Submitted to: Proceedings of Southern Weed Science Society
Publication Type: Abstract only
Publication Acceptance Date: 1/23/2004
Publication Date: 1/23/2004
Citation: Shivrain, V.K., Burgos, N.R., Moldenhauer, K.A., Gealy, D.R., Gbur, E.E. 2004. Phenotypic and genetic diversity of red rice (Oryza sativa L.) in Arkansas [abstract]. Proceedings of Southern Weed Science Society. 57:207. Interpretive Summary:
Technical Abstract: Red rice (Oryza sativa L.) and rice (O. sativa) belong to the same genus and species. It is the most troublesome weed in rice growing areas of southern U.S. due to its competitiveness, propensity to lodge, and red seed color which contaminates rice grain. Strawhull and blackhull are two major types of red rice, the former being more abundant than the latter. A study was conducted at the Rice Research and Extension Center (RREC), Stuttgart, AR, in 2003 to determine the phenotypic and genetic variability of red rice. One hundred thirty six red rice accessions were collected from 26 rice-growing counties of Arkansas in summer 2002. The collection site of each accession was separated by at least 5 miles and GPS coordinates were recorded. Each accession was composed of one plant, the seed of which was collected for characterization studies. Arkansas was divided into four regions, northeast (NE), centraleast (CE), central (C), and southeast (SE). Four accessions representing distinct phenotypes were used to identify natural variation in the ALS (Acetolactate synthase) gene. This information may enable us to correlate genetic variability to the weeds propensity to develop herbicide-resistant population in response to selection pressure. Accessions were planted in the greenhouse on April 20th and transplanted to the field on May 12th. Plants were grown in non-competitive condition. Data collected were: initiation of flowering, plant height, tiller number, culm angle, leaf texture, stem color, awn color, panicle number, flag leaf characteristics (length, width, angle), seed yield, hull color, and awn length. Accessions 4, 9, 50, and 106 were used for the ALS gene study. DNA was extracted using a modified CTAB (Hexadecyltrimethylammonium bromide) protocol. The ALS gene was amplified by PCR using five sets of overlapping primer pairs. Amplified fragments were cloned into a pGEM® T Easy vector and sequenced. These sequences were aligned to the full ALS gene sequence of Stuttgart strawhull and that of ALS-resistant rice line from Japan. Red rice accessions fall into 2 major categories: strawhull and blackhull types. Besides the two major hull color, straw and black, other hull colors were also observed including brown and orange. There was no difference in plant height and tiller number among strawhull red rice across regions. Among strawhull types, accessions from the NE region produced the most seed (190 g/plant) and flowered earliest. Among blackhull accessions, those from the CE region produced the most tillers (mean=115), but were the shortest blackhull types (mean=133 cm). Blackhull accessions from central Arkansas had the highest seed yield (196 g/plant) and were earliest to flower. The period from planting to flower initiation increased with decreasing latitude. The date of first flower initiation ranged from 11th July to 5th September. Seed yield decreased with decreasing latitude in strawhull types, due to accessions not reaching full maturity, but no such trend was observed in blackhull types. Phenotypic diversity in red rice was documented based on hull color, presence of awns, height, tillering capacity, flowering dates, and seed yield. Preliminary data on sequence analysis of the ALS gene revealed six nucleotide mutations that resulted in alteration of the amino acid sequence. Most of these mutations fall into 'hot spots' for developing herbicide resistance based on information from other species. These natural mutations indicate a possibility for selection for resistance to ALS inhibitor herbicides in red rice. Thus, it is prudent to rotate to other herbicide chemistries for sustainable red rice management.