PERSPECTIVES OF MOLECULAR MARKER ASSISTED BREEDING FOR EARLINESS IN TOMATO

In a tomato (Lycopersicon esculentum) breeding programme aimed at earl iness, a breeding line, designated 'IVT-KT1', was developed by several rounds of crossing and selection. Among its ancestors were the two wi ld relatives L. pimpinellifolium and L. parviflorum. The breeding line flowered and set fruit one to four weeks earlier than old and modern cultivars. To identify QTLs for earliness, an F-2 population was obtai ned by crossing 'IVT-KT1' with the 'late' true breeding cultivar 'Prem ier'. In winter and early spring, 690 plants of this F-2 population we re evaluated for earliness of which 292 were selected for RFLP analysi s. Only limited parts of the genomes of 'IVT-KT1' and 'Premier' were p olymorphic and these polymorphisms were likely due to introgression fr om the ancestor wild species. By using the interval mapping method on the combined data of the greenhouse evaluations and RFLP analyses, thr ee loci were identified that were associated with earliness. One was m ainly associated with flowering time, another with fruitset time and a third one with ripening time. Two of these loci were also associated with fruit weight. F-3 progenies selected for earliness on the basis o f the QTL-data did confirm the F-2 results. Two major earliness genes explained a difference in earliness of more than three weeks. The asso ciation with reduced fruit weight seemed to be due to pleiotropic effe cts rather than to linked genes. Consequently, the gain in earliness w ill cause a reduction in fruit weight that may not be acceptable for b reeding applications.