Expression of Heterosis by Hybridization

Tomato breeding initially focused on yield and ancillary traits (adaptation, disease resistance, earliness). Presently a large number of cultivars adapted to specific growing conditions (glasshouse, plastic tunnel or field) and for commercial use (fresh-market or processing tomatoes) are released each year. Tomato breeding objectives evolved with the performance of released cultivars and the modification in growing conditions, with increasing emphasis on fruit quality.