| Cadmium(Cd),one of the most toxic metallic elements,is easily absorbed by rice.It not only affects the yield and quality of rice,but also can harm human health through food chain.To breed rice varieties with high tolerance and low accumulation to Cd is an economical and feasible means to solve this important rice production and food security problem.In this study,3 multi-parents advanced generation inter-cross(MAGIC)populations(DC1,DC2 and 8-way)with rich genetic diversity was used to identify seedling Cd tolerance and grain Cd content,combined with55 K high-throughput SNP genotype to genetic location analysis.The main results are as following:1.The cadmium tolerance of the three MAGIC populations had large phenotypic variation under cadmium stress and normal conditions,and the 8 parents had significant differences in shoot length,root length,shoot dry weight and root dry weight.The transgressive segregation phenomenon exists in all three populations,and the genotype variation of the 8-way population is larger than that of the DC1 and DC2 populations.In addition,The cadmium accumulation related traits in MAGIC population also showed large phenotypic variation under cadmium stress and normal conditions.Parents B and D had high cadmium concentration(0.363 mg/kg and 0.499 mg/kg,respectively)and high cadmium concentration ratio between shoot and root(19.9 % and 18.9 %),and parent A was a line with low cadmium concentration(0.149 mg/kg),parent E is a line with low cadmium concentration ratio between shoot and root(12.6 %).2.With Cd stress treatment in seedling stage(third leaf)for 3 MAGIC populations(2mg/L),18 QTLs related to root length,root dry weight,shoot length and shoot dry weight were located under Cd stress conditions,which distributed on chromosomes 1,2,3,4,5,7,and 12,the phenotypic variation of QTL ranged from 1.1 % to 12.1 %.With ratio of Cd stress to normol conditions,6 QTLs related to the shoot length and shoot dry weight were located on chromosomes 1,3,7,9 and 12.The phenotypic variation of QTL ranged from1.5 % to 5.9 %.The content of cadmium was measured in seedlings stage for DC1 population.8,2 and 4 QTL were found in those chromosomes except for 4,5,9 and 11,which affected the content of cadmium in the shoot and root and cadmium concentration ratio between shoot and root of them,explaining the phenotypic variation range is 3.0 % to4.3 %.To DC1 population,the content of cadmium for grain in the stage of maturity was measured in cadmium-polluted areas(Guangxi).5 QTLs affecting the the content of cadmium in grain were found in chromosome 1,2 and 3,which explained the phenotypic variation range is 5.2 % to 8.4 %.3.Using 654 rice germplasm resources that have been sequenced for cadmium-contaminated area planting,11 cadmium levels exceeded the standard,9 out ofjaponica rice,one over-standard variety in temperate japonica rice and tropical japonica rice,the over-standard rate of indica rice reached 2.28 %,japonica rice reached 0.78 %,which means Xian(indica)exceeded the standard rate higher than Geng(japonica).In addition,78 materials with low Cd accumulation were selected and most low cd accumulating materials exist in the japonica resources.These germplasm resources were used to analyze the favorable haplotypes of the cadmium transport gene OsNRAMP1.The haplotype GTAC cadmium accumulation(0.032 mg/kg)was significantly lower than the haplotype ACTG cadmium accumulation(0.057 mg/kg).Finally,combined with bioinformatics analysis and gene expression pattern analysis,36 candidate genes that may be involved in Cd tolerance in seedlings and grain Cd accumulation in rice were initially screened,which needs further verification. |
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