Identification of Genetic Factors Affecting Fruit Weight in the Tomato (Solanum lycopersicum L.) Cultivar ‘Micro-Tom’

‘Micro-Tom’, a dwarf tomato cultivar, has been used as a convenient model system in tomato research. Previous studies have shown that several genes are involved in the phenotype, but to date no study has focused on the fruit weight. In this study, we tried to clarify genetic factors that regulate the fruit weight of ‘Micro-Tom’ using an F2 population derived from ‘Micro-Tom’ and ‘MPK-1’, a mid-size tomato cultivar. The F2 population showed a continuous and transgressive segregation in terms of fruit weight, suggesting that the fruit weight was regulated by multiple loci. To identify these loci, quantitative trait loci (QTL) analysis was performed. Three QTLs located on chromosomes 4, 7, and 9 were found to regulate fruit weight, and were designated as qfw4.1, qfw7.1, and qfw9.1. Of these QTLs, qfw4.1 exhibited the highest logarithm of the odds score. We confirmed the effect of qfw4.1 in the F3 population and showed that it regulates fruit weight without affecting locule number. In addition, being homozygous for the Micro-Tom allele at the marker linked to qfw4.1 reduced vegetative size, suggesting that qfw4.1 regulates not only fruit weight, but also vegetative size in ‘Micro-Tom’.