Strawberries: red, tempting and bland. Is it really all the fault of the weather?

It all started with a tweet by Nataša Briški, the editor of Meta’s List: “Hey, strawberries, this was not our deal, you look like strawberries, you are red like strawberries but when I take a bite, you taste like coloured water in the shape of a strawberry :(.” Nataša was certainly not the only one tempted by the appearance of strawberries in early April but disappointed by their flavour. Even in sunny Spain, the winter sun does not shine as bright as it does in the summer, but still, is it really all fault of the weather? Let me explain what the experts in plant breeding say and what the future holds.

Today, the garden strawberry is one of the most widespread fruit species in the world. It can be cultivated in temperate zones, in the subtropics and in the tropical highlands. However, this was not always the case. This year we could be celebrating its 300th anniversary. This raises the question – why?

An important milestone for the modern strawberry was actually a “spying” expedition by the French navy that sent a ship along the Pacific coast of South America to spy on the Spanish bases and look for opportunities. In 1714, exactly three hundred years ago, naval officer Amédée-François Frézier brought back to Europe five pots of extremely large strawberries, which were given to him by local Native Chileans from the city of Concepción. The strawberries survived the six-month voyage to Europe and the officer presented two precious plants to the ship’s quartermaster, one to the Royal Gardens in Paris, one to his supervisor in Brest, and he kept one for himself. These plants, today known as Fragaria chiloense, spread throughout France and the neighbouring countries. Unfortunately, the officer only brought plants with female flowers. At that time, the strawberry was still a dioecious species and so seed could not be produced until the day it was coincidentally crossbred with Fragaria virginiana, another strawberry species from North America. This species was already known in Europe, it had abundant growth and many flowers but the fruits were smaller in size. Somewhat by mistake, a London gardener named this extremely popular cross Fragaria x ananassa, a name that resembles the then highly appreciated pineapple. However, events did not move rapidly at that time. The new strawberries spread gradually until 1764, when a seventeen-year-old botanist, Antoine Nicholas Duchesne, offered Louis XV of France a bowl of strawberries that were crosses between F. chiloense and F. moschata. This event was followed by extensive collecting of varieties, similar to today’s plant breeding, and a new fruit species was born. The British wanted to keep up with the French and they were quite successful. The variety Keen’s Seeding, which was dominant in the nineteenth century, remains to this day hidden in the genes of numerous modern varieties.

The reason for the large size of the American strawberries was discovered two centuries later when counting chromosomes became a major priority in botany. It was discovered that the European and the Asian species are generally diploid, which means they have two sets of chromosomes, whereas both American species were octaploids, which means they had eight sets of chromosomes but only two of them belonged to the European wild strawberry variety. We are now aware that higher ploidy level usually results in abundant growth. However, octaploid crops are rare. At this point we have to make a distinction – considering we live in the era of genomics, we know that numerous apparently diploid species in the remote past actually doubled or tripled the number of their genomes, but further changes in their development made it impossible to instantly observe this change. Furthermore, the garden strawberry is special even with regard to what we have just explained and slightly resembles wheat because they both behave as functional diploids. This means that the majority of their genes are passed on as if each of them had only two and not eight variations. But the special nature of strawberries does not end here because, despite being octaploid, they have a relatively small genome. The wild strawberry, whose sequence we already know in detail, has only 481 mega DNA base pairs whereas the garden strawberry has 1,193. The wheat genome, in comparison to the garden strawberry genome, is thirty-three times larger.

Strawberry harvest in Oxnard, California (Photo: Alex Proimos via Flickr)
Strawberry harvest in Oxnard, California (Photo: Alex Proimos via Flickr)

Well, we have certainly wandered far away from Nataša’s question, but let us continue. If the garden strawberry is octaploid, it means that cultivators obtain different descendants each time two species are crossbred. Experts estimate that there are currently around forty major plant breeding programmes around the world, each of them creating tens of thousands of crosses every year. However, not all of them look like the ones in the supermarkets or in your garden. Not at all, actually, because the majority of crosses have numerous bad characteristics and only a few of them combine characteristics that both the producer and the customer desire. Over decades of plant breeding, this fruit species has actually seen significant improvement, although we are not really aware of this. What everyone seems to notice is that new species have increasingly larger fruits, which are also firmer. The American species originally weighed 1–3 grams per fruit, whereas today it weighs up to 20 grams. The selection of species insensitive to day length has also proven to be a major success. In the past, strawberries would only bloom in spring, whereas today they bloom all year round and can therefore be produced in autumn and in winter as well. Many species are also very resistant to cold and can survive temperatures as low as -34 °C.

Even though we buy strawberries because they look good, and we have to wait for our nose and taste buds to determine their sweetness, fragrance and flavour once we arrive home, experts in plant breeding have been actually trying to change this for a long time.

For example, the Californian species Chandler, which has been produced since 1983, is still grown in some parts of the world due to its excellent quality. A more recent example is the Australian Rubygem (since 2002). However, there are hundreds of other strawberry species in the world. A detailed description of strawberries grown in Italy in 2002 lists 129 strawberry varieties, which are being replaced by new ones every year. Regarding the fragrance and the flavour of strawberries, the global public was shaken by two articles published a few days ago in the renowned journal BMC Genomics, in which American and Spanish authors ascribed great significance to a particular gene (FaFAD1), which supposedly influences the flavour of strawberries. Naturally, this theory is quite complicated because strawberries produce as many as 360 evaporative substances, twenty of which are thought to significantly influence their fragrance and flavour. Well, the previously mentioned gene is supposed to be one of the key genes stimulating their production. The discovery of this gene means that it will now be easier to identify good-flavoured crosses using genetic markers.

I hope I have managed to explain, at least partially, why strawberries have a good flavour and why sometimes they have none. The main reason is in the genes, but it also depends on production conditions. In reality, strawberry producers have to deal with many other concerns, especially fungal diseases and pests, in particular mites. The list of strawberry diseases is very long, and many of them cause great losses or even the death of plants. Even though the strawberry is a perennial, large producers rarely grow them in the same field for more than two consecutive years. They are usually grown only for one season. The next year, new plants are bought and crops rotated.

Micropropagated strawberries in Hungary (Photo: Borut Bohanec)
Micropropagated strawberries in Hungary (Photo: Borut Bohanec)

But how do new plants stay healthy? They are reproduced in tissue culture laboratories and sold under close inspection surveillance. The closest plant “factory” to Slovenia is in Budapest, but there are similar ones in Italy. Large producers, the leading strawberry producers in the world being California and southern Spain, even disinfect the soil, which facilitates production. Despite efforts in plant breeding, the solution to these problems is yet to be found. Even though genetic modification could help solve this problem, it is simply not introduced due to the existing negative attitude towards GM species. Thus we are left with crop rotation and the unavoidable use of pesticides. Unfortunately. Well, we can expect the situation to change but certainly not tomorrow, at least not in your supermarket.

Micropropagated strawberries in Hungary (Photo: Borut Bohanec)
Micropropagated strawberries in Hungary (Photo: Borut Bohanec)

And what can be said about the popular slogan – “buy local”? Does it also apply to strawberries? Should we avoid early strawberries due to local principles? Maybe it really does sound bad that the strawberries we bought today (my wife already baked a strawberry cake) had to travel by lorry all the way from southern Spain. But still, in Spain alone, especially in the region around the city of Huelva, this “red gold” employs 50,000 people and generates an income of 400 million Euros. Similarly, strawberries are also a good source of income for Slovene producers, only that they sell them later in the year. Even successful Slovene businessmen export their crops throughout Europe. Buy local is thus a double-edged sword.

 

Author: Borut Bohanec, lectures on plant breeding and plant biotechnology, as well as being Head of Chair and Deputy Dean at the Department of Agronomy at the Biotechnical Faculty, University of Ljubljana. He is a lightning conductor for politicians, self-proclaimed environmentalists and ringleaders of organic agriculture. Follow him on twitter @BorutBohanec.

 

Translated by: Valentina Rebec.

Več od Dr. Borut Bohanec

Plant breeding and genetically modified food

The Slovene word for plant breeding žlahtnjenje is really difficult to pronounce....
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