Fruit size is a complex trait determined by cell division and expansion. While these core cellular processes are controled by genetic factors, they are also greatly dependent on plant vegetative features and physiology, which determine the source/sink relationship within the plant, and on the environmental context. In the past, the exploration of tomato natural variability successfully revealed fruit weight alleles related to tomato domestication, and a number of underlying genes were identified. In this work, we searched for novel alleles regulating tomato fruit size in a Micro-Tom EMS mutant collection. P17F7 and P22H3 tomato mutant families presented a steady increase in fruit yield from 13% to 27% associated with larger fruit size and were selected for identification of causal mutations. A mapping-by-sequencing approach using phenotyping of yield-related traits in BC1F2 segregating populations enabled the identification of two loci on chromosomes 4 and 8 positively associated with the increased yield and fruit size in both mutants. In addition, a significant deleterious mutation limiting yield and fruit size was identified on chromosome 9 in P17F7 mutant (y9m allele). Characterization of BC1F3 progenies from homozygous y9WT and y9m BC1F2 plants confirmed the association of the y9m allele with smaller fruit size. Examination of the EMS mutations with potential effect on protein primary sequence led to the identification of a missense candidate mutation. The characterization of genome edited lines is underway and will allow to understand the implication of the underlying candidate gene in fruit size control.< Réduire