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MAKE TOMATOES GREAT AGAIN!
MODERN TOMATOES don’t taste as good as they did in the old days. Nor are today’s commercial varieties as tasty as their heirloom counterparts.
How come? Is there any hope of improved breeding?
Yes, there’s hope, thanks to science (you’ll excuse the word). “Why Tomatoes Got Bland—And How to Make Them Sweet Again,” by Michael Price, appeared online January 26, 2017, at the Science website of the American Association for the Advancement of Science.
Solanum lycopersicum, “sugary” tomatoes, made the cover of AAAS Science, January 27, 2017.
“A Chemical Genetic Roadmap to Improved Tomato Flavor” is the accompanying technical article in Science, the magazine published weekly by AAAS. An international effort, the paper’s authors include researchers from the Chinese Academy of Agricultural Sciences; the Hebrew University of Jerusalem; the Instituto de Biologia Molecular y Cellular de Plants, València, Spain; RAPID Genomics, Gainesville, Florida; the Sino-Dutch Joint Laboratory of Horticultural Genomics, Beijing; and the University of Florida, Gainesville. An abstract summarizes the results of researcher Denise Tieman and her 19 colleagues.
Cross-section and full view of a hothouse tomato. Image by Fir0002/Flagstaffoto.
The tomato is an edible fruit of Solanum lycopersicum, part of the nightshade family together with the potato and eggplant. It gets its name from the Nahuati (Aztec) word tomātl, meaning “fat water” or “fat thing.” Like others of the nightshade family, the tomato is of Western Hemisphere origin.
Researchers writing in Science report that “Modern commercial tomato varieties are substantially less flavorful than heirloom varieties. To understand and ultimately correct this deficiency, we quantified flavor-associated chemicals in 398 modern, heirloom, and wild accessions.”
Then consumer panels helped the researchers in “identifying the chemicals that made the most important contributions to flavor and consumer liking.… Whole-genome sequencing and a genome-wide association study (GWAS) permitted identification of genetic loci that affect most of the target flavor chemicals, including sugars, acids and volatiles.”
It turns out that volatile compounds activate olfactory receptors [our sense of smell] tracing good flavor. Refrigeration selectively alters a tomato’s volatile content, a reason why cold tomatoes aren’t as tasty as those at room temperature. What’s more, as noted by the researchers, “Flavor-associated volatiles are present at picomolar and nanomolar concentrations in fruits and are extremely difficult to quantify.”
Measurements at the nano (one billionth, 10-9) and pico (a trillionth, 10-12) levels are all but impossible for fruit breeders to assess. The researchers write, “Therefore, most breeders focus on yield, disease resistance and firmness, which are essential for shipping, long-term storage and external appearance rather than flavor quality.”
The researchers also identified a negative correlation between fruit size and sugar content. That is, tomatoes bred for size had less sugar content, to the detriment of their perceived taste.
Compared with volatiles, sugars are present in millimolar concentrations (i.e, in the thousandths, 10-3). And, thus, breeding for size has an inordinate effect on sugar content.
By contrast, the researchers’ GWAS suggests that certain volatiles also have significant effects on perceived sweetness. Two in particular, geranylacetone and MHO (6-Methyl-5-hepten-2-one), were studied in analyses of tomato alleles (genetic identities in the same place on a chromosome).
Above, allele distributions of MHO. Below, allele distributions associated with geranylacetone. Cerasiforme is the wild, cherry, tomato. Transitional tomatoes, as the name suggests, are those genetically between heirloom and modern. Both MHO and geranylacetone are volatiles.
Researchers suggest that breeding with these particular volatiles in mind, though more complex, would provide better tasting tomatoes with less deleterious affect on crop yield and marketing. They conclude, “The genes and pathways identified here in the tomato almost certainly point to pathways worth investigating for improvement of flavor quality in other fruit crops.”
A win-win for tomatoes. And one for science too. ds
© Dennis Simanaitis, SimanaitisSays.com, 2017
Simanaitis Says 
Now I’m looking for some bacon research. BLT’s are a high point of summer…
Would the distribution charts make more sense if the colors were labeled? I’m having trouble with them.