|Shivrain, Vinod - Arkansas Agricultural Experiment Station|
|Burgos, Nilda - Arkansas Agricultural Experiment Station|
|Agrama, Hesham - Arkansas Agricultural Experiment Station|
|Lawton-rauh, A - Clemson University|
|Lu, Baorong - Fudan University|
|Sales, Marites - Arkansas Agricultural Experiment Station|
|Boyett, Virginia - Arkansas Agricultural Experiment Station|
|Moldenhauer, Karen A - Arkansas Agricultural Experiment Station|
Submitted to: Weed Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/25/2010
Publication Date: 4/23/2010
Citation: Shivrain, V.K., Burgos, N.R., Agrama, H.A., Lawton-Rauh, A., Lu, B., Sales, M.A., Boyett, V.A., Gealy, D.R., Moldenhauer, K.K. 2010. Genetic diversity of weedy red rice (Oryza sativa) in Arkansas, USA. Weed Research. 50:289-302. DOI: 10.1111/j.1365-3180.2010.00780.x.
Interpretive Summary: Problem: The weed, red rice, is a major problem in rice grown in the southern USA. About half of US rice is produced in Arkansas and 60% of this is infested with various red rice types, which can differ markedly in size, shape, and appearance. Using DNA marker techniques, we investigated the genetic diversity of more than 100 red rice types collected from Arkansas rice fields and measured the extent to which these types contained genetic material that may have been obtained from rice varieties historically grown over the past century. Accomplishment: The awnless strawhull red rice was genetically distinct from dark hull colored red rice types. The gene diversity of blackhull and strawhull red rice types was affected by the geographic location of origin. Twenty-five percent of the red rice accessions shared some genetic material with cultivated rice. Contribution: It is apparent that a diverse complex of weedy populations has developed in this region of the southern USA that is devoid of other weedy and wild relatives of rice.
Technical Abstract: Weedy red rice (Oryza sativa L.) is a problematic weed in rice. About 50% of US rice is produced in Arkansas and 60% of these fields have some red rice infestation. Red rice populations are morphologically and phenologically diverse. We hypothesize that red rice in Arkansas has high genetic diversity, which varies by place of origination, and that some alleles from cultivated rice have been introgressed into red rice in more than a century of coexistence. We tested 137 red rice accessions from four ecological zones in Arkansas and 36 cultivars that have been grown in Arkansas in the past century. Twenty-seven rice microsatellite primers, distributed across 12 chromosomes, were used to generate molecular markers. The overall genetic distance (GD) of red rice accessions was 0.70. Rice grown in the last century had an overall GD of 0.26. The awnless strawhull red rice was genetically distant from blackhull (GD = 0.55) and brownhull (GD = 0.60) red rice types. The GD between blackhull and brownhull red rice was 0.42. Brownhull and blackhull formed one genotypic cluster while the majority of strawhull red rice formed another cluster. Within blackhull red rice the GD was 0.76; awnless strawhull, 0.68; awned strawhull, 0.75; and brownhull, 0.80. The gene diversity of blackhull and strawhull were affected by zone of origin. Twenty-five percent of the red rice accessions shared genetic material with cultivated rice. A diverse complex of weedy populations had evolved in a region devoid of other weedy and wild Oryza species.