By Chris Barbey
Ph.D. Candidate, University of Florida
Flavor Sells Strawberries
Consumers want sweet, fruity-tasting strawberries, yet little improvement has been made in this area. This is partly because of the immense genetic and chemical complexity of flavor. Strawberry flavor actually consists of hundreds of unique chemicals, each contributing an important musical note in the orchestra of flavor and aroma. These individual compounds typically have a distinct genetic origin, determining if that flavor is (or isn’t) produced in the ripe fruit. Adding to this complexity each person’s ability to sense various flavor compounds is different, explaining why a universal success is impossible to pin down. Because of these challenges, variety improvement has historically prioritized yield and shipping qualities, often at the expense of flavor.
If we know which genes control flavor and aroma, we can develop new strawberry varieties that are tastier and healthier. However, connecting strawberry flavors to their underlying genetics has been slow and difficult.
Gene Discovery for Strawberry Flavor
Our work at the University of Florida has recently led to a number of discoveries in this area. We use a combination of genetic and chemistry techniques to identify the strawberry genes responsible for important flavors.
The gene discovery process starts in the field. Thousands of fruits from different plants are analyzed at the chemical level. We use a technique called mass spectrometry, which gives us a chemical parts-list of the strawberry fruit. We then group strawberry plants by their ability to produce a given aroma compound, and ask a simple question: What unique genes do they have in common? These common genes are likely related to the aroma compound.
The scientific method is a simple process of deduction—anyone can do it. If certain plants make a unique flavor, we simply look for their unique genetics. But how do we study plants at the genetic level?
Forget Microscopes, We Need to Go Smaller
In an ideal world, we might use a DNA sequencer to read each strawberry’s genome. However this is impractical and expensive. What we actually do is sequence a tiny bit, very frequently—35,000 times, actually. Sounds complicated, but it boils down rather simply. The graph above tells the story:
Each colored dot represents one of our 35,000 different genetic tests, performed along strawberry’s seven chromosomes. We are looking for a genetic test where all flavor-producers have the same test results. The more consistent the results, the higher-up the colored dot. In this case the data indicate that strawberry plants that make linalool (Froot Loops®-like aroma) all share a common genetic sequence near the start of chromosome three!
This is a special example. The linalool-producing gene is already known, and it is located exactly where our results indicate. In other words, we re-discovered the linalool-producing gene, so it says that we can trust the rest of the data. It is like a positive control for the whole approach.
We’ve now discovered the genetics controlling almost a dozen strawberry flavors, including pineapple and grape aromas! Some of these strawberry flavors haven’t seen grocery stores for decades. We’re bringing flavor back.
These discoveries are a big deal.
Using these genetic tests, we can know how a strawberry is going to taste even before a single fruit is made. We can test the genetics of ten-thousand seedlings in the lab, and choose only the best tasting ones for field trials. Instead of searching by hand for a needle in a haystack, we build an electromagnet. This doesn’t just speed up the process by years—it makes it feasible to breed for flavor at all.
There is no shortage of feelings about food and technology. However we all agree that we need to eat healthier. Developing tastier and healthier fruits and vegetables encourages consumers to eat better, and brings better profits to farmers.