Submitted to: Proceedings of Southern Weed Science Society
Publication Type: Abstract Only
Publication Acceptance Date: January 23, 2001
Publication Date: N/A
Technical Abstract: Red rice is one of the most troublesome weeds of rice (Oryza sativa) in the southern United States. It is a crop mimic and is the same species as commercial rice cultivars. Numerous types of this weed species are known to exist in farmers' fields and intercrossing between commercial cultivars and red rice can occur, further increasing the complexity of control strategies. However, this close genetic relationship presents a valuable opportunity to exploit red rice as a potential source of desirable genes for commercial rice cultivars. In these studies, we evaluated the genetic relationships among numerous types of red rice (including known crosses with rice) from the southern USA using 10 simple sequence repeat (SSR) (also called microsatellite) DNA Markers. We related the resulting DNA types to tolerances to the herbicides glufosinate, glyphosate, imazethapyr, and molinate, and to rice blast (Pyricularia grisea) (races IC-17, IB-49, IH-1,IG-1, and IE-1K), the most severe rice pathogen in US rice. Red rice types exhibited a wide range of tolerance to the herbicides and to blast. Low to moderate levels of herbicide tolerance were observed in only a few instances. Only one of 150 red rice types (1995-14) was rated resistant to all 5 races of blast suggesting that this type might be a useful source of blast resistance genes. Highest tolerances to herbicides and blast generally occurred in awned, black hulled red rice. Multidimensional scaling (MDS) analysis and cluster analysis of SSR reseults indicated clear genetic differences among several groupings of types (e.g. red rice vs rice vs red rice-rice crosses; awned vs non awned types; and straw colored vs black colored hulls). Genetic groupings for several of the red rice types suggest that these types had previously hybridized with cultivated rice.