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United States Department of Agriculture

Agricultural Research Service


item Gealy, David
item Agrama, Hesham
item Estorninos, Jr, L
item Wilson,jr, C

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 4/1/2007
Publication Date: 6/25/2007
Citation: Gealy, D.R., Agrama, H.A., Estorninos, Jr, L.E., Wilson,Jr, C.E. 2007. Characterization of weedy rice populations in the southern U.S. and their gene flow interactions with rice using DNA markers. 4th Temperate Rice Congress, Novara, Italy, June 23-25, 2007. [abstract]

Interpretive Summary:

Technical Abstract: Weedy (red) rice (Oryza sativa) is a major weed problem in rice (Oryza sativa) in the southern US. Outcrossing between these plant types can lead to gene flow that negatively impacts the rice industry. We have been using SSR molecular marker analysis in combination with phenotypic traits to systematically characterize weedy rice populations collected throughout Arkansas and adjoining rice-producing states, and to evaluate gene flow interactions between weedy rice and rice. SSR analysis has revealed clear differences in the genetic backgrounds of major phenotypic groupings of US weedy rice (e.g. awned vs. awnless types), weedy rice x rice hybrids, and commercial US rice cultivars. These genetic differences have facilitated reliable SSR differentiation between US rice and weedy rice types using few markers. We used such an approach to conduct reciprocal outcrossing tests in a controlled field setting for five years, to show that outcrossing was 4.5 times greater with weedy rice than with rice as the male parent. These results strongly support the advice of experts, that replanting harvested seed from weedy rice-infested fields can be risky (especially where herbicide-resistant rice is grown). Several suspected first generation hybrids produced by natural crossing between imidazolinone (IMI)-resistant rice and weedy rice were identified in farm fields based on F1 phenotypic traits, and subsequently confirmed using SSR analysis and STRUCTURE software. F2 plants from these accessions produced the expected SSR allele profiles and segregation ratios for traits such as red pericarp, leaf pubescence, and IMI resistance, confirming that the original accessions were F1 hybrids. However, the degree to which rice alleles may have introgressed into US weedy rice populations over many generations is less clear. To address this question, we used 19 SSR markers and STRUCTURE to analyze weedy rice types (~10% of a 450-accession collection) with unusual, rice-like traits (e.g. short plants). US rice alleles were essentially absent from these accessions. Thus, the rice-like traits may not have originated from outcrossing or could have been lost over several generations after crossing occurred. Analyses of additional markers, including markers for semi-dwarfism and blast disease resistance will be discussed.

Last Modified: 08/22/2017
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