|Mitten, Donna - AVENTIS CROPSCIENCE|
Submitted to: Weed Science Society of America Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: February 12, 2001
Publication Date: N/A
Technical Abstract: Red rice has long been a troublesome, conspecific weed of cultivated rice. Rice varieties with genetic-based herbicide tolerances, now offer new options for red rice control. In concert with this innovation is the risk of gene flow, which can result in the transfer of herbicide tolerance to red rice and thus, render the weed control measures non-effective. Gene flow in concept is simple, however the parameters that determine the establishment of a new trait in a weed population are complex. Cross- pollination to make hybrid seed and the subsequent fate of those hybrid families in the general weed population are some of the inter-related factors that influence gene flow between red rice and cultivated rice. Natural outcrossing among rice plants is generally very low. A fifty-year- old study indicated that rice-rice outcrossing rates were less than 0.5%, and evidence from field surveys during the last decade suggest that rice- red rice outcrossing rates were even lower. Recent studies have documente very low outcrossing rates between red rice and herbicide-resistant rice. However, other studies have documented greater outcrossing rates between rice and red rice indicating that natural outcrossing rates may be highly variable. If hybrid seed families are to persist, they must successfully compete in the crop-weed complex. In studies to measure the fitness of rice-red rice hybrid families, both herbicide and sensitive, key traits like panicle shattering and seed dormancy were found to be intermediate between cultivated rice and red rice, and not related to the presence of herbicide tolerance. Thus, established principles of weed resistance should be used along with avoidance of coincident flowering to mitigate the impact of gene flow.