QTL Mapping For Seedling Cd Tolerance In Rice (Oryza Sativa L.) And Analysis Of QTL×Environment Interaction

In order to investigate the genes related to heavy metal cadmium we established a mapping population of 123 F₁₀lines(recombinant inbred lines,RILs),derived from a cross between Indica variety Lemont(Tolerance rice to Cd,introduced from USA)and Japonica variety Dular(sensitive rice to Cd,introduced from Korea).The phenotyping was conducted for QTL analysis and QTLs interaction with environment for cadmium tolerance in rice at seedling stage in hydroponics,in which all rice lines including parents were grown in Hoagland solutions treated with 0.2mg/L additional cadmium,and all entries grown in Hoagland solutions without additional cadmium were taken as controls.The chlorophyll content(CC),root length(RL),shoot height (SH),leaf length(LL)in 2006 and 2007 were determined and transformed to ITs(Index of tolerance to Cd,IT)for QTL location involving 109 SSR markers by ever composite interval mapping(CIM).The results showed that a total of 16 additive QTLs were detected,and mapped to chromosomes 1,2,3,4,6,7,11,respectively.Of which,in 2006,3 QTLs evaluated with a CC index,were located on chromosomes 2,3,11,and explained 14%,9%,9%of the phenotypic variations,respectively,and in 2007,2 QTLs were detected,explaining 38%and 7%of the phenotypic variations in 2006.One QTL in terms of a RL index,was mapped to chromosome 1, accounting for 9%of the phenotypic variations,and in 2007,one QTL was detected and mapped to chromosome 6,explaining 12%of the phenotypic variations.Three QTLs evaluated with a SH index,were mapped to chromosomes 1,1,11,and contributed 10%,27%,10%to the total phenotypic variations in 2006,and in 2007,two QTLs were mapped to chromosomes 6 and 7,and both of them explained 8%of the phenotypic variations.Two QTLs in 2006 by a LL index located on chromosomel and 11 with 21%and 12%of genetic contribution rates,and in 2007,two QTLs were detected and located in chromosomes 2,and 6,respectively.They explained 11%and 12%of phenotype variations.At the same time,five QTLs of additive effect and environment were detected.Of which two QTLs by a SH index were detected,accounting for 10.94%and 34.64%of the phenotype variations,respectively.Two QTLs by a CC index were found,explaining 9.66% and 18.37%of the phenotype variations.One QTL by a RL index,explained 8.88%of the phenotype variations.Finally,six epistasic QTLs were found.Of which two QTLs using SH,as an evaluation index,were mapped to chromosomes 1,1 and chromosomes 4,11,the contribution of epistasic effect phenotype variations was 0 and 3.44%,respectively,and QTLs×environment interactions explained 3.58%and 16.38%of phenotype variations,respectively.One QTL by RL evaluation,was located in chromosomes 10,10,the contribution of epistasic effect was 7.65%, and QTLs×environment interaction accounted for 12.71%of phenotype variations.One QTL evaluated by CC index,was mapped to chromosomes 2,3,the contribution of epistasic effect was 2.93%,QTLs×environment interaction accounting for 7.37%of phenotype variations.The QTLs loacted in chromosomes 1,10 and chromosomes 1,1 were detected by using LL index,the contribution of epistasic effect was 21.93%and 0,and QTLs×environment interaction explained 3.84%and 10.47%,respecitively.It was also showed that based on different evaluation indexes,12 out of 27 QTLs in total associated with Cd tolerance detected in this study,were located in chromosome 1.It was also found that it seemed to be better to use SH and CC as evaluation indexes than RL for the genotyping of Cd tolerance,by which 3 QTLs associated with Cd tolerance ware detected, respectively.The present study also showed that several QTLs associated with Cd tolerance, respectively located in the same marker intervals,were detected in chromosomes 1 and 11 simultaneously,implying that different alleles with the same functions might exist in the same interval in a close linkage way or just only one locus was there in different manners in terms of different evaluation indexes.This result suggested that the evaluation indexes were properly selected and can be recommended to further investigate the genotyping in relevant study.