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Courtesy of The University of Tennessee, Knoxville.

The birds and the bees are amazing. Not the proverbial kind – but the actual birds and bees that pollinate plants and helped make that juicy pear you bought at the farmer’s market last weekend. About 87 percent of the world’s flowering plants depend on pollinators– like birds and bees – for sexual reproduction. This probably makes you imagine a beautiful, harmonious scene with blue skies and a perfect ending, like that pear. However, pollination can have a darker side. It turns out any organism that uses sex to reproduce can contract and spread venereal diseasesThat’s right, even plants. How are STDs spread in plants? The birds and the bees are the answer, literally and proverbially. 

While some diseases may be transmitted by wind pollination, they are mostly spread via animal and insect pollinators. Because they travel near and far in search of nectar and pollen, bird and insect pollinators make the perfect carriers for the bacterial and fungal diseases that infect plants. Because most plant STDs are not contagious to birds or insects, pollinators act as vectors and merely carry the disease from plant-to-plant. When a plant is contaminated with an STD, its nectar, pollen or leaves contain the infection. When pollinators make contact with nectar, pollen or leaves, they then carry and spread the infection. Once a plant is infected, all its seeds also carry the disease. So, plants become contagious when they are just wee seedlings!

Plant STDs are relatively understudied in the world of science,but three of the best-knownare anther smut (a fungal disease), bud blight (a virus), and fire blight (a bacterial disease). Anther smut is spread to and from plants by insect pollinators making contact with infected plants’ pollen. When a vector pollinator brings anther smut to another plant, the disease sits dormant in the plant over the winter,becoming full-fledged in seedlings and ready to spread again upon germination. Anther smut originates from several parasitic fungal species, including Ustilago violacea,Microbotyrum violaceum, and Microbotryum lychnidis-dioicae. It can be found in white campion,red campion and other members of the campion plant family. The disease causes these plants to become infertile.

Fire blight is caused by the parasitic bacterium Erwinia amylovora and can be spread by insect- or (rarely) bird-pollinator contact with leaves. It affects many fruit plants that are members of theplant family Rosaceae, like apples and pears. The hawthorn, firethorn, serviceberry, juneberry, and mountain ash plants are just a few others that can be infected. Fire blight is a bit more detrimental than anther smut in that it is often fatal to the fruit trees it overtakes. Incidences of fire blight outbreak can be devastating to the apple and pear industry. Entire apple and pear orchards have been destroyed by it, as it spreads very rapidly once a small number of trees have become infected.

Bud blight is especially interesting, because plants and pollinators can become infected by its causing pathogen, tobacco ringspot virus, or TRSV. It is spread by pollinators making contact with leaves, and susceptible plants include the agriculturally-important plants blackberryblueberry, tobaccosoybeans, and squash. It causes deformations and growth stunting in plants. Scientists have found that honeybees can contract the causing pathogenas well. TRSV has been found to decrease winter colony survival and to contribute to a decrease in colony size. Because of this, some experts point to TRSV infection as a possible cause of colony collapse disorder in honeybees, which seriously threatens the world’s food supply. Who knew plant sex was so dangerous?! 

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