Diversity of weedy red rice (Oryza sativa L.) in Arkansas, U.S.A. in relation to weed management.

Abstract: Weedy rice, specifically red rice (Oryza sativa L.), is a major weed in rice which causes up to 80% yield loss and reduction of grain quality. Red rice accessions from Arkansas, U.S.A., were characterized to classify red rice accessions into certain phenotypic groups relevant to weedy rice management. The red rice accessions were 70% strawhull, 22% blackhull, 7% brownhull and <1% goldhull. Generally, blackhull red rice was the tallest (139cm) and strawhull the shortest (133cm) among all accessions. Blackhull red rice had more tillers (102/plant), smaller flag leaves (13cm wide, 34cm long), and flowered later (1225 heat units) than strawhull red rice which had 85 tillers/plant, 15cm-wide and 34cm-long flag leaves, and flowered after accumulating 1195 heat units. Morphological differences between accessions within each hull type were highly significant, showing great diversity within a hull color group as indicated by large ranges in traits. For example, blackhulls were 75–190cm tall with 18–69cm long flag leaves, 21–188 tillers and produced 40–949g seed. Strawhulls were 46–189cm tall with 18–66cm flag leaf length, 16–172 tillers and produced 100–608g seed. Some traits, such as seed production, differed widely between accessions within each hull color group such that the average seed production/accession for blackhull did not differ from that of strawhull weedy rice (196 vs. 192g/plant). The onset of flowering among all accessions ranged from 56 to 126d after planting. Red rice accessions formed six phenotypic clusters generally segregated by plant size or flowering time. Each morphotype would have different competitive abilities; thus, weedy rice management could be geared toward plant types. Highly competitive plant types would require intensive control measures to minimize yield losses and reduce the soil seed bank. Flowering dates impact stewardship strategies for herbicide-resistant or any genetically modified rice. [Copyright &y& Elsevier]