PARENT SESSION
Oral Session # 9: Invasive Species I: Theory and Modeling.
Presiding: E Rykiel
Monday, August 4. 8:00 AM to 11:30 AM, SITCC Meeting Room 201.

Effects of hybridization on allelochemical expression in invasive Centaurea.

Marrs, Robin^*,1, Hufbauer, Ruth ¹, Pal Bais, Harsh¹, Vivanco, Jorge¹, ¹ Colorado State University, Fort Collins, CO, USA

ABSTRACT- Non-indigenous species become ecologically injurious when they displace species native to the areas they invade and alter patterns of productivity in an ecosystem. It is still fundamentally unclear which attributes enable benign pioneers to become aggressive invaders. In some cases hybridization or allele frequency shifts can lead to increased invasiveness. Centaurea maculosa and C. diffusa (Asteraceae, spotted and diffuse knapweed) are native to Eurasia and have become highly invasive in North America, causing ecological and economic damage. These species have taken over millions of hectares of rangeland and wildland since their introduction and are capable of invading undisturbed plant communities. Several different mechanisms may facilitate this displacement, including negative chemical interactions between species or allelopathy. These invaders each exude a phytotoxic compound into their rhizosphere; C. maculosa exudes (-)-catechin while C. diffusa exudes a-hydroxyquinoline. Each species is immune to the phytotoxic effects of its own exudate but is susceptible to the other species' toxin. Interestingly, the two species are capable of hybridization. Hybrid individuals are intermediate in morphology between spotted and diffuse knapweeds, but little is known of their ecology and physiology. Which exudate is being produced by the hybrid individuals? They could be producing both compounds, just one, or neither. To address this question, seeds were collected from a hybrid swarm population in Hood River, OR, where morphological phenotypes ranged from "pure" C. maculosa to "pure" C. diffusa, with all gradations in between. These plants were grouped into five categories depending on how many characters they shared with either "pure" species. Three offspring from five plants in each of the five categories are being assayed for production of (-)-catechin and hydroxyquinoline. This research will help elucidate the role of allelopathy and hybridization in the invasion of exotic plants.

Key words: hybridization, Centaurea, allelopathy, invasive species