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United States Department of Agriculture

Agricultural Research Service

Research Project: Genomic Approaches and Genetic Resources for Improving Rice Yield and Grain Quality

Location: Dale Bumpers National Rice Research Center

Title: US cultivar grain quality as assessed using objective and subjective methods

Authors
item McClung, Anna
item McClung, Anna
item Yeater, Kathleen
item Jodari, Farman -
item Linscombe, Steven -
item Walker, Tim -
item Ottis, Brian -
item Wilson, L.T. -
item Moldenhauer, Karen -

Submitted to: Rice Technical Working Group Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: December 2, 2013
Publication Date: N/A

Technical Abstract: For decades USA rice was considered to have excellent milling quality, grain appearance, and cooking quality as compared to much of the rice in world trade. This was largely due to a concerted effort by breeders to eliminate genotypes that did not possess grain quality characteristics that were considered acceptable by the USA rice industry. Since the 1950’s breeders have relied upon grain quality evaluations performed by the USDA ARS which assessed various parameters associated with cooking and processing quality. In addition, southern US public breeders collaborate in the Uniform Regional Rice Nursery which is a multi-state test of promising breeding lines for agronomic, pest resistance, and grain quality traits. The outcome has been the development of rice varieties by public researchers that have consistent grain quality which meet industry standards and can be sold at a premium in the global market. Although the USA exports almost 50% of its crop, over the last decade there have been increasing concerns that US produced rice is declining in quality and competitiveness in the world market. As a result, the USA Rice Federation partnered with breeding programs and commercial rice mills to critically assess currently produced US rice cultivars for quality and to compare these with high quality international samples of rice. A series of three studies were conducted, each using sets of US rice cultivars and imported samples that were evaluated by both subjective and objective methods. The US rice samples were all milled to the same degree, subdivided, and sent to analytical labs and industrial mills for assessment in a blind test. The imported samples were commercially milled overseas. Subjective scoring using a 1 to 5 scale was conducted by staff at private mills and included grain uniformity, bran streaks, chalk, and kernel color. The objective tests included image analysis for chalk, kernel length and width, and bran streaks, as well as caliper measurement of grain thickness. The first study consisted of 18 US rice cultivars produced in various environments and 1 sample from Vietnam. Mills evaluated the samples for 8 visual grain traits. From this study the traits luster, creamy and clear were dropped from further analysis because they were deemed not very informative. The second study included 9 US varieties, some grown in multiple locations during 2011 and imports from Brazil and Thailand, for a total of 25 samples. Major differences in quality among the varieties and among the locations where they were grown were observed. The third study was conducted in 2012 and included 17 US varieties, 3 hybrids, and imported samples from Thailand and Uruguay. The US cultivars were grown in unreplicated trials at 6 locations and at two planting dates (1 month apart) providing a total of 226 samples for evaluation. In addition, a repeated check sample of milled CL111 was included 13 times to assess consistency in the various measurements. Several of the findings from the previous studies were confirmed in this more extensive study. The results demonstrated that rice mills differ greatly in how they judge rice samples and they are not highly consistent in their evaluations. This indicates that developing clear, uniform standards for evaluating samples that all mills would use, may be a better way to communicate with breeders and other researchers about rice grain quality issues. Two image analysis systems were used, Winseedle and S21, which gave similar results for grain dimension traits, although the S21 system was more precise. Although they were highly correlated (r=0.64), these two methods produced very different measures of grain chalk. Samples averaged 38% chalk with the S21 system and 3.8% chalk with the Winseedle, however, the Winseedle method was more repeatable. In addition, the subjective measures of chalk by the mills were more highly correlated with the Winseedle system (r=0.59) than the S21 system (r=0.35). The delayed planting date resulted in earlier maturity, shorter grainfill period, larger grain size, lower milling quality, greater chalk, and overall lower scores by the mills. The cultivars with the best quality scores by the mills were the two imported samples and L206, Presidio, Cheniere, and Bowman. These also had the lowest levels of chalk as measured using the Winseedle method. The cultivars with the poorest scores by mills and the highest levels of chalk were CL151, XL723, CLXL729, CLXL745, and CL111. The cultivars L206, Presidio, Cheniere, CL151, and CL111 had been evaluated in the previous studies and all were consistent with the third study’s rankings except for CL111 which was more variable in quality depending on the location grown. In all three studies, the imported samples were ranked moderate to high for quality, however there were US varieties that had better quality. This demonstrates that the USA has germplasm that can deliver excellent grain quality and can be incorporated into new high yielding cultivars.

Last Modified: 12/20/2014
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