Drought tolerance

Like all plants, sugar beet requires water to grow. A lack of water can drastically reduce plant yields.

Drought stress in sugar beet: what is the state of play?

Sugar beet is a robust crop with better drought tolerance than many other crops. By ensuring the best conditions for a good start (e.g. by using quality, primed seed), farmers benefit from the crop's natural defence system. 

Climate change is behind a rise in temperature during the important growth phase of sugar beet, but also causes alternating periods of drought and heavy rainfall. While the beet may benefit from the heat at one point, it may also be penalised later, as high temperatures slow its growth. At temperatures above 35°C, a beet will stop growing. Especially the high light intensity on sunny, warm days causes the beet's leaves to heat up. The water requirement generally arises mainly in summer, when the crop grows to its maximum. 

In the long term, changes in the summer climate therefore pose a real threat to sugar beet, even though a beet can naturally withstand drought reasonably well. It is therefore important to bet on robust varieties to increase the crop's resilience to stress conditions such as drought. To adapt to this situation while helping to increase yields, we have developed strategies in recent years that deliver concrete and measurable results. 

How do plants and especially sugar beet respond to drought stress?

There are 4 strategies generally adopted by plants to cope with drought:

1. Ignore drought stress: These varieties will continue to develop normally as if there is no drought and conditions are normal. This strategy is interesting when drought is of short duration and low intensity, but very negative in case of long droughts.
2. Avoiding drought damage: Through adaptations at physiological and cellular levels, varieties can avoid water deficit and avoid drought damage.
3. Improved water efficiency: These varieties require less water for growth. They use a mechanism to reduce water transpiration during CO2 exchange and temperature regulation (through leaf curling or wilting to reduce leaf surface, closing stomata in dry periods to reduce transpiration ...).
4. Increased water absorption: These varieties develop a deep and highly branched root system for improved water uptake.

The success of each of these strategies depends on the nature of the drought (severity, duration, abruptness or gradualness, earliness, etc.). For example, behavioural mechanisms to reduce transpiration are of interest when the drought is of short duration or occurs only during the hottest hours of the day. The yield loss is thus limited.

How to improve tolerance to drought stress?

The strategy to tolerate drought depends on the type of drought the plant encounters. Drought tolerance is a complex issue because it requires different functions in the plant and thus may involve many genes: modification of rooting, modification of leaf area, modification of stomatal opening, etc. Under moderate drought stress, maintaining leaf growth promotes photosynthesis and thus yield. Under larger and longer dry conditions, this trait - which also leads to high evaporation and transpiration by the plants - can lead to faster depletion of the water supply and thus more difficult plant survival. 

In summary, in drought conditions, plants are subject to a major compromise between limiting water loss and continuing to absorb CO2for photosynthesis. 

In breeding, we need to consider the general response of plants to water deficit, for each climatic context (dates, intensity and frequency of droughts, more or less deep soil, etc.). We will never be able to obtain hybrids that maintain their productivity without high transpiration since this is required for photosynthesis and growth. So we focus on other traits that enhance drought resistance without negatively affecting yield, such as more efficient water uptake. In recent years, SESVanderHave has successfully identified varieties that can significantly reduce yield losses during prolonged drought.

What tools do we use to improve drought tolerance?

1. At SESVanderHave, we have an extensive testing network in areas regularly affected by drought stress. Most test platforms are equipped with weather stations that allow detailed analysis of environmental conditions. We monitor the extent to which drought occurs on our different test plots to assess the impact on the performance of our different varieties.
2. We also conduct comparative tests between irrigating and non-irrigating plots to evaluate differences in behaviour.
3. Drones have also been used for this drought stress problem for several years now. SESVanderHave is working with the company VITO, an expert in this field. Thanks to the measurements made by the drone during the drought period, we can identify genetic differences on certain criteria that play a role in drought stress. We do this using a method developed by SESVanderHave. So selection on this criterion is accelerated and improved.