486:	Impact of intra-species variability on the weediness of common cocklebur.

Authors:	Wassom, James(A)Wax, Loyd, M.(B)Tranel, Patrick, J.(A)
Affiliations:	(A): Department of Crop Sciences, University of Illinois at Urbana-Champaign (B): USDA/ARS, Crop Protection Research Unit
Presenter:	Tranel, Patrick J., tranel@uiuc.edu

Common cocklebur is an adaptable and widespread plant species found in diverse temperate and subtropical environments in the USA and around the world. Cocklebur is one of the most troublesome weeds in crops, especially in soybeans and cotton where it is a major competitor. The objective of our ongoing study is to compare morphological, physiological, and weediness traits among cocklebur accessions obtained from different regions. In addition, we are investigating genetic variation among accessions using molecular markers. Results from such studies should aid development of regionally specific weed management strategies as well as provide insights into the ecological success of this species. Twenty-eight cocklebur accessions from 14 states were planted in a field plot at Urbana, IL in May, 1998. Various traits (including plant height and width, photosynthetic activity, days to flowering, leaf size, and bur production) were measured during the growing season. Genetic variation among approximately 200 common cocklebur accessions was investigated using PCR-amplified inner-sequence simple repeat (ISSR) markers. Most traits measured varied significantly among accessions: final plant heights ranged from 50 to 82 cm, days to flowering ranged from 61 to 98, and photosynthetic activity at one date ranged from 22 to 39 mmoles CO2 m-2s-1. Preliminary results from subsequent greenhouse experiments corroborated substantial variability for photosynthetic rates among accessions. ISSR marker analysis confirmed previous reports that cocklebur contains limited intra-population but substantial inter-population variability. Implications of intra-species variability to the success of common cocklebur will be presented.