Association Analysis Of Important Agronomical Traits Of Maize Inbred Lines

The genetic markers of important traits are evaluated in order to improve the maizeinbred lines. The objectives of our research were to find some important yield related traitswith strong associations of loci, which would be useful for genetic improvement andmolecular maker-assisted breeding in maize. Ninety-four maize inbred lines were used toassess the genetic and phenotypic diversity and make association analysis of26agronomicaltraits with204genome-wide SSR markers. The results were summarized as follows:1. Extensive phenotypic variations were observed for all the measured quantitative traitsin this maize panel. Correlation analysis was conducted for each trait of2010and2011. Dataof the two years’ traits were averaged, then we used SPSS to descriptive the statistics. Cobweight, with an average of23.97g/cob, showed the largest variation, ranging from7.56to48.37g/cob, CV is37.88%. Whereas, days to mature （MD, day）, with an average of97days,exhibited the least variation, ranging from87to107days, CV is4.76%. All of the26traitswere consistent with normal distribution. Because of such extensive phenotypic and geneticvariations, it is clear that we should be able to conduct the association analysis by using thisassociation panel.2. To evaluate the genetic diversity of the94inbred lines, we used204SSRs which arerandomly and uniformly distributed within the whole maize genome. High polymorphism ofthese SSRs within the94inbred lines was detected:1286alleles with an average of6.30alleles per locus, ranging from2-16alleles. Whereas, the polymorphic information content（PIC） with the mean of0.61. Meanwhile, the average genetic diversity was0.66. Themaximum gene diversity and PIC value is0.8849and0.8738, respectively. Results showedthat this association panel showed a high diverse genetic variation.3. Population structure analysis showed that the inbreds can be classified into5subgroups which corresponding to the five main germplasm sources: LRC, Sipingtou, PB,Reid and BSSS, respectively. Lines with membership probabilities of0.70and <0.70wereassigned to match clusters and to represent a mixed group, respectively. Of all inbred lines,73.40%were assigned into the corresponding subgroups based on their Q values.4. Association analysis of traits with strong associations with markers. The association analysis conducted in2010and2011resulted in417and347SSR loci, all of which wereassociated with the26traits （P<0.05）. This result indicated that the same association locuswere39. When considering P<0.01level,138SSR loci and96SSR loci were associated withall26traits in our2010and2011study, respectively. However, compared with the sameassociation locus that were used for association analyses in both2010and2011, only six locishowed similar association levels with several traits. The association analysis with the mixedlinear model （MLM） indicated that106and318SSR loci were strongly associated with the26agronomical traits and such association significance reached the P<0.01and P<0.05levelbased on the meaning of the two years of data. Twenty-five and three same marker-trait lociwere detected （compared the39and six same association results with the mean of two yearsof results at P<0.05and P<0.01level）. The strongest association locus were umc1917withAD and HKW （P<0.01）, umc1397associated with CD and HKW, umc2025with CD（P<0.0001）, etc. Five association loci were new discovery, which were bnlg2162, bnlg1118,phi077, umc1161with BYC, and bnlg1118with GLN.5. To discuss the relationship between the heterosis of maize yield and the geneticdistance of its parents, correlation analysis showed that the genetic distance had significantcorrelation with the acre yield, r=0.45^**, the mathematical model was y=0.3442x³-9.969x²+9.729x-2.089. The correlation between ΔQ and acre yield was r=0.50^**, the mathematicalmodel was y=-0.069x³-0.136x²+0.399. Changqi-2is a typical SPT group, otherwhise, Qi-319is a typical PB group, the genetic distance is1.1049and hybrid acre yield is belonged to highyield. Otherwise, the genetic distance of some other inbred lines is near, hybrid acre yield isbelonged to low yield. Some high yield group models were: Reid×SPT, Reid×LRC, SPT×PB,which would provide assistance for breeding.