Genotypic diversity of bran weight of whole grain rice and its relationship with grain physical traits

Abstract Background and objectives Rice bran, the outer most layer of the whole grain, is where nutrients, minerals, and bioactive compounds, except starch, are primarily deposited. Rice bran accounts for a small portion of the whole grain weight. Increasing the weight proportion of bran will enhance the health beneficial value of whole grain rice. Findings We determined the physical and bran traits of 135 rice genotypes grown in two years. More than a 2.3‐ and 2.5‐fold variation was found for bran weight per gram of whole grain and bran weight per surface area of the whole grain (BWS, representing bran thickness), respectively. Principle component analysis of the seven physical traits and two bran traits grouped the bran traits into PC3 and accounted for an average of 15.5% of the total variance, whereas kernel weight, width, thickness, and grain surface area were in PC1, and kernel length and length/width ratio were in PC2. Mean comparison among bran color classes showed that purple bran genotypes had the highest BWS, followed by red, white, light brown, and brown. BWS moderately correlated with kernel weight, width, and thickness. Conclusions This report demonstrates high bran weight genotypes can be selected to improve the nutritional value of whole grain rice. Significance and novelty Expressing bran weight based on grain surface area removed the confounding factor of differences in grain size and allowed identification of genotypes having high bran weight consistently across two years, suggesting this trait is genetically regulated and can be used in traditional breeding to improve bran weight proportion of whole grain rice leading to higher nutritional value of the rice.