Mapping Quantitative Trait Loci Conferring Palatability and Viscosity of Rice
Date Issued
2012
Date
2012
Author(s)
Tseng, Meng-Chun
Abstract
Physiochemical properties of milled rice could be employed as a selection index of grain quality in early generations of rice breeding programs, which could reduce labor costs and improve breeding efficiency. However, grain qualities of rice are inherited quantitatively and influenced severely by environment. It is imperative to QTL map and clone genes conferring physiochemical properties in prior for marker assisted breeding to promote selection accuracy of grain quality. A total of 190 RILs derived by japonica cultivar TNG 78 crossed with indica cultivar TCS 17 were planted in two cropping seasons, the 2nd crop in 2010 and 1st crop in 2011. The palatability and 7 RVA characteristics were measured of rice grains of each RIL harvested from these two seasons. The objectives herein were to find QTLs expressed stably in two cropping seasons for further grain quality breeding and genetic research, and to study the environmental effects on rice grain quality.
Eight physiochemical properties, included palatability (PLS), peak viscosity (PV), hot paste viscosity (HPV), cool paste viscosity (CPV), brekdown viscosity (BDV), setback viscosity (SBV), peak time (PeT), and pasting temperature (PaT), exhibited continuous distribution, and displayed significant positive correlation between any two traits. Significant differences between two cropping seasons were observed in most traits except palatability and setback viscosity. By using 133 molecular markers covering 12 chromosomes, the linkage map of a total length of 1501.6 cM with an average of 11.4 cM were established. A toal of 59 markers showed segregation distortion which 55 markers skewed to homozygote of TCS 17 genotype, leading marker order of linkage map in chromosome 12 inconsistent to the order of the physical map. We employed composite interval mapping to uncover QTLs associated these eight traits measured in the two cropping seasons, 34 QTLs were obtained with phenotypic variance explanation (PVE) ranged from 1.2% to 78%. The QTLs were mapped on chromosomes 2, 3, 4, 5, 6, 7, 9, and 10; in addition, QTLs conferring 7 traits except pasting temperature were clustered on chromosomes 3, 6, 7, and 10. Twenty (10 pairs) QTLs were detected significantly in two environments, and qHPV6, qBDV6, qCPV6, qSBV6, qPKV7, qCPV7 and qSBV7 identified in this study were conservative with previous studies, suggesting these QTLs expressed stably not only in different environments but experimental populations. The QTLs nearby Wx, which regulates biosynthesis of amylopectin, displaying the largest effect on traits PLS, HPV, BDV, CPV, SBV and PeT, with phenotypic variance explanation ranged from 29% to 78% . The effect of six starch biosynthesis-related genes on these 8 traits was performed a single point analysis and revealed, besides Wx, that SBE4 displayed significant effect on hot paste viscosity, PUL displayed significant effect on cold paste viscosity and setback viscosity. We also proposed that more genes are found carrying significant effects at specific Wx gene haplotypes or interaction combination. Such as PUL:SBE4 interaction exhibits significant effects at PLS, PKV HPV and PeT.
Subjects
Palatability analysis
Rapid visco analysis
Quantitative trait loci
Recombinant inbred lines
Rice grain quality
Type
thesis
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