| Recently,contamination of agricultural soils with cadmium(Cd)is increasingly serious.Rice(Oryza sativa L.)is one of the most widely consumed cereal in China.Compared to other crops,rice tends to accumulate more Cd.Rice produced on Cd-contaminated agricultural soils may led to a risk of food quality and human health.Therefore,reduce the Cd accumulation in rice grain has been an important issue for food security.In this study,8 F1 hybrids were obtained by crossing a low grain Cd accumulating restorer line with 8 male-sterile lines of rice.A pot experiment combined with a field experiment was conducted to evaluate the Cd accumulation characteristics of rice lines and F1 hybrids.Furthermore,quantitative trait locus(QTLs)for Cd accumulation in rice were analyzed using F2 population of 120 lines grown in Cd-contaminated field soils,which wasderived from a over-parent heterosis cross C268A/Yahui2816.The main results arepresented as follows:(1)The F1 hybrids were grown better at all Cd treatments as compared to rice lines,and the biomass of F1 hybrids were less greatly affected than that of rice lines under different Cd treatments in the pot experiment.Cd concentrations in different organs of the rice lines and F1 hybrids significantly increased with increasing Cd treatments.For different organs of rice cultivars,the highest concentration of Cd was observed in root,followed by stem and leaf,and the concentration of Cd in ear was the lowest.The variations of Cd concentration among rice cultivars in different organs were smaller in stem and leaf,but larger in root and ear.Average proportion of Cd in root of F1 hybrids was 1.16?1.39 times higher than those of rice lines under different Cd treatments.Cd concentrations in ear of F1 hybrids were significantly lower than rice lines with the reduction from 29.24%to 50.59%.F1 hybrids showed lower translocation of Cd from root to shoot and grain than that of rice lines under Cd exposure,which eventually caused the lower Cd accumulation in brown rice.Cd concentrations in brown rice of all hybrids were less than 0.4 mg kg11 at 1 and 2 mg Cd kg-1 soil.Lu98A/YaHui2816,5406AA/YaHui2816 and C268A/YaHui2816 could be screened out as potential cadmium-safe cultivars(CSCs),for which Cd concenttations in brown rice were less than 0.2 mg kg-1.The results of field experiment further confirmed the consistency and repeatability of the potential CSCs,which were safe for human feeding when cultivated in Cd-contaminated field soil(<1.92 mg kg-1).(2)Average biomass in root,leaf and ear of Fi hybrids were higher than that of rice lines under different Cd treatments.The heterosis analysis indicated that there were significant heterosis in these three organs.The highest mid-parent heterosis and over-parent heterosis were observed in root,with the values of 92.15%?119.09%and 64.26%?92.22%,respectively.In contrast,the average biomass in stem of F1 hybrids were lower than that of rice lines.Most of F1 hybrids showed negative over-parent heterosis.In addition,Cd concentrations in different organs of F1 hybrids showed different degrees of negative heterosis.The highest mid-parent heterosis and over-parent heterosis were observed in ear,with the values of-23.10%?-39.22%and-27.57%?-51.75%,respectively,F1 hybrids had declined the Cd concentration in brown rice by 15.28%?22.12%relative to low grain Cd accumulating rice line and all the hybrids showed a negative over-parent heterosis under different Cd treatments.The highest negative over-parent heterosis were observed Lu98A/YaHui2816,5406AA/YaHui2816 and C268A/YaHui2816,with the values of-24.75%?-40.67%,-22.83%?-36.43%and-19.73%?-36.08%,respectively.Furthermore,these 3 F2 populations were selected as materials in the analysis of quantitative genetic.Cd concentration in brown rice conformed to the 2 major genes plus additive-dominance-epistasis model.The gene additive function was the main in the genetic code and genetic heritability for major gene more than 50%.(3)1132 SNP makers were used to construct a genetic linkage map in a F2 population of 120 lines,which was derived from a cross between C268A and Yahui2816.It spans 1596.94 cM in length covering all 12 chromosomes,with an average density of 1.45 cM.A total of 61 QTLs related to Cd accumulation in rice under Cd-contaminated field soil(1.92 mg kg-1),including 18 QTLs for biomass,19 QTLs for Cd concentration,18 QTLs for Cd accumulation and 5 QTLs for translocation coefficient.The explained phenotypic variance of one QTL for Cd concentration in root and one QTL for Cd accumulation in stem were 11.55%and 10.09%,respectively.The explained phenotypic variance of others were lower than 10%.QTLs for Cd accumulation in brown rice were detected in two regions of chromosome 7,in which qBCdA-7-1 located near the QTL(qLCdA-7)for Cd accumulation in leaf and qBCdA-7-2 located near the QTL(qRCdA-7)for Cd accumulation in root and QTL(qTCs-B-7)for translocation coefficient of Cd to brown rice.The QTLs(qBCdC-5,qBCdC-11 and qBCdC-12)for Cd concentration in brown rice were near the QTLs for root biomass(qRB-5),ear biomass(qGB-11)and translocation coefficient of Cd to brown rice(qTCs-B-12),respectively.In addition,the region of one QTL(qBCdC-9)for Cd concentration in brown rice were detected on chromosome 9 in accordance with the QTL(qRCdA-9)for the accumulation in root. |
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