Non‐Uniformity of Grain Characteristics and Milling Quality of California Rice ( Oryza sativa L.) of Different Maturities

Head rice recovery is one of the most important factors in determining a grower's income. While previous investigators have shown that certain physical characteristics of rice kernels influence per cent head rice, the impact of the non‐uniformity of these characteristics on rice milling quality is largely unknown. The objectives of this study were to investigate the effect of non‐uniformity of kernel characteristics on the milling quality of rice cultivars with different maturities, and to determine the plant traits that are associated with the non‐uniformity of kernel characteristics. Six rice cultivars representing different maturities and grain shapes were used in the experiments. Kernel characteristic data were obtained for grains at the upper, middle and lower parts of a panicle. The range values amongst these panicle parts were used to measure the non‐uniformity of the characteristics. There was a trend for a decrease in kernel dimensions, volume and density from the upper to the lower parts of the panicle. This indicated that growth and development of grains were associated with the position of the grains on the panicle. There was also a trend for a decrease in the non‐uniformity of kernel characteristics from very early and early maturing cultivars to intermediate and late maturing cultivars. The results also demonstrated that selection of phenotypes that have a low ratio of panicle length to phytomass can improve the uniformity of kernel characteristics, which in turn leads to higher recoverable head rice yield.