Genetic Analysis And QTL Mapping For Citric Acid Content, Titratable Acidity And PH In Melon (Cucumis Melo L.) Fruit

Melon (Cucumis melo L.) is a very important commercial crop in the world horticultural industry.Melon is favored by consumers mainly due to its refreshing, pleasant taste and aroma and rich nutrient.The kinds and contents of organic acids in ripe fruits are crucial factors influencing flavor quality. Theyare also important for fruits’ nutrients and metabolisms.In this study, six generations of P1, P2, F1, BC1, BC2and F2derived from a cross of ‘60’(acidless)and ‘61’(acid) were used to study the inheritance of melon citric acid content, titratable acidity(TA) andpH traits by joint analysis method of multiple generations; The F2generation was used to construct alinkage map and analysis the QTLs of citric content, TA and pH traits. These results were useful forimproving efficiency of quality breeding for melon and taking full advantage of the flavor melonresources. The results showed below:(1) We use joint analysis method of multiple generations to study the inheritance of melon citricacid content, TA and pH traits. The results showed that citric acid content was controlled by one pair ofadditive–dominance major gene plus additive–dominance-epitasis polygene model (D-0), The majorgene heritability of F2population was31.06%, and the polygene heritability was30.84%.The majorgene had a larger additive effect than dominant effect; pH was controlled by D-0model, the major geneheritability was84.07%, and the polygene heritability was12.09%; The TA was controlled by two pairsof additive-dominance major gene plus additive-dominance-epitasis polygene model (E-0), the majorgene heritability of F2population was78.06%, the polygene heritability was0; The results also showedthat citric acid content, TA and pH were highly correlated.(2) A genetic map of melon was initially constructed using JoinMap4.0software based on SSRmarkers. The map consisted of12linkage groups spanning923.2cM with an average of8.71cMbetween markers. The longest group was131.7cM, and the shortest was11.0cM.(3) The multiple QTL mode（lMQM）method of software package MapQTL version4.0was usedto map and analyze QTLs.3QTLs (cit7.1, cit8.1and cit8.2) were detected for citric acid content locatedon Chr7、Chr8respectively, including one major QTL (expl≥10%) named cit8.1, which explained34.8%of the phenotypic variation;4QTLs (ta5.1, ta8.1, ta8.2and ta10.1)were detected for TA locatedon Chr5、Chr8、Chr10respectively, including one major QTL named ta8.1, which explained47.5%ofthe phenotypic variation;2QTLs (ph8.1and ph11.1) were detected for pH located on Chr8、Chr11respectively, including one major QTL named ph8.1, which explained82.7%of the phenotypicvariation. The three major QTLs were co-located on Chr8at79.9cM, indicating that citric acid content,TA and pH were highly correlated in the molecular level.