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Chapter 21

Genetic Adjustment to Changing Climates:SugarcaneGeoff Inman-Bamber, Phillip Jackson, and Maryse Bourgault

Introduction

Sugarcane makes an important contribution tothe economies of many tropical and subtropicalcountries, contributing about 70% of raw sugarproduced worldwide, with the remainder fromsugar beet. Sugarcane is also being increasinglytargeted and used for bioenergy production, par-ticularly production of ethanol (from fermenta-tion of sugar) and electricity from burning thefiber component. Climate change could affectsugarcane production directly through biophysi-cal processes and indirectly through socioeco-nomic processes as governments start imple-menting energy and environmental policies todeal with climate change and compliance withKyoto Protocol commitments, urban air pollu-tion, and energy security (Jolly 2007). Somecountries have already started selecting for “en-ergy canes” (Leal 2007), and it is likely that thefirst response in breeding programs to climatechange will be to exploit the opportunity to usesugarcane as a feedstock for the energy marketrather than to prepare for changes in climate perse. This chapter will consider first the geneticbackground of the commercial sugarcane vari-eties, then the substantial interest in breeding forthe energy market, and finally possible adaptive

strategies in breeding for longer term climatechange.

Genetic background

Sugarcane is an aneuploid polyploid heterozy-gous grass in the Andropogoneae tribe, whichalso includes sorghum and maize. Cultivars areclones of a single genotype that are propagatedvegetatively by planting cuttings of stems. Untilthe early twentieth century, sugarcane cultivarswere mostly clones of the domesticated speciesSaccharum officinarum (2n = 80), originating inthe east Indonesian/New Guinea region (Danielsand Roach 1987). Sugarcane breeders in Indiaand Indonesia achieved a breakthrough in sugar-cane improvement when they developed hybridsbetween S. officinarum and the wild species Sac-charum spontaneum (2n = 40–128) and then cul-tivars by backcrossing these hybrids to S. offic-inarum. S. spontaneum is a highly polymorphicspecies with an extensive distribution through-out Asia, and found growing in diverse habitats(Daniels and Roach 1987). The resulting cul-tivars derived from these early interspecific hy-brids were higher yielding, better adapted to vari-ous environmental stresses, better ratooning (i.e.,regrew better following harvesting), and more

Crop Adaptation to Climate Change, First Edition. Edited by Shyam S. Yadav, Robert J. Redden, Jerry L. Hatfield,Hermann Lotze-Campen and Anthony E. Hall.c© 2011 John Wiley & Sons, Ltd. Published 2011 by John Wiley & Sons, Ltd.

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440 CROP ADAPTATION TO CLIMATE CHANGE

resistant to some diseases than the S. officinarumcultivars they replaced (Jeswiet 1930; Berdingand Roach 1987). Modern sugarcane cultivarsmostly trace back to the interspecific hybridsoriginating in Indonesia and India, with limitedadditional infusion of S. spontaneum germplasmsince (Roach 1989).

The complexity of the sugarcane genome isgreater than any other important crop (Grivetand Arruda 2001). One important feature of isthe high level of ploidy. Chromosome in situhybridization has indicated a basic chromosomenumber of x = 10 for S. officinarum, implying oc-toploidy, while S. spontaneum has a basic chro-mosome number of x = 8, implying a ploidy levelof between 5 and 16 (D’Hont et al. 1998). Mostmodern cultivars retain a complex polyploidyand aneuploid genome containing between 2n =100 and 2n = 130 chromosomes (D’Hont et al.1996; Grivet and Arruda 2001). About 80% ofthe chromosomes in these cultivars are believedto be from S. officinarum, 10% from S. sponta-neum, and the remainder derived from recom-bination between the chromosomes of the twoprogenitor species (D’Hont et al. 1996).

Modern sugarcane breeding programs relyon some form-of recurrent selection, wherebyclones performing well in selection trials andwith other generally desirable traits (e.g., dis-ease resistance) are evaluated as parents throughtheir progeny. Elite parents are crossed generat-ing large numbers of seedling clones each yearin a number of regions. The seedling clones thenenter multistage (3–6 stages) selection systems,whereby over a period of around 10 years ormore, elite clones are identified and releasedcommercially (Skinner et al. 1987).

S. spontaneum is considered to contribute im-portant traits to modern cultivars such as adap-tation to environmental stresses, ratooning abil-ity, resistance to diseases and pests, and generalvigor (Berding and Roach 1987; Wang et al.2008). However, the species also contributessome negative traits such as low sucrose andhigh fiber contents both undesirable for produc-ing sugar but not necessarily energy. S. sponta-

neum clones have been found growing in widelydiverse habitats ranging from tropical jungles,deserts, swamps, and altitudes over 3000 m withtemperatures well below freezing (Brandes et al.1939; Warner and Grassl 1958). These traits mayassist with breeding for changing climatic con-ditions.

Erianthus (sect. Ripidium), Miscanthus (sect.Diantra), Sclerostachya, and Narenga are relatedgenera thought to be involved in the origin ofsugarcane and are considered to be a potentiallyinterbreeding group known as the Saccharumcomplex (Mukherjee 1957; Daniels and Roach,1987). Erianthus arundinaceus (Rez.) Jeswiethas been targeted as having a number of traitsdesired by sugarcane breeders including good ra-tooning performance, tolerance to environmentalstresses, vigor, and disease resistance (Berdingand Roach 1987). Fertile hybrids between Sac-charum and Erianthus have been produced (Caiet al. 2005), but so far there are no reports ofcontribution to commercial sugarcane cultivars.

Use of sugarcane for bioenergy

Sugarcane has been targeted as a potentially low-cost provider of bioenergy because it produceshigh yields of fermentable sugars and becausethe fiber component is also transported to sugarmills and is readily available (as “bagasse”, fol-lowing crushing of cane to extract the juice) forburning and electricity generation, or other pro-cessing to produce biofuels. Life cycle analysesof sugarcane have indicated that sugarcane offerslarge advantages over other crops such as cornfor biofuel production (e.g., Goldemberg 2007;Renouf et al. 2008).

Goldemberg and Guardassi (2009) claimed anenergy output to input ratio of 10.2 for sugarcane(in Brazil), 2.1 for sugar beet (in Europe), and1.4 for maize (in the United States). An earlieranalysis by Austin et al. (1978) provided a ratioof total energy produced to energy consumed inproduction of 1.6 for sugarcane in Australia andSouth Africa compared to 0.6 for sugar beet inthe United Kingdom. In Brazil, sugarcane has



GENETIC ADJUSTMENT TO CHANGING CLIMATES: SUGARCANE 441

been used to produce ethanol for transportationpurposes (Moreira and Goldemberg 1999) withapproximately 24.5 billion liters produced fromsugarcane in 2009 (RFA 2010), representing ap-proximately 50% of the sugarcane production(Muller et al. 2008). Notwithstanding this con-siderable proportion, according to Goldemberg(2007), competition between biofuel and foodproduction is still not substantial, with biofuelsbeing produced on less than 10% of the agricul-tural land area in Brazil.

Estimates in the IPCC Second AssessmentReport (IPCC 1996) suggested that 300–1300Mt C (equivalent to about 1100–4800 Mt CO2-eq/yr) from fossil fuels could be offset by us-ing 10–15% of agricultural land to grow energycrops, with crop residues potentially contribut-ing 100–200 Mt C (equivalent to about 400–700Mt CO2-eq/yr) to fossil fuel offsets if recoveredand burned (Smith et al. 2007). Sugarcane fiber(bagasse) is commonly used to generate steamand electricity in sugar mills such that excesspower is delivered to the grid (Cheesman 2004).Traditionally, most sugar mills have generatedsufficient power only for their own needs, butinvestments in factory efficiency and electricitygenerating capacity that allow for exporting ofsignificant quantities of power may occur at eco-nomically feasible electricity prices (Hodgsonand Hocking 2006). Bagasse may also be usedfor a range of liquid or gaseous biofuels using arange of different processing technologies (Edyeet al. 2005). Although the economic feasibilityof such technologies is still under question, yethigh level of investment and steady progress be-ing made is encouraging. Increased productionof bioenergy from the fiber component of sug-arcane may be obtained by including trash (topsand dead leaves) in the harvested material deliv-ered to the sugar mill, although careful analysisof potential costs and benefits is required (Bee-hary 2001; Thorburn et al. 2006).

Up to now, in breeding programs, the in-creasing fiber has been considered to have neg-ative economic impacts because of adverse ef-fects on sugar extraction and milling rate, and

fiber has been weighted negatively in selectionindices (Wei et al. 2008). In contrast, a veryhigh selection pressure has been maintained onsugar content because of the high economic im-portance of this trait in producing sugar withminimal harvesting, transport, and milling costs(Jackson 2005). If the fiber component of sug-arcane becomes more valuable in future, thenthis will change selection indices used in breed-ing programs, and focus attention on higher totalbiomass production than in the past. In particu-lar, material more closely related to the high fiber,low sucrose species S. spontaneum may becomemore commercially attractive. Clones of S. spon-taneum have been reported with fiber content ashigh as 56% fiber on a fresh weight basis. Inter-specific hybrids with up to 33% fiber content arebeing tested as “fuel canes” in the West Indiessince they produce up to five times more fiberyield than commercial sugarcane varieties (Raoand Kennedy 2004). Wang et al. (2008) evaluatedprogeny from 43 biparental crosses between sug-arcane and S. spontaneum clones, against severalcommercial “sucrose” cultivars and reported adoubling of stalk biomass in clones with dry mat-ter content as high as 41% and fiber up to 29%,although only small plots were used and resultsneed to be interpreted cautiously. These resultsalign with those from the West Indies where“energy cane” produced 51 tons compared to19 tons fiber per hectare from “sugarcane” (Leal2007). It is possible that high fiber genotypes canproduce higher biomass yields than high-sucrosetypes because sucrose may feedback on photo-synthesis either through end product suppressionor through sucrose signaling compounds suchas Trehalose-6-phosphate (McCormick et al.2009). Sucrose feedback inhibition was thoughtto be involved in higher rates of photosyn-thesis when sugarcane plants were modifiedto produce isomaltulose as well as sucrose(Wu and Birch 2007). Irvine (1975) measuredhigher rates of photosynthesis in S. spontaneumwith low-sucrose contents than commercial hy-brids (Saccharum spp.) with high-sucrose con-tents, possibly because of feedback inhibition.




Botha (2009) compared three strategies for im-proving the value of sugarcane for both food andfuel markets based simply on the heat of combus-tion of sucrose and fiber. More energy would bederived by improving fiber than sucrose contenteven without the benefits of increased photosyn-thesis and new technologies for lignocellulosicfermentation.

Traits for climate change

Park (2008) provided a list of factors that couldaffect the Australian sugar industry through cli-mate change. The list covers five main produc-tion regions that are well into the tropics inthe north (<20oS) and well in the subtropics inthe south (>30oS), thus highly representative ofthe latitudinal transect of sugar-producing areasworldwide. All regions in the Australian sugarindustry are expected to experience increases inrainfall variability, temperature, evapotranspira-tion (ET), and water stress. In addition, increasedcyclone activity in the north and decreased oc-currence of frost in the south are expected (Park2008). Increased temperatures will hasten cropdevelopment leading to higher yields if wateris available, but lodging will also be exacerbatedleading to harvesting difficulties resulting in poorcane quality through extraneous matter (Berdingand Hurney 2005) and through reduced sucrosecontent in cane stalks (Singh et al. 2002).

Elevated CO2

Few studies have investigated the response ofsugarcane to elevated CO2, and these have beenrestricted to enclosure studies (De Souza et al.2008; Vu and Allen 2009a, 2009b). Work onother C4 crops such as maize and sorghum sug-gest that the response of these crops to ele-vated CO2 is modest, especially in field con-ditions (reviewed in Ghannoum et al. 2000;Long et al. 2006; Ainsworth 2008). The responseis attributable to the lower stomatal conduc-tance, which creates an interaction between thelower evaporative cooling (and thus higher leaf

temperature) and a reduction in water consump-tion that delays water stress (Ghannoum et al.2008). In sugarcane, Ziska and Bunce (1997)showed a 10% increase in photosynthesis andabout 7% stimulation of biomass under doubleambient CO2 concentrations. However, some re-cent studies on sugarcane indicated that water-use efficiency (WUE) would increase by 35–60%leading to large increases in biomass yields (upto 40%) even with irrigation regimes designedto limit water stress (De Souza et al. 2008; Vuand Allen 2009a). Very few studies have lookedat genetic variability in the response of crops toelevated CO2, but considerable variability seemsto be present in common bean (Bunce 2008),rice (Ziska et al. 1996; DeCosta et al. 2007), andwheat (Ziska 2008).

Increases in photosynthesis rates in C4 cropshave led some researchers to suggest that C4

photosynthesis is directly improved by elevatedCO2 (Ziska and Bunce 1997). Although Ghan-noum et al. (2000) argue that direct carbon fix-ation does not occur in mesophyll cells becausethese lack several of the C3 photosynthesis en-zymes, they do consider that phosphoenolpyru-vate (PEP) carboxylase might play a direct rolein the stimulation of growth under elevated CO2.Selection for the maintenance of PEP carboxy-lase activity, which has been shown to decreaseunder elevated CO2 (Vu and Allen 2009a), couldpotentially lead to higher photosynthesis ratesand higher biomass accumulation.

Elevated CO2 and N2 fixation

The largest biomass increases under elevatedCO2 have been reported in soybean, and is dueto improved carbohydrate availability for bio-logical nitrogen symbiosis (Long et al. 2006;Oikawa et al. 2010). Sugarcane has been shownto establish such nitrogen fixing symbiosis withendophytes in Brazil, with some varieties ob-taining up to 150 kg N ha−1 yr−1 from suchsymbiosis (Boddey et al. 1995), although thiscontribution to N requirements has been foundto be insignificant in South African commercial




sugarcane plantations (Hoefsloot et al. 2005). Ifthere is genetic variability in the capacity for ni-trogen fixing symbiosis, and if effective strains ofendophytes could be found, this could be highlybeneficial from an ecological perspective, as in-organic nitrogen fertilizers can cause substantialdamage to ecosystems such as the Great Bar-rier Reef in Australia, or the Everglades in theUnited States (Inman-Bamber et al. 2005). Forthis same reason, regardless of whether or notsubstantial symbiotic nitrogen fixation is achiev-able in the near future, improvements in nitrogenefficiency are seen as a high research priority(Inman-Bamber et al. 2005).

Water stress

Production in most regions in Australia is al-ready limited by water (Inman-Bamber 2007)and growers in the subtropics are concerned mostabout increased water stress with climate change(Park 2008). Variation in response to water stressin sugarcane has received limited attention in thepast and variation in WUE even less. If dry pe-riods become more intense with climate change,there will be greater interest in such variation.Cultivars with a reputation for drought resistancetend to avoid stress by slowing down water up-take through early stomatal closure, leaf rolling,leaf senescence, and increased root resistance(Inman-Bamber and de Jager 1986; Saliendraand Meinzer 1989; Inman-Bamber and Smith2005). In one case, a drought-resistant cultivarcontinued to take up water longer than drought-susceptible cultivars (Smit and Singels 2006)possibly through a more vigorous root system.Research on selection for drought resistance andimproved WUE has started recently in Australia(Basnayaka et al. 2009). The research acknowl-edges the complexity of the “drought resistance”conundrum, where some traits would help tomaintain yields in some dry conditions but notin others depending on the frequency and sever-ity of dry periods. Simulation of various droughtresistance or avoidance traits indicated that traitssuch as leaf senescence and decreased leaf or root

conductance were mostly negative for biomassyields in rainfed Australian and South Africanclimates even where these climates were toodry for current commercial production (Inman-Bamber et al. 2011).

Sinclair et al. (2005) predicted a 5–7% in-crease in sorghum yield in Australia by reducingtranspiration (and photosynthesis) during the daywhen vapor pressure deficit is high. They theo-rized that a trait for reduced stomatal conduc-tance during the mid portion of the day wouldlead to increased transpiration efficiency (TE).In our simulations with sugarcane, increased TEincreased sugarcane biomass yields by 1–11%in water-limited environments even though in-creased TE was combined with reduced conduc-tance, which on its own proved to be mostlynegative for yield (Inman-Bamber et al. 2011).TE or rather its surrogate, delta (�), which is de-rived from the ratio of 13C to 12C captured duringassimilation of CO2 by C3 plants, is not alwaysassociated with yield (Blum 2009). 13C discrim-ination as a means of measuring TE might notbe available for sugarcane improvement becauseof the small contribution of Rubisco (C3) to theassimilation process (Ranjith et al. 1995). How-ever, the potential benefits of improved TE needsto be explored more fully at least by modelingthe association between TE and conductance andthen determining the variation of TE and conduc-tance responses in the sugarcane gene pool. Sub-stantial genotypic variation for stomatal conduc-tance was found in 131 clones of S. spontaneum× S. officinarum and Miscanthus sp. × S. offic-inarum hybrids in the work of Basnayaka et al.(2009), and early indications from this work werethat TE varies substantially among these hybrids.This augurs well for improving sugarcane bothfor dry climates expected with climate change orfor expanding the industry into more marginalareas for renewable energy production.

High temperature

If greenhouse gas emissions continue to in-crease as they currently are, there are 5–17%




probabilities that temperatures might exceed by6.4◦C or more their current values by 2100(Schneider 2009). Sugarcane was grown com-mercially for about 10 years in the Ord RiverIrrigation Scheme, northwest Australia (15.6oS,128.7◦E), where the mean annual temperature is3◦C higher than the next hottest sugarcane regionin the country (Muchow et al. 1997). Growthrates and yields were much lower than expectedfrom applications of the Agricultural ProductionSystems Simulator (APSIM), sugarcane module(Keating et al. 1999). The upper limit for maxi-mum photosynthesis assumed in APSIM is 35◦C,but upper cardinal temperatures for vegetativegrowth and for photosynthesis may be higherthan 35◦C (Bonnett et al. 2006; Inman-Bamberet al. 2008). Water use determined with a Bowenratio-energy balance was lower than expectedfrom algorithms in the APSIM model and thepoor growth could not be explained by excessivedemand for water (Inman-Bamber et al. 2006).Bonnett et al. (2006) showed that sucrose contentwas lower at a temperature regime of 25–38◦C,than at 23–33◦C, and that there were differencesbetween the two cultivars tested. Clearly, ourknowledge of the physiology of sugarcane athigh temperature is limited and it is thereforedifficult to anticipate what traits would be usefulfor such an environment. Jackson et al. (2007)conducted a genotype × environment study in-volving seven diverse production regions includ-ing the Ord and up to five sites in each region,a total of 24 trials. Most trials had 42 largelyunselected clones in common. Trials within re-gions had only slightly greater genetic correla-tions with each other than with trials from otherregions suggesting that gains achieved from se-lection trials in other regions would be nearlyas good as selections from trials within the re-gion. The Ord with only one trial site was theoutstanding exception suggesting that distinctlyhigher temperatures in this region would requiremarkedly different traits than are required forthe wide range of cooler climates spanning some1700 km of latitude. In addition, Gbetibouo andHassan (2005) suggested there might be more

gains in investing in research for heat tolerancethan drought tolerance in South African crops, asaverage temperatures are already supraoptimal.

Conclusions

Climate change could benefit sugarcane-basedindustries for many of the reasons cited in thischapter. Sugarcane is already contributing toglobal sweetener and energy requirements, notnecessarily in competition but the possibility ofcompetition between food and fuel is of con-cern. Energy from fiber and reducing sugars is,and probably will continue to increase the valueof sugarcane by better use of the nonsucrosecomponents. Higher temperatures and CO2 lev-els will probably also increase the value of thiscrop through higher yields and WUE. However,it is clear that relatively little is known about thephysiology of sugarcane at elevated temperaturesand CO2, and we suggest that research now befocused on both in the search for germplasm thatcan contribute to adaptation to climate change.More extreme rainfall causing more waterlog-ging as well as more water stress is what con-cerns farmers the most. Unfortunately, there islittle known about the value of drought adaptiontraits and where to find them. Therefore, we rec-ommend more projects such as those in Australiaand possibly China and South Africa, to look forsuch traits and to understand how they can con-tribute to cultivars for future climates with morevariable rainfall.

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