Abstract: In order to improve the selection efficiency of melon materials with different pulp firmness types. The crispy melon inbred line 20S11 and the soft melon inbred line 20S75 were used as parents to construct F2 and BC1F1 populations，analyzed the fruit pulp firmness trait is inherited by a single gene，and crispy is dominant relative to soft. A mixed pool of extreme fruit flesh hardness traits was constructed based on the F2 segregation population. Using whole genome sequencing combined with map based cloning technology，the pulp firmness gene CmPf1 was located in a region of approximately 54.71 kb on chromosome 10. Through resequencing analysis，it was found that the gene MELO3C012216（CmGATL3） encoding GATL3（galacturonosyltransferase-like 3）in 20S75 had a termination codon mutation located at the 567th base（C–G）of the coding region，leading to early termination of protein translation and resulting in complete deletion of the transferase protein domain. The expression pattern analysis of CmGATL3 using qRT-PCR showed that the expression level in crispy melon 20S11 was significantly higher than that in soft melon 20S75. Based on the above mutation sites，PF-KASP molecular marker was developed and performed genotype detection on 56 melon inbred line materials. Among them，the crisp materials were C︰C type，and the soft materials were G︰G type，and the markers were codominance. Further utilizing PF-KASP for genotype identification of F2 population，compared with the results of pulp firmness phenotype identification，the accuracy reached 100%.

Key words: melon, pulp firmness, gene mapping, KASP marker, assisted selection breeding