Insect pests can severely damage Arkansas crops, but the plants are not exactly defenseless when under attack.

Plants possess some means to defend themselves against chewing insects, said Dr. Ken Korth, University of Arkansas Division of Agriculture plant pathologist.

“Self defense often involves the production of chemicals in the plant that are distasteful or toxic to insects,” Korth said. “Other chemicals can be released from insect-injured leaves that attract enemies of the insects damaging the plant.

“This type of natural defense doesn’t have to be sprayed on, it’s always there,” he said. “It’s targeted specifically to the insects that are causing the damage and doesn’t harm those that are beneficial to the plants.”

Beneficial insects include those that feed on the pests, reducing their impact on crops.

With funding from the Division of Agriculture, USDA and the Arkansas Rice Research and Promotion Board, Korth and graduate student Karen Gomez of Santa Cruz, Bolivia, are studying the genetics of how plants protect themselves. Armed with such information, plant breeders could develop crop plants that are less reliant on chemical pesticides.

“We’re asking, ‘what is the plant’s defense strategy?’” Korth said. “How does the plant defend itself, and how can we tap into that and enhance those defenses?”

Korth has identified genes that encode proteins he believes are involved in defense. “These genes and proteins are active in damaged plants and not in undamaged plants,” he said.

He uses Medicago truncatala, a relative of alfalfa that is a good research model because the plant’s genetics have been mapped. “What we learn from it can be applied to rice or other plants,” he said.

To see how the genes react, undamaged plants are compared with plants that have been chewed on by caterpillars. A third set of plants is damaged mechanically.

The defensive genes go to work only on the plants damaged by the caterpillars.

In another test, mechanically damaged plants responded when regurgitated matter from the caterpillars was applied to the damaged tissues.

“Our tests show there is a chemical response to insect damage that is different from purely mechanical damage,” Korth said.  “A plant senses the biological damage from a chewing insect and responds chemically to protect itself.”

Gomez is researching how the plants respond to individual purified chemicals from caterpillar regurgitant in order to understand how much response each one sparks.

“We’re looking for genetic markers for plant defense traits that plant breeders can use to produce improved crop varieties,” Korth said. “The challenge is connecting the gene with the trait desired.”

He said this area of research is still at an early stage and a lot of work remains before the results are useful for plant breeders.

“Down the road, it could provide another, targeted layer of protection for crops,” he said.