Crop Adaptation to Climate Change (Yadav/Crop Adaptation to Climate Change) || Genetic Adjustment to Changing Climates: Pea

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Chapter 8

Genetic Adjustment to ChangingClimates: PeaClarice J. Coyne, Rebecca J. McGee, Robert J. Redden, Mike J. Ambrose, Bonnie J.Furman, and Carol A. Miles

Introduction

Peas (Pisum sativum L.) are herbaceous annu-als. Peas are adapted to cool, semiarid to subhu-mid growing conditions, and although they arewidely grown throughout the world, they per-form best in the cool, relatively dry areas of themid-latitudes (areas between approximately 30◦

and 60◦ north or south of the equator).In mid-high latitudes, peas are typically

planted early in the spring as they do not tol-erate hot weather or drought stress during flow-ering. Germination and seedling establishmentcan occur at soil temperatures as low as 4.5◦C. Attemperatures greater than 30◦C, the germinationpercent decreases (Olivier and Annandale 1997).Vegetative growth is maximized when daytimehighs are 13–23◦C. Haldimann and Feller (2005)found that net photosynthesis in peas decreasedwith increasing leaf temperature and was morethan 80% reduced at 45◦C. Daytime tempera-tures in excess of 27◦C during flowering maycause flowers to abort, resulting in reducedyield (Miller et al. 2002). These temperatureeffects generally restrict pea production to the

mid-latitudes and to high elevations in regionscloser to the equator.

Peas are adapted to many soil types as longas the soils are well drained. They do best insilt loams, sandy loams, or clay loams. Althoughpeas are tolerant of cool soil temperatures, theyare sensitive to flooded or excessively wet soils. Itis generally recommended to inoculate pea seedswith an appropriate strain of Rhizobium legumi-nosarium at sowing. While most cultivated soilsmay contain indigenous populations of Rhizo-bium leguminasorum bv. viciae, these strains ap-pear to be less effective at fixing nitrogen (Vessey2002). If soil pH is below 5.7, inoculation is rec-ommended. When pea seed has a good qualityinoculant, there is generally no yield gain fromnitrogen fertilizer; however, peas grown on soilswith less than 22 kg/ha available N may benefitfrom 11–49 kg/ha of N applied at seeding. P andK are required in relatively large amounts andshould be added based on soil test results. Sulfuris required to ensure adequate N fixation—addbased on soil test results. Lime is frequentlyadded to fields with soil pH of 5.2 or less. Rec-ommended cultural practices for specific sites are

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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GENETIC ADJUSTMENT TO CHANGING CLIMATES: PEA 239

presented in various university, government, andindustry crop production manuals (e.g., Oelkeet al. 1991; Siddique and Skyes 1997; Gardneret al. 2000; McKenzie et al. 2001a, 2001b; Schatzand Endres 2003; Kee et al. 2004; Miller et al.2005; McVicar et al. 2007).

The genetics of flowering in peas has beenextensively reviewed (Murfet 1985; Murfet andReid 1993; Weller et al. 1997; Weller et al.2009; Wenden et al. 2009). Flowering time isdetermined by a complex response of a spe-cific genotype to photoperiod and temperature.The wild-type pea and most commercial culti-vars are long day plants. There are numerousmutations and allelic combinations of four ma-jor flowering loci that result in five maturityclasses: day neutral (sn), early initiating (E, Sn,lf), late (e, Sn, hr), late high response (e, Sn,Hr), and very late (Lfd, Sn, Hr). Most autumn-sown, over-wintering peas in the mid-latitudeshave the dominant allele at the Hr locus. Plantswith Hr dominant allele have delayed floralinitiation and remain vegetative until daylengthexceeds 13.5 hours (Murfet 1973, 1981;Lejeune-Henaut et al. 1999). Hr has been demon-strated to colocalize with a quantitative traitloci (QTL) for frost-tolerance (Lejeune-Henautet al. 2008).

Time to maturity varies with cultivar, culti-var type, and end use. Accumulated Heat Units(HU) (Barnard 1948) are used to predict the de-velopment of vegetable peas that are harvestedat a physiologically immature stage for canningand/or freezing. HU are the sum of daily meanair temperatures above the plant’s base temper-ature (4.5◦C for peas). Current vegetable peacultivars reach processing maturity (tenderom-eter values = 110) in 1150–1600 HU (approxi-mately 45–70 days) (USDA, Risk ManagementAgency 2010). Time to maturity of dry ediblepeas and wrinkle seeded peas grown for seed istypically measured in days. Mean days to matu-rity of the spring-sown USDA pea core collectionranged from 66 to 102 days in Pullman, Wash-ington, USA (46o43′′N, 117o11′′W) (McPheeand Muehlbauer 2001). Mean days to maturity

of autumn-sown peas is typically in excess of250 days.

Research on climate changeand pea

The literature to date on the potential effects ofclimate change specifically on pea productionis limited. However, pea production will be af-fected, and given the studies summarized here, astrong agroecosystem approach will be needed asclearly the parameters of climate change (CO2,temperature, UV, and water) interact (Caldwellet al. 2007; Newton et al. 2007). Both the growthand utilization of pea are extremely plastic andpotentially could play an important role in pro-viding food and feed in various climate changescenarios (e.g., Burstin et al. 2007). It is notablethat studies to date are confined to cultivars, andwe lack knowledge on the genetic variation inPisum (wild and cultivated) for adaptive traitsfor climatic change.

CO2

Elevated CO2 results in faster relative growthrate (Sicher and Bunce 1997) and earlierflowering in pea as with most crop species(Craufurd and Wheeler 2009). Looking at theeffect of ambient and elevated CO2 on biomassportioning and nutrient uptake of mycorrhizaland nonmycorrhizal pea, cultivar (cv.) “Solara,”elevated CO2 and mycorrhizal colonization hadsimilar positive but independent effects on peaplant biomass (Gavito et al. 2000). The biomassresponse to mycorrhizal inoculation was not sig-nificantly affected by level of CO2.

Elevated CO2 may increase water-use effi-ciency (WUE) through greater closure of stom-ata and associated reduction in transpiration(Morison 1985).

Temperature

Rising temperatures pose the greatest threat toproduction of cool season pea as the tradition-ally temperate regions shift northward (Olesen



240 CROP ADAPTATION TO CLIMATE CHANGE

and Bindi 2002; Battisti and Naylor 2009). Forpea, failed seed-set from heat-stress (Lambertand Linck 1958) causes the greatest damage toseed yields (Karr et al. 1959; Guilioni et al. 1997;Hedhly et al. 2009). Heat stress negatively affectspeas through negative effects on photosynthesisand other physiological processes, e.g., repro-duction (Hall et al. 2002; Hamilton et al. 2008).In pea, there is a strong impact of high tempera-ture stress on chloroplast biogenesis and importof plastidic proteins required for the replacementof impaired proteins (Dutta et al. 2009).

CO2 and temperature

For heat-stressed peas at normal or warmergrowth temperatures, high CO2 may decreasetolerance of photosynthesis to acute heat stress(Hamilton et al. 2008; Wang et al. 2008), as wellas exacerbate heat stress through reduced tran-spiration (Ainsworth et al. 2002). Interactive ef-fects of elevated CO2 and warmer growth tem-peratures on acute heat tolerance may contributeto future changes in pea productivity, distribu-tion, and diversity.

Exposure to current CO2 levels or above, andincreasing temperatures above the thermal op-timum reduces the activation state of Rubiscoand causes declines in photosynthetic capacity(Haldimann and Feller 2005; Sage et al. 2008).

CO2 and water

Interactions between CO2 enrichment anddrought on water status and growth of pea plantswere discovered in the cv. “Alaska” (Paez et al.1983). Under drought conditions, total leaf wa-ter potential decreased, with a slower decreaseunder the high CO2 regime. With the additionof water, total leaf water potential recoveredwithin one day under high CO2. High CO2 coun-teracted the reduction in height that developedin low CO2 water-stressed plants. Removingdrought conditions resulted in a rapid recoveryof the internal water status and rapid recovery ofmost plant growth parameters under high CO2 in

comparison with control plants under well-watered and low CO2.

Water use

Much of the world’s pea production is grownunder rainfed conditions, including dryland pro-duction for fresh, dry, and feed types. Water usehas decreased due to the wide-scale adoption ofsemileafless pea that uses less water than con-ventionally leafed pea (Baigorri et al. 1999).Semileafless pea “Solara” is less sensitive todrought and has better WUE than convention-ally leafed “Frilene.” Semileafless peas also havemore effective osmotic adjustment carried outby tendrils, which may contribute to increasedWUE (Gonzalez et al. 2001). Early stage selec-tion methods were developed to identify drought-tolerant pea genotypes by water stressing 12pea cultivars and examining the growth of epi-cotyls as an indirect measure of turgor main-tenance through osmotic adjustment (Sanchezet al. 2004). At high latitudes, such drought tol-erance is relevant to specific crop rotations ofpea with cereal grains, and the rotation sequenceinteracts with WUE and yield (Jia et al. 2009).

UV

There is conflicting literature on the effects ofultraviolet-B (UV-B) on pea. Contrary to glasshouse studies of pea previously published, afield study by Allen et al. (1999) with the cv.“Meteor,” using 30% increase in ambient UV-B,with UV-A and ambient controls, found no ef-fect on photosynthetic performance or productiv-ity in well-watered or water-stressed pea. How-ever, growth inhibition at the whole-plant levelcorrelated with reduced leaf expansion and maybe more sensitive to UV-B radiation than pho-tosynthesis per unit leaf area (Gonzalez et al.1998). The negative effects of higher UV-B ra-diation was observed in the cv. “Greenfeast” inwhich photosynthetic activity was found to bereduced, total leaf chlorophyll content declined,and mRNA levels for chloroplast-localized




proteins were reduced (Savenstrand et al. 2002).Additionally, protective mechanisms were in-duced, including synthesis of UV-B-absorbingpigments and increased antioxidative enzyme ac-tivity. Further gene expression and protein stud-ies on the stress reaction from low to high levelsof UV-B radiation found deleterious effects onpea (Scherbak et al. 2009; Katerova and Todor-ova 2009; Katerova et al. 2009). A study of theeffects of compounding temperature, UV-B radi-ation, and watering regime on aerobic methane(CH4) emission in the pea cv. “234 Lincoln”found that enhanced UV-B decreased stem heightbut increased leaf area and above ground biomass(Qaderi and Reid 2009).

Genetic resources, gene pools,populations

Pisum is a small monophyletic genus. There isgeneral agreement over the number of taxa andless agreement over their rank. The classificationof Maxted and Ambrose (2001) recognizes threespecies in the genus Pisum: P. sativum L. (subsp.sativum with var. sativum and var. arvense, andsubsp. elatius with var. elatius, var. brevipendun-calutum, and var. pumilio), P. abyssinicum, andP. fulvum. Kosterin and Bogdanova (2008) useddata from studies of plastidial, mitochondrial,and nuclear markers to place taxa into eitherlineage A, considered to be the most ancient, orlineage B. Both P. fulvum and P. abyssinicumwere placed in lineage A, P. sativum subsp.sativum in lineage B, while both A and B lin-eages are found in P.sativum subsp. elatius.This information has been used by Maxted andKell (2009) to categorize the crop wild rela-tives (CWR) of pea and primary wild relativesare noted as P. sativum subsp. sativum var. ar-vense and P. sativum subsp. elatius var. elatius,P. sativum subsp. elatius var. brevipedunculatum,and P. sativum subsp. elatius var. pumilio (syn.P. humile). Secondary wild relatives include P.abyssinicum and tertiary wild relatives includeVavilovia formosa. The reference to P. sativumsubsp. sativum var. arvense as a wild relative

reflects the occurrence of representative materialexisting in the wild. This taxon is very broad, andwhile some discrimination from P. sativum var.sativum has been reported (Burstin et al. 2001),other studies have found them to be intermixed(Baranger et al. 2004; Tar’an et al. 2005).

Pisum sativum L. was most likely domes-ticated in the fertile crescent of the MiddleEast around 10,000 years ago (Zohary andHopf 2000). The wild progenitor of domesti-cated pea (Pisum sativum var. sativum) is Pisumsativum var. elatius, which also includes thepumilio and/or humile types (Mikic et al. 2009;Smykal et al. 2009). The cultivated/wild speciesPisum abyssinicum A. Br. (syn. P. sativum subsp.abyssinicum) is suggested to have diverged fromcultivated P. sativum several thousand years agoafter loss of pod dehiscence, retaining a mix-ture of wild and cultivated characteristics andthus was likely a semi-independent domestica-tion event (Weeden et al. 2004). Molecular di-versity studies show P. abyssinicum to share alarger component of its genetic makeup with P.fulvum and P. elatius than P. sativum, thus sup-porting the idea that the taxon represents a fullyindependent domestication event to that of Pisumsativum (Lu et al. 1996; Vershinin et al. 2003).

Centers of crop diversity

Vavilov (1926) developed the theory of centersof origin of domesticated plants and identified 8regions around the world where the major cropsof the world have been cultivated and where thereis a high abundance of wild relatives and geneticvariation. Vavilov (1949) considered the centreof origin for peas to be Ethiopia, the Mediter-ranean, and central Asia with a secondary centrein the Near East. An update of a review of thegeographic distribution of Pisum by Maxted andAmbrose (2001) is presented in Table 8.1.

The primary centre of origin for Pisum isthe Fertile Crescent or Eastern Mediterraneanthat correspond to the 3rd Vavilovian Centre(VC3). Important secondary centers of diver-sity for pea include the Central Asiatic (VC6),




Table 8.1. The geographic distribution of Pisum and taxa(Maxted and Ambrose 2001).

Taxon Geographic distribution

P. sativum var. sativum Pan-temperate

P. sativum var. arvense Europe, Central, andSouthwest Asia

P. sativum var. elatius ALB, ALG, ARM, AZB,BGR, CYP, EGY, ESP,FRA, GEO, GRC, HUN,ISR, IRQ, IRN, ITA,JOR, LBN, LBY, MOR,PRT, ROM, SYR, TUN,TUR, UKR, YUG

P. sativum var.brevipedunculatum

CYP, TUR, SYR

P. sativum var. pumilio(P. humile)

CYP, EGY, IRN, IRQ,ISR, LEB, JOR, SYR,TUR

P. abyssinicum ETH, YEM

P. fulvum CYP, GRC, IRQ, ISR,JOR, LBN, SYR, TUR,YUG

covering the highland Asiatic region fromAfghanistan and the Hindu Kush and along thelength of the southern slopes of the Himalayanmountain range. Much of this region is at highaltitude and has been an important source of re-sistance to root pathogens and cold tolerance.The Middle East (VC4) includes Transcaucasia,which is the distributional range of germplasmformally referred to as P. sativum ssp. tran-scaucasicum Gov. The highlands of Ethiopia(VC5) is exceptionally diverse and include P.sativum var. sativum, P. sativum var. arvense andP. abyssinicum, which grow sympatrically.

Gene pools

Harlan and de Wet (1971) formulated a system-atic means for categorizing wild species in termsof their utility for improving cultigens. For ex-ample, the primary gene pool (GP1) includesthe biological species in which members readilycross with each other. Members of the secondary

gene pool (GP2) contain species more distantfrom the cultivated species, making hybridiza-tion often difficult and resulting in somewhatsterile offspring. Tertiary gene pools (GP3) con-tain distant species that result in completely ster-ile offspring. Smart (1984) further subdividedthe primary gene pool into first and second or-ders, differentiating domesticated and wild com-ponents. Muehlbauer et al. (1994) placed allmembers of P. sativum into GP1 and P. ful-vum into GP2. Smart (1984) differentiated P.sativum subsp. sativum from all other membersof the species. There are no known members ofthe GP3 (Muehlbauer et al. 1994), although in-tergeneric crosses with Vicia faba (Gritton andWierzbicka 1975) and Vavilovia formosa havebeen suggested.

Different gene pools within P. sativum subsp.sativum have been shown to correspond to us-age and geographic source: European fodder(arvense), Georgian fodder (transcaucasicum),spring vegetable, spring feed types, primitivegarden pea of central and western Asia (asi-aticum) and China (Baranger et al. 2004; Tar’anet al. 2005), and a separate grouping of wild rela-tives (subsp. elatius). The evidence from numer-ous molecular studies has confirmed this highlevel of infra-specific variation. The high levelof genetic diversity in P. sativum subsp. elatiusacross its distributional range and the presenceof material exhibiting characteristics from bothelatius and sativum forms support the view thatintrogression has been frequent between theseforms and they should be considered as a speciescomplex (Vershinin et al. 2003). There is wideseparation among P. fulvum, P. abyssinicum, andthe P. sativum wild and cultivated subspecies(Lu et al. 1996; Vershinin et al. 2003; Zonget al. 2009a). Chinese landraces were comparedto a worldwide collection of landraces and sub-species utilizing SSR assays, and results showedgreater diversity within China than worldwideplus a separate spring gene pool from north-central China (Zong et al. 2009b). The exis-tence of a separate gene pool for China is nowsupported by retrotransposon diversity analysis




(Smykal et al. 2010). The source of increaseddiversity in China has not been reported. Possi-bilities may include an independent domestica-tion event with subsequent addition of diversityfrom the Middle East, or further introgression ofP.s. subsp. elatius diversity, while genetic isola-tion with selection of mutations in diverse en-vironments in China may have also occurred inEthiopia and central Asia.

The vast array of available genetic resourceshas the potential to provide necessary varia-tion for improvement of crops, especially in im-parting resistance to biotic and abiotic stresses.For example, new sources of salinity tolerancehave been found in spring landraces from north-central China, and there may be different expres-sions for other morphological traits (Leonforteet al. 2009; Redden et al. 2009).

Chinese germplasm has been collected athigh altitudes above 2000 m and will be eval-uated for possible frost tolerance by the SouthAustralian Research and Development Institute.Germplasm was also collected from low rain-fall dryland agriculture and will be evaluated fordrought tolerance by the Department of PrimaryIndustries, Victoria. The transcaucasicum andarvense gene pools are potentially useful sourcesof diversity for abiotic stresses such as low soilmoisture and cold. P.s.subsp. elatius, found upto 1700 m on rocky and grassy slopes, field mar-gins, and forests, is likely to have diversity formoisture stress. Var. brevipendunculatum, whichoccurs as a weed between 700–1800 m elevation,and the more distant relative Vavilovia formosa, aperennial alpine above 1500 m, possibly have di-versity for frost tolerance (Maxted and Ambrose2001). It is less clear whether sources of heat tol-erance can be found in Pisum, though landracesfrom the semiarid agriculture of the Middle Eastcould be usefully screened.

In situ and ex situ resources

The distributional ranges of extant wild and cul-tivated Pisum germplasm gene pools representa dynamic and ongoing exercise in evolution,

where populations continue to evolve and adaptin response to abiotic stresses. Access to suchmaterials will continue to be important as morefocus on particular combinations of ecogeo-graphic and more diversity studies enable poten-tially useful or under-sampled genetic diversityto be identified more precisely. Breeders’ con-siderations of the distributional ranges of wildoccurring germplasm and the identification of ar-eas or locations particularly rich in both wild andlandrace genetic diversity will generally focuson the Vavilovian Centres of Crop Diversity pre-viously mentioned. However, turning these intomore focused conservation strategies requiresconsiderable coordination of effort on both na-tional and international levels. The importanceof such efforts will only increase as pressures ofurbanization and changes of land use impinge onthese regions that will only be compounded byclimate change. Pisum CWR are not currentlybeing actively conserved. The in situ conserva-tion of CWR has only recently started to developinto a discipline as methodologies have been de-veloped to identify regions of maximal diversitytogether with management and monitoring plans(Maxted and Kell 2009). The most comprehen-sive assessment of the genetic diversity of CWRof Pisum led to the identification of four specificsites of maximized genetic diversity across thewild taxa as being highly desirable areas wherein situ reserves might be established, namely (1)Troodos Mountain, Limassol, Cyprus for P. var.brevipedunculatum, (2) Jabal Simeon, Aleppoprovince, Syria for P. fulvum and P. var. elatius,(3) Salkhad, Suweida province, Syria, and (4)Akna Lich, Geghama mountain ridge, Yerevanprovince, Armenia (V. formosa). P. abyssinicumis not represented within these sites and furtherwork is required to identify appropriate loca-tions for its conservation. Such in situ approacheswould need to be backed up by ex situ sampling.

The trans-global utilization of peas is un-derlined by the fact that ex situ holdings arereported for 153 institutions in 75 countries(FAO/WIEWS 2008) with the majority (87.6%)of the estimated 76,000 accessions held in 18 of




Table 8.2. Ex situ germplasm collections of Pisum with holdings in excess of 2000 accessions.

FAO institutecode Country

No. ofacc. Status No. of GS Web site for germplasm searches

ATFC Australia 6567 W, LR, C http://www2.dpi.qld.gov.au/extra/asp/AusPGRIS/

SAD Bulgaria 2787 LR, C, GC http://www.genebank.hit.bg/

ICAR-CAAS China 3837 W, R, C http://icgr.caas.net.cn/cgris_english.html

GAT Germany 5336 W, LR, C http://fox-serv.ipk-gatersleben.de/

BAR Italy 4297 W, LR, C http://www.ba.cnr.it/areagg34/germoplasma/2legbk.htm

WTD Poland 2899 W, LR, C, GS 2500+ http://www.ihar.edu.pl/gene_bank/

VIR Russia 6790 W, LR, C http://www.vir.nw.ru/data/dbf.htm

ICARDA Syria 6129 W, LR, C http://singer.grinfo.net/index.php?reqid=1151843332.3126

NordGen Sweden 2821 W, LR, C, GS 760 http://www.ngb.se/sesto/index.php?scp=ngb

JIC UK 3540 W, LR, C, GS 575 http://www.jic.ac.uk/GERMPLAS/pisum/index.htm

USDA-ARS USA 5741 W, LR, C, GS 711 http://www.ars-grin.gov/npgs/searchgrin.html

IPK Germany 5508 W, LR, C http://gbis.ipk-gatersleben.de/gbis_i/home.jsf;jsessionid=c25e8cb8ce9a70751ab591c4981b69cfa21dde381cf?autoScroll=0,113

AGRITEC CzechRepublic

2208 W, LR, C http://genbank.vurv.cz/genetic/resources/asp2/default_a.htm

NBPGR India 3070 W, LR, C

URVT-TILLING

France GS 4817 http://urgv.evry.inra.fr/UTILLdb

Status of stocks: W, wild accessions; LR, landraces; C, cultivars; GS, genetic stocks/mutant collections.

the larger public sector gene banks (Table 8.2).There has been considerable exchange betweencollections over many years with an estimatein excess of 60% duplication (van Hintum andVisser 1995). This trend has reduced signifi-cantly in recent years with improved electroniccommunications and accessibility and a greatersharing of responsibility through regional andinternational networks, which is being furtherstimulated through the stability resulting fromthe ratification and implementation of the Inter-national Treaty on Plant Genetic Resources forFood and Agriculture in 2004.

A number of mutagenesis programs havebeen undertaken on peas over the past 40 yearsand a substantial number of mutants havebeen accessed into long-term collections (Blixt1972; Swiecicki 1987). A listing of some ofthe most prominent of these mutants is pre-sented in Table 8.2. The John Innes Cen-tre hosts the working collection of mutantstocks on behalf of the Pisum Genetics Asso-ciation, which has recently been mirrored atthe USDA collection to further enhance theaccessibility of these resources (Ambrose andCoyne 2008).




Despite the large array of germplasm re-sources from a broad range of ecogeographic lo-cations available in Pisum, the challenges posedby climate change will require more concertedefforts to pool together and integrate our re-sources and information data sets so as to developthem into usable research and investigative tools.One such approach is the focused identificationof germplasm strategy, which aims to exploit theGIS information associated with germplasm andto overlay data relating to climate, soil type, andother environmental factors to assist in identify-ing those accessions most likely to contain thegenetic variation that is required (Bhullar et al.2009). The development of core collections (sub-sets of maximizing diversity) drawn from largercollections to facilitate use were first proposedby Frankel (1984), and numerous core collec-tions of Pisum have been developed (Matthewsand Ambrose 1994; Swiecicki et al. 2000; Coyneet al. 2005). While the focus on core collectionsand their more detailed characterization has beenuseful, the high level of genetic diversity and thefrequency of introgression between various taxamean that such strategies should focus on themore distinct grouping within the genus ratherthan the broad spectrum of variation. From thebreeders perspective, it is interesting to ask thequestion: where does the most useful variationactually reside? Further developments of markersystems, sequencing technologies, and their ap-plication have now brought us to the point wherewhole germplasm collections can be genotyped.

Genetic manipulation

Gene discovery and MAS

McPhee (2007) summarized the significant im-provements in pea achieved by recurrent selec-tion breeding for adaptation, multiple diseaseresistance, improved plant architecture, and re-sistance to seed shatter. Classical pea breed-ing is relatively rapid: four cycles per yearcan be grown in controlled environments andutilization of off-season nurseries is common.

Additionally, consensus linkage maps, singlegene, and QTL studies of production character-istics (McPhee 2007) have resulted in breedersbeing able to make useful early generation selec-tions of desired genotypes. Genomics-assistedbreeding is providing the next methodology forimproving breeding efficiencies.

Molecular analysis of germplasm collectionswith genomic tools is accelerating trait discov-ery by combining traditional linkage and QTLmapping with association mapping (Varshneyet al. 2009). Studies have been conducted, whichbridge pea trait QTL knowledge with associationmapping for gene discovery in pea germplasm.These studies include the population structureof pea core collections (Brown et al. 2007; Jinget al. 2010) and linkage disequilibrium estimatesfor the pea genome (Jing et al. 2007). Further,success of association mapping utilizing onepea core collection has been reported (Murrayet al. 2009). Pea-specific genomic resources arerapidly accumulating. Two pea BAC librarieshave been published and have resulted in rapidgene discovery (Coyne et al. 2007; Hofer et al.2009). Sanger and “next generation” sequencinghas resulted in the beginnings of an expressed se-quenced tag (EST) and haplotype resource: fromGermany 17,000 ESTs (Brautigam et al. 2008),from Australia 10,346 ESTs (Wong et al. 2008;Liang et al. 2009), and from Canada 50,000ESTs (Sharpe et al. 2009). Currently, GenBankhouses 34,508 pea ESTs (accessed January 1,2010). Proteomics and metabolomics are activeareas of pea research (e.g., Charlton et al. 2008;Vigeolas et al. 2008; Bourgeois et al. 2009).The emergence of the forward genetics techniqueof EMS-TILLING has further added to the ex-isting resources and to a pea-specific resource(Dalmais et al. 2008; Le Signor et al. 2009). Weanticipate that the pea genome will be completelysequenced within 5 years (Cannon et al. 2009),this started with next generation sequencing ofthe repetitive DNA in the genome of cv “Carrera”by Macas et al. (2007). These genomic tools,combined with association mapping and phe-notyping Pisum germplasm for climate change




adaptation, should result in rapid developmentof needed cultivars (Thompson et al. 2009).

Transgenic approach

Approximately 250 million acres ofbiotechnology-engineered crops under pro-duction now have reduced greenhouse gasemissions by approximately 960 million kg ofCO2 (Brookes and Barfoot 2006). Ainsworthet al. (2008) identified a number of potential tar-gets for biotechnologically improved crops withgermplasm with greater abiotic stress resistanceunder climate change. Consistent transformationof pea was achieved using the method of Grantet al. (1995), as reviewed in McPhee et al.(2004). Functional genomic studies present agrowing resource of approaches for engineeringstress-resistant pea cultivars. Pea is poised tomake full use of gene function discoveriesfrom model plant species and specific peagenes through transformation. Recent examplesinclude identification of metabolites expressedin pea under drought stress (Charlton et al.2008) and identification of mRNAs coding forshort-chain alcohol dehydrogenase-like proteinsin response to abiotic stress treatments, such aslow intensity UV-B (280–315 nm) (Scherbaket al. 2009).

A recently published molecular analysis of3220 pea germplasm accessions provides an ex-cellent framework for selection of pea geneticdiversity from which exploitation by agriculturecan be made rationally in response to climaticchanges (Jing et al. 2010). International cooper-ation for such collaboration is in place (Smykalet al. 2010).

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