| Fresh sweet corn has unique flavor,rich nutrition and significant economic benefits,and its high-quality breeding is increasingly valued.In this experiment,40 new inbred lines of sweet corn were selected and classified into groups through phenotypic clustering and clustering analysis based on SSR markers.According to the results of clustering analysis,this experiment further screened 9 sweet corn varieties with significant genetic differences,and assembled 20 hybrid combinations using incomplete diallel cross(NCII).Furthermore,this study analyzed the general combining ability(GCA),specific combining ability(SCA),heterosis and heritability of14 major agronomic and qualitative characters of the hybrid combinations and parents.Besides,a correlation analysis was also conducted on the major characters of sweet corn.The present study is expected to provide theoretical basis for the breeding of sweet corn varieties.The main test results are as follows:1.Phenotypic clustering was performed on 10 agronomic characters of 40 sweet corn inbred lines via hierarchical clustering.Using 35 pairs of corn fluorescent-labeled SSR makers,170 alleles were detected in 40 sweet corn inbred lines,with 2-8 alleles detected per primer pair.The polymorphism information content(PIC)value for the SSR loci ranged from 0.09 to 0.79,with an average value of 0.47.According to the genetic similarity coefficient matrix,40 sweet corn inbred lines were divided into 3 major groups using UPGMA clustering.The population structure analysis showed that the ΔK value showed a significant peak at K=3,which was most suitable for dividing these inbred lines into three groups in terms of population structure,which is basically consistent with the result from SSR clustering results and the Principal Component Analysis(PCA)results.The above result all suggested that three groups exist in genetic relationship among of sweet corn inbred lines.2.As indicated by the results of GCA analysis of parental inbred lines,inbred line J6 had the highest GCA effects in yield traits,such as single ear weight,ear length,ear diameter,ear row number and axle diameter.Inbred line J3 showed all positive GCA effects in quality traits(e.g.,reducing sugar and total soluble sugar),and agronomic traits(e.g.,ear position,plant height,stem diameter,branches,single ear weight,ear length,ear diameter,number of grains per row,axle diameter,hundred-grain weight and grain length).J3 has high utilization potential in maize hybrid breeding.Furthermore,according to the analysis of the SCA effects of 20 hybrid combinations,hybrid combination J19(J3×J9)not only had high SCA effects in quality traits(e.g.,reducing sugar and total soluble sugar),but also high SCA effects in agronomic traits(e.g.,plant height,stem diameter,single ear weight,ear length,ear diameter,hundred-grain weight and grain length).These data suggested a high utilization potential of this hybrid combination.3.Further analysis of 14 characters of 20 hybrid combinations revealed the presence of heterosis in the major characters of sweet corn F1 generation generally,and there were heterosis combinations in these 20 hybrid combinations.Hybrid combination J23 showed the strongest midparent heterosis in yield traits(e.g.,single ear weight,ear diameter,grain length,hundred-grain weight and number of grains per row).Moreover,hybrid combinations J19,J21,and J24 also had relatively stronger mid-parent heterosis in quality traits such as reducing sugar and total soluble sugar.4.Analysis of heritability indicated that both the narrow-sense and broad-sense heritabilities of plant height,ear height,branches,hundred-grain weight and other traits were >50%,and it was suitable to select purposefully in early generations when breeding sweet corn inbred lines.While the narrow-sense and broad-sense heritabilities of the two traits,ear row number and axle diameter,were <50%,suggesting that it was suitable to select in the late generation.Meanwhile,the broadsense heritabilities of traits(e.g.,stem diameter,single ear weight,ear length,ear diameter,number of grains per row,grain length,reducing sugar,and soluble total sugar)were >50%,but the narrowsense heritabilities were <50%.It suggested that the selection criteria for target traits could be broadened in early generations,and targeted selection could be made in later generations.5.Genetic correlation analysis of the major characters of sweet corn showed a highly significant positive correlation of plant height with ear height,and a significant positive correlation with stem diameter.Meanwhile,the single ear weight of sweet corn was highly significantly positively correlated with ear diameter and number of grains per row,and significantly positively correlated with ear length and ear row number.In addition,a highly significant positive correlation was found between ear length and number of grains per row;ear diameter also showed a highly significant positive correlation with ear row number and grain length,and significant positive correlation with hundred-grain weight. |
