Submitted to: Rice Technical Working Group Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: January 1, 2006
Publication Date: February 15, 2006
Citation: Bergman, C.J., Pinson, S.R., Chen, M.H. 2006. Genotype and environment effects on the tocotrienol, tocopherol, and gamma-oryzanol fractions of an international rice germplasm collection. Rice Technical Working Group Meeting Proceedings, February 29-March 1, 2006, Houston, Texas. pp. 117-118. 2006. Technical Abstract: Rice bran contains many phytochemicals with proposed health-benefits and industrial applications. To-date the levels of these fractions from samples grown under controlled conditions have been reported for only a few Southern U.S. cultivars. Thus little is known about how genetics, the environment or their interactions impact the levels of these compounds in rice germplasm at large. This information is needed to determine the possibilities for manipulating the levels of these fractions using cross breeding techniques. In addition, an understanding of the role genetics versus the environment plays in creating the variation in these phytochemicals’ levels is needed to design robust field experiments during the breeding process. The objectives of this research were to quantify the levels of individual E-vitamers and total gamma-oryzanol in an international germplasm collection, and to determine the effects of the environment on their levels. Rice accessions (n = 200) from over 50 countries were selected in an attempt to capture as much genetic diversity as possible within the constraints of the amount of labor available for the grow-out and the requirement that genotypes needed to flower within 120 days of planting to be compatible with the experiment’s growing environment. The accessions were obtained primarily from the USDA Germplasm Resources Information Network. The cultivars were grown during two seasons in Beaumont, Texas using cultural management practices common for the region. Sample size availability was low; therefore, the accessions were cultivated in single plots, arranged in a completely randomized design. To limit environmental effects, genotypes were planted in blocks designed to synchronize heading times. The effects of planting dates and micro-environment differences across the field were captured by planting a control, ‘Lemont’, randomly spaced throughout each block. At maturity, the plants were threshed by hand, the grains were dehulled, and all broken, diseased and immature kernels were removed. The dehulled kernels were milled, the bran fractions sieved and then stored at -20ºC, under nitrogen, until analysis. Surface lipid content was determined using petroleum ether in a Goldfish extraction apparatus. This measurement was used to ensure that all samples were milled within a similar range in degree of milling (i.e., <0.5% surface lipid content). An enzymatic procedure was used to determine the starch content of the bran. These values were then employed to express the phytochemical data on a zero starch basis. The E-vitamer and gamma-oryzanol contents of the samples were determined using a method previously published by the authors which uses reverse-phase HPLC with UV and florescent detection. All analytical procedures were performed in duplicate. The phytochemical levels varied significantly due to genetics, year, and planting date. Across the two growing seasons the accessions varied in E-vitamer content from 0.18 to 0.43 mg/g and in gamma-oryzanol content from 2.9 to 6.5 mg/g. These values are of the same magnitude as previously reported, but can not be directly compared due to the differences in analytical procedures used. The variability for the control’s tocotrienol, tocopherol and total E vitamer contents were greater in year two (RSD 12.9%, 27.7% and 18.0%, respectively) compared to year one (RSD 5.2%, 7.1% and 5.0%, respectively). Thus indicating the effects of micro-environment and planting date on E-vitamer levels interacts with growing year effects. This was not the case for gamma-oryzanol, as the control’s values for this fraction varied to a similar degree in both year one and two (RSD 4.85 and 5.6%, respectively). The within laboratory repeatability for the HPLC method used for this study was previously reported to be low for all phytochemical fractions (RSD < 5.3%). Thus, the effects of the environment are much greater on E vitamer levels than gamma-oryzanol content. The germplasm collection studied contained 47 US accessions. Of these, the long and medium grain cultivars with the greatest mean total E vitamer and gamma-oryzanol levels were ‘L-201’ and ‘M-201’ and ‘A201’ and ‘Vista’, respectively. Thus, programs interested in developing high yielding US rice cultivars with superior phytochemical levels will need to consider both recent and historical cultivars as breeding parents, depending on their breeding objects.