Introduction
Drought is an ever-present challenge for farmers around the world. It can greatly damage crops and reduce agricultural yields. According to research, drought conditions are projected to worsen due to climate change in many regions that are vital for global food production. For farmers residing in drought-prone areas, the development of drought-resistant crop varieties provides hope and resilience against the impacts of increasingly erratic rainfall patterns. Drought-tolerant crops have played an important role in agriculture for centuries and continued advancements will help secure food security as the planet warms. In this article, I will discuss the importance of drought-resistant crop varieties and provide examples of some varieties that have shown promise.
History and importance of drought tolerance
Farmers have long selected crops best suited to their local conditions. Over many generations of traditional plant breeding, landraces or indigenous varieties adapted to moisture stress developed. For example, native maize varieties in drought-prone regions of South America and Africa have evolved drought tolerance traits over thousands of years. Modern crop breeding and biotechnology now allow more targeted development of drought resistance compared to traditional practices. However, breeding drought-tolerant crops remains vitally important given the critical need to mitigate impacts on global food security from a changing climate. Some key reasons why drought-resistant crop varieties are so important include:
Higher and more stable yields: Drought-tolerant varieties maintain good yields even during drier than average years when conventional crops might fail completely. This provides farmers in drought-prone regions a more reliable source of income and food. Higher and more stable productivity also increases the resilience of agricultural systems against drought impacts. Research has found yield increases of 10-60% for drought-resistant maize, sorghum and other crops compared to conventional strains under moisture stress conditions.
Wider adaptation: Drought tolerance allows crops to be grown in more marginal semi-arid environments where conventional varieties would be too risky. This expands the land area suitable for productive agriculture. For example, drought-resistant rice and wheat extended cultivation of these important staple crops into drought-prone regions of Asia, Africa and Latin America. More land available for farming helps meet the challenge of feeding a rising global population expected to reach 10 billion people by 2050.
Reduced vulnerability: Traditional rainfed agriculture is highly dependent on the timing and amount of annual rains. A missed rainy season can spell disaster for farmers. Drought tolerance buffers crop production against unpredictable or insufficient precipitation during the growing season. This reduces the vulnerability of farmers in the developing world, as one failed harvest does not lead to devastating hunger or debt. Farmers have more flexibility to withstand periodic drought that will increase with climate change impacts.
Environmental benefits: Drought tolerance means crops require less irrigation water to achieve good yields when rain is limited. This conserves scarce freshwater resources, especially important as water tables fall in many regions. Drought-resistant varieties are also better suited for rain-fed or dryland farming systems with minimal external inputs. Their superior performance under low rainfall conditions preserves natural ecosystems and biodiversity compared to conventional crops that don't fare as well under drought stress.
Major drought-resistant crop varieties developed
Significant progress has been made in developing drought-resistant varieties of many major food and commodity crops through conventional breeding as well as modern biotechnology approaches:
Maize: New drought-tolerant maize varieties released by international agricultural research centers have increased yields in Africa by over 1 million tons per year according to one study, directly benefiting thousands of small-scale farming households. Two prominent varieties are drought-tolerant 'ZT Maize' introduced to southern Africa in the 1990s and 'BH660' developed by Zimbabwe's agricultural research institute with support from international partners.
Sorghum: Considered one of the world's most drought tolerant cereal crops and important in semi-arid regions of Asia and Africa. Scientists have mapped genes conferring drought tolerance in sorghum which is aiding breeding drought-resistant varieties. The International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) has developed multiple high yielding, Striga weed resistant sorghum cultivars for Asia and Africa.
Rice: Drought is a major constraint facing rice production globally, especially in South and Southeast Asia. IRRI rice scientists have introgressed drought tolerance genes from wild varieties into popular high-yielding rice cultivars. Promising new varieties include 'Swarna-Sub1' and 'BR11-Sub1' that maintain 80% of normal yields under drought versus 50% for other rice. New drought tolerance traits are also being introduced using modern molecular biology techniques.
Wheat: Drought drastically impacts wheat yields worldwide especially in South Asia, Middle East and North Africa. CIMMYT, the International Maize and Wheat Improvement Center in Mexico, has bred multiple wheat varieties exhibiting an average 15-30% increase in yield during drought conditions. Popular cultivars incorporating drought tolerance include 'Attila' and 'Opata 85' introduced to Southeast Europe and Central Asia. Scientists are continuing to improve wheat's complex drought response traits.
Cotton: The world's most important commercial non-food crop, cotton faces major moisture stress challenges, especially in rainfed areas of India, U.S. and China. Drought-resistant cotton varieties identified by CGIAR centers and national agricultural programs offer a 10-20% production advantage versus conventional cultivars under water stress. Notable cotton varieties pioneered by ICRISAT include 'DHH-11' released in India during the 1980s.
Soybean: The U.S. is the largest soybean producer globally with over 30 million harvested acres annually, much of which relies solely on rainfall. Drought-resistant soybean varieties allowing cultivation of soy in more drought-prone western regions are being developed through genomic and marker assisted selection by universities and private seed companies. Promising stress tolerant lines possessing ‘ stay-green’ traits maintain photosynthesis longer under drought versus normal cultivars.
beans and lentils: Pulses like kidney beans, pinto beans and lentils are critical dryland crops in Latin America, West Asia and Africa, yet drought is their number one constraint. International research centers have successfully bred early maturing bean and lentil varieties better able withstand periodic drought. Varieties developed offer a 15-25% higher and more dependable yield than traditional pulses commonly grown.
Other crops: Drought tolerant strains of other food and feed crops beneficial to smallholder farmers in developing nations include sorghum-sudangrass hybrids, millets, cassava, pigeonpea, chickpeas, groundnuts and forages. Genetic diversity within each crop species allows selecting drought adaptive traits through plant breeding programs focused on low rainfall conditions.
Role of biotechnology for drought tolerance
While conventional plant breeding has delivered many drought-resistant crop varieties, modern biotechnology also offers opportunities to enhance drought tolerance more precisely and efficiently compared to previous methods. Some key applications of agricultural biotechnology for developing drought tolerant crops include:
Marker-assisted breeding: Molecular marker techniques help rapidly screen large breeding populations for desirable drought adaptive traits. This speeds developing new varieties by directly selecting stress resistant parent lines and progeny rather than phenotypic evaluation alone. Marker-assisted breeding has aided many breeding programs for drought tolerance traits.
Introducing novel genes: Genes conferring novel drought tolerance mechanisms from sources like soil bacteria or other crop species are being successfully introduced using genetic engineering into important staple food crops. For example, a gene from the soil bacterium Bacillus subtilis that regulates production of chemicals protecting plants from drought stress is being tested in cotton and soybean.
Precision gene editing: Techniques like CRISPR are being used to precisely modify plant genes associated with drought response pathways such as stomatal control, root structure and osmotic adjustment. This enables stacking multiple resilience mechanisms into a single variety through accelerated breeding versus conventional methods. While regulatory approval remains a challenge, gene editing shows promise as a precision breeding tool for many traits including drought tolerance.
Metabolic engineering: By fine-tuning plant biochemistry and signaling networks, scientists are exploring how to enhance crops’ intrinsic water and nutrient use efficiencies under drought stress through metabolic engineering strategies. For instance, modulating hormone and sugar signaling could optimize closure of stomatal pores balancing photosynthesis and water loss. Further research aims to develop such innovative solutions to strengthen drought resistance.
Though biotechnology approaches remain controversial in some circles, they could potentially aid developing climate resilient crops more robustly avoiding severe impacts of forecast increases in drought frequency and intensity brought by global warming impacts on agriculture. Still, continued breakthroughs in conventional breeding also hold potential as a complementary sustainable approach which has already delivered drought tolerant crop varieties addressing food security needs. Sensible integration of both traditional and modern techniques may offer greatest benefits.
Opportunities and challenges ahead
As drought conditions projected to worsen worldwide, developing new drought-resistant crop varieties adapted to local growing conditions must continue as a vital agricultural priority. Ongoing achievements and potential for further advances also exist on multiple fronts:
Expanding catalog of drought genes: Elucidating the complex genetic basis for drought tolerance in different crops will identify novel sources of resilience. Introgressing beneficial wild relatives’ genes into elite cultivars has significant scope for enhancing crops’ traits. Further gene discovery and breeding applications hold opportunity for building resistance to drying trends.
Pyramiding multiple traits: Combining drought tolerance genes and traits through marker assisted breeding and modern breeding approaches like genomics and genome editing enables ‘pyramiding’ complementary drought adaptive mechanisms such as early maturity and deep root system into a single variety for better performance.