Red rice (Oryza sativa) plant types affect growth, coloration, and flowering characteristics of first- and second-generation crosses with rice

Red rice is a major weed of rice in the southern U.S. and can intercross with rice. Knowledge of the plant phenotypes from such crosses would be valuable for identification and management of these plants. Male-sterile long-grain tropical Japonicas 'Kaybonnet-1789' and 'Cypress-1819' were crossed with two awned and two awnless U.S. red rice types. F-1 plants produced pubescent leaves, red pericarp, and medium-grain seeds. Crosses involving awned LA3 and TX4 red rice produced F-1 plants with reddish-purple basal leaf sheaths and usually flowered within the same time periods as the parents, whereas those involving awnless StgS red rice had green basal leaf sheaths, flowered much later than either parent, and produced awnless F-1 and F-2 offspring. Crosses involving awned red rice produced F-1 plants with long awns and F-2 plants with awns ranging in length from zero to that of red rice parents. F-1 plants were taller than either parent and produced intermediate culm angles similar to red rice, whereas F-2 plants had culms ranging from erect (like rice) to more open than red rice. Thus, true F-1 hybrids from crosses between pure breeding (homozygous) rice and red rice can be positively identified by a combination of traits including pubescent leaves, medium-grain seeds with red pericarps, open plant types, and heights greater than the red rice parent. F-1 hybrids may be awned or awnless, have purple or green stems, or have normal or delayed heading. F-2 plants have a broad combination of phenotypic traits found in both parents and F-1 hybrids.