Genetic Map Construction And QTL Mapping Of Fruit And Seed Related Traits In Melon

Melon is one of the top ten fruits in the world.The fruit is the edible organ of melon.Therefore,genetic improvement of fruit related traits in melon has always been a common concern for breeders.Melon has a wide range of phenotypes and genetic diversity,showing significant differences in fruit and seed-related traits such as size.Shape and colors.Therefore,the genetic map construction and QTL mapping for fruit and seed related traits using different materials will be helpful for mining the elite genes,which will be not only helpful for analyzing their genetic basis and regulatory networks,but also for laying a solid foundation for genetic improvement and molecular breeding.In this study,two melon inbred lines DHL92 and M323 with morphological difference were selected for developing a F2 population and genetic map construction.The main results are as follows:1.The statistical analysis of 11 important agronomic traits such as single fruit weight,soluble solid content,fruit length,fruit diameter,fruit shape index revealed that the average values of single fruit weight,fruit length,fruit thickness,1000-seed weight,seed length and seed diameter in the F1 generation were between the two parents,while the fruit diameter,fruit shape index,flesh thickness,soluble solids content and seed shape index showed heterobeltiosis.Correlation analysis of these traits showed that there was a positive correlation between fruit weight,fruit length,fruit diameter and fruit thickness,significantly.The fruit shape index was positive correlated with fruit length and fruit width,significantly.The seed diameter were positive correlated with the 1000-seed weight,significantly.The seed shape index was positive correlated with the seed length,significantly.The results of the field trait survey showed that all traits were in a normal distribution and belonged to typical quantitative traits.2.With Screening 1,400 SSR markers,291 of them were shown good polymorphism which were used for genotyping in 93 F2 individuals.Finally,a genetic map was constructed containing 283 SSR markers which spanned a total length of 996 cM with a genetic distance of 3.52 cM between adjacent markers.It contained twelve linkage group,which was named according to 12 melon chromosomes.Among of them,the most number of markers was on LG XI which contained 62 markers,and the least marker number was on LG Ⅰ which contained only 11 markers.The longest genetic length was LG IV which spanned 124 cM,and the shortest one was LG ⅧI spanning only 32.76 cM.The collinearity analysis of the map was compared with the physical map by aligning their positions on melon chromosomes,and nine of them showed that the fitting coefficient was greater than 0.8,suggesting the map constructed in this study with a high quality.3.A total of 16 QTLs were detected for fruit and seed related traits in this study.Among of them,there was only one QTL detected for single fruit weight,fruit length,fruit shape index,and soluble solid content,and the related QTL fw5.1,fl2.1,ft5.1 and ssc7.1 were mapped on linkage group LG Ⅴ,LG Ⅱ,LG Ⅴ,LG Ⅶ,respectively,which explained 3.11%,3.73%,5.54%and 5.51%of the observed phenotypic variation,respectively.Two QTLs,fsi10.1 and fsi12.1,detected for fruit shape index,were mapped on linkage group LG X and LG XI.The QTL fsi10.1 with LOD value of 6.76,which accounted for 17.77%of the total phenotypic variation,and it was mapped in a genetic interval of 8.19 cM between CmSSR23531 and CmSSR23609.There were four QTL detected for fruit diameter,fd5.1,fd 7.1,fd9.1and fd11.1,which was mapped on LG Ⅴ,LG Ⅶ,LG Ⅸ and LGXI.Among of them,the QTL fd7.1 showed the highest contribution rate of 10.79%.Six QTLs were detected for fruit hardness,and two of them mapped on LG II.The LGVIII showed the highest contribution rate of 13.31%and 16.18%,respectively.4.QTL analysis of seed related traits in melon showed that only one QTL was detected for seed diameter and seed shape index,which was mapped on LG Ⅲ and LG Ⅳ,respectively.These QTL could explain 3.37%and 5.24%of the observed phenotypic variation for seed diameter and seed shape index,respectively.