| Kernel size related traits,including kernel length,kernel width,and kernel thickness,are critical components in determining the final performance of yield and kernel quality in maize(Zea mays L.).Dissecting the phenotypic characteristics of mazie kernel size reated traits,and discovering the candidate chromosomal regions(QTL)for these traits,are of potential importance for mazie yield and quality improvement.In the present study,F3 population derived from the cross of B73 and EHel,a distinct lines with extremely low ear height(EHel),was used for phenotying and QTL mapping of three kernel size relatd traits,including KL,KW,and KT.The main results are as follows :1.Phenotypic characterization of kernel size related traits of parents and populationPhenotyping results showed that among three kernel size related traits,statistical diffrenes(P<0.01)were observed for both 10-kernel length(KL)and 10-kernel width(KW)between the years of 2018 and 2019 among the individuals of two parental lines,i.e.EHel and B73,correspondingly.No statistical difference was observed for 10-kernel thickness(KT)for EHel in both 2018 and 2019(P=0.6788),while for B73,the average performance of KW in 2018 was significantly lower than that in 2019(P=0.0098).Between two parental lines,significant differences were ovserved for both KL and KW between EHel and B73 in both years(P<0.01),while KT exhibitd similar performance between EHel and B73 in 2018(P=0.0959)and 2019(P=0.4806).Among 139 lines of F3 population,three kernel siez related taits,i.e.KL,KW,and KT correspondingly ranged from 7.43 cm to 12.23 cm,5.78 cm to 8.73 cm,and 3.92 cm to 6.70 cm,with the average performance of 10.10 cm,7.26 cm,and 5.08 cm,respectively.Results from Shapiro-Wilk test showed that frequency distribution of all these three traits matched well with theoretical normal distribution,presenting tyipcal quantitative characteristics.2.Construction fo linkage map139 F2 individuals and both parental lines were tensily genotyped with Maize 10 K SNP chipset.2108 polymorphic SNPs were screened from ~10000 SNP by comparing the genitypes of EHel and B73.The genotype data of these polymorphic 2108 SNPs among all 139 F2 indiviuals were used to construct the linkage map.The total length of the map was 3309.35 cM,and the average distance between SNP markers was 1.57 cM.Among 10 chromosomes(Chr)(or 10 linked groups),three chromosomes,i.e.Chr1-Chr3,captured more than 250 SNPS each.Considering the average length of pairs of SNPs,six chromosomes,i.e.Chr1(1.10 cM),Chr2(1.19 cM),Chr4(1.14 cM),Chr6(1.31 cM),Chr8(1.45 cM),and Chr10(1.12 cM)possessed smaller average length than the total average(1.57 cM)of the whole genome.3.QTL mapping of kernel size related traitsBy integrating the phenotypic values of KL,KW,and KT of F3 population,using QTL IciMapping V4.1 software via both fixed LOD(2.5)and permutation(1000,P=0.05)methods,only one QTL(qKW9)for KW was detected,and no QTL was detected for both KL and KT by both methods.qKW9 located within a 4 cM interval on Chr9 between SNPs of AX-86269371 and AX-86255482,with explained phenotypic variance(PVE)of 13.4%.qKW9 acted as over dominance(OD)to KW,and the positive allele with increasing phenotypic effect to KW of this QTL was from pollen parent B73.4.Primary verification of q KW9 via bulked sample analysis(BSA)Four groups of family lines(Group1 to Group4)were selected from F3 populationa ccording to the phenotypic comparisons of KW to EHel and B73.Among the average KW performance of these four gouprs,Group1 possessed significantly lower KW than that of EHel(P=0.0455),Group2 similat to EHel(P=0.34),while bot Group3 and Group4 statistically higher than EHel(P<0.05).Besides,except Group4 exhibited similar KW to that of B73(P=0.11),KW of the other three groups were statistically lower than that of B73(P<0.00).By comparising the bulked genotypes of four groups to EHel and B73,for the chromosomal region on Chr9 between SNPs of AX-86298372 to AX-86263154,bulked individulals of Group1 with the lowest KW possessed no genotype of B73/B73,while those of Group4 with the highest KW presented no genotype of EHel/EHel.Individuals of Group2 and Group3 with middle KW performance exhibited all three genotypes of EHel/EHel,EHel/B73,and B73/B73 at this chromosomal region.The BSA results indicated that the SNP interval between AX-86298372 to AX-86263154 on Chr9 served as a tightly linked region with KW,with positive allele of increasing phenotypic effect to KW from B73,similar to that of qKW9.Besides,two flankering SNPs of qKW9 located within the chromosomal region discoveded via BSA,just next to the beginning marker of AX-86298372,suggesting qKW9 a potential QTL for KW in maize. |
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