Mitigating Climate Extremes with Climate-Adapted Crops
The world’s main food staples are wheat, rice, maize, barley, sugarcane, soybeans, and ten other vegetables. Other important food staples include millet, sorghum, rye, barley, oats, roots and tubers (potatoes, cassava, etc.), as well as animal products (meat, eggs, milk, fish).[i],[ii]
Climate-adapted maize, wheat, rice, beans, and potatoes are available, both commercially and through the plant breeding programs of international crop development organizations. These organizations include the International Maize and Wheat Improvement Center, International Rice Research Institute, The Pan-African Bean Research Alliance, International Crops Research Institute for the Semi-Arid Tropics, and the International Potato Centre (collectively, “crop stakeholders”).[iii]
These crop stakeholders maintain gene banks, seed collections, and breeding programs for the development of climate-adapted crop staples. Crop stakeholders have also assembled global networks to help the farmers of developing nations grow climate-adapted crops in a sustainable and equitable manner. In the future, once a climate switch and other climate risks are recognized worldwide as distinct possibilities, then crop stakeholders will need to increase their efforts to develop cold- and drought- adapted crops. The sooner crop stakeholders change their focus the better, given that it takes years to introduce new climate-adapted crops to farmers in developing nations.
Crop Staples Adapted for Harsh Winters and Cold Climates
A cold temperature threshold must be crossed for a minimum amount of time before plant damage occurs. The species and variety of plant, its stage of development, soil conditions, and climate factors associated with the freeze (such as wind chill factor) influence this temperature threshold. Inadequate acclimation of young plants in the autumn, and the duration and intensity of sub-zero temperatures, determines how well crops survive the winter cold or frosts.
Vernalization is a natural adaptation mechanism by cereal crops growing in harsh winters or short growing seasons. This adaptation ensures flowering occurs in the spring and seeds mature before the next winter.[iv] Winter cereals must be planted before the end of the winter’s intense cold phase for vernalization to occur, whereas spring cereals will flower soon after their spring sowing without the need for vernalization.[v]
Wheat is a very important global crop in Asia, Eurasia, and North America.[vi] Wheat has the broadest adaptation of all cereal crops, and has good cold tolerance.[vii] Spring and winter wheat varieties have been bred, and the most cold-tolerant wheat varieties are killed at just below –200C.[viii] With adequate cold acclimation in the autumn, winter wheat can withstand freezing temperatures for extended periods,[ix] making wheat a versatile winter and cold climate crop.
Winter rye has historically been the national crop in colder lands, such as northern and central Russia and northern Europe.[x] Rye is the most cold-tolerant and drought- tolerant of the cool season grass crops, followed by wheat, barley, and then oats.[xi],[xii] The most cold-tolerant rye varieties are killed at about –300C, which gives hope that it can be a staple crop during a climate switch.[xiii]
Rice is an important crop, especially in Asia, [xiv] and is widely cultivated between the mid-latitude regions, and at up to 3,000 meters in altitude. The Japonica varieties have a higher degree of cold tolerance than the Indica varieties.[xv],[xvi],[xvii] Further efforts to improve rice’s tolerance for the cold are currently in progress.[xviii]
Maize is also a very important global crop, grown in most tropical and temperate latitudes and at altitude. Early sowing of maize increases yields and helps avoid late summer drought, but this early sowing requires cold tolerance traits. Selective breeding of maize for cold tolerance has resulted in varieties able to withstand cold spring temperatures and short-term frosts,[xix],[xx],[xxi],[xxii] which has improved maize’s ability to survive in a colder climate.
Drought-Tolerant Crop Staples Need More R&D
Conventional maize breeding has resulted in improved grain yields under drought conditions. This selective breeding has targeted such traits as increased plants per hectare, ears per plant, seeds per ear, and seed weight.[xxiii],[xxiv]
The International Maize and Wheat Improvement Center (CIMMYT) develops drought-resistant maize, and supplies half of the world’s maize varieties.[xxv] The CIMMYT’s drought-tolerant varieties are products of conventional plant breeding, and these have provided improvements in yield of up to 50 percent.[xxvi] Progress has also been made with genetically modified maize varieties that minimize drought impact.[xxvii]
More than half of the wheat acreage in developing countries utilizes CIMMYT- developed varieties.[xxviii] The reality, though, is that progress in breeding drought-tolerant wheat varieties has been slow,[xxix] and has so far provided insufficient yield improvements to feed a growing population in a more drought-prone world.[xxx]
This limited progress in breeding drought-resistant wheat is the result of the fact that other plant stresses such as high temperatures, solar irradiance, and nutrient deficiencies typically accompany drought. These stressors complicate plant breeding selection by multiplying the number of variables to study in the selection process.[xxxi],[xxxii],[xxxiii]
Integrating genetic material from distant wheat ancestors or drought-tolerant rye would be a quick route to improving yields under drought conditions.[xxxiv],[xxxv],[xxxvi] Hybrids (i.e., wheat-rye) provide fast-track development options to more rapidly improve wheat’s drought tolerance, as opposed to using traditional plant breeding methods.
Given Asia’s high dependency on rice that is highly vulnerable to drought, it will be necessary to improve the drought tolerance of rain-fed rice. Two main options are offered for improving the drought tolerance of rice.[xxxvii],[xxxviii]
First is the transfer of genetic material from upland drought-tolerant rice varieties to lowland rice varieties vulnerable to drought and grown in drought-prone regions.[xxxix] The second option is the development of genetically modified drought-tolerant rice, which currently is an area of active research.[xl] Alternatively, and in the face of a worsening drought, changing the palates of Asians and Africans to less thirsty wheat and maize, which require half the water needed by rice, would provide another water-saving solution.
Drought-tolerant cover crops such as millets,[xli] sorghum,[xlii],[xliii] pigeon pea,[xliv],[xlv] and cowpea[xlvi] help farmers survive drought, especially during the hunger months of the dry season when food supplies run low. Pearl millet and sorghum are among the most drought-tolerant of all the main staples, and are important crops in arid and semi-arid regions.[xlvii],[xlviii]
Millets are small-grain grasses, and are the most drought-tolerant of the summer annual grass crops. They will germinate when very little moisture is available.[xlix] The fast growth and maturation of millets make them well suited to intensive cropping systems in semi-arid and arid climates, particularly as drought progresses and limits the potential use of irrigation.
At the other extreme of water supply, rice normally dies within days of its complete submergence, making rice in flood-prone regions (like parts of India and Bangladesh) vulnerable to extreme rainfall. Progress has been made in the development of submergence-tolerant rice that is able to survive completely submerged for up to two weeks.[l],[li] Regional differences in the impact of grand solar minima make rice’s ability to tolerate submergence important for parts of Asia, which could experience more monsoon rainfall while other areas experience more drought.
[i] Kate A Brauman et al., “Improvements in crop water productivity increase water sustainability and food security—a global analysis.” Environmental Research Letters. 8 (2013) 024030 (7pp). doi:10.1088/1748-9326/8/2/024030. (See Figures 1, 5, and 6).
[ii] Tony Fischer et al., “Crop yields and global food security. Will yield increase continue to feed the world?” Australia Centre for International Agricultural Research. Grains Research and Development Corporation. (See Table 1.2, page 11).
[iii] Crop Stakeholder Organizations: 1) International Maize and Wheat Improvement Center (CIMMYT), https://www.cimmyt.org/, 2) International Rice Research Institute (IRRI), http://irri.org/. 3) The Pan-African Bean Research Alliance (PABRA), http://www.pabra-africa.org/seeds-systems. 4) International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), http://www.icrisat.org. 5) International Potato Centre, https://cipotato.org/.
[iv] E. Jean Finnegan et al., 2010, Vernalization. In eLS, (Ed.). doi:10.1002/9780470015902.a0002048.pub3.
[v] P Chouard, “Vernalization and its Relations to Dormancy.” Annual Review of Plant Physiology. Volume 11:191-238 (Volume publication date June 1960). https://doi.org/10.1146/annurev.pages11.060160.001203.
[vi] Tony Fischer et al., “Crop yields and global food security. Will yield increase continue to feed the world?” Australia Centre for International Agricultural Research. Grains Research and Development Corporation. (See Table 3.1, page 67).
[vii] United States Department of Agriculture. Natural Resources Conservation Service. Fact Sheet. Cover Crop (340) Tennessee. 2015. https://efotg.sc.egov.usda.gov/references/public/TN/CoverCrop_340_FactSheet_Final_July2015.pdf. [See Table 1 Comparison of Maturity and Cold Tolerance of Small Grains and Annual Ryegrass, page 2.].
[viii] N.N. Sãulescu and H.J. Braun, Chapter 9, “Cold Tolerance.” Extracted from: Reynolds, M.P., J.I. Ortiz-Monasterio, and A. McNab (eds.). 2001. Application of Physiology in Wheat Breeding. Mexico, D.F.: CIMMYT. http://www.plantstress.com/articles/up_cold_files/cold_chapter.pdf.
[ix] Vernalization of Winter Wheat. http://igrow.org/agronomy/wheat/vernalization-of-winter-wheat/.
[x] US Department of Agriculture (USDA). Commodity Intelligence Report, 2016. Russia: Sown Area for 2016/17 Winter Grains Falls Short of Ministry Forecast. https://pecad.fas.usda.gov/highlights/2016/01/rs_13jan2016/index.htm.
[xi] United States Department of Agriculture. Natural Resources Conservation Service. Fact Sheet. Cover Crop (340) Tennessee. 2015. https://efotg.sc.egov.usda.gov/references/public/TN/CoverCrop_340_FactSheet_Final_July2015.pdf. [See Table 1 Comparison of Maturity and Cold Tolerance of Small Grains and Annual Ryegrass, page 2.].
[xii] L.V. Gusta and B.J. O’Connor, “Frost Tolerance of Wheat, Oats, Barley, Canola and Mustard and the Role of Ice-Nucleating Bacteria.” Canadian Journal of Plant Science, 1987, 67(4): 1155-1165, https://doi.org/10.4141/cjps87-155.
[xiii] N.N. Sãulescu and H.J. Braun, Chapter 9, “Cold Tolerance.” Extracted from: Reynolds, M.P., J.I. Ortiz-Monasterio, and A. McNab (eds.). 2001. Application of Physiology in Wheat Breeding. Mexico, D.F.: CIMMYT. http://www.plantstress.com/articles/up_cold_files/cold_chapter.pdf.
[xiv] Tony Fischer et al., “Crop yields and global food security. Will yield increase continue to feed the world?” Australia Centre for International Agricultural Research. Grains Research and Development Corporation. (See page 137).
[xv] Renata Pereira da Cruz et al., 2013, “Avoiding damage and achieving cold tolerance in rice plants.” https://doi.org/10.1002/fes3.25.
[xvi] E. Shakiba E et al., 2017, “Genetic architecture of cold tolerance in rice (Oryza sativa) determined through high resolution genome-wide analysis.” PLoS ONE 12(3): e0172133. doi:10.1371/journal.pone.0172133.
[xvii] Moon-Hee Lee, “Low Temperature Tolerance in Rice: The Korean Experience. Increased Lowland Rice Production in the Mekong Region.” Edited by Shu Fukai and Jaya Basnayake. ACIAR Proceedings 101. (printed version published in 2001).
[xviii] International Rice Research Institute. “Stress-tolerant Rice for Africa and South Asia.” http://strasa.irri.org/stresses/cold-tolerant.
[xix] V.M. Rodríguez et al., “Combining maize base germplasm for cold tolerance breeding.” http://digital.csic.es/bitstream/10261/9598/3/Combining_maize_base_germplasm.pdf.
[xx] H. A. Eagles, “Cold tolerance and its relevance to maize breeding in New Zealand.” Proceedings Agronomy Society of New Zealand 9; 1979.
[xxi] Pedro Revilla et al., “Association mapping for cold tolerance in two large maize inbred panels.” BMC Plant Biology (2016) 16:127. DOI 10.1186/s12870-016-0816-2.
[xxii] Alicja Sobkowiak et al., “Molecular foundations of chilling-tolerance of modern maize.” Sobkowiak et al. BMC Genomics (2016) 17:125. DOI 10.1186/s12864-016-2453-4.
[xxiii] H. Campos et al., “Improving drought tolerance in maize: a view from industry.” Field Crops Research, Volume 90, Issue 1, 2004, 19-34, https://doi.org/10.1016/j.fcr.2004.07.003.
[xxiv] H. Campos et al., “Changes in drought tolerance in maize associated with fifty years of breeding for yield in the US Corn Belt.” January 2006Maydica 51(2):369-381.
[xxv] CGIAR. Research Program on Maize. http://maize.org/maize-impacts/
[xxvi] Monica Fisher et al., “Drought tolerant maize for farmer adaptation to drought in sub-Saharan Africa: Determinants of adoption in eastern and southern Africa.” Climatic Change (2015) 133: 283. https://doi.org/10.1007/s10584-015-1459-2.
[xxvii] Examples of Genetically Modified Drought-Tolerant Crops: 1) DroughtGard hybrids. https://www.genuity.com/corn/Pages/DroughtGard-Hybrids.aspx. 2) Syngenta US. Agrisure Artesian. http://www.syngenta-us.com/corn/agrisure/agrisure-artesian. 3) DuPont Pioneer Optimum AQUAmax. https://www.pioneer.com/home/site/us/products/corn/seed-traits-technologies-corn/optimum-aquamax-hybrids.
[xxviii] CIMMYT Global Wheat Program http://www.cimmyt.org/global-wheat-research/.
[xxix] Delphine Fleury et al., “Genetic and genomic tools to improve drought tolerance in wheat.” Journal of Experimental Botany, Volume 61, Issue 12, 1 July 2010, 3211–3222, https://doi.org/10.1093/jxb/erq152.
[xxx] Learnmore Mwadzingeni et al., “Breeding wheat for drought tolerance: Progress and technologies.” Journal of Integrative Agriculture. Volume 15, Issue 5, 2016. 935-943. https://doi.org/10.1016/S2095-3119(15)61102-9. [See table 1, page 936 for progress made with CIMMYT programs].
[xxxi] Learnmore Mwadzingeni et al., “Breeding wheat for drought tolerance: Progress and technologies.” Journal of Integrative Agriculture. Volume 15, Issue 5, 2016. 935-943. https://doi.org/10.1016/S2095-3119(15)61102-9.
[xxxii] Delphine Fleury et al., “Genetic and genomic tools to improve drought tolerance in wheat.” Journal of Experimental Botany, Volume 61, Issue 12, 1 July 2010, 3211–3222, https://doi.org/10.1093/jxb/erq152.
[xxxiii] Saeed Rauf et al., “Breeding Strategies to Enhance Drought Tolerance in Crops.” January 2015. DOI: 10.13140/2.1.2343.9682. In book: Advances in Plant Breeding Strategies; Agronomic, Abiotic and Biotic Stress Traits Edition: 2 Chapter: 11 Publisher: SpringerEditors: J.M. Al-Khayri et al. (eds)
[xxxiv] Matthew Reynolds et al., “Raising yield potential of wheat. Overview of a consortium approach and breeding strategies.” Journal of Experimental Botany, Volume 62, Issue 2, 1 January 2011, 439–452, https://doi.org/10.1093/jxb/erq311.
[xxxv] Saeed Rauf et al., “Breeding Strategies to Enhance Drought Tolerance in Crops.” January 2015. DOI: 10.13140/2.1.2343.9682. In book: Advances in Plant Breeding Strategies; Agronomic, Abiotic and Biotic Stress Traits Edition: 2 Chapter: 11 Publisher: SpringerEditors: J.M. Al-Khayri et al. (eds)
[xxxvi] Delphine Fleury et al., “Genetic and genomic tools to improve drought tolerance in wheat.” Journal of Experimental Botany, Volume 61, Issue 12, 1 July 2010, 3211–3222, https://doi.org/10.1093/jxb/erq152.
[xxxvii] Todaka Daisuke et al., “Recent advances in the dissection of drought-stress regulatory networks and strategies for development of drought-tolerant transgenic rice plants.” Review Article. Frontiers in Plant Science. Volume 6 18 February 2015. doi: 10.3389/fpls.2015.00084.
[xxxviii] Arvind Kumar et al., “Breeding high-yielding drought-tolerant rice: genetic variations and conventional and molecular approaches.” Journal of Experimental Botany, Volume 65, Issue 21, 1 November 2014, 6265–6278, https://doi.org/10.1093/jxb/eru363.
[xxxix] Arvind Kumar et al., “Breeding high-yielding drought-tolerant rice: genetic variations and conventional and molecular approaches.” Journal of Experimental Botany, Volume 65, Issue 21, 1 November 2014, 6265–6278, https://doi.org/10.1093/jxb/eru363.
[xl] Todaka Daisuke et al., “Recent advances in the dissection of drought-stress regulatory networks and strategies for development of drought-tolerant transgenic rice plants.” Review Article. Frontiers in Plant Science. Volume 6 18 February 2015. doi: 10.3389/fpls.2015.00084.
[xli] United States Department of Agriculture. Natural Resources Conservation Service. Fact Sheet. Cover Crop (340) Tennessee. 2015. https://efotg.sc.egov.usda.gov/references/public/TN/CoverCrop_340_FactSheet_Final_July2015.pdf. [See Table 1 Comparison of Maturity and Cold Tolerance of Small Grains and Annual Ryegrass, page 2.].
[xlii] United States Department of Agriculture. Natural Resources Conservation Service. Plant Guide. SORGHUM. Sorghum Bicolor (L.) Moench Plant Symbol = SOBI2.
[xliii] Belum VS Reddy et al., “Genetic improvement of sorghum in the semi-arid tropics.” http://bit.ly/2ydg2AQ.
[xliv] G. Qiao et al., “The enhancement of drought tolerance for pigeon pea inoculated by arbuscular mycorrhizae fungi.” Plant Soil Environ., 57 (2011): 541-546.
[xlv] M. E. Emefiene et al., “The use of Pigeon pea (Cajanus cajan) for drought mitigation in Nigeria.” International Letters of Natural Sciences. Volume 1, 6-16. doi:10.18052/www.scipress.com/ILNS.1.6.
[xlvi] United States Department of Agriculture. Natural Resources Conservation Service. Warm Season Cover Crops and Planting Specifications Plant Materials Technical Notes. https://www.nrcs.usda.gov/Internet/FSE_PLANTMATERIALS/publications/etpmctn12917.pdf [Cowpea, page 5.].
[xlvii] Peter J. Matlon, 1990, “Improving Productivity in Sorghum and Pearl Millet in Semi-Arid Africa.” Food Research Institute Studies, Stanford University, Food Research Institute, issue 01.
[xlviii] Belum VS Reddy et al., “Genetic improvement of sorghum in the semi-arid tropics.” http://bit.ly/2ydg2AQ.
[xlix] United States Department of Agriculture. Natural Resources Conservation Service. Fact Sheet. Cover Crop (340) Tennessee. 2015. https://efotg.sc.egov.usda.gov/references/public/TN/CoverCrop_340_FactSheet_Final_July2015.pdf. [See Table 1 Comparison of Maturity and Cold Tolerance of Small Grains and Annual Ryegrass, page 2.].
[l] International Rice Research Institute. Flood-tolerant rice saves farmers livelihoods. http://irri.org/our-impact/increase-food-security/flood-tolerant-rice-saves-farmers-livelihoods.
[li] Suzanne K. Redfern et al., “Rice in Southeast Asia: facing risks and vulnerabilities to respond to climate change.” http://bit.ly/2JN7AtE.
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