| Breeding for rice grain quality is receiving more and more attentions lately. Rice with intermediate amylose content that cook moist and tender and retain a soft texture upon cooling is generally preferred in most of rice-growing areas, although consumers' preferences vary greatly due to the regional differences in eating habits. Obvious advances in improvement of rice eating quality have been achieved in China. Currently, there are two major problems due to a lack of breakthroughs in breeding techniques. Many recently released conventional early indica rice varieties, cytoplasmic male sterile (CMS) lines or restorers of hybrid rice have a low apparent amylose content (AAC) and fail to meet the demand of the rice market, and many varieties with intermediate AAC still have a poor cooked rice texture. The objective of current study is to develop a combined assisted-selection method in support of rice eating quality breeding programs, by examining the "mist" trait, the Wx microsatellite marker, and starch pasting viscosity. These three properties reflect exterior, molecular and physical/chemical properties of starch quality, respectively.The "mist" trait is a distinct endosperm specific to breeding materials with low AAC roughly ranging from 9% to 15%. Physiologically, the formation of the mist trait is related to the morphology and structure of starch granules in the endosperm. The extreme aging experiment (100% RH at 40癈) indicated that there might be two feasible ways to quickly identify the mist trait via decreasing seed moisture and an aging treatment. Based on this information, the methods for rapid identification of low AAC varieties were tentatively explored. Endosperm appearance of low AAC varieties would change from transparent to misty as the treatment time at 40癈 increases. At 40癈 for 40h, all low AAC varieties expressed the mist trait, however they kept transparent endosperm when exposed to sunshine or were kept in room conditions. Higher temperature (45癈) and maintaining moisture pretreatment at 40癈 significantly accelerated the expression of the mist trait. A 40癈 for 4h pretreatment plus 40 for 16h was preliminarilyregarded as the optimal treatment for the detection of the mist trait, depending on treating time and seed germination rate. Using this method, endosperm phenotypes such as milky white (white), mist, transparency and mixtures were observed in the segregating populations, which were derived from different crosses between low amylose early indica and intermediate amylose rice. AAC was closely related to endosperm phenotypes. Generally, milky white (white) endosperm was very low in AAC, and mist endosperm was basically similar to the low amylose early indica parent. However, transparent endosperm had a variable AAC with some being similar to the intermediate AAC parent. Genetic studies revealed that the mist trait was controlled by a single recessive gene, and its related low AAC was regulated by a major gene with slight modifications by minor gene(s). The results above suggested that the mist endosperm be used as phenotypic marker to assist in the elimination of low AAC materials at an early breeding generation.Starch pasting viscosity indicates changes in rice texture during cooking. During the heating, higher temperature, and cooling processes, rice flour has a pasting viscosity profile, which can be determined by Rapid Visco Analyser (RVA). RVA analysis can be used to distinguish low AAC varieties from intermediate AAC varieties and evaluate eating quality based on the major characters of an RVA profile, the setback value (SBV) and breakdown value (BDV). Studies on major interfering factors indicated that higher temperature pretreatment and rice flour power types did not affect the evaluation of rice quality, although they influenced RVA results to a great extent. Water resources had a slight impact on RVA testing, while sample quantity had serious effects on the final result and subsequent assessment of rice eating quality. A simplified protocol for RVA determination was f...
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