Abstract: The introgression line 14h616 was derived from cultivated tomato inbred line 1052（Solanum lycopersicum 1052）and contained a 2.66 Mb fragment on chromosome 3 from S. pennellii LA0716，which contained a fruit cracking-resistance gene Cr3a. A sub-introgression population of tomato Cr3a resistance gene was constructed using 14h616 and 1052 as parents. Making paraffin sections and measuring the water content of fruits from the crackable fruits and cracking-resistant fruits containing the Cr3a gene in introgression population F5 generation. Histological examination suggested that fruit cracking- resistant Cr3a did not significantly affect the thickness of the cuticle and the number of epidermal cells of fruits. Water content analysis showed that the fruits from the sub-introgression line embodying Cr3a contained less water than that from cultivated tomato inbred line 1052 in mature green stage. Genetic analysis and phenotypic identification of sub-introgression populations showed that tomato cracking-resistant gene Cr3a was incompletely dominant，and its genetic contribution rate is 27.41%. Cr3a was narrowed down to a 349 kb interval between molecular markers 3-ZY75 and 3-ZY43，which encoded 47 putative genes. Using molecular markers，the F2 population constructed with the cracking-resistant material 182h640 as the maternal and the crackable material 182h680 as the paternal，and 200 high-generation materials with different genetic backgrounds were analyzed. The conformity is good and the accuracy of assistant selection was 96%. The study results laid a solid foundation for the map-based cloning of Cr3a and the molecular improvement of tomato cultivars resistant to fruit cracking.

Key words: tomato, fruit, cracking-resistant, fine mapping, QTL