Plants can cope better with heat and drought

Grains and potatoes suffer from dry and hot summers. New varieties are needed so that food does not become scarce and expensive.

That’s what it’s about:

Plants suffer from dry and hot summers

Summer 2019 broke records: hottest June since measurements began across Europe, new national heat record for July. After 2018, this year is the second in a row with extremely high temperatures and far too little rainfall in the region.
But not only humans and animals groan under the temperatures, plants are also under great stress. For farmers this means crop failures, for consumers rising prices. Since they cannot run away from heat and drought, plants have developed strategies to defend themselves against lack of water and direct sunlight. But they don’t do much in unusually hot and dry summers.

How do plants protect themselves from heat and drought?

Heat alone is not a problem for most plants. It becomes difficult if there is no additional moisture: “Dryness intensifies the effect of high temperatures. With a good water supply, plants can cool themselves by evaporation, but that no longer works under drought stress, ”explains Dr. Dirk Hincha from the Max Planck Institute for Molecular Plant Physiology. In Potsdam, he and his employees are researching how rice and potatoes adapt to heat, cold or drought – so-called abiotic stress factors.

It doesn’t work without water

Water is essential for plants because it enables stability, nutrient transport and photosynthesis. In order to save water in drought, plants close their stomata on the underside of the leaves, for example. Water evaporates through this, but the carbon dioxide necessary for photosynthesis also enters. Plants also roll up their leaves in drought or shed them completely. The plant lives on the back burner.

At the same time, the plants try to penetrate deeper water-bearing soil layers with increased root growth. In this way they can cope well with short-term water shortages. However, if the drought lasts for a long time, the overall plant growth is reduced – in the worst case, the organism dies.

What are the consequences of drought for agriculture?

About half of Germany’s area is used for agriculture. 71 percent of this is arable land on which wheat, maize or potatoes are grown. Heat and drought are also noticeable in these crops bred for maximum yield; They too are under stress and react accordingly: “Flowering times and fruit formation are postponed,” says Dr. Friedrich Kragler from the Max Planck Institute for Molecular Plant Physiology in Potsdam.
For example, if fruit trees bloom earlier in the year because it is already warm, a late frost can destroy the entire harvest. In addition, so-called stress blooms can arise, says Friedrich Kragler. “That means that few or sterile flowers are formed.” No fruit is produced from sterile flowers. As a result, the harvest is sparse: the farmer harvests fewer plants of poor quality.
Plant physiologist Kragler researches how plants grow and how they can be changed in a targeted manner. Plants are particularly sensitive to heat and drought stress during the early development stages of flowering and seeds.

In the case of flowers, heat and drought damage the pollen, which in the worst case can no longer fertilize the flowers. “If the stress affects the early stages of the seed, it mainly results in qualitative damage,” says Dirk Hincha. This means that after successful fertilization, grains are produced, but they are smaller.
In concrete terms, this means: corn on the cob remain empty, ears of barley carry smaller grains, potato plants can only supply fewer or smaller tubers.

What does this mean for us consumers?

There were already significant crop failures in 2018 compared to the previous year. The corn harvest collapsed by almost 30 percent, with wheat it was about 13 percent less than in 2017, with potatoes about 24 percent. And the forecasts for the grain and potato harvest for the current year are anything but rosy. This hits the farmers who live from agriculture particularly hard. But the consumer could already feel the consequences of the drought last year: Potatoes were more than 50 percent more expensive.
Article section: Why do plants not adapt to climatic changes?

Why don’t the plants adapt to the climatic changes?

Natural adaptation assumes that plants are repeatedly exposed to the same stimuli, such as drought stress or infestation with pests, over many years. Among their offspring there would be – by chance mutation – some who can cope better with these stress factors. These could then prevail and represent a new, more robust variety.

Our crops such as wheat, barley, maize or potatoes are grown annually in Germany. This means that the farmer sows fresh seeds every year and, for example, plows under the plants after the fruit harvest. There is no natural selection.

There are many different types of grain and potatoes that the farmer can choose from. In doing so, he takes into account criteria such as the nature of the soil, susceptibility to certain plant pests or the future intended use. That means: “The” wheat or “the” potato does not exist. Over 200 different potato varieties are approved for arable farming in Germany alone, and plant breeders bring new varieties onto the market every year: higher-yielding, more resistant, better. But there is no such thing as a variety that can do everything. Stress-tolerant varieties are usually less productive, whereas high-performance varieties are susceptible to drought stress or pests.

Science is looking for active ingredients

One possibility is to treat plants with pesticides, for example. This offers the plants a growth advantage because pests and weeds are kept in check. However, such approaches are harmful to the environment.
Plant researchers are therefore on the lookout for “drugs” for plants that can provide targeted help in periods of drought. A group of researchers from the University of California, for example, has developed an active ingredient that is based on the plant hormone abscisic acid: opabactin. This ensures that the stomata close when there is a lack of water.

The synthetically produced opabactin binds significantly better to abscisic acid receptors and also extends the water-saving effect. However: it is basic research. It takes many years to answer open questions, similar to medicines for humans: How stable are possible active ingredients in the field? Are there any side effects or long-term effects? How expensive will such an active ingredient be and how often does it have to be used?

Can plant breeders create stress tolerant crops?

At the same time, plant breeders are constantly working on new varieties that are optimally stress-tolerant. Over time, however, the demands on and the idea of ​​an optimal potato plant change. The current focus is on heat and drought tolerance. But: “Resistance to the cold and protection against pest infestation are also important factors, because climate changes will generally result in more extreme weather,” says Friedrich Kragler. In addition: “Climate change also changes the types and number of pests.”

Plant breeding is complex

Prof. Claus Schwechheimer from the Technical University of Munich sees further difficulties in modern plant breeding and research: “With different plants, different parameters are considered relevant to yield.” For example, many and large seeds, i.e. grains of grain, are important for cereals, because only they become afterwards processed into bread. When it comes to tomatoes or potatoes, the seeds do not play a role for us consumers. There it depends on attractive fruits or tubers.
The systems biologist and his working group are researching how plants react acutely to salt or cold stress.
So plant breeding is a very complex matter because there are many factors that need to be considered.

How do new plant varieties arise?

Mainly in Germany new plant varieties are produced with the help of classic conventional breeding methods. Plants are crossed with one another and the offspring selected for the desired new characteristics. Biologists call this selection selection. For a new stress-tolerant grain variety, for example, plant breeders would then cross an old, frugal variety with a modern, high-yielding variety. The difficulty: these crossings are random processes.

Classic plant breeding takes a long time

Even if classical breeding now makes use of modern molecular biological methods, the breeder cannot predict whether and which of the offspring will combine the desired traits. In addition, it is not immediately apparent whether other properties have changed due to spontaneous mutations.

“Classic breeding needs a very long time to provide suitable stress-tolerant varieties, for example over ten years for wheat,” says Friedrich Kragler. It can take a long time for a new variety to be approved. Time that agriculture may not have given the climatic changes that are already taking place. Claus Schwechheimer demands: “It would be important that breeders and basic researchers can react quickly. But legal restrictions hold back breeders when it comes to applying knowledge from basic science specifically to their elite varieties. “

How does genetic engineering work in plant breeding?

Scientists around the world do research to understand stress mechanisms and regulations in plants. How does a wheat plant react to drought stress? Which molecular processes take place inside the plant cell? The researchers already know quite a bit about this and can even name individual gene locations that play a role in drought tolerance, for example. Using genetic engineering methods, crops can now be modified in a targeted manner in order to produce the desired properties. This is much faster than the classic methods of plant breeding; lengthy selection steps over several plant generations are no longer necessary. In addition to time, “green genetic engineering” also saves a lot of money.

Genetic engineering and genome editing

In genetic engineering, genes or parts of them are artificially introduced into a plant. In this way, crops become resistant to weed killers, for example. The genome, i.e. the genetic material of the plant, is not changed.
With genome editing or gene editing, however, mutations are made to the genome of the plant with pinpoint accuracy. Researchers do this with the gene scissors CRISPR / Cas. If they mutate a gene that plays a role in heat tolerance, the plant will ideally cope better with heat.

Gene editing is targeted and fast

Specifically genome-edited plants cannot be distinguished from classically bred varieties after the procedure. “The political decision not to use modern methods such as gene editing in plant breeding is all the less understandable. Because these procedures not only accelerate and optimize breeding successes; they are also much more accurate than conventional methods that are based on unpredictable random mutations, ”says Friedrich Kragler.

The European Court of Justice (ECJ) sees it differently: In 2018 it ruled that genome-edited plants are also to be treated as “genetically modified organisms” (GMOs), the cultivation of which outside of a laboratory is subject to special regulations and statutory provisions. In fact, no GMOs have been grown commercially on German fields since 2012. “For scientists who understand the genetic basis and know the molecular methods, this is incomprehensible,” says Claus Schwechheimer.

And now?

The genetic engineering fronts remain hardened

Critics of “green genetic engineering” argue that the risks of such modified plants cannot be foreseen; there are too many uncertainties: Will the changed genes spread via seeds and pollen? And if so, what influence does this have on the local flora? These are just some of the questions.
However, numerous long-term studies on the biosafety of GMOs show that they are no more dangerous for the environment or human health than conventionally grown plants. The acceptance of genetically modified plants is still low in Germany and Europe; the fronts between opponents and supporters of genetic engineering are too hardened. It is therefore not possible at present to predict the direction in which modern commercial plant breeding in Germany will move.

The legal situation, on the other hand, is clear: commercial cultivation of genetically engineered and genome-edited crops is not desired. This also applies to varieties that can withstand drought and heat better.

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