What’s at stake
Plant science can make crops more resilient to drought. This, in turn, could prevent famine and reduce climate migration. Nearly 700 million people worldwide will be living in extreme drought conditions by 2100. Hundreds of thousands of people are already fleeing areas beset by drought and famine, driving migration both within and beyond national borders. But we can reduce the impact of drought through science and technology.
Have some vinegar with that
Eight hundred million people around the world rely on cassava as a staple food. About eight million farmers grow cassava. This crop supports the rural economy in Asia. Cassava, an edible root, is naturally drought tolerant. Now, Japanese scientists have found a way to make it even more resilient.
Acetic acid is a component of white vinegar. Researchers watered one group of cassava plants with acetic acid and the other group with plain water, then held back all fluids. About a week into the drought, the acetic acid plants were less wilted. Their leaves had higher water content and healthier chlorophyll than plants that only received water. The acetic acid acted on plant hormones responsible for closing the plants’ pores, helping them seal in moisture. The cassava plants that received acetic acid released proteins that helped them adapt to stress. Acetic acid helps other crop plants survive drought, including rapeseed (similar to canola), maize (corn), rice, and wheat.
To get to the root of the science, see the 2019 cassava study in Frontiers in Plant Science.
Probiotics for plants
Plants have a microbiome, sort of like humans do. The beneficial bacteria and fungi that grow near crop roots can help them tolerate drought. Scientists want to study what happens if they add probiotics to the soil to protect crops against dry conditions.
A 2018 story by Elaine Smith in Phys/Org gives more details. For more science, see this 2018 PNASstudy referenced by Smith, a 2018 microbiome review paper in Frontiers in Plant Science, and a review paper from 2020 in Science.
A Chinese study found that applying melatonin to coffee seedlings made them significantly more drought tolerant. Melatonin is known for helping humans sleep. But in plants, it acts as an antioxidant. It protects against stress at a molecular and cellular level during drought.
For scientific details, see the 2020 study in the Journal of the American Society for Horticultural Science.
Taking root in dry soil
Penn State researchers have discovered a gene that makes crop roots stiffer. This helps roots penetrate the hard, dry soils found in drought conditions. The plants grow deeper roots, seeking water well below the surface. The gene that makes this possible causes the plants to armor their roots with a substance called lignin. Corn with this gene grew roots that were 22 percent deeper. This gene could possibly be engineered into other crop plants. See the 2021 Penn State press release.
Biodiversity matters. Researchers found that a small, hard-to-find bean has excellent drought-resistance. Scientists had stored samples of the tepary bean in a crop gene bank. Native Americans developed the tepary bean in the Southwest U.S. and Mexico, where the environment was hot and dry. Nicknamed “heat beaters,” tepary beans could provide a valuable source of protein and iron for people in hot, dry conditions. Researchers face challenges getting the seeds to farmers. See this article by Mark Kinver for BBC News. See also this story by Chris Arsenault for Scientific American.
The secret’s in the soil
According to a decades-long study by the Rodale Institute, organic farming methods keep soil healthier than conventional chemical-reliant methods. As a result, organically farmed crops are up to 40 percent more productive during drought. Organic soil retains nutrients and water. Organic soil also contains humic acids, released when organic matter breaks down. Humic acids bind to plant roots and help them absorb water and nutrients. A Brazilian study found that humic acids can prime, or prepare, maize to handle stressors such as drought, salinity, and heavy metal toxicity.
For scientific details on humic acids, see the 2020 study in Chemical and Biochemical Technologies in Agriculture.
Wet and dry rice
You might not think of rice and drought together, but farmers frequently grow rice in an alternate wet-and-dry cycle as a way to save water. Sometimes the dry phase is a bit too dry. Scientists tested new drought-resistant rice cultivars. They found that the drought-resistant rice yielded 26 percent more grain than regular rice under drought conditions. The plants also developed healthier root systems.
For scientific details, see the 2018 study in The Crop Journal.
Supporting farmers in Kenya
A USAID program trains farmers on effective water management and provides them with seeds for drought-tolerant plants. Over 144,000 farmers in Kenya have received seeds for special cereals and legumes. They were trained in “good agricultural practices for higher productivity,” focusing on water-efficient practices. The result is more food for the region and better incomes for the farmers. See this 2020 story by the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT).
More crop per drop
A new mobile app launching in 2021 will let farmers monitor water in real-time. The app, called OpenET, tells farmers how much water their crops consume, at the field level, daily. This knowledge helps farmers create more accurate water budgets. Satellites and existing agricultural models feed data to the app through cloud computing. The app’s developers include NASA, the Environmental Defense Fund, the U.S. Geological Society, the USDA, Google Earth, and others. See this EDF press release.
The resurrection plant, Xerophyta viscosa, can dry out completely for weeks and then return to life when watered. Researchers in Australia sequenced its genome to find out which genes allow it to do this. The plant can become crispy and brown and then regenerate. Further study is needed to see if it would work to engineer these genes into crop plants. Here’s a video of the resurrection plant doing its thing:
For a deeper dive into the science, here’s a link to the 2017 study in Nature Plants.
Some genes make plants more drought tolerant. Signals from the environment can turn these genes on or off. Researchers are investigating how this works at the molecular level. The more we understand about this, the more likely we are to find actionable solutions. Agronomists could selectively breed plants for drought-resistant genes. Or there could be substances we could apply to crops that turn on drought-resistant genes.
Here are some examples of research into drought-resistant plant genes. A 2020 study found genes in soybeans that make the plants’ leaves wilt more slowly. When activated, this characteristic makes soybeans more tolerant to drought. Scientists have found a protein that switches genes off and on in maize. This protein tells the maize to reduce their pores’ size, so they lose less moisture to evaporation. An Iranian study identified gene-switching mechanisms that help barley adapt to drought stress. An international study found genes that help wheat adapt to drought and salinity. And a Chinese study found 16 genes related to plant stress hormones that help Jerusalem artichokes survive drought.
For scientific details, see the 2019 soybean study, the 2020 maize study, the 2020 barley study, the 2020 wheat study, the 2020 Jerusalem artichoke study, a 2021 bean study, a 2021 tomato heat tolerance study on and a 2020 review paper on plants and climate change, all in the Journal of Experimental Botany. See a 2019 RIKEN review article in F1000 Research.
RNA to the rescue
Plants do better in drought conditions when they release drought-stress hormones. Now scientists are learning how and why plants release these hormones. Scientists have found that small RNAs and micro RNAs affect hormonal and metabolic changes that help plants survive drought. These RNAs communicate with plant cells and influence gene expression. Scientists have identified such RNAs in maize (corn), barley, wheat, apples, tomatoes, and rice.
For more on the science, see the 2020 maize study in G3: Genes, Genomes, Genetics, a 2019 study on apples in Nature, a 2017 study on tomatoes in BMC Genomics, a 2019 rice study in International Journal of Molecular Science, and a 2015 review article in Plant Biotechnology Journal.
While the global outlook on drought is disturbing, it’s good to know that so many researchers are working on ways to feed people in dry regions.