Whole-genome resequencing of Japanese large-sized tomato cultivars provides insights into the history of modern breeding

Tomatoes have the highest agricultural production among vegetables in Japan and worldwide. Japanese large-sized fresh-market tomatoes have a unique breeding history that differs from that of other countries, represented by pink-colored and juicy fruits with a good taste and flavor. We performed whole-genome resequencing of 150 Japanese large-sized fresh-market tomato cultivars released from the 1940s to the 2000s to unveil how breeding selection has changed the genome of Japanese tomato cultivars and provide a genomic basis for future Japanese tomato breeding. The genomic population structure of the cultivars was highly correlated with the year of release. Comparison between the agronomic performance and release year of the cultivars reflected trends in recent breeding selection: an increase in fruit sugar content and a decrease in yield performance. Multiple selection signatures were detected on all the tomato chromosomes. One of the selection signatures was related to the introgression of a resistance gene (Tm-2) from a wild relative. Interestingly, some of the putative QTLs detected by genome-wide association studies did not co-localize with the selection signatures, indicating that the genetic diversity of Japanese tomato cultivars still has the potential for genetic improvement of agronomic performance.