Reported in the current issue of Science, the joint US-Spanish research found that a mutation present in most modern cultivated tomatoes that confers uniform ripening also brings a reduction in their ability to synthesise sugars and other compounds.
One of the lead authors of the study, University of California, Davis, biochemist Ann Powell, said: "This provides a strategy to recapture the quality characteristics that have been unknowingly bred out of modern cultivated tomatoes."
The researchers discovered that the tomatoes that were darker-green when unripe went on to produce ripe fruit with increased levels of sugars or carotenoids as well as the health-promoting compound lycopene. This was due to the presence of transcription factors that control photosynthesis in the plants' cells.
They then turned on the disabled genes while leaving the uniform ripening trait alone, creating evenly dark-green then red fruit that had 20 per cent more sugar and 20-30 per cent more carotenoids when ripe. However, health regulations meant the genetically-engineered fruit could not be tasted.