Genetic Analysis And Mapping Of The Grain Chalkiness QTL QPGWC-1 In Rice(oryza Sativa L.)

Chalkiness,including white core,white belly and white back,refers to the opaque part of rice endosperm caused by the loose starch granules.As an important agronomic trait of rice,chalkiness is a major index of the appearance quality of rice and it also has influence on physical and chemical properties and processing quality.Chalkiness,including percentage grains with chalkiness?PGWC?,degree of chalkiness?DC?and so on,which is greatly influenced by the environment,is a quantitative character controlled by nuclear genes and maternal effect.In this study,detection of quantitative trait loci?QTLs?for chalkiness in rice was conducted using BC₄F₃ residual heterozygous lines?RHs?and progeny populations derived from a backcross between nonrecurrent parent Xieqingzao B?XB?and recurrent parent Zhonghui9308?9308?.The populations were grown in Lingshui?LS?,Hainan and Fuyang?FY?,Zhejiang.The results were as the follows:1.A QTL of PGWC was located within the region from 26Mbp to 43Mbp on the long arm of chromosome 1 after the preliminary detection.Then,three populations derived from three residual heterozygous individuals with heterozygous target interval,named P1,P2 and P3 respectively,were planted in FY and LS respectively to verify the result.The interval mapping results by WinQTL Cart 2.5suggested that a QTL controlling PGWC was detected in three populations in FY and in population P1and P2 in LS.But no QTL was detected in population P3 in Lingshui.The lowest contribution to the phenotypic variance of the QTL was 6.8%and highest was 21.9%.This QTL had influence not only on PGWC but also on DC and the effect of allele from Zhonghui9308 was decreasing the PGWC.2.Using the residual heterozygous method,four residual heterozygous individuals named RH1-4 respectively were selected from population P1.By comparing the PGWC between four sets of NILs derived from RH1-4 and according to the difference of heterozygous interval,the QTL was mapped between RM212-RM11872 with physical distance 3.3Mb.Then,eight residual heterozygous individuals named RH5-12 respectively were selected from progeny population derived from RH3.By comparing the PGWC between eight sets of NILs derived from RH5-12 respectively and according to the difference of heterozygous interval,the QTL was mapped between Z345-Z383 with physical distance 1,251kb.The QTL was named qPGWC-1 for it influenced on PGWC mainly.3.Chalkiness was greatly influenced by the temperature in the filling stage,especially on 20d or so after heading in this study.Investigation results of PGWC in LS and FY suggested that PGWC was higher by the filling stage with higher temperature.4.Scanning electron microscope analysis suggested that there were great differences in the shape,structure and arrangement of starch granule between the chalky part and transparent part.In chalky part,starch granules were irregular polygon and round or oval.There were bulges with different size on the surface of starch granule.Starch granules were loosely packed and there were lacunas among them.The difference in the shape,structure and arrangement of starch granule was the main reason why the chalkiness occurred in endosperm.5.Amylose content in NIL which brings the allele from XB is lower than which brings the allele from 9308 and there are no difference in gelatinization temperature between NILs in this study.6.By comparing main agronomic traits between NIL^XBB and NIL⁹³⁰⁸,there was no significant difference in heading date,plant height,number of effective panicles,grain number per panicle,thousand grains weight and so on which preliminary indicated that qPGWC-1 has no influence on many agronomic traits while changing the percentage grains with chalkiness.It might be useful in rice breeding for it brings little negative effect on grain yield while reducing the chalkiness.