Genetic characterization of red rice (Oryza sativa L.) and control in imidazolinone tolerant rice (Oryza sativa L.)

Red rice from the southern United States was collected and analyzed using Simple Sequence Length Polymorphism (SSLP) markers in an effort to test the assumption that red rice is Oryza sativa ssp. indica. The 18 markers used are distributed across all 12 chromosomes of the rice genome and can be used to distinguish between sibling cultivars. The results indicate that traditional classification of red rice based on morphological characteristics alone is inadequate. Some red rice was closely related to Oryza sativa ssp. indica, while other red rice was more closely related to Oryza sativa ssp. japonica. Some red rice samples collected from Arkansas, Louisiana, Mississippi, and Texas are very closely related to the noxious weed, Oryza rufipogon accession IRGC 105491. This research revealed that different classes of red rice are intermingled across the southern United States rice belt. Within individual commercial production fields, Oryza sativa ssp. indica-like red rice and Oryza rufipogon-like red rice can be found within a single 9 m² collection site. In 2000 and 2001, studies were conducted at several locations across the Texas rice-producing region with imidazolinone tolerant rice to determine the most efficacious sequential application rate and timing of imazethapyr for control of red rice and other weeds. At Beaumont, red rice and barnyardgrass control was greater than 94% with 0.07, 0.09 and 0.10 kg/ha preplant incorporated or preemergence followed by at least 0.04 kg/ha early postemergence on a clay soil. Broadleaf signalgrass control near Eagle Lake showed that preplant incorporated and preemergence applications followed by early postemergence applications provided greater than 86% control in 2000, and greater than 90% control in 2001. Sequential postemergence applications at Beaumont resulted in greater than 95% red rice and barnyardgrass control when 0.04 kg/ha late postemergence followed any early postemergence application. Sequential postemergence applications controlled broadleaf signalgrass greater than 98% in both years. Red rice control at Lissie on a fine sandy loam soil was at least 98% with all sequential treatments. Crop injury was found to be a function of the postemergence application in all studies. Crop yields were not reduced by early season crop injury from imazethapyr applications, regardless of soil type.