|Clements, Darin - Charlie|
|Harmon, Daniel - Dan|
Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/5/2005
Publication Date: 10/1/2005
Citation: Young, J.A., Clements, C.D., Pitcairn, M.J., Balciunas, J.K., Enloe, S., Turner, C.E., Harmon, D.N. 2005. Germination-temperature profiles for achenes of yellow starthistle. Weed Technology. 19:815-823. Interpretive Summary: Yellow starthistle is a winter annual of Eurasian origin that has become widely spread throughout the western United States. Yellow starthistle was reported in the Sacramento Valley of California as early as 1879 and is thought to be from contaminated alfalfa seed. The aggressive spread of this winter annual has caused serious problems to private land owners and resource managers. Yellow starthistle only prpagates by seed germination and seedling establishment. Obviously, seed production, dispersal, germination, and seedling establishment are essential aspects of the invasive invasive ecology of the weed. Yellow starthistle infestations have been reported to produce 250 million achenes per hectare annually. Germination temperature profiles were developed for achenes of yellow starthistle collected from 15 sites in California, Nevada, and Oregon. For most profiles, germination occurred at all of the temperature regimes except a constant 40ºC. No single temperature regime always supported optimum germination when all the profiles were combined. The most frequent optima was 2/20ºC.
Technical Abstract: Yellow starthistle is an annual that is dependent on achene production, dispersal, germination for renew stands. Our purpose in this study was to determine the temperature relations for germination of achenes of this species. Germination temperature profiles were developed for achenes of yellow starthistle collected from 15 sites in California, Nevada, and Oregon. Each profile consisted of achenes germination at 55 constant or alternating temperatures from 0 through 40 C. A total of 85 germination temperature profiles were developed by using the germination data to construct quadratic response surfaces through regression analysis. For most profiles, germination occurred at all of the temperature regimes except a constant 40 C. This includes a constant 0 C and 0 alternating with 40 C. Rarely, there was no germination at 35 and 35 alternating with 40 C. The only evidence of afterripening requirements we for achenes of yellow starthistle that we noted, occurred at very cold temperature regimes. At these temperatures, the germination of dark colored achenes without pappus increased with 3 months after harvest, and the reverse occurred for light colored achenes with a pappus. No single temperature regime always supported optimum germination when all the profiles were combined. The most frequent optima was 2/20 C. Comparing all profiles for the Davis, California accession, there were 5 regimes (5 and 10 C cold periods alternating with 15 through 25 C warm periods) that always supported optimum germination. Light colored achenes with pappus tended to have optima for germination at colder temperatures and the dark colored achenes at higher temperatures.