Can not a stone escape drowning by some chance twist of fate catching its more polished and flatter side against the tension of the waters surface and bouncing it along until it gently glides to the opposing shore and rolls to a stop in the wettened ground?

      …and the epic battle between little boys and rocks wages on!

      “Oh rock! Was it thy painful drop upon my toe or flattened sides found on you that made me hate you while loving you and then did I cast away and drown my lovely grey thus sunk below on that fateful day?”

      “Rock!”

      “Why do you pain me so?”

  • Doc Lem

    All plants must now sign up for Obama-care or else!

  • Defiant

    I know a few women who operate this way…

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Inkfish

Like the wily and many-armed cephalopod, Inkfish reaches into the far corners of science news and brings you back surprises (and the occasional sea creature). The ink is virtual but the research is real.

About Elizabeth Preston

Elizabeth Preston is a science writer whose articles have appeared in publications including Slate, Nautilus, and National Geographic. She's also Editor of the children's science magazine Muse, where she frequently writes in the voice of a know-it-all bovine. She lives in Massachusetts. Read more and see her other writing here.

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