Back off, bugs: Sweet potato cultivars use a specific odor to warn other plants of herbivores

A variety of sweet potato emits a specific odor that not only deters incoming pests – it also alerts neighboring plants of its kind to the presence of a threat.

That’s according to researchers from the Max Planck Institute for Chemical Ecology (MPICE) in Germany and National Taiwan University, who examined a sweet potato cultivar called Tainong 57, which is known to release a distinct odor bouquet when attacked. Their findings were published in the journal Scientific Reports.

The compound behind sweet potato variety’s high pest resistance

Past studies showed that the Tainong 57 plant is highly resistant to field herbivores compared to the cultivar known as Tainong 66. But prior to the present study, it was unclear whether the plant’s high pest resistance is due to its odor bouquet.

To that end, the researchers exposed Tainong 57 to herbivores to identify compounds that activate its defense mechanisms when attacked. The plant emitted a bouquet of odors that activated the formation of a protein called sporamin on the unaffected leaves. Known as the main protein of sweet potatoes, sporamin inhibits digestive enzymes in attacking insects and causes them to lose their appetite.

Among all odors the plant emitted, only a compound called DMNT was found to be abundant enough to activate sporamin formation. A volatile organic compound, DMNT smells almost like an herbal balm.

“To our surprise, only one single volatile is enough to induce a specific defense reaction in a sweet potato plant of the Tainong 57 cultivar,” said Axel Mithofer, the chief of MPICE’s Research Group Plant Defense Physiology and one of the study researchers.

DMNT also triggered the formation of the defense protein in neighboring Tainong 57 plants that have not yet been attacked. These plants were able to perceive the smell quickly, allowing them to prepare for the incoming threat.

The researchers noted that only Tainong 57 plants release high concentrations of DMNT and are able to perceive the compound. Tainong 66 plants, in contrast, release significantly less DMNT. Even when the amount of the volatile is increased, these plants still fail to mount adequate defenses. (Related: Stunning discovery reveals that plants and parasites engage in “social media” information sharing for self-defense.)

Anja Meents, first author of the study and a doctoral researcher at MPICE, said about the study’s potential applications: “Our results are of great agricultural importance, because the consistent cultivation of resistant cultivars, such as Tainong 57, could help to considerably reduce the damage caused by herbivores in a natural way.”

Developing cultivars that release higher amounts of DMNT and perceive the compound efficiently can minimize the use of pesticides.

Tomato plants eavesdrop on pests

Sweet potatoes are not the only plants that can ward off pests. A study shows that tomato plants head off attacking snails at the pass by “eavesdropping” on them.

John Orrock, an ecologist at the University of Wisconsin–Madison, said that tomato plants increase their levels of an anti-pest enzyme called lipoxygenase when exposed to snail slime – a lubricating mucus that snails produce as they slide along.

“None of the plants were ever actually attacked,” Orrock said. “We just gave them cues that suggested an attack was coming, and that was enough to trigger big changes in their chemistry.”

In their latest study, Orrock and his team examined whether tomato plants’ defenses work against other kinds of pests. They squirted snail slime near the plants and then unleashed hungry caterpillars. But the bugs no longer had an appetite for tomato leaves after getting released.

Orrock said that this nonspecific defense may be helping tomato plants improve their chances of survival. He recommended more studies that will determine the mechanisms that allow the plants to respond to relatively distant cues.

Learn more about plants and their fascinating, anti-pest abilities at Ecology.news.

Sources include:

ScienceDaily.com

ScientificAmerican.com