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DNA Study Points to the Potential Impact of Toadflax Hybrids on Biocontrols

LAWRENCE, Kansas – July 20, 2016 – Researchers with Colorado State University and the U.S. Forest Service have uncovered new information that may explain why insect biocontrols used to manage toadflax infestations can sometimes exhibit mixed results.

Both yellow toadflax and Dalmatian toadflax are non-native plant species that have become widespread and difficult to control invaders in large areas of the western U.S.  Experience shows herbicides are not always effective at toadflax control. In addition, many invasions are found in sensitive public forests, open rangelands and wilderness areas where widespread spraying simply isn’t an option.

As an alternative to herbicides, weed managers have relied on stem-boring weevils that have very specific preferences about the plants they will attack. One species (Mecinus janthinus) is drawn only to yellow toadflax, while another (Mecinus janthiniformis) attacks only Dalmatian toadflax. When yellow and Dalmatian toadflax plants cross-pollinate to produce hybrids, though, there are indications that species-specific weevils may become confused.

To better understand the genetics of hybrid toadflax and how cross-pollination might impact insect biocontrols, researchers analyzed chloroplast DNA to investigate the extent and direction of cross-pollination between toadflax species in natural habitats. Hybrid plants were most often found to have yellow toadflax chloroplast DNA, indicating that yellow toadflax is typically the female parent pollinated by Dalmatian toadflax.

The research team also made another unexpected discovery.  Plants from two toadflax populations in Colorado that were thought to be pure Dalmatian toadflax based on physical appearance and growing location were found to contain yellow toadflax cytoplasm instead. Scientists suspect this phenomenon is the result of an initial cross-pollination with yellow toadflax, followed by several generations of pollination by Dalmatian toadflax.

“The plants look like Dalmatian toadflax, but may contain enough yellow toadflax DNA that weevils normally feeding on Dalmatian toadflax will not attack them,” says Sarah Ward of Colorado State University. “This may explain reports by weed managers that weevils preferring Dalmatian toadflax are choosing not to feed on some invasive Dalmatian toadflax populations.”

Full text of the article “Plastid DNA Analysis Reveals Cryptic Hybridization in Invasive Dalmatian Toadflax (Linaria dalmatica) Populations” is available in Volume 9, Issue 2 of the journal Invasive Plant Science and Management.

About Invasive Plant Science and Management

Invasive Plant Science and Management is a journal of the Weed Science Society of America, a nonprofit scientific society focused on weeds and their impact on the environment.  The publication focuses on invasive plant species. To learn more, visit www.wssa.net.

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