The Tastiest Tomato

Now, to combat widespread public dissatisfaction with 'supermarket-perfect' tomatoes like mine - in other words, ones that look great but are deceptively bland and tasteless when you eat them - scientists have tracked down and published the cocktail of chemicals that need to be there to constitute a much more flavoursome fruit.  Professor Harry Klee, from the University of Florida, explained to Chris Smith that it was his own displeasure at the inferiority of shop-bought tomatoes that motivated him to embark on the search for the perfect tomato...

Harry - If you're of a certain generation and you've grown your own tomatoes, or had access to them, you realise that some of them taste great and then you go to the store and they taste incredibly bland, and it's clearly a huge problem.  It's the number one complaint in the US of consumers with regard to produce and so, yeah, it was a daunting task, but one that just cried out to be done.

Chris -  So how did you approach this?  Did you say, "well, the ones that are in the supermarket have been bred that way.  Let's look upstream of that, at the ones that they came from, and see if we can put some of the flavours back?"  How did you approach it?

Harry -   Yeah, that's precisely it.  Breeders over the years have worked very hard to give customers what they want.  Unfortunately, their customers, or the growers just want more and more yield, and the growers are not paid for producing objects that taste good.  So basically, the breeders have, through selection over the last 50 or more years picked out varieties that have really high yields but have absolutely no taste.  And so, if you go back to the pre-intensive breeding periods you have what in the US we call "heirloom" tomatoes - varieties that have been around for a hundred years or more which have fabulous taste.  They're not very farmer friendly.  You get very poor yields, they're very susceptible to diseases, but they taste great.  So you know that out there, there's a massive reservoir of really good tasting material and so, the trick was in our case, to go back to that material that preceded the intensive breeding, and understand what is good flavour.

Chris -   How did you do that?  Did you literally put samples of these hundred plus species of heirloom tomatoes in front of tasters and say what's good, what's bad?

Harry -   That's exactly what we did.  We're now up to about a couple of hundred different varieties that have vastly different chemical profiles and vastly different tastes.  Some of them are outstanding, some of them really aren't very good, and you wonder why people grew them in the first place.  But that incredible diversity that's out there gave us this opportunity to do a big test where we could take upwards of a hundred of more varieties.  

Basically, we gave them to a large consumer panel and said, "What do you think of them?"  And then we took samples of those and ground them up, and determined what chemicals related to flavour were in each of them and basically, you can take all of that massive amount of data of chemistry and consumer preferences, and through statistics, you can extract out what's in the good ones and what's in the bad ones.  And in theory, you can put together a recipe for the ideal tomato.

Chris -   So, you screen them across all these people, you see trends emerging where certain combinations of chemicals appear to associate with people saying, "This is very nice.  It tastes very nice.  It's nice and sweet.  That's what I like."  Other chemicals seem to be less important.  You hone in on what those chemicals are.  Do you now know then exactly what constitutes the ideal tomato in terms of its chemistry?

Harry -   The simple answer is yes.  The more complex answer is, there are still differences with people in terms of what individuals like.  And so, the way I like to describe it is to say, we can optimise for the chemical composition of a great tasting tomato.  It won't necessarily be everybody's favourite, but I think everyone would say it's right up there with the very best.  Certain individuals might like something that's a little sweeter.  Some individuals like some that's a little more acidity to them, but by and large, yes, we can extract out the recipe for a great tasting tomato.

Chris -   And would the idea be then that you can now rationally breed strains of tomatoes, going back to those  heirloom strains and selecting out chemically the ones that have the right biochemical proportions of these chemicals, breed from those and then slowly, arrive at one that does have good shelf life in 'supermarket-friendly' characteristics but also, blends in a lot of these other important flavourants?

Harry -   Yeah, that's exactly the approach.  I mean, unfortunately, until a large commercial grower is paid to produce something that tastes really good, we have to work within those constraints at the commercial level.  We have to have a tomato that really does produce high yield, and really is resistant to all the diseases the farmer encounters.  But by going back and knowing the specific chemistry of what is great tasting, and we know that the genetics is there within the heirloom populations, we just have to go back and recapture it and that's going to take time because of those constraints of yield and disease, and shelf life, but I think we know how to do it.  We basically have provided the road map for what genetics we need to combine to get the product that tastes good.

Chris -   So ironic that modern day breeding gave us something we don't like and we're now having to go back to what people have done originally to put it right.  But tell us then what are the important chemicals you found that constitute the perfect tomato and were there any surprises?

Harry -   Yes, there were.  I mean, number one is sugar.  We know that people, through genetics over eons, have been selected for picking out things that have lots of calories.  So sugar is really the number one, but beyond the sugar, you very quickly get compounds which are the smell components, the volatile chemicals that we smell, and there are a few of those that are really important.  They're actually the chemicals that are related to the same compounds that give the fruit colour - from the carotenoids.  There are carotenoid breakdown products that are very, very strong contributors to flavour and they really make a huge difference in terms of preferences.

Changing climate has caused range shifts in many species, altering the area they are able to survive over. It is not as simple however as species being able to just move to warmer or cooler areas as the climate shifts. Constraints like limits on dispersal, and dependence on other species for food or shelter (particularly plants) can limit a species' ability to shift.

Now research led by Rachel Pateman from the University of York, and publishing in the journal Science has shown that increasingly warm summers in the UK have allowed the northwards expansion of the range of a species of butterfly by allowing it to use a wider range of host plants.

The brown argus butterfly, Aricia agestis, is at the northernmost boundary of its range in Britain, and is also found on the Continent, in warmer climates. It requires a sufficiently long, warm summer to have enough time for the eggs laid at the start of the summer to hatch into larvae and eat enough before pupating over winter.

Historically, argus females have laid their eggs primarily on the common rock rose. These plants are generally only found in grassland on south-facing slopes, which are the warmest type of microclimate found in the British Isles. The restriction of the butterflies to using this species is most likely down to this warmer microclimate effect and not down to any innate female preference or due to larvae growing better - because the team tested these exact conditions between rock rose and another plant the butterflies occasionally used, called dovesfoot cranesbill. In fact, it was shown that the larvae actually grow better on the cranesbill plants.

By analysing climate data and observational data of argus butterflies, the team have found that the increased frequency of warm summers over the past 20 years has coincided with an increased use of dove's foot cranesbill by the butterflies. And because cranesbill grows far more widely than does rock rose, the range of the butterflies has expanded, spreading north by nearly 80km in those 20 years - more than twice as fast as would be expected from the global mean.

Another factor that may have allowed the population of argus butterflies to increase is that the shift in plant species has allowed the butterflies to escape from harmful parasitoids - organisms that act like parasites on their hosts, and then ultimately kill them.

So while this is good news for the argus butterfly, it's unclear what the impacts could be on the ecosystems they are now managing to exploit. They might end up outcompeting other species that rely on these cranesbill plants, or transfer diseases or parasitoids to new hosts.

But the important point from this story is that interactions between species don't have to be constraining factors when climate change causes range shifts, but can actually allow species to expand their range.