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Pollination and therefore fruit set in tomato (Solanum lycopersicum) is very sensitive to temperature. Parthenocarpy can be a very useful trait in tomato breeding in sustainable agriculture faced with global warming. Within a collection of Moneymaker tomato mutants a monogenic and recessive mutant with high fruit number was identified in heat stress conditions and named high fruit set under stress (hfs). No morphological alterations in vegetative and reproductive organs were observed except the bigger size of ovary. hfs is parthenocarpic, pollination not being required for fruit set, although this trait was not absolute since it produced some under-seeded fruit. When plants were grown under extreme temperatures (higher than 35 degrees C), hfs exhibits higher fruit yield than wild-type (WT) due to increased fruit number. Another very interesting characteristic of hfs is its improved fruit quality under heat stress, exhibiting a better sweetness/acidity balance than WT. Interestingly, hfs was also tolerant to the combination of heat and salt stress, and the positive effect on production was due to both components of yield, fruit number and fruit weight. The generation of mostly seedless fruit and the high productivity and fruit quality under extreme temperatures make hfs a very interesting mutant to obtain new breeding high-yield lines in adverse environmental conditions.