By Jerome Bossuet
Plants germinate, grow, flower, then produce seeds for reproduction. To achieve their life cycle, plants need many things, including soil nutrients, sun, optimal temperatures and of course water, in enough quantity and at the right time.
If rains stop too early, plants may not have enough water to produce grain. For example, the yield from a field of chickpea can drop by 58 percent to 95 percent if it suffers drought during the critical flowering-to-grain-producing period.
Ninety percent of farmers in developing countries still practice rain-fed agriculture, which means they have no irrigation and are solely dependent on rain for their water needs. As the climate becomes drier in many regions, development agencies are advising these farmers to grow drought-tolerant crops.
This will help mitigate the impact of water scarcity and unpredictable rains as such crops should give farmers some harvest even after a drought. But what are drought-tolerant crops and how can we select crops to be more resilient to droughts?
This is where crop physiologists, such as Vincent Vadez, a research scientist at the International Crop Research Institute for the Semi-Arid Tropics (ICRISAT), come in.
Crop physiology is about understanding how a plant grows according to the local soil, water and climate conditions. Plants can’t read weather forecasts, but species adapted to dry climates have developed physical traits to grow at the right time (when it rains) and to look for water, which helps them become resilient during a drought.
DAYLIGHT AND ROOTS
Certain plants, for instance, have the ability to flower at the right time, after the rains. In the Sahel, where the rainy season is very short, plants may be photo sensitive, flowering according to specific daylight length that usually corresponds to the end of rains.
A deep and diffuse root system can also help a plant survive drought conditions, as it can absorb water from deeper in the ground and in larger quantity.
But that may not be enough when dry weather lasts and plants need to use water very efficiently.
Plants use a complex water pumping system, extracting water via their roots and circulating it through the stem using various cellular water exchange processes. Water is lost from leaves through organs called stomata by evapo-transpiration.
When the climate is dry, such water loss becomes a problem as plants could dry out before producing grain. Very water efficient crops, however, are able to pump just enough water to fill their pods but not dry out.
An interesting research finding is that within a plant species (such as chickpea), certain crop varieties can change their water use and extraction during the growing and flowering stages depending on soil water content.
Some plants are able to open and close the stomata and reduce water pumping during drought. Comparing water-saving cereals (such as barley) with water-greedier cereals (such as maize), researchers found that some plants can reduce the water flow at root level using water transporting proteins called aquaporins, which can be activated or not depending on the change of weather.
For Vadez, these climate-adapted water extraction processes are very important to explain drought-tolerance between crop varieties. Further research is underway by ICRISAT and other agricultural research centres to better understand these water-saving mechanisms, which will help produce new drought-tolerant varieties for climate smarter agriculture.
Encouraging farmers in arid regions to cultivate water-efficient crops such as sorghum or chickpea will help them adapt to unpredictable weather.
Vincent Vadez, an agronomist and crop physiologist, has led the crop physiology laboratory of ICRISAT since 2004. His work at ICRISAT focuses on the characteristics contributing to drought adaptation in cereals and legumes.