Posted on behalf of Alice Lighton.
Tomatoes bred to have a uniform colour are not as sweet as their more mottled counterparts. Decades of selecting fruit that begin life with pale green skin may have inadvertently contributed to the bland flavour of the modern supermarket tomato.
Uniform tomatoes are easier to harvest and preferred by consumers. Researchers have pinpointed the genes responsible for even-coloured fruit, and found an association with photosynthesis in plants. Tomatoes with the mutation do not produce a protein responsible for chloroplast development in fruit, and pale unripe fruit produce less sugar while they develop, resulting in a less-sweet tomato. Their results are published today in Science.
But consumers cannot try before they buy, and they make choices based on looks. “The general perception is that consumers prefer uniformly coloured fruit,” says James Giovannoni, a molecular plant biologist at Cornell University in Ithaca, New York, and an author of the study. “They’ll pick up a fruit that’s more evenly coloured over one that’s splotchy.”
Farmers also prefer the pale, uniformly coloured fruit. Tomatoes destined for processing and tins are mechanically harvested, and colour is used to decide when to send in the machines.
Darker unripe fruits contain more chlorophyll and ripen into tastier red tomatoes, with more glucose, fructose and carotenoids. “The differences are not huge — around 10 to 20%,” says Giovannoni. But that is still enough to taste.
Heritage varieties of tomato — which have never been bred commercially — contain the original version of the allele responsible for chloroplast development in fruit. The fruits often have a darker green top that ripens to a different colour from the bottom.
Low sugar content is not the only problem with the flavour of the commercial tomato. Last month, researchers in Florida reported that supermarket tomatoes lacked volatile organic compounds present in heritage varieties that make the fruit taste sweeter (see ‘It’s not sugar that makes heirloom tomatoes taste sweeter‘).
At present, the tomato is the fleshy fruit of choice for plant geneticists: tomatoes grow quickly, have a relatively short genome and are easy to genetically modify. Giovannoni’s team contributed to the sequencing of the tomato genome, reported last month (see ‘Tomato genome sequence bears fruit’).
However, genetically modified crops are not popular among consumers, and a return to a patchy tomato may not be popular among farmers. Instead, breeders could try to produce a fruit with a uniform dark green colour. Otherwise, consumers may have to resort to growing their own fruits in search of a delicious, if wonky-looking, tomato.