Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 20, 2005
Publication Date: December 31, 2006
Citation: Gealy, D.R., Yan, W., Rutger, J.N. 2006. Red rice (Orzya satira) plant types affect growth coloration and flowering characteristics of first and second generation crosses with rice. Weed Technology. 20:839-852. Interpretive Summary: Red rice infests much of the rice in the southern U.S. and can intercross with this crop, leading to the development of hybrids. These hybrids and their offspring can damage rice production, especially if they were derived from herbicide-resistant rice and have become tolerant to herbicides. In order to manage these crosses most effectively, farmers must detect them early and accurately. However, characterizing the crosses that could be derived from the numerous red rice ecotypes on rice farms can be confusing. Thus, we developed hybrid (F1) and second generation (F2) populations between two long grain rice cultivars and four different red rice ecotypes broadly representing the range of the red rice types found ion farms. We evaluated several plant and seed characteristics, including growth habit (erect vs open), plant height, leaf roughness, color of the lower stem and leaves (green vs purple), days to flowering, seed color (red vs white), and seed dimensions. First generation plants produced rough leaves, and red medium-sized seeds similar to those of red rice, confirming that these red rice traits were dominant. F1 and F2 characteristics differed depending on the combination of parents involved. Crosses from awned red rice produced F1 plants with purplish lower stem color (even though all parents were green) and flowered relatively early. Those from awnless red rice produced F1 plants with green stems and flowered many weeks later. F1 plants were taller than either parent. F2 plants typically exhibited a highly variable combination of the traits found in both parents and the F1 hybrids, and had particularly noticeable variation in leaf color (purple vs green) and growth habit (erect vs open/spreading) which should be easily discerned from a distance. Ultimately, this kind of information can be useful to farmers who are dealing with management of red rice and its crosses with herbicide-resistant and non-resistant rice. Thus, the discovery of a group of herbicide-resistant and extremely variable plants with a wild and weedy appearance (presumed F2 population) indicates that an outcrossing event probably occurred at least two years earlier and that remedial management options (e.g. rouging, spot spraying, or rotating out of rice) should be considered immediately.
Technical Abstract: Red rice (Oryza sativa L.) is a major weed of rice (Oryza sativa L.) in the southern U.S. and can intercrosses at low rates with rice cultivars. Knowledge of the specific plant phenotypes produced from such crosses has been lacking, but would be valuable to farmers during the early stages of identification and management of red rice hybrids in herbicide-resistant and non-resistant rice crops. F1 hybrids were produced by crossing southern male sterile long-grain tropical japonica cultivars, Kaybonnet-1789 and Cypress-1819, with two awned and two awnless U.S. red rice types. Parental, F1, and F2 (>150) plants from these crosses were transplanted to the field and grown under flooded conditions in 2002 at Stuttgart, AR. Phenotypic characteristics including culm angle, plant height, leaf texture, coloration of the basal leaf sheath (i.e. lower stem) and leaves, days to flowering, awn length, seed pericarp coloration, and seed dimensions and weights were determined. F1 plants produced pubescent leaves, red pericarp coloration, and medium-grain seed dimensions confirming that these were dominant traits. Some characteristics in F1 and F2 plants differed greatly depending on the red rice parent, and to a lesser extent, on the rice parent. Crosses involving awned red rice such as LA3 and TX4 produced F1 plants with reddish-purple basal leaf sheaths (not expressed in any of the parents) and usually flowered within the same time periods as the parents, whereas those involving awnless Stuttgart strawhull red rice produced F1 plants with green basal leaf sheaths and flowered much later than either parent. F1 and F2 offspring derived from awnless red rice were also awnless. Crosses involving awned red rice produced awned F1 plants and F2 plants with awn lengths ranging from zero to those of the red rice parent. F1 plants had an intermediate culm angle (similar to red rice), while F2 plants produced culm angles ranging from erect (similar to rice) to more open than red rice. F1 plants were usually taller than either parent. Based on the results from these rice x red rice crosses, true F1 hybrids derived from crosses between pure breeding (homozygous) rice and red rice parents can be positively identified by a combination of traits including pubescent leaves, medium-grain seeds with red pericarps, open plant types, and plant heights greater than the red rice parent. F1 hybrids may be awned or awnless, have purple or green stems, or have normal or delayed heading depending on the red rice type. F2 plants have a broad combination of phenotypic traits found in both parents and F1 hybrids.