Kirk-Othmer Encyclopedia of Chemical Technology || Climate Change, Crop Adaptation

CLIMATE CHANGE, CROPADAPTATION

1. Introduction

The publication of the Stern Review on the Economics of Climate Change in2006 and the Fourth Assessment Report by the Intergovernmental Panelon Climate Change (IPCC) in 2007 have pushed the scientific and public debateon climate change a decisive step forward. It is now beyond doubt that anthro-pepgenic greenhouse gas (GHG) emissions are the main cause for the recentlyobserved climate change. The agricultural sector is directly affected by changesin temperature, precipitation, and CO2 concentrations in the atmosphere.In many developing countries, about 70% of the population lives in ruralareas where agriculture is the largest supporter of livelihoods. A largeshare of this population lives in arid or semiarid regions that are already char-acterized by highly volatile climate conditions. These populations will bemore affected by climate change than those less reliant on agriculturemade more evident by the fact that the industrialized nations to the northproduce more GHGs.

2. Overview

Table 1 summarizes the main driving forces for four emissions scenarios by theend of the century (1). The A1 storyline describes a future world of very rapideconomic growth with a global population that peaks at 9 billion and thendeclines. The A2 storyline describes a very heterogeneous world with populationincreasing to about 15 billion and economics regionally oriented. Fig. 1 shows theprojected increase in temperature for all four scenarios (2).

2.1. CO2 Fertilization. Yields of most crops increase under elevatedCO2 concentration. Free air carbon enrichment (FACE) experiments indicateproductivity increase in the range of 15–25% for C3 crops (such as wheat, rice,and soybeans) and 5–10% for C4 crops such as maize, sorghum, and sugarcane.Higher levels of CO2 also improve the water efficiency of these crops. However,experiments do not address important colimitations because of water andnutrient availability. Some studies expect much less favorable crop responseto elevated CO2 in practice than that asserted on experimental sites (3). Othersagree with the FACE findings (4). The magnitude of the effect is still uncertain(5).

2.2. Higher Temperatures. Warming is observed over the entire globe,but with significant regional and seasonal variations. Highest rates in the North-ern Hemisphere, in higher latitudes, rising temperatures imply lengthening ofthe growing season. This allows for earlier planting in spring, earlier maturingand harvest, and the possibility of two crop cycles. Expansion of suitable cropareas could be possible in the Russian Federation, North America, NorthernEurope, and Northeast Asia. In contrast significant losses are predicted in Africa,due to the expansion of arid and semiarid regions (6). Temperature increases arelikely to support positive effects of enhanced CO2 until temperature thresholds

1

Kirk-Othmer Encyclopedia of Chemical Technology. Copyright John Wiley & Sons, Inc. All rights reserved.

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are affected. Increased water supply can help balance the high temperature.In the tropics, additional warming of less than 2�C will lead to crop loss. Cropsin the temperate regions will broadly benefit from temperature increases upto 2�C.

Further warming will negatively affect plant health in temperate regions(5).

2.3. Water Availability. Agriculture highly depends on water availabil-ity. More than 80% of global cropland is rain-fed, but irrigated cropland with anarea share of 16% produces about 40% of the world’s food. Agricultural irrigationaccounts for 70% of global freshwater withdrawals (7). Because of food demand,more water will be required in the future. Climate impacts on crop productivitywill fundamentally depend on precipitation changes. Precipitation projectionsshow large variability of quantity and distribution. Historical precipitationdata are not available in many poor countries. Annual mean runoff largelyfollows projected changes in precipitation with an increase in the high latitudesand the wet tropics and a decrease in mid-latitudes and some parts of the drytropics (8). Decline in water availability will affect the areas growing rain fedcrops. Moreover, in warmer, dryer regions, agricultural water demand willincrease. Global irrigation requirements are expected to increase 5–8% by2070. Water supply may be insufficient. Glaciers may supply necessary waterdue to their meltdowns, but once they are completely melted, shortages willoccur. In some areas, eg, Northern India and the Mid-west U.S. depletion ofground water can cause serious effects. Agriculture must also compete withhousehold and industry need for water.

2.4. Climate Variability. Extreme climate events such as heat waves,heavy storms, floods or drought have severe impacts on crops. A large number

Fig. 1. Projected temperature increases for the four SRES emission scenario groups (2).

CLIMATE CHANGE, CROP ADAPTATION 3

of heavy rainfalls are expected even when total precipitation amounts decrease(7). Heavy rainfalls are expected in Southern and Eastern Asia and in NorthernEurope, which are major agricultural areas. In many regions, especially the tro-pics and the sub-tropics, droughts have been more intensive since the 1970sbecause of higher temperatures and reduced precipitation. Climate change willdeepen these trends. Higher rainfall intensity will increase the risks of soilerosion and salinization. Rice yield is already close to the limit of maximumtemperature tolerance in South Asia. In low-lying countries, sea level rises cancause salt water intrusions, which will impact negatively on the soil. Soil degra-dation occurs from nutrient leaching and soil erosion. Nutrient conservation isaffected by warmer temperatures because of the natural decomposition oforganic matter. If mineralization exceeds plant intake, nutrient leaching willoccur. A 1% increase in precipitation is expected to lead to 1.5–2% increase insoil erosion (9).

2.5. Weeds and Pests. In current agriculture, preharvest losses topests in major cash crops are estimated to be 42% of potential production (7).Temperature rise and elevated CO2 concentration could increase plant damagefrom pests in the future although a few quantitative analyses exist (5). Weedsshow a larger range of responses to CO2 increase, including larger growth dueto their greater genetic diversity. Changes in weed and crop completion is uncer-tain. While elevated CO2 will not directly affect pathogens, it will alter plantdefense mechanisms. Higher winter temperatures will lead to an increasingoccurrence of plant diseases in cooler regions (10).

2.6. Adaptation Options. In the past adaptations in agriculture werethe norm rather than the exception. Farmers have demonstrated sufficient adap-tive capacity to cope with weather variations. Impacts have been minimized bythe use of irrigation, use of pesticides and fertilizers, and the manipulation ofgenetic resources (11). Rich countries are more well-equipped to cope with cli-mate variations. Lack of information and financial support are problems andnew technologies are not often available to poorer countries. Some technicaladjustments have been recommended: (1) Shift dates of planting to allow theadvantages of a longer growing season; (2) new crop varieties can providemore appropriate thermal requirements and increased resistance to heatshock and drought; (3) altering and widening existing crop rotations can helpadaptations to climate conditions by introducing better adapted crop types;and (4) rising water demand caused by higher temperatures can be balancedby improved water management and irrigation. Various types of low-cost‘‘rainwater harvesting’’ practices have been developed in poor countries (12).

Adaptive capacity at the farm level is unlikely to be sufficient in manypoor regions. Non-climatic conditions also come into play. The weight given toclimate change policies will depend on other needs of a country or region.Further reform in developed countries should make agricultural productionmore climate-friendly and help provide better options for poorer countries.Improved policies can guide transitions where major land use changes, changesin industry location or migration occur. Planning can cause less environmentaldamage. The establishment of functioning and accessible market for inputssuch as seeds, fertilizers, labor, and financial support can improve security forfarmers.

4 CLIMATE CHANGE, CROP ADAPTATION

3. Agroecology and Plant Response

Agricultural ecosystems capture the raw materials of light, water, carbondioxide, and nutrients and convert these into diverse plant products, eg, carbo-hydrates proteins, and starch. In plants, the overall process is driven bysolar radiation and the chemical transformation process of photosynthesis.However, the changing climate affects all the raw materials and growthprocesses of plants with be affected by these changes. It is important tounderstand the plant response to these changes and the impact on the supplyof food for the human race. Atmospheric carbon dioxide concentrations haveincreased to levels never experienced by modern agriculture. Currently theatmospheric concentration is 380 ppm and rising 2 ppm every year. Worldwidetemperature and precipitation patterns as projected by the IntergovernmentalPanel on Climate Change (IPCC) in the latest report suggest a rise in tempera-ture of 0.8–1�C over the next 30–50 years and more variation in precipitationamounts (13). In the U.S., a warming trend of 1.5–2�C over the next 100 yearsis predicted (14). The number of heat-wave days in which the temperature willbe higher than the climatic normal by 5�C will increase and there will be anincrease in the minimum night temperatures. These changes result in adecrease in the number of frost days by 10% and an increase in the growing sea-son of over 10 days. Although there is uncertainty about the absolute magnitudeof the changes over the next 50 years, there is general agreement that CO2 levelswill increase to near 450 ppm, temperatures will increase by 0.8–1.0�C, andprecipitation will become more variable. It has become necessary to understandthe potential physical and physiological impacts of changes in climate onagroecosystems.

3.1. Energy Balance. Changes in climate will affect the energy balanceof leaves and canopies. One of the easier ways to examine these impacts isthrough the transpiration rates of leaves or the evapotranspiration (ET) of cano-pies. For an individual leaf, the transpiration rate is governed by the net radia-tion balance of the leaf, the water supply to the leaf, the leaf shape, which affectsthe rate of water vapor movement to the atmosphere or the water conductance inresponse to wind speed, and the leaf conductance, which determines how thestomata are responding to the water potential and the light regime. This ismore easily describe by eq. 1

St 1� alð Þ þ Ld � esT4a ¼

rCp Tl � Tað Þra

þ rCp

g�eo � eað ÞrS þ ra

; ð1Þ

Where St ¼ the incoming solar radiation ðW m�2Þ; al ¼ the albedo of leaf, Ld ¼the incoming long-wave radiation, ðW m�2Þ; Ld; eT4þ the long wave radiationemitted by the leaf at the leaf temperature ðTlÞ; r ¼ the density of the airðkg m�3Þ; Cp ¼ the specific heat of the air ðJ kg�1 K�1Þ; Tli ¼ the leaf tempera-ture (�C), Ta ¼ the air temperature (�C), ra ¼ the aerodynamic conductance toheat transfer ðs m�1Þ; g� ¼ the psychrometric constant ðkPa=�CÞ; eo ¼ thesaturation vapor pressure at TlðkPaÞ; ea ¼ the actual vapor pressure of the air(kPa), and rs ¼ the stomatal conductance ðs m�1Þ.


3.2. Leaf Level Feedback. One way to understand the impacts ofchanging climate on energy balance of a leaf is through the energy flows (seeFig. 2). It is necessary to realize that a small change in temperature affectsmany of the variables expressed in eq. 1. Increasing temperature will affectthe incoming long-wave radiation, which will add to the heat-load of the leafand also change the saturation vapor pressure of the atmosphere leading to anincrease in the actual vapor pressure deficit. Both of these parameters willincrease the rate of water vapor loss to the atmosphere and increase water useby the leaf because of the evaporative demand. This is a simplistic representationof the dynamics of leaf use of water in response to temperature and CO2 increaseHowever, increase in CO2 concentrations leads to a decrease in stomatal conduc-tance, which in turn reduces water loss from the leaf, and increases leaf tempera-ture. This decreases the gradient of the leaf-air temperature that is feedback thatreduces water use by the leaf. There are interacting effects in the climate vari-ables in which a change in temperature alone would increase water use by theleaf, while the single effect of increasing CO2 would decrease water use rate.These offsetting factors would depend on precipitation or irrigation amounts.

3.3. Canopy Level Feedback. A more realistic representation of theenergy balance of the leaf would be to change eq. 1 to represent a plant canopy.This change can be expressed by Fig. 3. A move from a leaf to canopy level, theadditional effect cause by soil surface will provide feedback to the canopy. In rowcrop agriculture, where the canopy can be treated as an expanding volume overthe course of the growing season, the interactions between the soil surface andplant canopy vary with microclimatic variables, eg, wind, speed, temperature,vapor pressure, and soil wetness. When the canopy is small, the water use is gov-erned by soil surface wetness. If the soil is dry, there is little soil evaporation andthe solar radiation increases leading to a warmer plant. These conditions lead toplant stress and offset any benefit of CO2 on stomatal conductance. Conversely awet soil increases the water pressure of the air surrounding the canopy and low-ers the evaporative demand and reduces water use by the canopy. This results ina negative impact on canopy water use. As the canopy develops and completelycovers the soil surface, the energy balance is not dominated by the processes atthe soil surface and becomes more typical of what is shown in Fig. 2 for a leaf.

Energy balance of a leaf

Air temperature

Vapor pressure

Water-use rate

Leaf-air temperature

Leaf temperature

Water-use rate

Stomatal conductance

Atmospheric CO2

Fig. 2. Schematic of the energy balance of a leaf and the feedback caused by changingclimate.


When an extension is made from a leaf to the canopy, multiple layers of leavesrequire the consideration of both the soil and plant canopy as sources of water forthe evaporation process, which expands an expansion of the conductance termsto include multiple layers of the canopy. It is not possible to assess the impact ofchanging temperature in isolation from the changes in CO2 and precipitationbecause of the interactions on the dynamics of plant water use.

3.4. Changes in CO2 Concentrations. Increase in CO2 concentrationson plant growth begins with the process of photosynthesis. Most plants fix CO2

with the C3 photosynthetic pathway using ribulose-1,5-biphosphate carboxylase(rubisco) as the primary enzyme. Plants that use C3 pathways include wheat,rice, soybean, sunflower, cotton, and potato. The process of photorespirations(oxygenation) releases CO2 to the atmosphere when rubisco reacts with O2; how-ever, rising CO2 levels cause the carboxylation process of rubisco to increasewhile the oxygenation is suppressed. Moore and co-workers reported that photo-synthetic acclimation to increased CO2 occurred because plants exposed to long-term elevated CO2 levels did not continue to exhibit the enhanced impacts on thephotosynthesis rates (15). These observations would suggest that exposure tohigh levels projected in climate change may not produce the same degree ofresponse when plants are exposed to high concentrations. The C4 pathway inwhich CO2 is concentrated within the cell to concentrations that saturate photo-synthesis and in doing so render the photorespiration rate to near zero in value.Plants in this category are maize, sorghum, and sugar cane. Since these plantshave an internal mechanism that concentrates CO2 internally, there is a smallphysiological response to increasing CO2 concentrations. Although the number ofC4 crops is small, they are valuable crops on a worldwide basis in terms of pro-ductivity. Plant responses to increasing CO2 are through an increase in assimi-lation rates and a decrease in stomatal conductance to water vapor (rs in eq. 1),which reduces leaf transpiration rate. These responses are observed when thereis adequate water available for transpiration. The increase in assimilation rate

Canopy energy balance and feedbacks

+

+

+

+

–

–

Tc

TaTa

TsTs

ea

ea

Tc

Canopyvolume

Canopyvolume

Canopy water use – Canopy water use +

SoilDry soil Wet soil

Canopyvolume

Fig. 3. Schematic of energy balance feedback in canopy water use and canopy tempera-ture with a dry and wet soil surface.


and reduced leaf transpiration leads to an increased leaf temperature. Thisinduces conditions for enhanced growth rate.

Experiments on plant responses to elevated CO2 may not be representativeof actual field conditions in pasture species. Thornley and Cannell suggested thatelevated CO2 and temperature experiments to determine these effects on photo-synthesis and other ecosystems were limited in use (16). They reasoned thatlaboratory or field experiments incorporating sudden changes in temperaturewere short term in nature and rarely produced quantitative changes in net pri-mary productivity (NPP) ecosystem C or other properties connected to long-termresponses. Also these studies do not include the grazing component. Their stu-dies used the Hurley Pasture model to simulate ecosystems responses to grazedand ungrazed land and came up with the following: Rising CO2 induces a carbonsink; rising temperatures produce a carbon source; a combination of the twoeffects is likely to generate a carbon sink for decades. They also concluded thatnutrient dynamics in plants and soil must be understood.

3.5. Temperature Interactions. Temperature optimums for C3 plantsare lower than that for C4 plants and have an optimum temperature in the10–25�C range while C4 plants have more efficient responses in the 20–35�Crange. As the temperature increases there is an increase in C3 plants to elevatedCO2 levels. (17). Although increasing CO2 causes a positive response in terms ofphotosynthesis and stomatal conductance, these are offset by temperature effectson plant growth and these effects may be evident across seasons in perennialcrops.

3.6. CO2 Interactions with Nutrients. In plant ecosystems growth islimited by nitrogen. Terrestrial nitrogen occurs in organic forms that are notreadily available to plants and the guiding principle on how rangeland willrespond to global changes will depend on the rate of N cycling between organicand inorganic N compounds. In native grass ecosystems, soil fauna and micro-fora decompose and fall to the soil surface and become part of the soil organicmatter (SOM) pool. Rising temperatures increases the rate of SOM decomposi-tion with even greater effects in colder regions where small increases in tempera-ture can have dramatic effects. Soil water evaporation will increase, which maylimit microbial activity. The extension of the growing season affects decomposi-tion rates and lower soil water contents will lead to reduced decomposition rates.

A greater plant demand for N will occur caused by the effects of elevatedCO2 on plant growth. The continual accumulation of N in organic compoundsmay eventually reduce N soil availability and limit plant growth (18). Theseprocesses are not well-defined and vary among ecosystems.

In cultivated agroecosystems interactions of elevated CO2 and N areequally as complex as in native species. Various studies have found that criticalN concentration for adequate growth was reduced for a number of species withincreasing CO2 (19). Also the amount of N fertilizer required in C3 crops toachieve maximum productivity under increasing CO2 would not increase dueto the fact that critical N concentration decreases in C3 species with increasesin CO2 (20).

However in C4 plants the N required for maximum production may increasebecause there is no evidence for a decrease in N concentration with elevated CO2.Greater attention will have to be given to N management in cultivated crops with


climate change in order to maintain both yields and protein concentrations ingrains.

3.7. Water-Use Efficiency. One of the responses to elevated CO2 is anincrease in water use efficiency (WUE). This is summarized as a positive impactof increasing CO2 concentrations. Increased WUE would be advantageous inplant communities because of the increased variability of rainfall during thegrowing season. The increase of CO2 causes an increase in growth and createsmore leaf area with a reduced stomatal conductance and thus increasingWUE. There have been a series of mathematical relationships to explain thisprocess. Eq. 2 describes a physiological basis for WUE (21).

Nc ¼ cCa=1:5ð ÞLAI= rb þ rsð ÞDþ LAI � LAIDð Þ= rb þ rsð Þo

" #; ð2Þ

Where c ¼ 0.7 for corn, Ca ¼ CO2 concentration in air, LAI ¼ the leaf area indexof the canopy, rb ¼ the boundary layer conductance (s m�1), rs ¼ the stomatalconductance (s m�1), subscripts, D and o ¼ leaves in direct sunlight and leavesin shade respectively.

Eq. 3 describes a similar form of a relationship to describe transpirationfrom the canopy (22).

Tc ¼re

P

� � LAID

e�D � e� �rb þ rsð ÞD

þ LAI � LAIDð Þe�o � e� �rb þ rsð Þo

26664

37775; ð3Þ

Where e ¼ the ratio of the molecular weight of water vapor to dry air, P ¼ theatmospheric pressure, e ¼ the water vapor density in the air, and e� ¼ thesaturation vapor pressure of the air.

These equations have been tested on various canopies with acceptableresults.

4. Potential for Crop Adjustments

A doubling of food/feed production will be required by 2050 to provide for the pro-jected human population at a satisfactory level. Climate changes add much moreuncertainty. As stated earlier, extreme high temperatures and drought arealready having impacts in the production of annual crops in rain-fed agriculture.The most vulnerable growth state for grain crops is at anthesis and grain filling.In some regions drought stress can be relieved by irrigation from rivers andground water, but temperatures above 35�C will threaten seed-set in mostcrops and failure often occurs at 40�C. The figures in Table 2 indicate thateconomic losses due to drought at a global level are very high.

Crops that have been bred for prevailing tropical and mid-latitude environ-ments will be exposed by 2050 to average increases of 1�C and 3�C in the worstcase scenario which now appears more likely (23). Crops will need to be bred for


anticipated rises in temperature and to be more tolerant to extreme stresses.Since these considerations are outside current crop environments, managedstress environments are now important options for international breedingprograms.

1. A switch to crop species with regional adaptation to important stressesespecially tolerance to heat and drought stresses

2. Intraspecific genetic improvements of existing crops.

3. Agronomic improvements in production for rain-fed and for irrigated farm-ing systems, including strategies for water efficiency, reduced tillage, tar-geted fertilizer application, etc.

4.1. Crop Options. The change in crop profiles will vary by region andpreferred crops, but will generally be affected by shorter growing seasons withwider variations in temperature. Thus, both earliness and greater crop reliabilitywill be sought in tropical and temperate latitudes of low to medium elevation. Yetfor some regions with high altitudes or high latitudes, the growing season may beincreased with more frost-free days. In other regions moderate increase in tem-perature may initially favor crop production, but then a further increase wouldincrease the events of heat stress. Adaptation needs by crops have been reviewedby Lobell and co-workers with modeling indicating high vulnerability for west andsouthern Africa and South Asia (24). Crop improvement priorities include wheat,rice, millet, rapeseed, and soybean in South Asia, maize in southern Africa and sor-ghum, groundnut, and yams in West Africa.

The choice of cereal crops for different agroecological conditions is displayedin West Africa. Among tropical cereals, the shorter season pearl millet is betteradapted to the heat and drought stress of sub-Saharan Sahel region than sor-ghum, which is more widely cultivated in the wetter Savannah zone, whilemaize is better suited to the higher rainfall of the Savannah rainforests. Plusmaize is more responsive to fertilizer inputs. Where fertilizer distribution hasbeen established in association with local credit schemes, maize has becomemore profitable than sorghum and has become a major crop in West Africa.

Very recently, hybrid early maturing pigeon pea has been introducedto East Africa. This is an attractive and more reliable food option than thetraditional local maize.

Table 2. Continental Contrasts, Impacts of Drought, 1970–2009

No. ofevents

Totalkilled

Total affected(millions)

Damage(millions US$)

Africa 184 553,000 266.8 4,817America 97 <100 47.2 15,433Asia 100 >5,000 1,293.0 27,620Europe 34 <10 10.4 18,561Oceania 13 <100 8.0 10,103Total 428 558,000 1,625.4 76,533

Source: EM-DAT, Centre for Research on Epidemiology of Disasters, Leuven.


Among the cereals in the temperate zone, barley is regarded as fastermaturing and more heat and drought tolerant than bread wheat (25) than inturn has wider adaptation than durum wheat. Oats are comparatively adaptedto high altitude and cooler temperature, as too is cereal rye. Ref. 26 is an exam-ination of the relative changes in area of different crops with the Ecocrop modeland indicates that with global warming cold weather crops such as wheat (18%)and rye (16%) suffer significantly with significant decreases in suitable areascompared with barley (2% gain). Larger gains are predicted for pearl millet(31%), chickpea (15%) and soybean (14%).

Among the temperate legumes, in the winter rainfall zone of southernAustralia, peas are best adapted to semiarid zones and have versatility in enduse. The presence of widespread saline subsoils may favor peas over chickpeas,whereas chickpeas are widely grown in India on reserve soil moisture after themonsoon main crop season where deeper rooting plus better adaptation to warmtemperatures make it more attractive for climate changes (26).

Genetic variation for heat stress tolerance under major gene control in somecases has been found in wild tomato, pepper, cabbage common bean, and mungbeans. It is likely that more genetic variations for tolerance of heat stress will befound in other crops and in crop wild relatives that have a wider variation thanin the domestic gene pool

4.2. Gene Diversity. There is a wide range of conclusions whethergenetic improvement of crops will be necessary for adaptation to climate change.The conclusions range from little adjustment will be needed for cassava to majoradjustment for rice, cowpea, maize, and sorghum.

Legume Crops. The legume crops are well placed to doubly benefit fromelevated CO2 with increased photosynthetic carbon fertilization directly enhan-cing growth and indirectly enhancing nitrogen fixation. However there are likelyto be differences among species. The increased availability of nitrogen would sup-port both the expansion of the plant sink for vegetative growth and for grainyield and more rubisco-mediated carbon fixation. The legumes will likely havea more significant role in farm rotations as an alternative source of nitrogen.An example in this category is soybeans that have genetic variance for water-use efficiency (WUE), rooting depth, and mass photoperiod control of phrenologyand adaptive portioning to roots under water deficit. It has a high heat tolerancewith seed size maximized at 23�C, compensation of smaller seeds at 28�C with anincrease in seed number, and yield decline at above 32�C. The grain-filling periodis reduced at high temperatures. Trait combinations for ‘‘stay green longer’’ grainfilling, rate and depth of root growth, and WUE have cumulative effects on yield.Response to CO2 enrichment is greater under drought stress. Stomatal conduc-tance is reduced with the doubling of CO2; however, transpiration reduces by10% and the canopy is 2�C warmer. Soybeans are adapted to current range ofhigh temperatures in the tropics and subtropics. Higher temperatures, however,make novel sources of genetic variations very important especially in the harshenvironments of Australia.

Nonlegume Crops. In other crops, nitrogen fixation is mostly absent,except for endophytes in sugarcane, but apparently confined to Brazil withincreased rate of photosynthesis with climate change, mineral nitrogen levelsmay be relatively diluted in nonlegumes to result in reduced levels of protein.


Climate change effects are more direct, with CO2, with enhanced photosynthesis,a rise in mean and extreme temperature for crops, and greater uncertainty ofrainfall, For many crops, there is little knowledge of crop response to CO2,drought and temperature stress. Bread wheat and rice are major world staplesand have received the greatest attention. As an example, rice responds toelevated CO2 levels; however increased photosynthesis and decreased stomatalconductance is down-regulated at maturity to a 10% photosynthetic gain com-pared with 30% mid-tillering, with 15–30% biomass/yield gain. Down-regulationof photosynthesis is greater in grasses than in legumes especially if N supply islimiting. Stomatal conductance is reduced with elevated CO2 and WUEincreased, leading to an increase in temperature in the canopy. A 2�C increasein temperature will increase yield in cool areas, but reduce yield in dry seasontropics and other warm environments. Above 32�C the temperature reductionof photosynthesis and of yield is greater than the CO2 enhancement. Unknownissues with climate change include sink regulation and partioning of photosynth-esis and nitrogen uptake. There are good prospects to select for climate adapta-tions with wider exploitation of landraces and wild relatives.

5. Wild Relatives

Genetic variation in many crop species is relatively limited due to the focus onyield potential during the domestication of crop species. A lack of allelic variationwill restrict the development of drought- and heat-resistance cultivars suitablefor future warmer and drier climates. Wild species are usually better adaptedto harsher climate. However, crosses between crop species and wild relativesfrequently have a negative effect in agricultural production environments.

A recent review indicated that of 19 species surveyed, wild gene incorpora-tion reaching the released cultivar stage was found to be 13(27). They found thatmore than 60 wild species had contributed more than 100 beneficial traits to 13crops. While the most common use of wild relatives was as a source for pest anddisease resistance, wild relatives also contributed to abiotic stress-resistancetraits.

5.1. Drought Resistance Traits. Superior drought-resistance traitshave been identified in wild relatives of many important crops species such asrice, wheat, potato, wheat, chickpea, sunflower, and groundnut. The drought-resistance traits reported or derived from wild wheat species are high WUE(28), early vigor (29), high productive tillers, high grain weight and betteryield stability under water-limited conditions (30).

In wild rice species, a number of useful traits for the improvement of uplandrice drought resistance have been observed such as high WUE, greater mem-brane stability, increased root biomass, and better maintenance of leaf elonga-tion under drought stress (31). Some wild species such as Glycine latifolia areable to tolerate a very low soil moisture and low leaf water content. The criticalleaf content is about 23% while that of soybean cultivars is about 35%. Thecritical relative leaf water content is the threshold at which the leaf can nolonger be hydrated. This cellular drought-tolerant property is rare in cultivatedspecies.


Wild species have contributed drought tolerance to released cultivars oftomato, chickpea, barley, rice, sorghum, sunflower, and wheat (31).

5.2. Heat Resistance Traits. Only a limited number of reports describethe heat resistance traits between cultivated crops and their wild relatives. How-ever, superior heat resistance has been observed is some wild crops. Solanumgandarillasii exhibits remarkably higher membrane thermostability than culti-vated potato (32). Heat resistance traits can also be derived from inter- or intras-pecific hybrids such as synthetic wheats (33). One interesting aspects of heat-resistance genetics from wild relatives is that some wild crops inhabiting hotenvironments might provide superior alleles for thermostable proteins.

To date there are few reports of released cultivars with heat tolerance fromwild species. A chickpea cultivar with thermotolerance has been reported (34).

5.3. Molecular Basis of Traits. Although a number of drought andheat-resistance traits have been characterized in crop wild species, the molecularbasis for these traits is essentially unknown. The identification of these criticalgenes underpinning the trait can be extremely useful for the introgression ofstress resistance genes from wild species into crops by either marker assistedbreeding or transgenic technology. Recent advance in the elucidation of molecu-lar mechanisms of abiotic stresses and progress in functional genomics have pro-vided appropriate tools for the genes in question. Two approaches can be used foridentification of these critical genes: analysis of known candidate genes and agenome-wide search.

Candidate Gene Approach. This approach is based on the currentknowledge of about hundreds of stress adaptation and regulatory genes thatare involved in plant response to drought and heat stress. The effect of wildrelative’s genes can be envisioned as either a difference in protein sequence orthe concentration of a given protein that is often reflected by mRNA level. Com-parative studies are relatively few. Some drought upregulated genes such asdehydrins are expressed in drought resistant genotypes of Hordeum spontaneum(35). MRNa level of a drought unregulated TF (DREB) is higher in a drought-resistant Glycine soja than a sensitive soybean cultivar (36).

The candidate approach has serious limitations as the molecular basis for thedesired traits is relatively unknown even in crop species. Therefore the genome-wide search is generally more appropriate for identification of desired genes.

Comparative Functional Genomics. Comparative functional genomics isa rapidly expanding branch of functional genomics. With the availability of ESTsequences in major crop species and large-scale expression profiling platforms(eg, cDNA microarray and Affymetrix arrays), genome-wide searches for differ-entially expressed genes between stress resistant and susceptible genotypes hasbecome feasible. To date, a number of comparative functional genomic studies inthe area are based on identification of genes associated with genotypic variationsin drought and heat resistance (37). There are also studies on a defined adaptivetrait such as osmotic adjustment in rice (38), transpiration efficiency in wheat(39), and photosynthetic maintenance in potato plants (39). These types of stu-dies provide a list of candidate genes that are associated with a trait for furtherstudy.

Comparative functional genomic studies between a crop species and its wildrelatives have not been reported to date. Among the many reasons: gene


sequence information on wild relatives is scarce; sequences of many gene tran-script may differ considerably between a crop and a wild species; and geneticdifferences between a crop species and its wild relatives are generally too largeto pinpoint the association of differentially expressed genes with the drought andheat resistance traits.

5.4. Genetic Engineering. The advantage of genetic engineering forimprovement of a plant trait is that any genetic modification can be designedand tailored by introduction of one or a few known genes. This is in contrast tothe conventional crossing or somatic hybridization, which has a severe drawbackof unintentional introduction of a large chunk of unknown DNA with undesirablecharacteristics. Another advantage is its ability to greatly amplify the expression(hundreds of folds if necessary) of the gene of interest, in a transgenic linecompared to the parental genotype, while allelic variation in gene expressionlevels is generally within a few folds (39,40). Despite the advantages, transgenictechnology requires known candidate genes for the traits. For drought- orheat-resistance traits, some candidates underlying certain physiological andbiochemical mechanisms have been identified such as genes coding dehydrins,antioxidant enzymes or rubisco activase. However candidate genes for mostdrought- or heat-resistance traits are still unknown. In the past decades manydrought- or heat-responsive genes, particularly the upregulated ones, have beenselected as potential candidates for functional evaluation in transgenic plants.

Numerous studies have demonstrated the enhanced drought resistance intransgenic plants. Many transgenic studies documenting the improvements ofheat resistance have been covered in a recent review (41). For more details,please see chapter 27 in the publication from which this article has beenextracted (see Acknowlegdment).

6. Energy Crops for Combating Climate Change

The development and deployment of dedicated energy crops (DECs) have pro-posed a strategy to produce alternative energy without impacting food securityor the environment. Potential DECs are mainly perennial herbaceous andwoody plants and may include algae. Potential DECs should be easy to propagateand establish, capable of rapid growth in a wide range of environments, and haveconsiderable genetic diversity, especially for water-use efficiency (WUE) andnitrogen-use efficiency. Moreover DECs should have the added benefit of provid-ing certain ecosystem services, including C sequestration, biodiversity enrich-ment, salinity mitigation, and enhancement of soil and water quality.Inevitably DECs will compete with food crops for land, water, nutrient resources,and other inputs. A significant advantage of development and use of DECs isplants can be bred for that purpose and they have a rich and largely untappedgenetic resource base to develop high yielding cultivars. Genetic resources for thedevelopment of DECs with low requirements are expected to be more environ-ment-friendly and contribute positively to global climate change more than cur-rent energy crops (42). Some crops favored for investigation as DECs includecellulosic crops including short rotation trees and shrubs, perennial grasses,nonedible oil crops, and trees and shrubs.


6.1. Breeding Dedicated Energy Crops. Breeding of DECs impliesbreeding for adaptation to long term global climate change and the replacementof crops with new ones having high interannual yield variability with new oneshaving more stable yields (43) and may involve innovative plant design via accel-erated domestication (44). It is unrealistic to assume that plantations of DECScan be started with little or no domestication; large deployment of wild speciesin the landscape as energy crops is bound to lead to unforeseeable biologicaland environmental problems.

A basic breeding program for DECs entails collection and evaluation ofgenetic resources, genetic analysis, and development of criteria for selection,development of novel tools for selection, and testing novel varietal concepts,and genetic improvement for biomass yield and energy-related properties(45). Breeding objectives include the improvement of biomass yield, quality,and conversion efficiency, either through selection among progeny obtainedby crossing by crossing parents with desirable traits or a way to enhance theagronomic performance of promising mutants and transgenic plants (46). Breed-ing challenges of DECs are numerous and include long-yield cycles, complexgenetics, multiplication and implementation of long term experiments. Criteriafor the development of novel hybrid DECs include large seeded crops with vigor-ous establishment to simplify biofuel production systems, delayed floweringthrough photoperiodism to enhance greater biomass accumulation and poten-tially prevent seed-borne weed risks and sterility based on cytoplasmic-,genetic-, or wide hybridization to enable larger bioenergy production andreduced invasiveness potential. Improvement of these traits can be achievedthrough classical breeding and selection based on existing genetic variation,whereas transgenic and genetic modification technologies can be used to intro-duce new genes and modify existing genes or to interfere with gene expression(44).

6.2. Genetic Modification of Energy Crops. The next generation ofDECs is being developed by using marker-assisted breeding and the creationof hybrids and transgenic with a broad portfolio of proven traits such as drybiomass yield (DBY), plant architecture, tolerance to biotic and abiotic stresses,and NUE and WUE. Genomic information gathered from across the biosphere,including potential energy crops and microorganisms able to break downbiomass will be significant for improving the prospects of significant cellulosicbiofuel production from current and future DECs with reduced costs andfavorable GHG profiles genomic information and resources are being developedtowards domestication. Genetic engineering could produce crop plants withreduced biomass conversion costs by developing crop cultivars with lesslignin, crops that self-produce cellulases enzymes for cellulose degradation andliginase enzymes for lignin degradation or plants that have increased cellulosecontent or an overall larger dry biological yield using genes for delayed flowering(48).

Genetic modification could be a useful also in developing fast growing DECsto gain larger yields from lower inputs, to reduce GHG emissions through lowerinputs and reduced or no tillage of potential energy crops. Other potential advan-tages of modifications could include multiple resistances or tolerance to abioticor biotic stress, herbicides, salinity, and environmental toxicity (47).


One of the immediate objectives of tree genomic research is to identify genesfor increased C portioning to above-ground woody matter, increased celluloseavailability for enzymatic digestion, manipulating genes for N metabolism,delaying senescence and dormancy, increased photosynthesis, and adaptationto drought and salinity. Populius trichocarpa was the first tree and potentialenergy crop to have its genome sequenced (44).

6.3. Balancing Food and Biofuel Production. The growing threat offood insecurity, which was confounded by the emphasis on biofuels, necessitatesa critical appraisal of agronomic strategies. Bioenergy is expected to create addi-tional demands for crop production. The actual or perceived negative impact ofbiofuel production on food prices may have tempered the enthusiasm about theirpotential to reduce GHG emissions and address energy security concerns. Sub-stantial opportunities are projected for developing countries to produce DECs(eg, sugarcane) and transition away from subsistence farming; bioenergy cropswould not displace food crops in these countries. It is suggested that a substan-tial proportion of bioenergy can be produced on marginal lands in South Americaand sub-Saharan Africa where agricultural land base can be quadrupled toaccommodate DECs (49). Based on current biofuel production technologies, itis highly unlikely that most countries will be able to displace any significantshare of their fossil fuel consumption. The United States, Canada, and Europecould displace about 10% of their gasoline consumption with biofuel if theyrecruit 30–70% of their respective croplands. Until DEC-based sustainable pro-duction systems on marginal lands are developed more productive land will bediverted for bioenergy production. Another option is double or mixed croppingin which food and energy crops are grown on the same land. This could lead toextractive farming practices and would lead to agrarian stagnation and perpe-tual food deficits as was the case in sub-Saharan Africa (50). Retention of cropresidues is essential to a large number of ecosystem services such as C seques-tration, soil and water conservation, and sustaining soil fertility and productiv-ity. Future investments in research on food crops and DECs should be viewed asa policy to enhance food security.

6.4. Environmental Impact. Biofuels have the potential to reduce netGHG emissions to the atmosphere through enhanced C management and maycontribute to the development of a sustainable bioenergy system with positiveenvironmental, economic and social impact. However the impacts of biofuels ofGlobal Climate Change (GCC), Land Use Change (LUC), water resources, defores-tation, and energy and food security vary be feedstock and method and location ofproduction. There are numerous complex models for predicting these impacts (51).

Water is needed to grow energy crops and the conversion process is also waterintensive. One liter of ethanol produced from corn and sugar beets requires 3500–5800 liters of water. These values suggest that in �90 years water use by biofuelscrops could exceed that total water being used by global croplands. If DECs aregrown on land that is unsuitable for crop production, they will be dependent onchemical outputs and irrigation; these factors will disrupt the energy balanceand lead to N2O emissions with the potential to over compensate all GHG gains.Grassland ecosystems are usually more biodiversity friendly than cropping sys-tems. Perennial polycultures offer a less polluting and more efficient alternativeto annual monocultures for bioenergy production. Non-native grass species


may have invasive traits. Any of the Short Rotation Cropping (SRC) plantationsestablished today are causing a range of environmental and social problemsincluding loss of biodiversity, soil erosion, and displacement of local people.

Research on direct production of hydrocarbons from plants or microbial sys-tems is needed to develop energy crops with higher photoconversion efficiency,can couple CO2–neutral biofuel production and C sequestration and produce non-toxic and highly biodegradable biofuels. It is essential that DECs have a positiveand sustainable impact on global climate change (GCC) adaption and mitigationeffects.

7. Role of Gene Bank Collections

Gene bank collections were established to conserve the diversity of cultivarsdeveloped over millennia through selection by farmers all over the world. Inthe early twentieth century, the Russian scientist Nikolai Vavilov mounted expe-ditions to the centers of diversity and origin of crops obtaining nearly 250,000seed samples of cultivars grown by farmers (landraces) that were stored at thecollection in St. Petersburg that now bears his name. His efforts were followedby others. The diversity in these collections of landraces provided the raw mate-rials that plant breeders used to create high yielding varieties combining thetraits of multiple ancestors. The genetic qualities of these improved varietieswere estimated to have contributed to an increase in crop yields of 21–43%, fuel-ing the ‘‘Green Revolution’’ (52). The success of plant breeding resulted in thedecision of farmers to plant high yielding varieties and abandoning their tradi-tional landraces. Recognizing that this process would lead to the loss of geneticresources that could continue crop improvement, the Food and Agriculture Orga-nization (FAO) of the United Nations established the International Board forPlant Genetic Resources (IBPGR) (now Bioversity International) specifically tocollect agriculture biodiversity and conserve it in gene banks. Today in total,the world has 1750 gene bank collections that conserve 7.4 million samples.About 30% of them are distinct (53). However today’s gene bank collections arenot representative of the full range of crop gene pools and traits of interest foradapting to climate change. Many crop species that are regionally, rather thanglobally important, remain generally underrepresented. An example is maize(Zea mays), which originated in Mesoamerica, yet has been grown by farmersin Africa for hundreds of years. Varieties were adapted to the harsher conditionsof the African continent. Under projected future conditions some of these vari-eties will become important in regions beyond those where it is currently grown.

Wild relatives of crops that have continued to evolve under pressure of theenvironment have crucially important traits and will be needed for breeding.Genes of wild relatives can provide cultivated crops with resistance to pests, dis-ease and stresses from temperature extremes, salinity, or flooding (27). Popula-tions of crop relatives growing in the wild are threatened by habitat destruction,deforestation, urbanization, grazing, and harvesting (54) as well as climatechange (55). Samples of wild crops are generally expensive to maintain in genepools. Because they have not been selected for qualities that facilitate storage ofseeds, they are not well represented in gene banks (53).


A gap occurs in the representation of wild relatives. Thirteen globallyimportant wild relatives include Chickpea (Cicer arietnnum), common bean(Phaseolus vulgaris), barley, cowpea (Vigna unguiculata), wheat, miaze, sorghum(var. Sorghum), pearl millet (Pennisetum americanum), finger millet (Eleusinecoracana), pigeon pea (Cajanus cajan), faba bean (Vivia faba), and lentil(Lens culinaris). Steps have been taken to establish the conservation of thesespecies with special attention to the effects of climate change. Because as manyof 39 species occur sympatrically in parts of Africa, multiple gaps could be filledwith targeted collecting or establishment of genetic reserves there (56).

7.1. Collection Integrity and Security. Gene banks conserve seedsand other reproductive materials ex situ in the absence of natural and artificialselection pressures. Cereals and legumes are stored as seeds, usually at low tem-perature. Species that are regenerated vegetatively, eg, bananas, potatoes, yams,cassava, are stored in vitro (in slow growth) or under liquid nitrogen at �196�C.Filed gene bans and botanical gardens conserve living plants typically of speciesof which seeds cannot be stored, eg, coconut. To retain viability of stored seeds,gene bank managers must periodically regrow plants from the stored seed to pro-duce fresh seed (regeneration). The aim is to maintain the genetic integrity of thematerial by following best practices to reduce genetic drift and the loss of geneticdiversity in samples. Challenges to regeneration include the control of plant dis-eases, prevention of cross-pollination, and regenerating material requiring ecolo-gical conditions not available in the vicinity of the gene bank. Backlog inregeneration is a critical problem due to lack of funding (53).

Many gene banks collections cannot be considered secure. A recent reviewfound that the number of individuals conserved per sample is frequently belowthe optimum for maintaining heterogeneous populations (53). Most national col-lections lack sufficient financial resources. Natural disasters and changes in gov-ernments have led to the loss of important collections.

Increased awareness of the importance of these collections has led to someimportant recent investments. Two World Banks grants totaling approximately$20 million allowed by the Consultative Group on International AgriculturalResearch (CGIAR) Centres to improve the status of their collection and makeavailable information around the world. Other important aid has come fromthe crop Gene Bank Knowledge Base and the Global Crop Diversity Trust(GCDT) founded by FAO. The GCDT is raising an endowment and defining stra-tegic actions to ensure the sustainable availability of plant genetic resources inthe public domain.

7.2. Making Information Available. In order for farmers, breeders,and researchers to select appropriate materials, they need information aboutthe various samples. The degree of completeness for gene bank information var-ies. Some banks have databases, others rely on noncomputerized lists of samples.In most cases ’’passport data’’ include the name and origin of the sample, but notall samples are accompanied by geographical coordinates of their collection sites.Most samples lack characterization and evaluation data and even fewer havemolecular characterization data (54). However, data are scattered and fragmen-ted. A major effort is underway to integrate and enhance existing informationand create a global information system on the World Wide Web. GENESYS isbeing developed to link collection managers/data providers with breeders,


researchers and other (57). Users will be able to query and search all crop collec-tions worldwide. Most initiatives to use gene bank materials to confront climatechange focus on development of new climate-resistant species. New crop vari-eties to ensure future food supply will require new sources of genetic variationscombined with more efficient breeding. Now more than ever, internationalexchange of germplasm must be sustained as many countries will need to accessgenetic information not available within its borders.

The World Summit of Food Security has declared a target of producing 70%more food by 2050 to feed projected increases in world population. This willrequire that production increase at a rate of 38% greater than the historicalrate of increase and be sustained for 40 years. This unprecedented increasewill have to take place despite limited options for expanding the amount of arableland, rising energy costs, a decline in the availability of phosphorus, and a needto reduce emissions of NO2, a major greenhouse gas. These increases must beachieved against the backdrop of climate change where redistribution of climatesand disappearance of some current climates will be expected. If agriculture can-not meet the challenges, millions of people will go hungry. The effective use ofgenetic resources will be greater than ever.

8. The Need for Future Research

The scale of demands for the future on plant science will be toward an historiccrisis in producing food for an increasing world population.

An overview of the phases of crop domestication, development and use iscontained in Table 3.

The emphasis of research into crop improvement has evolved from a singu-lar or narrow focus on factors limiting potential yield and production to one thatencompasses a production-environmental approach such as the adjustment oflocal agriculture to climate change, the management of agricultural systemsand catchments to avoid physico-chemical imbalances (soil and water pollution,nutrient exhaustion, acidification, salinization, air quality including the emis-sion of greenhouse gases), improving adaptation of crops to environmental stres-sors and the need to achieve improvements in crop water use efficiency anddrought tolerance. In recent years research has been further expanded to includeenvironmental, financial, and social issues on the farm (59). Unfortunately pastresearch into on-farm business management and off-farm supply chains have notbeen relevant to farm profits (60).

The history of crop science has been varied and complex. However, the focusof this article is on crop production and the impending effects of climate change.

There are several influences that will determine the capacity of plant breed-ing to cope with climate change. The demand side is determined by the rise ofpopulation and more affluent consumers. On the supply side are potentiallynegative impacts of climate change, the availability of fertilizers, chemicals,energy and the policies of governments.

In recent years, research institutions have experienced shifts in the policiesof governments and foundations, who, noting the decline in the proportion (2.5%)of gross national product contributed by agriculture, have failed to adjust


Table 3. A Brief History of Crop Improvement

PhasesExamples of crops, processes, and activities alongthe pathway to commercialization

Domesticationand selectior

� Wild forms of wheat (Triticum spp.) were grown inMesopatamia as early as 20,000 years ago, broughtinto cultivation through the selection of materialsthat were not shattering, nondormant,large-seeded, even ripening, lighter color,and better-tasting. Dispersed along trade routesinto Europe.

� Maize (Zea mays), originating in Mesoamericaaround 10,000 years ago, spread through theAmericas as a food staple, then worldwide.

International trade � The culture of coffee (Coffea spp.) began inEthiopia, thence to the Arabian Peninsula(1100 AD) where the roasting/boiling recipeswere perfected to popularize coffee. In theearly 1700s, coffee beans/plants weresurreptitiously introduced to Latin America(early 1700s) and other geographical areas.Tea, originating in China, had a similarhistory.

� Potato (Solanum tuberosum), domesticated inPeru-Chile between 3000 BC and 2000 BC; introducedto Europe (fifteenth century), Asia(sixteenth to seventeenth centuries), Africa(twentieth century).

Genetics and purposefulplant breeding

� This phase includes the deliberate collection,conservation, and storage of useful cropplants and their progenitors (land races,wild relatives), beginning with plantcollection expeditions of earlycivilizations and culminating in a networkof international plant genetic resourcecenters (CGIAR network establishedin 1974).

� The purposeful improvement of crop plants bypropagation, crossbreeding, and selectionfor desirable traits began as a scienceduring the past two centuries, followingon from the pioneering workand publications of Mendel and Darwin in themid-nineteenth century.

Hybridization � Natural hybridization occurred in the developmentof tetraploid durum (Triticum durum, AABB,2n ¼ 28) and Timopheev wheats(Triticum turgidum, AAGG, 2n ¼ 28)and hexaploid bread wheat(Triticum aestivum, AABBDD, 2n ¼ 42).

� In maize, the morphology of this monecious plant(terminal male florets on the main stem, female floretson cobs in axillary and lateral positions) is suitable forthe exploitation of plant hybrids to simplify breedingand gain from heterosis.


production levies and grants to counter the declining pool of research funds foragriculture research. Less money is being spent while research costs are escalat-ing. This negative trend could be balanced by better access to and communicationwith agricultural researchers around the world. Improved communication and aslower adoption of findings. Predictions of a hotter climate may bring greateroperational diversity in agriculture at least at the regional level. Producersmay seek a lower input and put more focus on more ecological systems. In crop-ping zones, crop production may give over to meat and wool production (61). Thestrong demand for food may lead to a greater number of specialized farms thatinclude both livestock and crops.

While considerable benefits may come from innovation in the economic andsocial aspects of agriculture there is an acute need to redefine the technology ofproduction.

In summary the following areas of agriculture improvement must beaddressed.

A list of studies in progress are listed below.

1. Drought tolerance improvements in crops plants. Cattivelli and co-workershave outlined an integrated approach to improving traits that reduce thegap between potential and actual crops yields in drought prone environ-ments (62). They concluded that genomics-assisted breeding has so farmade only a marginal contribution to selecting drought-tolerant genotypes.The way forward for research is discovery of physiological traits identifyingfavorable loci, MAS, gene cloning and insertion of elite genotypes and fieldvalidation.

2. Drought tolerance and water use efficiency in rice. The general tone ofstudies is optimistic in terms of manipulating physiological mechanisms

The green revolutionThe ecogreenrevolution

� Refers to the introduction and widespread use ofdwarfing genes to enhance the standability and harvestindex of wheat and rice varieties. Great progress wasmade during the 1960s and 1970s. Followed by an‘‘ecogreen revolution’’ in which crop management wasrefined to reduce adverse environmental effects andto ensure social equitability.

� Broadening of the base of useful crops such as legumesto provide biologically fixed nitrogen. For example, theproduction of sweet lupin varieties for use in WesternAustralia from the 1970s.

The biotechnology era � DNA extraction and amplification (PCR). The developingsciences of molecular genetics (genomics, transgenics,genetic markers) provide new tools for plant breeders.

Future innovation � Marker-assisted plant breeding and strategic releasesof transgenic crops.

Table 3. (Continued )

PhasesExamples of crops, processes, and activities alongthe pathway to commercialization


of stress tolerance/avoidance, adjustment of crop management, turning to amore efficient water use, and enhancing adaptations of farmers. CO2 effectswill be different for rice grown at cooler temperatures than those nowcultivated at higher temperatures so these effects need further study.Humidity and soil nitrogen content must also be examined (63–65).

3. Improving tolerance of heat stress in cotton. From the literature (66) it isexpected that rising temperatures will affect the world’s cotton crop in anegative way. Most of the world crops are nearing the limit of heattolerance. The pathway to heat tolerance is not clear cut and these heat-tolerance traits must be identified. Breeding for high temperature toler-ance in cotton, usually with traits such as stomatal water conductance,smaller and thicker leaves and flowering characteristics is likely to be char-acterized by incremental steps rather than rapid advances.

4. Variation in nitrogen tolerance in soybeans. Genetically based variation innitrogen fixation has been demonstrated for soybeans and other legumesspecies, but incorporation into cultivars has had little success. Theresearchers have reasoned that their chances were low since the N2 fixationtrait must be combined with several other desired traits and it is difficultto assess in large breeding populations. They suggested that soybeanbreeders should be encourage to conduct their entire program in low N2

soils (67).

5. Problem with salinity. Enhancing the soil tolerance of plants has met withlittle success due to the complexity of the trait (68). Salt tolerance dependson plant and leaf morphology compartmentation (salt storage in vacuoles).,the presence of organic solutes that protect plant metabolism, regulation oftranspiration, control of ion movement, and tolerance of Na/K ratios in thecytoplasm. There has been some success in mapping salt-tolerant traitsusing a QTL approach (69), selecting genotypes with low Naþ accumulationin wheat, thereby opening the way for MAS, the overall utility of the ap-proach has yet to be confirmed.

In summary, these are challenging times for plant physiologists, geneti-cists, and plant breeders. For major crops such as rice, wheat, and maize, withscientist building up a wealth of information combined with international coop-eration, the likelihood of both occasional breakthroughs and steady progress ishigh. Spillover effects can be expected from environmental science and studieson lesser crops, but investment from private/public sources as well as ensuringeffective and unselfish collaboration is undeniably very important.

Acknowledgment

This article was abstracted from Shyam S. Yadav, Robert J. Redden, Jerry L.Hatifield, Hermann Lotze-Campen, and Anthony E. Hall, eds., Crop Adaptationto Climate Change, John Wiley & Sons, Ltd., 2011. Chapters 1.1, 2, 24, 25, 27, 28,and 29 were used for this condensation. Please refer to the original work for moreinformation.


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SHYAM S. YADAV

International Advisor in AgricultureGovernment of Islamic Republic of Afghanistan

ROBERT J. REDDEN

Australian Temperate Field Crops Collection

JERRY L. HATIFIELD

USDA-ARS

ANTHONY E. HALL

University of California, Riverside

HERMANN LOTZE-CAMPEN

Potsdam Institute for Climate Impact


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Kirk-Othmer Encyclopedia of Chemical Technology || Climate Change, Crop Adaptation