The red fruit on fire – the tomato is the edible fruit of the Solanum lycopersicum plant. It is a member of the Solanaceae family, which includes plants such as Irish potatoes, peppers, eggplant, and tobacco. We can get tomatoes easily in the market today, but did you know that the tomato originated from the Andean region now encompassed by part of Chile, Bolivia, Ecuador, Colombia, and Peru?
The plant was first domesticated in Mexico where a variety of sizes and colors were selected. The yellow fruit was believed to be introduced to Europe in the 15th century with the name pomodoro in Italian, which means “golden apple.” Tomatoes were then domesticated further on an intense level throughout Europe during the 18th and 19th centuries. To date, varieties of tomatoes with different shapes, colors, and sizes have been developed via breeding.
Rising Demand Due to Culinary Culture and Awareness
What types of tomatoes do you prefer for your salad? Is it the size or the color that matters? From marble-sized cherry tomatoes and juicy salad tomatoes to huge, sweet beefsteak tomatoes, their colors may range from deep crimson to orange, yellow, green, and purple. Which are your favorites?
Some might choose cherry tomatoes and others might prefer salad tomatoes, depending on what type of food they are preparing, and this is largely affected by the culinary culture of the countries or races. As we all know, there are many different races residing in different continents across the world, and people in certain countries prefer tomatoes over other vegetables to be included in their daily diet. For instance, there is a popular dish called stir-fried tomatoes and eggs in China. It’s a must-try dish for everyone who visits the country, and almost every Chinese person from the country is able to cook this signature dish.
To the west of China is India – a country in which the tomato is an essential ingredient in most cultural foods. The recent tomato price hike in India was caused by the shortage of supply due to the heavy monsoon rains that damaged the crops. We can imagine how important the tomato is to India as they even have armed guards protecting the valuable tomatoes from being stolen after the spike of tomato prices.
Other than being consumed raw as in salads and cooked with eggs and curries, tomatoes are also made into paste for pastas and pizzas, or processed into ketchup and tomato juice. These are the most common ways of consuming tomatoes nowadays.
Apart from that, awareness of the nutritional value of tomatoes has been increasing across the globe due to the advancement of technology and social media. Various studies showed that tomatoes are the source of important nutrients which have positive impacts on human health, particularly the lycopene which is an extremely powerful antioxidant that has been linked to risk reduction for a number of types of cancers, including prostate, lung and stomach, pancreatic, cervical, and colorectal cancers.
On top of that, it is proven that a medium ripe tomato (~145 grams) can provide up to 57 percent of the recommended daily allowance of Vitamin C and 25 percent of Vitamin A. Tomatoes also contribute β-carotene, vitamin B, potassium, iron, and calcium to the diet.
World’s Largest Tomato Producer, Exporter, and Importer
All the reasons above coupled with the growing world population cause the rising demand for tomatoes. China is the largest producer of tomatoes in the world followed by India, the United States, Turkey, Egypt, Iran, Italy, and Spain. China alone accounts for more than 30% of the global tomato production. Almost all Chinese tomato production is for domestic use whereas about 1.5% is exported, of which over 60% is destined for Russia.
Moving across to the European Union, Spain is the largest European tomato producer for the fresh market, growing about a third of Europe’s production. Spain exported 950 million kg of tomatoes in 2015.
Mexico is the world’s largest tomato exporter with over 1.5 million tons. In fact, over half (52%) of the tomatoes consumed in the U.S. come from Mexico.
On the other hand, the U.S. is the world’s largest tomato importer, though internal production accounts for about 40% of their need for tomatoes. The remainder is imported, as mentioned earlier, mostly from Mexico.
The production of tomatoes need to be increased so as to keep up with global demand, especially during the time when climate change is one of the major problems currently occurring.
Gene Editing for Improvements of Tomato Varieties
Climate change is poised to affect the world’s food supply in three key ways – the quantity, quality, and location of the food we produce. This has made food security a pressing concern in the recent years. Breeders and genetic engineers have been working relentlessly to increase the yield of plants in order to feed 10 billion people on this climatically chaotic, hotter, more disaster-prone planet.
The question is how?
It’s simple yet complicated – by producing tomatoes that are the combinations of several characteristics such as disease resistant, stress tolerant, higher yield, longer shelf-life, increased nutritional value with desired shape, color, and flavor.
New crop varieties were created through traditional plant breeding for decades, but new technologies, such as gene editing, have the potential to create improved varieties within a shorter period of time via the precise introduction of favorable alleles into elite varieties.
Scientists have successfully generated a tomato variety – Tomelo which is fully resistant to the powdery mildew fungal pathogen Oidium neolycopersici using the CRISPR/Cas9 technology. These plants are not only morphologically similar to the wild type, but they also produce harvested fruit with weight similar to the wild type. This is certainly good news to growers as the powdery mildew fungus often causes crop loss when the tomato plants are infected with the disease. The infected tomato plants develop symptoms including white superficial mycelium on leaves and stems, yellowing, desiccation, necrosis, and defoliation.
To further strengthen the confidence of the public, the researchers used whole-genome sequencing to prove that this Tomelo variety does not carry any foreign DNA sequences but only a deletion that is indistinguishable from naturally occurring mutations.
Desired Branches and Flowering
Another problem in tomato farming is the excessive branching and flowering – characteristics which lead to less fruit and thus less yield for farmers. These characteristics exist due to the integration of wild tomatoes from the Galapagos islands with the commercial breeds in the 1950’s, so that the fruits stay on the vine longer to facilitate mechanical harvesting.
The scientists also found that for some reason, perhaps to hold heavier fruit, the green leafy cap on top of tomato fruits tend to grow larger now, after centuries of selective breeding. People might think that more branches on each inflorescence means more flowers and eventually more fruit, but in fact it’s the opposite. Plants with excessive branches often have lower fertility because they cannot handle the imbalance of bearing too many fruits. They will end up producing fewer tomatoes.
A team of researchers led by Zachary Lippman from Cold Spring Harbor Laboratory in New York has recently uncovered the genes associated with excessive branching and flowering in tomato plants. They are now working with plant breeders to use gene editing to develop tomatoes with branches and flowers optimized for the size of the fruit. Plants with larger fruit, for example, may have better yields if they have fewer flowering branches than those with smaller fruit.
You heard of seedless watermelon and seedless bananas, but did you know there are seedless tomatoes now? In fact, there are a few seedless varieties of tomato, but they have taken breeders many years to create through conventional breeding.
Researchers from Tokushima University in Japan used the CRISPR gene editing technology to deliberately introduce mutation in tomato plants, causing them to become seedless or parthenocarpic. The mutation increases the level of auxin hormone in tomato plants, and the fruits will continue to develop even though no seeds have begun to form.
Gene editing is precise and therefore no mutations will be introduced in other parts of the genome. The only significant difference of this gene-edited tomato plant is that the leaves have less intricate shapes compared to the normal ones. This is because leaf formation can be affected by the high level of auxin. Other than that, the shape, color, and size of the fruit are no different.
The success of these scientists has shed light on the problem that all of us are worrying about – food security.
How does seedless fruit help in food security? Let us explain.
Farmers rely on pollinators such as bees for the pollination of crops. However, the number of bees is reducing year after year due to destruction of habitats and the use of pesticides. This causes reduced pollinations and eventually lesser yield from our crops.
Parthenocarpic, or seedless, fruits do not require pollination at all. Thus, farmers do not need to rely on bees for pollination, but they still get fruit on their crops. This improves food security.
CRISPR gene editing technology could also be used to develop other types of crops to become seedless and hence do not require pollination. Apart from that, this cutting-edge technique could be used to introduce beneficial mutations that include stress tolerance. It will further improve food security.
Tomatoes That Flower and Ripen Earlier
Developing tomatoes that flower and ripen earlier means increasing the yield per season. This is a breeding goal that every breeder and farmer would love to achieve. Now, the researchers have made this a reality by using the CRISPR technology to rapidly improve the yield traits of tomatoes.
Wild tomato plants are very sensitive to the exposure of daylight, and the length of daylight brings different outcomes. It takes longer for the plants to flower and produce fruits if they are exposed to longer daylight. Domesticated tomato plants, however, are not sensitive to daylight changes and instead rely on time of planting to determine flowering and fruit production. Studies revealed that this is all related to the Self Pruning gene, SP5G, which work in contrast with the hormone florigen to promote or delay flowering.
The team of scientists studied the growth of wild and domestic varieties of Roma and Cherry tomatoes and noticed that while the wild tomatoes saw a surge in SP5G gene expression, making them sensitive to the daylight length and prolonging flowering, domestic tomatoes were insensitive to daylight length.
Therefore, the team thought that they would halt all SP5G expression in the domestic varieties to create plants that flowered even earlier and hence produced fruit earlier. Using CRISPR to induce small mutations in the SP5G gene to inactivate it, they created a new plant variety that had no expression of SP5G. The new plants flowered and produced fruits two weeks earlier than the original plants.
This success would possibly enable tomato growers to expand the geographical range of cultivation, by using the CRISPR gene editing technology.
The CRISPR technology could go beyond the tomato family, to include major food crops such as maize, wheat, and soybean, all of which the world strongly depends upon.
The Advantage of CRISPR
With CRISPR, scientists could possibly edit organisms, removing the DNA regions that lead to unfavorable outcomes. In fact, organisms are constantly undergoing this process naturally through evolution, to adapt themselves to environmental changes, but this takes time. Gene editing speeds the process, cutting off years, decades, and even millennia.
Gene editing promises giant leaps in agriculture in terms of yield enhancement, disease resistance, and stress tolerance. Gene-edited plants are very different from GMOs, or genetically modified organisms. GMOs introduce foreign genes to improve outcomes but in the case of gene editing, no foreign genes from other organisms are added into the crops. Changes are made to a plant’s existing DNA with the same precision that word-processing programs can edit text.
Two of the industry’s heavyweights, Monsanto and DuPont, have been the early supporters of this emerging technology. Early this year, Monsanto reached a new global licensing agreement with the Broad Institute of MIT and Harvard for the use of the novel CRISPR-Cpf1 gene-editing technology in agriculture. This is a sign that the gene editing era is approaching.
If the CRISPR technology could be utilized at its best, it could certainly help to ensure our food security as it is a game-changing gene-editing tool that could possibly end world hunger by creating plants with sustainable food production.
The perfect tomatoes on your dinner plate in the next decade might be produced using this powerful technology.
Image from flickr by sean_hickin