By Dr. Mohammed Sa’id Berigari, Senior Soil and Environmental Scientist, USA, 05/05/2012
Farmers everywhere throughout history have adopted new crop varieties and adjusted agricultural management practices to cope with the problem of changes in the environment. However, as global temperatures keep rising, the pace of environmental change will likely be astonishing. More intense and frequent precipitation, drought, higher temperatures, and other damaging parameters of weather are all expected to reduce crop yield and quality making the task of feeding 9 billion world population by 2050 extremely difficult.
Already extreme weather conditions are affecting agricultural sectors all over the world. For instance, after a ten year drought in Australia, it experienced catastrophic floods during fall 2010 and winter 2011 causing an estimated loss of $ 6 billion in grain harvest. Harsh and unpredictable weather patterns also, can affect the most volatile regions of the world and leave them more vulnerable to instability due to greater hunger and poverty. Therefore, knowing how to adapt food production systems to a rapidly changing climate is crucial for ensuring world food security and political stability.
The Crop Science Society of America (CSSA) issued a position statement on” Crop Adaptation to Climate Change.” The statement reviews the impacts of variable weather conditions resulting from climate change on cropping systems, reports the progress to date in adapting crops management practices to new conditions, and offers focus areas for increasing the speed at which global agricultural systems can adapt to climate change.
How Will Climate Change Alter Crop Production?
Climate change beside its direct effects on weather will increase both abiotic stresses such as drought, heat, and water-logging; and biotic stresses such as pest,and pathogens that affect agricultural systems. The biggest concern, however, and largely unknown are the effects that interactions among various stresses will have on crops and cropping systems.
Drought: Is anticipated to limit the productivity of more than 50% of the arable land on this planet in the next 50 years, and competition between urban and agriculture for water will make the problem worse. The use of saline and brackish water could help alleviate world’s water scarcity. However, this option is only feasible with the development of salt-tolerant crops or management practices that relief salt stress. Consequently to limit the impact of drought, there is an urgent need for crop varieties and cropping systems that conserve water consumption and sustain yields during periods of water shortage. However, developing these varieties of crops is difficult due to the interplay of crop responses to drought at the genomic, biochemical, and physiological levels. To develop drought- tolerant varieties and make them available to farmers, teams of scientists with different disciplines are needed at the cellular, plant, and field scales to work together to find ways to manipulate these complex, multi-level processes and improve crop response.
Temperature: Is a major factor influencing the growth and development of all types of crops and reflects potential yield during the entire growing season. Temperatures above the normal are expected to reduce yields of cereals and legume crops. Elevated temperatures are well- known to shorten the stage of grain-filling period. Furthermore, elevated temperature changes can lead to warmer, less severe winters, which sometimes allow pests and pathogens to survive winters, and increasing the probability of reduced yield the next cropping season. For all these reasons adopting crop systems to new seasonal variations and temperatures will require adopting strategies specific for each geographic region of any country.
Carbon dioxide: CO2 is essential for crop carbohydrate production that includes crop productivity, yield, and overall plant metabolism. It also plays a major role in climate change. According to the Intergovernmental Panel on Climate Change (IPCC) the CO2 concentrations of the atmosphere have increased significantly over the past two centuries and may reach 450- 1000 µmol/L of air by the end of this century. Elevating CO2 levels of the atmosphere will likely enhance photosynthesis and boost the overall productivity of many crops, although important tropical grasses like maize, sugarcane, sorghum, and some cellulosic biofuel crops do not respond as well to increased levels of CO2. Moreover, enhanced productivity may be offset by pressure from insects and fungal infections, ozone, and variable precipitation, even though the extent to which this occurs will depend on the physiology and biochemistry of each crop.
Ozone: Is an important greenhouse gas and plant pollutant that steadily increases due to fossil fuel combustion. Crop leaves absorb O3 gas during photosynthesis and reduces photosynthetic rates resulting in accelerated leaf death thus affecting crop maturity and productivity. Current global yield losses caused by ozone are estimated at 10% for wheat and soybean and 3-5% for rice and maize.
Biological stresses: Caused by bacteria, weeds, insects, fungi, and viruses will affect cropping systems. Temperature is ranked as the most important parameter in determining how insects affect crop yields, and some insect species such as flea beetles display signs of overwintering due to warmer winter temperatures. The pathogens bacteria, fungi, and viruses also respond quite well to temperature as well as to humidity and rainfall. Therefore, as the growing season gets longer and winters more moderate due to climate change, pressures from weeds, microbial, and insect pests are expected to rise due to enhanced capacity for overwintering, greater mobility of organisms, and expanded adaptation zones.
The climate has always been in a state of flux, however, the current rate of change is much faster, and the extent of weather variation much broader than ever witnessed before modern agriculture. Now two main approaches exist: 1) improving the existing crop cultivars and creating new ones and 2) developing new cropping systems and better methods for managing crops in the field. These approaches for specific strategies are discussed below.
Strategies for Creating New Crops and Improving the Existing Varieties
Integrate desirable traits into the existing crops by means of germplasm collections, related datasets, and breeding research. Crop scientists in the past have identified and selectively adapted crops with desirable traits that can achieve optimum yields while resisting stresses, such as drought, heat, and water-logging. However, the success and speed of breeding work depend on the ability of plant breeders to access optimal germplasm and quality information about germplasm samples.
Nowadays breeders depend on genetic and environmental information in both public and private germplasm collections, such as the USDA’s public National Plant Germplasm System. For continuous improvement of germplasm that can be used to develop new cultivars well suited to climate change, there is a need to obtain, preserve, evaluate, document, and distribute plant genetic resources for a wide range of crops and their wild relatives. However, biotechnology methods that help scientists to screen crop traits are already changing how germplasm banks are used. Extensive use of these resources and methods will help researchers to more rapidly identify adaptive traits, represented by genes or groups of genes that display stress tolerance.
Identify crop germplasm that resists stresses relative to climate change. Crop yield drops due to drought, excessive heat, or excess water deviating from the optimum for growth during critical stages, including pollination, flowering, and filling periods, when carbohydrates and nutrients assimilate inside grain, tubers, or fruit. Cultivars are being developed for cowpea and corn that resist excessive heat during pollination periods and for soybeans and rice to flooding early in the growing season. Maize hybrids also are being developed that display improved synchronization of flowering and pollination under heat and water stress.
Despite this progress, we have only accessed a fraction of the vast information available on abiotic stress resistance because information and research is often limited to the most important crops; therefore, broader investigation and datasets are needed to cover wider range of crops. And concerted efforts are needed for the screening of crop germplasm to susceptibility to biotic and abiotic stresses. Many countries, including USA, experience significant yield losses from pests despite the use of improved crop cultivars and chemicals for pest and pathogen control. As the climate changes and becomes more variable, the interactions among crops, pests, and pathogens are expected to become even more complex and need refocused research. Continued efforts in these areas will supply germplasm for plant breeders to incorporate into adapted cultivars that are productive.
Implement new mapping and cataloging methods. Fast high-output screening of crop genetic material and other novel methods are now possible because of computer imaging, robotics, and supercomputers. These techniques will help investigators to identify adaptive traits expressed in different environments more rapidly and increase the probability of finding key clusters or groups of genes that control traits for resistance to drought and other abiotic stresses.
As the cost drops for genome sequencing, investigators will be able to sequence more than one cultivar per crop. This will allow researchers to uncover the genomic basis of water, resource, and nutrient-use efficiencies and identify locations on the genome where breeders have best selected and bred for adaptive traits in the past. Moreover, genome-wide prediction and breeding simulations are helping plant breeders make better selections in their search programs because they can better predict the outcome of breeding decisions. Overall, high-through-put screening combined with advanced genomics and prediction methods will allow scientists to develop cultivars adapted to new environment at faster speed and widen the options for farmers.
Create New Crops. New crops are likely to play key roles in retaining and increasing agriculture production. Domestication of crops began only 50-120 centuries ago for the oldest crops such as maize, wheat, potatoes, and sorghum whereas blueberries and wild rice were domesticated more recently. Domestication and development of crops have enabled humans to modify them for optimum yield and nutritional qualities.
These days, some scientists are crossing perennial relatives of certain crops such as maize, millet, rice, sorghum, sunflower, and wheat with their annual, domesticated counterparts for use in developing perennial grain crops. Moreover, a real interest in bioenegy has also encouraged the domestication and breeding of C4 grasses, including switch- grass, and miscanthus. Domestication and breeding of new crops is a long-time solution that requires many years of hard work before formal testing can be performed.
Extend Field-level evaluations of crop germplasm. The plant breeder’s current toolkit which provides access to global genetic resources and technology, combined with large-scale field-level research, will help discover previously unknown genetic sources and locations on DNA associated with abiotic stress resistance. Unraveling the knowledge gap relative to abiotic stress tolerance will enable applied and basic researchers to develop long-term strategies that will maximize delivery of new and improved cultivars. Thus, field-based research and related breeding efforts must be intensified, integrated, and expanded to engage a full spectrum of crop development scientists, including plant breeders, physiologist, and geneticist.
Strategies for Developing New Crop Systems and Practices for Their Management.
New management systems are being developed to enhance crop resilience toward climatic changes and to maintain productivity and yield. Because agriculture will not experience the same vulnerability to climate change in various regions, site specific systems of cropping and management practices are needed that could match yield potentials with inputs, soil fertility, and the range of climate variations in each area
Farmers in the past needed to modify cropping systems, either in response to gradual climate change or as crops were moved into new geographical regions. This process of adaptation required intensive work of trial and error, disrupting farm economies and sometimes food supplies. However, research and development in the private and public sectors can provide information to producers to adapt greater fluidity. Research technology and management tools that can speed up the adaptation of crops include simulation modeling and remote sensing. These technologies when combined with faster and better communication of location-specific recommendations will more likely help minimize the negative economic impacts that otherwise accompany ad hoc, untested changes in cropping systems.
Decision-making based on crop models. Crop models are useful in integrating important information about processes and help scientists to assess the impact of changes in crop genetics, and crop and soil management practices. Those models can also be used to compare different crop- management strategies and in helping producers to weigh both economic and environmental considerations as they make decisions about crop varieties, crop dates, and management methods.
Monitor Crop Condition and production. Long- and short-term monitoring of various factors such as pests, pathogens, changes in field conditions, crop productivity, and weather patterns is essential for providing an information base on which future decisions and innovations can be made. For example, remote sensing of crops, weather, and pest conditions can be used by producers for adaptive practices or by government as an early warning signal for climate-based food securities. Databases also help modeling of both biotic and abiotic climate change impacts on crops in specific regions or areas. Briefly stating, long-term monitoring is needed to develop strategies for crop cultivar deployment and management practices that provide farmers the best options for productive harvest.
Optimize efficiency of water-use. As climate changes water supplies are expected to become limited in certain regions of the globe, but better water management strategies, such as drip irrigation, can conserve water and protect vulnerable crops from water shortage. To assess the effectiveness of these measures, agronomists often calculate the amount of crop yield per unit of water or water productivity also known as “more crop per drop”. Water productivity can be elevated through advances in cultivar, plant nutrition, and irrigation methods based on real-time crop need, and better drought and heat resistant crops grown in rain-fed systems or dry farming.
Optimize arable land use. More efficient use of the existing arable land through sustainable yield intensification can prevent bringing new land into production. Higher crop yields also have shown reductions in greenhouse emissions, thus minimizing contribution of agriculture to climate change.
Climate change has far- reaching impacts on food security, human and animal health, and their safety. The climate change impacts are already becoming evident, and there is no sign that such trends will reverse in the foreseeable future. Therefore, quick actions must be taken now to adapt crops and cropping systems in a timely manner and prevent unpredictable and undesirable results. New crop cultivars, cropping systems, and agricultural strategies are needed to offer farmers good options to out- weigh climate change impacts.
Every country should engage its crop scientists, agronomists, plant breeders, and growers from both public and private sectors to focus on how to face the challenge of the climate change by adopting far-sighted strategies for adapting crops and cropping systems to the changing environment to sustain optimum yields. Moreover, at global level, the international institutes and organizations like Food and Agriculture Organization (FAO), International Centre for Agriculture Research in Dry Areas (ICARDA), International Rice Research Center (IRRC), and others need to participate in such strategies for effective and well planned responses to climate change. Such organizations also must include sound provisions for adequate funding for crop science research to provide up-to-date state of knowledge and information on adapting cropping systems to the climate change.
The strategies should aim at 1) understanding the physiological, genetic, and molecular basis of adaptation to abiotic stresses such as drought, heat, and flooding; and biotic stresses such as weeds, insects, and pathogens that are likely to result from climate change, 2) translate new information into new agricultural systems that integrate genetic and management practices i.e. both breeding and agronomy will play key roles in such adaptation, and 3) transfer knowledge effectively and allow technologies and innovations to be widely accessible to increase food production and security worldwide.
*The above article is adapted from that listed below and the official CSSA position statement” Crop Adaptation to Climate Change” which is available online at: www.crops.org/science-policy/position.
Bijl, C.G.; and M.Fisher. 2011. Crop adaptation to climate change. CSA (Crops, Soils, Agronomy) news of Crop Sci.Soc.Amer., Soil Sci.Soc.Amer., Amer.Soc.Agron.: 5-9.
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