| A doubled haploid population, derived from anther culture of F1 hybrid between a typical indica and a japonica (ZYQ8 / JX17) is employed this study, to make clear of the genetic base of grain-shape traits, including grain length, grain width and length/width ratio and other quality traits, such as, rice embryo weight, embryo weight ratio, milled rice length, cooked rice length, and cooked rice elongation. The main results are summarized as follows:1. QTL analysis of grain-shape traits in different environmentThree grain shape traits, including grain length (GL), grain width (GW) and grain length/width ratio (GLW) were compared in three environments (Beijing, Hangzhou and Hainan) and their quantitative trait loci (QTL) were analyzed. Totally 28 QTLs were detected for grain-shape, being located on chromosome 1, 2, 3, 4, 6, 8 and 12, respectively. There were four, eleven and thirteen putative QTLs for grain length, grain width, and length/width ratio, respectively. The contribution of these QTLs to phenotypic variation ranged from 9.8% to 18.4% for grain length, from 8.4% to 25.6% for grain width and from 9.8% to 22.7% for length-width ratio, respectively. Correspondingly, their LOD values varied from 2.22 to 4.75 for grain length, from 2.43 to 5.77 for grain width and from 2.44 to 6.02 for length/width ratio. The illustration of QTLs analysis made the genetic base of grain-shape traits clearer.2. QTL analysis of rice embryo traitsThe embryo traits of rice were controlled by several genes. Two QTLs for rice embryo weight were detected on chromosome 3 and 4 (qEW-3 and qEW-4) . Positive additive effect of qEW-3 and negative additive effect of qEW-4 showed that allele from JX17 would increase and reduce weight of rice embryo, respectively. LOD values of these two QTLs ranged from 2.89 to 3.34, and the variance contributions from 13.8% to 14.1%. Two QTLs for rice embryo weight rate were detected on chromosome 4 and 9 (qEWR-4 and qEWR-9) , the additive effect was negative, showing that allele from ZYQ8 would reduce the rate of rice embryo weight. LOD value varied from 2.92 to2.63, and variance contribution from 10.6% to 11.2%. It is suggested from variable QTLs that the inheritance of rice embryo traits is quite complex.3. QTL analysis of rice cooked rice elongationTotally, 12 QTLs for rice elongation traits were detected on chromosome 1, 2, 3,5, 6, 7, 10, 11 and 12. One putative QTL for milled rice length (qMRL-2) was mapped on chromosome 2. Six putative QTLs for milled cooked rice length (qCRL-1 , qCRL-6, qCRL-7, qCRL-10, qCRL-11, qCRL-12) were mapped on chromosome 1, 6, 7, 10, 11and chromosome 12. Five putative QTLs for cooked rice elongation (qCRE-1, qCRE-3, qCRE-5, qCRE-6, qCRE-10) were mapped on chromosome 5, 6 and chromosome 10. In general, all detected QTLs had negative additive effects, except the QTL on chromosome 6. It is indicated that allele from JX17 would increase rice elongation. The region of TCT125-RG400 on chromosome 1, G30-RZ516 on chromosome 6 and G1082-GA223 on chromosome 10 were detected simultaneously for cooked rice length and cooked rice elongation. LOD of all traits related to rice elongation varied from 2.15 to 5.88, and variance contribution from 8.5% to 23.7%. It is indicated that cooked rice elongation is controlled not only by the main-effect QTLs, but also modified by many micro-effect QTLs, which was also closely related to apparent amylose content.
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