Key message A paralog of Cell Size Regulator ( CSR ), CSR-like1 , underlies the novel fw6.2 QTL in tomato. The gene and locus regulate fruit weight by increasing pericarp cell size and its function on fruit weight appears to be conserved in other crops. Abstract Fruit weight is a quantitative trait that was under strong selection during the domestication of fruit and vegetable crops such as tomato ( Solanum lycopersicum ). Whi...