| Flag leaf is a major sink organ of rice in grain filling stage.Ideal flag leaf traits are one of the important indicators for plant type cultivation and super high-yield breeding.In this study,a backcross introgression line population with two generations(BC3F3 and BC3F4)derived from an elite japorice cultivar Koshihikari(recipient)and a Portuguese rice landrace Bertone(donor)was used as plant marerials.The genotypes were constructed by using 85 pairs of SSR co-dominant markers with the BC3F3 population.Several parameters including flag leaf SPAD,flag leaf length,flag leaf width,flag leaf angle,length to width ratio of flag leaf as well as flag leaf area were measured in the parental varieties and BC3F4 population.In order to analyze the relationship between D value and the seven agronomic traits,membership functions and the index weight method were used to comprehensively evaluate the flag leaf characteristics of these 414 BC3F4 lines.In the BC3F4 population,293 lines with stable flag leaf traits were screened.Combining the genotypes of these 293 lines in the BC3F3 population,single-point analysis(SPA)and interval mapping(IM)were used to identify QTLs for traits related to flag leaf in rice.The main research results are as follows:1.Analyze the phenotypes of six flag leaf traits in 414 lines of the BC3F4 population,the six flag leaf traits of the BC3F4 population exhibited diverse phenotypic variations,whose overall performance resemble the recurrent parent(Koshihikari).The results revealed that flag leaf SPAD,flag leaf length,flag leaf width,flag leaf area,and flag leaf angle of flag leaf were significantly correlated with two parents.In addition,these five characteristics were significantly correlated in the BC3F4 population and Bertone.The correlation analysis showed that except for the flag leaf SPAD and flag leaf area,which did not have obviousily significant correlations,the other flag leaf traits all reached a significant correlations with each other.2.Using principal component analysis(PCA)and stepwise regression analysis,flag leaf width,length to width ratio of flag leaf,flag leaf area and flag leaf angle were selected as the key indexes of D value out of the flag leaf comprehensive evaluation.The results showed that the three traits including plant height,panicle length and grain yield per plant were all significantly higher in lines with a high D value than that in lines with a low D value.The correlation analysis results revealed that between flag leaf traits and agronomic traits of lines with high and low D values showed that flag leaf SPAD had no significant correlations with the seven agronomic traits,but the flag leaf length has the highest correlation value with the plant height.The D value showed a very significantly positive correlation with plant height,panicle length,basal culm thickness and grain yield per plant,a significantly positive correlation with tiller number and effective panicle number,and no significantly correlation with grain yield per panicle.3.A total of 59 QTLs were detected in single-point analysis associated with flag leaf SPAD,flag leaf length,flag leaf width,length to width ratio of flag leaf,flag area,flag leaf angle as well as D value,which were located on chromosomes 1,3,4,6,7,8 and 11 with phenotypic variation explained ranging from 4.00%to 22.00%,respectively.Except for qFLL6 and qFLWR6 the other 57 QTLs showed synergistic effect from Bertone alleles.4.A total of 21 QTLs were detected in interval mapping analysis associated with flag leaf SPAD,flag leaf length,flag leaf width,flag area,flag leaf angle and D value,which were located on chromosomes 1,3,7,8 and 11 with phenotypic variation explained ranging from 3.20%to 17.00%,respectively.All QTLs showed synergistic effect from Bertone alleles.Moreover,a QTL cluster was found in the RM22680-RM3395 interval on chromosome 8,included multiple traits QTLs controlled flag leaf length,flag leaf width,flag leaf area,flag leaf angle and D value.The phenotypic contribution rates of qFLW8e,qFLA8a and qFLA8b in this cluster were all greater than 10.00%,which is an important chromosomal region affecting flag leaf-related traits. |
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