Submitted to: Journal of Cereal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/14/2008
Publication Date: 3/1/2009
Publication URL: http://handle.nal.usda.gov/10113/27970
Citation: Gealy, D.R., Bryant, R.J. 2009. Seed physicochemical characteristics of field-grown U.S. weedy red rice biotypes: Contrasts with commercial cultivars. Journal of Cereal Science. 49:239-245. Interpretive Summary: Red rice (Oryza sativa L.), sometimes called weedy rice, is a difficult-to-control mimic of the cultivated rice (Oryza sativa L.) grown in the southern U.S. Presence of red rice grain in rice grain is undesirable and can reduce the value of rice to consumers because they generally prefer white-colored kernels. These studies were conducted to evaluate several chemical and physical characteristics of field-grown U.S. red rice grain that are commonly used to assess processing and cooking quality of commercial rice. Grain amylose (starch) content of U.S. red rice biotypes was higher than commercial rice cultivars and similar to a high-amylose Asian rice type. Amylose content in grain from plants derived from crossing between red rice and commercial rice plants ranged from the level found in commercial medium-grain rice to as high as that in the Asian rice. DNA fingerprinting (SSR analysis) confirmed that most red rice types possessed specific DNA sequences similar to those in the Asian rice. Key differences were observed between awned and awnless red rice biotypes. Alkali spreading value (inversely related to starch gelatinization temperature) and protein content were usually greatest in awned red rice types, whereas lipid (oil) content was greatest in awnless types. Because of their high amylose content, weedy red rice types are likely to be undesirable for many commercial uses of rice in the U.S. and could potentially degrade cooking quality if present in high amounts in medium-grain rice or rice that will be processed (such as for parboiling).
Technical Abstract: Red rice in the US is an aggressive weed that reduces the yield of rice and contaminates its grain. It is the same species as rice, which provides an opportunity for intercrossing. This genetic similarity complicates the management of red rice in fields and rice mills, but also indicates a potential for its use in rice breeding or niche markets. Physicochemical and cooking quality characteristics, which are important components of consumer desirability for rice, are virtually unknown for red rice. Thus, a survey of red rice accessions and rice red rice crosses was conducted to characterize these traits. Grain amylose levels of most indigenous red rice accessions were similar to those of high amylose indica cultivars from Asia. Amylose levels in crosses were highly variable, ranging as low as those in medium-grain commercial rice to as high as those in long-grains. Alkali spreading value was generally greater in awned than in awnless red rice accessions and the aroma chemical, 2-acetyl-1-pyrroline, was detected in two red rice crosses. The generally high seed amylose levels in red rice indicate that its cooking quality would not be suitable for most common uses of US rice, but may be acceptable for niche uses.