Verification of linkage group using PRINS labeling technique in cultivated strawberry

Recently, some linkage maps of cultivated strawberry have been reported using many SSR markers. It is desirable to evaluate an accuracy of the linkage maps, because cultivated strawberries are allo-octoploids. The accuracy of a linkage map can be confirmed, if chromosomes are fluorescently labeled with SSR markers that are located close to both ends on the same linkage group (LG), and their signals are detected close to both ends on a pair of the homologues chromosomes. The purpose of the study is to evaluate an accuracy of LGs 1A, 2A and 1B using a direct cycling-primed in situ (C-PRINS) labeling technique for physical chromosome mapping. The cultivar 'Sachinoka' was used for chromosome observation. A pair of SSR markers close to both ends of the LG was fluorescently labeled on chromosomes using red and green colors generated by tetramethylrhodamine-12-dUTP and fluorescein-12-dUTP, respectively. Within 56 chromosomes of one somatic cell, red and green signals were observed on 16 and 13 chromosomes, respectively. Two of 56 chromosomes had both signals on the both ends. The same tendency was observed in the 2A. Then, it could consider that the LG 1A and 2A were correct. In contrast, when conducted the C-PRINS labeling with 2 SSR makers of the 1B linkage group, red and green signals were observed on 37 and 19 chromosomes were observed, respectively. The images showed more than 2 of 56 chromosomes had both signals on both ends of the chromosomes. Then, it could not be confirmed whether the LG 1B was correct or not.