| The edible safety quality of rice is related to the health of human body and the frequent exposure of the “cadmium-rice event” in recent years shows that cadmium-polluted rice problem has been very serious in China,therefore,it is of great practical significance to study the cadmium accumulation mechanism of rice and cultivate varieties with low cadmium uptake and accumulation.In this study,the genetic linkage map of a DH population which derived from a cross between a super rice variety Zhongjiazao17(a low-cadmium-accumulation indica variety,YK17)and a tropic japonica variety D50 was constructed,then the cadmium concentration in brown rice and milled rice under pot trials and field trials were determined respectively to detect the QTLs which control two traits,and the main results are summarized as follows:(1)a DH population consisting of 101 lines was constructed by a cross between a super rice variety YK17(a low-cadmium-accumulation indica variety)and a tropic japonica variety D50,genetic composition analysis showed that the proportion of YK17 genome in the DH population ranged from 0.32-0.90,with an average ratio of 0.53,the DH population did not show a serious distorted segregation in general.(2)a genetic linkage map with a total length of 1215.2 cM was constructed using 170 SSR markers,the genetic distance of adjacent markers ranges from 0.5 cM to 26.9 cM and the average is 7.1 cM.Chi-square test showed that a total of 79 markers was significantly deviated from the expected 1:1 Mendel separation ratio,takes up 46.5% of the total number of markers used in the map.(3)pot trials and field trials with 5 different levels of soil total cadmium concentration were carried out in Hangzhou(2015,2016)and Hainan(2015),the determination result of cadmium concentration in brown rice and milled rice showed that there were 0,3.3%,2.1%,11.4% and 13% of lines which have a significant difference between two traits in five trials,respectively,and 0,1.1%,0,1.1% and 1% of lines which have an extremely difference,respectively.Correlation analysis indicated there was a significant positive correlation between two traits in each trial and the correlation coefficients ranged from 0.661 to 0.886.(4)QTL mapping results showed that 32 QTLs associated with cadmium concentration in grain were detected under 5 trials,among which there were 18 QTLs controlling cadmium concentration in brown rice and 14 QTLs controlling cadmium concentration in milled rice.The marker interval and peak position of 7 pairs of QTLs(qCCBR2b and qCCMR2 b,qCCBR3 and qCCMR3,etc.)for two traits were similar or almost identical,and the favorable aelles of the paired QTLs came from the same parents.(5)3,3 and 2 QTLs were detected respectively in the marker interval of RM6-RM6307 on chromosome 2,RM6770-RM16759 on chromosome 4 and RM6854-RM24537 on chromosome 9,the average proportion of phenotypic variance explained by the QTLs detected in three intervals was 13.1%,15.8% and 21.2%,these QTLs have a high stability and phenotypic contribution rate.(6)4 QTLs with additive×environment interaction were detected in DH population by conjointly analysing cadmium concentration in brown rice and milled rice in five trials,among which there were 1 QTL and 3 QTLs for cadmium concentration in brown rice and milled rice,respectively.In addition,2 pairs of epistatic QTLs for Cd concentration in milled rice were detected in DH population.The results of this study provide a theoretical basis and technical support for further elucidating the mechanism of cadmium uptake and transport in rice at the molecular level and cultivating low-cadmium-accumulation rice varieties. |
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