HORTSCIENCE 51(6):653–663. 2016.

Crop Vulnerability: CaryaL.J. Grauke1

USDA–ARS Pecan Breeding and Genetics, 10200 FM 50, Somerville, TX77879

Bruce W. WoodUSDA–ARS Southeastern Fruit and Tree Nut Research Laboratory, 21Dunbar Road, Byron, GA 31008

Marvin K. HarrisDepartment of Entomology (Professor Emeritus), Texas A&M University,College Station, TX 77843

Additional index words. Carya illinoinensis, germplasm, diversity, breeding, repository,characterization

Abstract. Long-established native tree populations reflect local adaptations. Represen-tation of diverse populations in accessible ex situ collections that link information onphenotypic expression to information on spatial and temporal origination is the mostefficient means of preserving and exploring genetic diversity, which is the foundation ofbreeding and crop improvement. Throughout North America, sympatric Carya speciessharing the same ploidy level tend to hybridize, permitting gene flow that contributes toregional diversity and adaptation. The topographic isolation of many fragmentedpopulations, some of which are small, places native Carya populations of United States,Mexico, and Asia in a vulnerable position and justifies systematic collection andcharacterization. The characterization of indigenous Mexican pecan and other Caryapopulations will facilitate use for rootstocks and scion breeding and will contribute topecan culture. The Asian species, as a group, are not only geographically isolated fromNorth American species, but also occur in disjunct, fragmented populations isolated fromother Asian species. Section Sinocarya includes the members of the genus mostvulnerable to genetic loss. With all species, recognition of utility based on characteriza-tion of ex situ collections may contribute to the establishment of in situ reserves. GlobalCarya genetic resources should be cooperatively collected, maintained, characterized,and developed. The integration of crop wild relatives into characterization andbreeding efforts represents a challenging opportunity for both domestic and in-ternational cooperation. Genomic tools used on the accessible collections of the NationalCollection of Genetic Resources for Pecans and Hickories (NCGR-Carya) offer greatpotential to elucidate genetic adaptation in relation to geographic distribution. Thegreatest progress will be made by integrating the disciplines of genetics, botany,pathology, entomology, ecology, and horticulture into internationally cooperative efforts.International germplasm exchange is becoming increasingly complicated by a combina-tion of protectionist policies and legitimate phytosanitary concerns. Cooperativeinternational evaluation of in situ autochthonous germplasm provides a valuablesafeguard to unintended pathogen exchange associated with certain forms of germ-plasm distribution, while enabling beneficial communal exploration and directedexchange. This is threatened by the ‘‘proprietary’’ focus on intellectual property.The greatest risk to the productive development of the pecan industry might well bea myopic focus on pecan production through the lens of past practice. The greatestlimitation to pecan culture in the western United States is reduced water quantity andquality; in the eastern United States the challenge is disease susceptibility; andinsufficient cold hardiness in the northern United States. The greatest benefit for theentire industry might be achieved by tree size reduction through both improvedrootstocks and scions, which will improve both nut production and tree management,impacting all areas of culture. This achievement will likely necessitate incorporation ofcrop wild relatives in breeding, broad cooperation in the testing leading to selection, anddevelopment of improved methods linking phenotypic expression to genomic charac-terization. The development of a database to appropriately house information avail-able to a diverse research community will facilitate cooperative research. Theacquisition of funds to pursue development of those tools will require the support ofthe pecan industry, which in the United States, is regionally fragmented and focused onmarketing rather than crop development.

Introduction to the crop

Biological featuresPecan [Carya illinoinensis (Wangenh.) K.

Koch] is a tree species autochthonous (native)

to North America (Fig. 1). It is the mosteconomically valuable and agriculturally sig-nificant member of Carya. At maturity, pecanis a large, long-lived, monoecious, polymor-phic, anemophilous, and deciduous tree. The

nut (seed) has hypogeal germination andforms a dominate taproot with abundant lat-eral roots. Leaves are odd-pinnately com-pound with 11–17 leaflets, borne in alternatearrangement, with reduction in leaflet number,size, and pubescence as the tree matures.Seedlings have long juvenility (5–12 years)and bear imperfect flowers at different loca-tions on the tree. Male and female flowersmature at different times (dichogamy). Maleflowers are borne on staminate catkins infascicles of three, with catkin groups formedon opposite sides of each vegetative bud,sometimes with a second pair above, borneopposite each other, at 90� to the first. Thecatkins are borne at the base of the currentseason’s growth or from more distal buds ofthe previous season whose vegetative axisaborts after pollen shed. This pattern of catkinformation is characteristic of all members ofsectionApocarya, but is distinct from the othersections of the genus (Figs. 2–4). Pollen isproduced in very large quantities and is carriedby wind. Pistillate flowers are borne on few-flowered (1–9) terminal spikes. Individualtrees whose catkins shed pollen before pistil-late flower receptivity are termed ‘‘protan-drous’’ or ‘‘first male.’’ Individual trees whosefemale flowers reach receptivity before pollenshed are termed ‘‘protogynous’’ or ‘‘firstfemale.’’ As a population, trees are hetero-dichogamous, with mixed periods of bloomenabling cross pollination and outcrossing(Thompson and Romberg, 1985). This repro-ductive system facilitates heterozygosity inindividuals and populations, and is accompa-nied by inbreeding depression. The fruit ofpecan is a nut enclosed in a dehiscent husk thatsplits along more or less winged sutures torelease the hard-shelled nuts. Nuts are tan tobrown, mottled with black stripes at the apexand spots at the base. Shells are relatively thinas compared with most hickories, and protectthe edible kernels, which are rich inmono- andpolyunsaturated fats. Young pecan trees areslow to bear fruit, but increase in fruit pro-duction with age and size. Mature trees tend tobe large and long lived, producing crops thatalternate with regional synchrony in a roughlyalternating manner with occasional masting(mass seeding) (Chung et al., 1995).

Ecogeographical distributionNative stands of pecan are distributed

primarily in well-drained soils of the Mis-sissippi River and its tributaries from north-ern Illinois and southeastern Iowa south tothe Gulf Coast of Louisiana and west to theEdwards Plateau of Texas in the UnitedStates (Fig. 1). Isolated populations occur asfar east as southwestern Ohio and centralAlabama, and as far west as Chihuahua,Mexico. Pecan has the westernmost distribu-tion of any of the Carya species.

Hybridity in sympatric species of Caryasharing the same ploidy level is evident in theabundance of known hybrids (Table 1) andhas recently been examined using molecularmarkers (Grauke and Mendoza-Herrera,2012). Distribution maps are provided hereby section and ploidy to aid in visualizing

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VIEWPOINT

potential gene flow among North AmericanCarya species (Figs. 5–7). Known distribu-tions of Asian Carya species are more frag-mented, with no species overlap (Fig. 8).

Plant breeding and its productsThe primary commercial crop is pecan

nuts, an increasingly global commodity. Pe-can is the only Carya species that hasbenefited from significant breeding and se-lection. Most attention has been focusedon scion breeding and selection. Open-pollinated seed stocks are used to growrootstocks, which vary by region. In addition,nuts of Carya ovata and Carya laciniosa areharvested from wild trees and consumedlocally. In China, nuts of local native hicko-ries [mixtures of Carya cathayensis and

Carya dabieshanensis (Liu and Li, 1984)]are collected from natural stands and mar-keted primarily in China.

Primary crop products and their value(farm gate)

Commercial U.S. pecan production is di-vided into two major categories: ‘‘Native/Seedling’’ and ‘‘Improved.’’ ‘‘Native’’ pecansare ungrafted trees growing in natural, regen-erating stands that were not established byhumans. Native pecans represent the originalforest, may hold the key to understandingclimatic and edaphic adaptation, and are thegenetic foundations for crop improvement.They also constitute large acreages producingrelatively low yields of often poor-qualitynuts. ‘‘Seedling’’ pecans are ungrafted treesgrown from nuts that have been introducedand are therefore evidence of some level ofselection. ‘‘Improved’’ pecans are selectedcultivars grafted onto seedling rootstocks.Highest yields are achieved in orchards of‘Improved’ pecans, with around 2000 kg/ha/year being realized as the statewide averagein some western states where all productionis solely from improved plantings. By contrast,states with large numbers of native pecans,such as Texas, have low production per unitarea. This is due to lower yields produced bynatives (<500 kg/ha/year), and because manynative pecans are not harvested annually (Areset al., 2006). Highest prices are obtained forwell-managed, improved pecans, whereas nutsfrom unmanaged improved cultivars may be

sold at reduced prices as ‘‘Seedling’’ nuts.Production is erratic, with years of low pro-duction (but high kernel quality) often followedby very heavy crops (but low kernel quality).Farm gate price per pound tends to alternate inopposition to yield, with heavy crop yearsgenerally bringing low prices. In the 4 yearsbetween 2011 and 2014, total U.S. pecan pro-duction averaged 125.2 million kg per year(276 million lbs) with a mean annual farm gatevalue of 525 million dollars. Production fromimproved pecans was relatively flat during the1990s, but has recently increased due to sub-stantial increases in crop value (Fig. 9).Increased exports to Asian markets havecontributed to the strong prices received andto increased planting in recent years, whichshould result in increased future production.U.S. exports to China increased dramaticallybeginning in 2007. Before that year, thepeak export to China had been almost 6000t in 2006. Since the 2007 crop year, exportsto China have not dropped below 20,000 tand in crop year 2012 exceeded 45,000 t(Zedan, 2015a). National area of bearing andnonbearing improved pecan orchards in-creased from 124,900 to 131,560 ha (anincrease of 6660 ha or 5%) between the2007 and 2012 agricultural census (NASS,2012). Production from native/seedling pe-cans has continued to decrease since the1970s (Fig. 10). National land area of bearingand nonbearing native/seedling pecan treesdecreased from 110,550 to 88,382 ha (a re-duction of 22,168 ha, or 20%) between the2007 and 2012 agricultural census (NASS,2012). If those figures are trustworthy, that isan alarming rate of loss in native area andshould increase the motivation to characterizeremnant stands of old native trees across therange.

Domestic and international cropproduction

United States (regional geography).Georgia produces the largest percent of theU.S. improved crop. Most production comesfrom mature orchards in the southern part ofthe state concentrated near the city of Albany.New acreage in middle Georgia, especiallyon the Fort Valley Plateau, is being planted tomore recently developed cultivars of pecans,while older orchards in southern Georgiaare being renovated to new cultivars (Wise,2010). New Mexico is the second leadingstate in improved pecan production. MostNew Mexico production comes from theMesilla River Valley in Dona Ana County.This production is primarily from ‘Western’and ‘Wichita’, with new plantings incorporat-ing ‘Pawnee’ and other more recent releases.Oklahoma is the center of native pecan pro-duction, followed by Texas. During the earlydecades of the 20th century, native produc-tion exceeded improved production. FollowingWorld War II, improved production increasedsharply and overtook native production duringthe 1960s. Increased planting of soybeans inLouisiana and Arkansas in the 1970s resultedin the destruction of thousands of hectares ofnative pecans (Grauke et al., 1995), beginning

Fig. 1. (A)Carya illinoinensis (Wangenh.) K. Kochindigenous pecan tree, Red River Valley, TX.(B) Native distribution of species, and area ofculture in North America. (C) ‘Pawnee’ nuts inhusk, in shell, longitudinal, and cross sections.(D) Diversity in shape and size of adult phaseleaves [‘Upton’ (BW 105-21); ‘Aggie’ (BW104-30); ‘Hadu 3’ (BW 104-35)]. (E) Diversityin pecan nut size and shape.

Fig. 2. Naked terminal buds (L) and single,3-fascicled catkins (R) of Sinocarya (Caryacathayensis).

Fig. 4. Imbricate terminal buds (upper L) that swellgreatly at growth initiation (lower L), and3-fascicled catkins borne in axils of bud scales(R) in Carya (Carya laciniosa). Catkins areborne at the base of the current season’sgrowth.

Fig. 3. Valvate terminal buds (L) and paired,opposite 3-fascicled catkins (R) of Apocarya(Carya illinoinensis). Catkins are borne at thebase of the current season’s growth as well asfrom buds lower on the shoot in which thevegetative apex aborts.

Received for publication 1 Oct. 2015. Accepted forpublication 12 Feb. 2016.Mention of a trademark, proprietary product, orvendor does not constitute a guarantee or warrantyof the product by the U.S. Department of Agricul-ture and does not imply its approval to theexclusion of other products or vendors that alsomay be suitable.1Corresponding author. E-mail: lj.grauke@ars.usda.gov.

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a consistent downslope in the production trendfor natives (Fig. 10). Since native pecans yieldless per acre, and nuts are sold at lower prices,there is an increasing incentive to convertnative stands to improved orchards.

International. Mexico is second to theUnited States in the world of pecan pro-duction and has recently harvested over100,000 t, accounting for over 40% of totalworld production (Table 2) (Branson and

Gibbons, 2011; Nu~nez, 2014). Mexican com-mercial pecan production is largely based oncultivars developed in the United States,primarily ‘Western’ and ‘Wichita’, althoughthe recent release of ‘Norte~na’ (P�erez et al.,2015) represents selection from local germ-plasm which is applauded. Recent crop in-creases have been due to both increasedplanting and improved cultural practices,including drip irrigation (Flores and Ford,2009). Area harvested was estimated at about70,000 ha in 2014, with over 82,000 haplanted. Chihuahua is the major pecan-producing state in Mexico, accounting for50% to 60% of national production, followedby Coahuila, Durango, Sonora, and NuevoLeon (Nu~nez, 2014; Puente, 2004). TheUnited States is the main export market forMexican pecans (Flores and Ford, 2009).

The world’s third largest pecan produceris South Africa producing about 2.5% of theworld pecan crop. Pecan production began inthe Nelspruit area of Mpumalanga. Currentplantings are concentrated to the west, in theNorthern Cape Province in the VaalhartsIrrigation district. The climatic conditionsof that area are very similar to the U.S.western pecan region. The dry climate isnot conducive to the pecan scab disease(Fusicladium effusum Winter) allowing forreduced production costs. Available land,water, and a strong international market forpecans has resulted in accelerated plantingof pecans in South Africa, averaging about4000 ha of new plantations per year. Cultivarsbeing planted there are primarily ‘Wichita’,‘Choctaw’, and ‘Navaho’, all products of theU.S. Department of Agriculture (USDA)Agricultural Research Service (ARS) PecanBreeding Program (Grauke and Thompson,1997). Production in the southern hemispherehas the advantage of being in the off-seasonof the northern hemisphere, placing theircurrent season crop in competition with theearly U.S. pecan harvest for the lucrativeThanksgiving/Christmas holiday gift market.However, about 90% of the South Africancrop is sold in-shell to China (Zedan, 2015b).

The pecan industry in Australia was de-veloped largely since the 1960s, when a por-tion of the Stahmann family migrated toAustralia from the Las Cruces area of NewMexico, where the family pioneered NewMexico pecan production in the 1930s. Mostpecans in Australia are produced in NewSouth Wales, with 80% of production beingfrom the Stahmann Orchards at Moree, NewSouth Wales. Total production area in Aus-tralia is currently 1400 ha, with annual pro-duction of about 3500 t in-shell or about 1.4%of the world production. Australian produc-tion has the advantage of being in the off-season of the northern hemisphere, placingthe current season Australian crop in partialcompetition with the early pecan harvest inthe United States for the lucrative holidaygift market. However, 66% of Australianproduction is consumed locally and theremainder is primarily targeted at Asian,rather than U.S. markets. The primarycultivars grown in Australia are standards

Fig. 5. Distribution of diploid species of section Apocarya.

Table 1. Taxa recognized as species by the National Collection of Genetic Resources for Pecans andHickories, listed alphabetically within section.

Section Sinocarya

1. Carya cathayensis Sarg. Chinese hickoryz (probably includes Carya dabieshanensis)2. Carya hunanensis Cheng and R.H. Chang–Hunan hickoryz

3. Carya kweichowensis Kuang and Lu–Guizhou hickoryz

4. Carya tonkinensis Lecomte–Viet Nam hickoryz

5. Carya poilanei (A. Chev.) J. Leroy–Poilane’s hickoryz

Section Apocarya6. Carya aquatica (F. Michx.) Nutt.–Water hickory7. Carya cordiformis (Wangenh.) K. Koch–Bitternut hickory8. Carya illinoinensis (Wangenh.) K. Koch–Pecan9. Carya palmeri Manning–Mexican hickorySection Carya10. Carya floridana Sarg.–Scrub hickory11. Carya glabra (Mill.) Sweet–Pignut hickory [includes Carya ovalis (Wangenh.) Sarg.–Red hickory]12. Carya laciniosa (F. Michx.) Loudon–Shellbark hickory13. Carya myristiciformis (F. Michx.) Nutt.–Nutmeg hickory14. Carya ovata (Mill.) K. Koch–Shagbark hickory [includes Carya carolinae septentrionalis (Ashe) Engl. &Graebn.–Southern shagbark hickory]15. Carya pallida (Ashe) Engl. & Graebn.–Sand hickory16. Carya texana Buckley–Black hickory17. Carya tomentosa (Poir.) Nutt.–Mockernut hickoryInterspecific hybrids1. Carya ·brownii (C. cordiformis · C. illinoinensis) Sarg.2. Carya ·collina (C. texana · C. tomentosa) Laughlin3. Carya ·demareei (C. cordiformis · C. ovalis) Palmer4. Carya ·dunbarii (C. laciniosa · C. ovata) Sarg.5. Carya ·laneyi (C. cordiformis · C. ovata) Sarg.6. Carya ·lecontei (C. aquatica · C. illinoinensis) Little7. Carya ·ludoviciana (C. aquatica · C. texana) (Ashe) Littley

8. Carya ·nussbaumeri (C. illinoinensis · C. laciniosa) Sarg.9. Carya ·schneckii (C. illinoinensis · C. tomentosa) Sarg.y

10. C. illinoinensis · C. ovata (see Manning, 1962)11. C. illinoinensis · C. myristiciformis (see Grauke and Mendoza-Herrera, 2012).zAsian species. Section Sinocarya Cheng and R.H. Chang (in Chang and Lu, 1979) has been proposed forall Asian spp. based on naked buds. Those listed in Sinocarya also lack lacunae in nut shells, which Caryapoilanei has, as do all members of Apocarya.yParentage disputed.

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of the U.S. western pecan industry, such as‘Wichita’ and ‘Western’.

Pecan nuts are also produced in Argen-tina, Egypt, Brazil, Uruguay, Chile, Peru,The Peoples Republic of China, India, andTurkey; with small plantings also in theDominican Republic, Zimbabwe, Israel,Georgia, Italy, Syria, and Iran.

Much of the global attention on pecan isdue to increasing consumption in China.China is working to develop its own pecanproduction industry, building on the historicrespect and value given to the perceivedhealth value of nuts in general (Yang and

Gale, 2015), and specifically the traditionalconsumption of its native hickory nut, C.cathayensis (Grauke et al., 1991). U.S.pecan grower and sheller groups haveexpressed concern over the threat posed bythe development of a pecan industry inChina. However, a vibrant Chinese pecanindustry based on existing U.S. cultivarsis ‘‘not likely to be realized in light ofresource- and climate-related constraints, thedifficulty of expanding production on the basisof fragmented, small-scale production devel-oped over the last two decades’’ (Yang andGale, 2015).

It was estimated (B. Garris, personalcommunication) that by 2025, there wouldbe worldwide production of over 441,000 t(973,000,000) lbs in-shell (an increase of182% over current production), with theprimary pecan-producing nations beingUnited States > Mexico > South Africa >Australia.

Urgency and Extent of CropVulnerabilities and Threats to Food

Security

Genetic uniformity in the ‘‘standingcrops’’ and varietal life spans

Improved pecan culture is a young in-dustry, developed from a diverse native forestof long-lived trees. The ‘‘standing crop’’ in-cludes both indigenous ‘‘native’’ trees and theestablished orchards of the ‘‘improved’’ pecanindustry. The first grafted pecan orchard waspropagated by the slave gardener Antoine atOak Alley Plantation, LA, in 1846 (Taylor,1905). Individual pecan trees are long livedand commonly survive over 200 years. Givenindividual tree longevity, unselected nativetrees still bearing nuts are older than the U.S.commercial pecan industry. The genetic di-versity of the native pecan forest has alwaysbeen assumed to be robust, but systematicmethods of characterizing that diversity havenot been applied. Increasing evidence indi-cates that the geographic distribution of ge-netic diversity reflects long-term adaptation(Bock et al., 2016; Grauke et al., 2011;Sagaram et al., 2011; Sparks, 2005). Char-acterization of extant diversity in ex situcollections should contribute to breedingand selection.

The historic trend in pecan culture hasbeen managed to increase uniformity. Prop-agation by grafting or budding allows devel-opment of large acreages of a few commongenotypes. As a cultivar gains regional ac-ceptance in the market, acreage increases.Four cultivars (Stuart, Western, Desirable,and Wichita) accounted for over 57% of totalimproved pecan acreage in 1990 (Thompson,1990). Once selected and propagated bygrafting, a cultivar becomes essentially ‘‘im-mortal’’, as it is re-propagated. ‘Desirable’,which originated in about 1933, is still amongthe most commonly planted cultivars inGeorgia (Wells, 2014), despite substantialsusceptibility to pecan scab disease thatnecessitates multiple prophylactic fungicidesprays (Wells, 2014). ‘Western’, introducedin 1916, is still the most commonly plantedcultivar in western orchards. ‘Pawnee’, intro-duced in 1984, was the first cultivar releasedfor early season nut maturity (Thompsonand Hunter, 1985). That trait has contributedto increased profits in the lucrative U.S.holiday markets surrounding Thanksgivingand Christmas. ‘Pawnee’ is among the mostpopular cultivars being propagated in Geor-gia (Wells, 2014), as well as in the north andwest (Thompson and Conner, 2012).

Tree longevity, coupled with the time andexpense to establish a new orchard, contrib-utes to the challenge of incorporating new

Fig. 6. Distribution of diploid species of section Carya.

Fig. 7. Distribution of tetraploid species of section Carya.

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cultivars. Unmanaged orchards that might beconsidered obsolete can be brought back intoproduction when the incentive of increasedprice returns, as has been the case since 2003(Fig. 9). That argues in favor of only offeringnew cultivars with significantly improvedtraits of bearing consistency, nut quality,and critical local adaptations for disease andinsect resistance.

Threats of genetic erosion in situU.S. Carya species. The genus Carya

consists of 17 species worldwide (Table 1).The focus of horticultural attention has his-torically been on pecan, with the emphasis of

research being on the development and man-agement of grafted cultivars. Reduction inthe area of native pecan stands is variableacross the range, but has been most extensivein Arkansas (Grauke et al., 1995). Theharvested resource we call ‘‘native’’ pecansis the result of thinning and minimallymanaging what was originally the ‘‘wild’’forest (Harris, 1980). The development ofmanaged native groves in Texas, Oklahoma,Louisiana, and Arkansas has historicallybeen inextricably linked to cattle grazing, astrees were thinned to allow pasture forgrazing, reducing tree crowding, and increas-ing nut production. Development of native

stands from wild populations is suspected tohave peaked by the middle of the 20thcentury, with existing native groves consist-ing of aging trees that are often too large foreffective spray management or mechanicalharvesting systems. Grazing cattle undertrees harvested for nuts raises food regulatoryissues that further threaten native culture,increasing the incentive to convert acreageto the less genetically diverse, but morelucrative grafted plantations. Designation ofin situ populations that preserve regionalgenetic diversity while continuing the resil-ient and historically important cattle/pecanmanagement system may be justified.

Characterization of the geographic distri-bution of genetic diversity in pecan consis-tently confirms that the forest holds morediversity than we know how to use (Graukeet al., 2011; R€uter et al., 1999, 2000).Evaluation of diversity in existing ex situcollections of pecan should include morecomprehensive screening for resistance tomajor pests (Harris, 1975). Research onexisting collections shows variation in leafmorphology (Grauke et al., 2003; Sagaramet al., 2011) and disease resistance (C. Bock,personal communication) related to geographicorigin. Increased resolution with improvedgenomic tools should aid interpretation ofthe geographic distribution of genetic diver-sity. This may motivate return to targetednative areas for further collection. Conser-vation of in situ populations is invaluable toallow future generations to continue theexploration of this valuable natural resource.

Of the other U.S. Carya species, the mostthreatened are Carya myristiciformis (Fig. 6)which was described as ‘‘nowhere abundant’’by Sargent (1918), and is represented byfragmented, disjunct populations that spreadfrom the Atlantic coast to central Mexico,and Carya floridana (Fig. 7) which is en-demic to central Florida and has the mostrestricted distribution of any North Americanhickory.

Incentive to incorporate valuable traits isnecessary to justify the time needed forbreeding with hickories. Clinton Graves(Mississippi State University, retired) sawthe potential of increased disease resistancewith pecan/hickory hybrids (Graves et al.,1982). He made several controlled crossesbetween pecan and nutmeg hickory that arerepresented in repository collections, but theyoffer neither morphological nor molecularevidence of hybridity. Evidence of hybriditywith other species in wild populations ofnutmeg hickory has been observed followinglimited examination (Grauke and Mendoza-Herrera, 2012) and should be systematicallyevaluated. Carya floridana has the smallestmature tree size among the hickories. Col-lections from across the species’ range weremade in 2009 and are well represented inrepository collections by self-rooted seed-lings. Ploidy is being examined using flowcytometry (Whittemore, Xia, and Grauke,unpublished data) and crosses are being madein the breeding program in an effort to devisestrategies to capture the beneficial trait of

Fig. 8. Distribution of species in section Sinocarya (all diploid).

Fig. 9. Fifty years of U.S. ‘Improved’ pecan yields (million lbs, 10-year running average) in relation tovalue (million $, 10-year running average). Data from NASS (2012).

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reduced tree size, either in rootstocks or scions,both of which will be long-term efforts. Exist-ing in situ populations of C. floridana are wellconserved by numerous public and privateconservation efforts.

Mexican Carya species. Carya in Mexicoincludes Carya palmeri, C. ovata, and C.myristiciformis, in addition to pecan (C.illinoinensis). The first three are unrepre-sented in systematic ex situ collections, butmay be represented in some de facto in situreserves. The three former species are allfound in mixed native populations in themountainous Parque Ecologico Chipinque,south of Monterey, Mexico, where there isevidence of hybrids that include pecan (GraukeandMendoza-Herrera, 2012). Manning (1962)reported the first interspecific hybrids betweenpecan and C. ovata from San Luis Potosi,Mexico. Observations in Mexico of early nutmaturation in association with low chillingshow that pecan accessions from Mexicanpopulations may contribute valuable traits forbreeding. Mexican pecan seedlings show out-standing vigor, manifest unusual patterns ofplastid diversity, and have patterns of root andleaf morphology likely indicating populationlevel adaptations of value in development ofboth rootstocks and scions.

Asian Carya species. All Asian hickoriesoccur in fragmented, topographically isolatedpopulations with limited (known) distribu-tions (Fig. 8). It would be valuable to know

more about all species of Asian Carya in-cluding the geographic extent of their distri-bution and their abundance and diversity overthat range. The focus of Chinese efforts hasbeen on C. cathayensis, the foundation ofa respected native nut industry centered atLinan, Zhejiang, People’s Republic of China.The species has been extensively sequencedand characterized using a variety of molecu-lar methods (Huang et al., 2013; Li et al.,2014; Wang et al., 2011). Apomixis has beenreported for the species (Zhang et al., 2012),an observation consistent with the lack ofpolymorphism in seedling accessions ofthe species observed over several years inthe NCGR-Carya collections (Grauke andMendoza-Herrera, 2012). AlthoughC. cathayen-sis may be well-represented in Chinese collec-tions, characterizations of its diversity acrossits limited range have only recently beenreported (Guo et al., 2015). Whether C.dabieshanensis deserves species rank or isa subspecies of C. cathayensis remains to bedetermined. The nuts of the two taxa areoften marketed together. Whether the col-lections of Guo et al. (2015) included pop-ulations of C. dabieshanensis in their geneticevaluations of Anhui Carya populations isunknown. Recent research (Li et al., 2014)comparing neutral genetic diversity betweenC.cathayensis and C. dabieshanensis imply in-creased interest in distinguishing and usingthat germplasm. Grauke and Mendoza-Herrera

(2012) reported patterns in maternally in-herited plastid profiles that consistently dis-tinguished specimens of C. dabieshanensisfrom C. cathayensis in limited numbers ofobservations, but such distinctions also sep-arate geographic populations of pecan thatare not recognized by even varietal, muchless species status (Grauke et al., 2011).

Carya hunanensis, Carya tonkinensis,Carya kweichowensis, and Carya poilaneiare not represented in any known systematicex situ collections. C. hunanensis was testedand found advantageous as a seedling root-stock forC. cathayensis (Huang J.Q. personalcommunication). C. tonkinensis is occasion-ally used as a rootstock in Yunnan, but use ofthe other western Chinese species C. kwei-chowensis is unknown. Given the ratherlimited distributions of the Asian Caryaspecies, their characterization and appropri-ate conservation is encouraged even in theabsence of known strategies of utilization.

Debate continues over whether the treeconsidered by Manning (1963) to be Caryasinensis Dode, is best classified as themonotypic representative of section Rham-phocarya or the monotypic species Anna-mocarya sinensis (Dode) Leroy (Lu et al.,1999). Regardless of its taxonomic classi-fication, the tree should be incorporatedinto studies of genetic diversity and itsexisting populations recognized and pre-served by both ex situ and in situ collec-tions. Chinese populations have recentlybeen studied using molecular markers fromplastid (matK, rbcL-atpB, rpoC1, rps16,trnH-psbA, and trnL-F) and nuclear ge-nome (ITS and phyA) (Zhang et al.,2013). No ex situ collections of the specieshave been observed, even at the NanjingBotanical Gardens. Indigenous stands ofthe species at Cuc Phuong Forest Reservein Vietnam were recognized as an impor-tant in situ reserve (Grauke et al., 1991) andshould be incorporated into systematiccharacterizations.

Living specimens of C. poilanei have notbeen seen since collections were made fromthe type tree in Vietnam by Poilane in 1937(Manning, 1963), although collection effortshave been made in the area where the typewas originally found (Grauke et al., 1991; D.Stone, personal communication) as well asin Laos (C. Philaphandeth, personal com-munication). Because that species had traitsthat linked Asian species to extinct Euro-pean species (Mai, 1981), it would be valu-able to locate surviving members, if theyexist.

Asian species are very poorly representedin U.S. repository collections. We hope towork cooperatively with Asian scientists indeveloping appropriate molecular methodsfor characterizing diversity. We encourageestablishment of representative Asian ex situcollections where those materials are acces-sible for study. It is important to establisha baseline profile for each species for phylo-geographic interpretations as well as to rec-ognize hybridization that may occur withinAsian species when pecan is introduced.

Fig. 10. Fifty years of U.S. ‘Native’ pecan yields (million lbs, 10-year running average) in relation to value(million $, 10-year running average). Data from NASS (2012).

Table 2. World pecan production.

Country Total bearing hectares Nonbearing hectares Metric tons % of total production

United States 188,622 30,607 126,174 52.0Mexico 70,000 20,000 105,000 43.3South Africa 6,000 21,000 6,000 2.5Australia 1,400 3,274 1.4Others 2,000 0.8Total 242,448

Land area based on information from NASS (2012).U.S. production = (Improved + Native/Seedling) pecans, 2012–14 (NASS, 2012).

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Current and emerging biotic, abiotic,threats and needs

Biotic (diseases, pests). Xylella fastidiosais emerging as an important factor in theglobal stewardship and dissemination ofpecan germplasm. The pathogen is a Gram-negative, straight, rod-shaped, aerobic, afla-gellate bacterium. It grows optimally from26 to 28 �C and is described as ‘‘nutritionallyfastidious,’’ requiring specialized media forgrowth in the laboratory. Sanderlin andHeyderich-Alger (2000) reported that X.fastidiosa causes leaf scorch in pecan, whichhas become known as Pecan Bacterial LeafScorch (PBLS). A disease screen of commer-cial cultivars for susceptibility to PBLS(Sanderlin, 2005) reported variable expres-sion of leaf scorch, with all susceptible toinfection and symptom development. Grafttransmission of the pathogen was demon-strated. Sanderlin and Melanson (2010) dem-onstrated insect transmission of X. fastidiosaby pecan spittlebug, Johnson-grass sharp-shooter, and glassy-winged sharpshooter.Melanson et al. (2012) reported that sub-species multiplex infects pecan. Currently,five subspecies of the pathogen are proposedbased on molecular sequence similarities:subsp. fastidiosa includes strains that causedisease in alfalfa, almond, grapevine, andmaple; subspecies multiplex includes strainscausing disease in pecan, almond, elm,peach, pigeon grape, plum, sycamore, andother hardwoods; and subspecies pauca in-cludes strains causing disease in citrus. Sub-species sandyi, was proposed for strainsinfecting oleander, whereas subspecies tashkewas proposed for strains infecting chitalpain New Mexico (Randall et al., 2009). Onceinfected with X. fastidiosa, the disease ischronic and yields are reduced (Sanderlinand Heyderich-Alger, 2003). Disease trans-mission via grafting can be reduced by hotwater treatment of scions before grafting(Sanderlin and Melanson, 2008). Melansonand Sanderlin (2015) recommended that hotwater treatment be adopted as standardphytosanitary treatment in regions that im-port pecan scion wood. Recent research bySanderlin (2015) reported that seedlingsgrown from seven open-pollinated seedstocks differed in susceptibility to infectionafter mechanical inoculation with X. fastid-iosa. ‘Cape Fear’, known to be extremelysusceptible as a scion, produced seedlingrootstocks that were among the most sus-ceptible, with ‘VC1-68’ and ‘Apache’ in thesame category. ‘Curtis’, ‘Elliott’, and ‘Riv-erside’ seedling rootstocks were less sus-ceptible. Seedling rootstocks from ‘Moore’and ‘Stuart’ were intermediate. Since X.fastidiosa can be transmitted at high fre-quency from infected rootstocks to newlygrafted trees, selection of resistant root-stocks would be beneficial to pecan nurser-ies and pecan producers. The foundationclone of the USDA ARS Pecan BreedingProgram has been ‘Schley’ (Grauke et al.,2015). The two most susceptible seed stocksin recent tests (Sanderlin, 2015) are ‘CapeFear’ and ‘VC1-68’, which both have

molecular profiles consistent with being di-rect progeny of ‘Schley’ (Grauke, unpub-lished data).

Since a draft of this report was presentedand discussed at the Crop Germplasm Com-mittee meeting in Frisco, TX, early July2015, PBLS was confirmed in Arizona andNew Mexico by Drs. Natalie Goldberg andRichard Heerema (Vitanza, 2015). Efforts tocharacterize the extent of disease distributionand to coordinate protocols for its pheno-typic and biochemical identification areunderway (J. Randall and K. Ong, personalcommunication).

International distribution of graftwoodhas been curtailed by this disease. Phytosani-tary inspection protocols call for seasonalinspections, with inventories found to be symp-tomatic being tested with enzyme-linked im-munosorbent assays (ELISAs). The efficacy ofELISA to detect PBLS may depend on refine-ment of sampling and testing protocols. Stepsnecessary to protect the domestic pecan indus-try from distribution of infected wood are beingexplored.

Regulatory officers dealing with phytosa-nitary issues require lists of insects anddiseases that attack pecan. These lists are inneed of update as new pests such as X.fastidiosa have been recognized and old pestshave been renamed. Updated lists are pro-vided, along with the full Crop VulnerabilityReport, at the website of the USDA–ARSPecan Breeding and Genetics Program(http://cgru.usda.gov/carya). Over time, ob-solete names used for a pest may obscure ourrecognition of an organism. In the list ofdiseases, synonyms are included to assistthose unfamiliar with updated nomenclature.The disease list began with Gottwald et al.(2001), and then relied on the database ofFarr and Rossman (2015) for confirmation.References to disease citations are includedin the table based on the latter database, withoccasional additions. The list of insects thataffect pecan began with an unpublished listgraciously provided by Bill Ree (TAMUEntomologist). Stan Wellso (USDA ARSEntomologist, retired) added many bupres-tids known to attack pecan and hickory, andcommon names have been added when ap-propriate. That list is also available at theabove mentioned website.

International distribution of germplasmrequires free exchange of information to helpguard against unintentional introduction ofpests. A list of insects affecting Carya inChina was provided to Marvin Harris byZhi-hong Xu (Zhejiang A&F University,Linan, People’s Republic of China) and is beingtranslated and compared with the U.S. list(M. Harris, personal communication). A re-port of diseases affecting pecan in SouthAfrica (Marais, 2015) includes some notreported in the United States [e.g., Neofusi-coccum parvum (Pennycook & Samuels)Crous, Slippers & A.J.L. Phillips, Neocosmo-spora vasinfecta E.F. Sm]. The active in-volvement of interdisciplinary specialists isnecessary to maintain accuracy and currencyin these lists.

Abiotic (environmental extremes, climatechange). The long-lived nature of pecanorchards and cultivars makes them vulnera-ble to substantial changes in climate andassociated weather events and patterns. Pe-can production can be injured by late springand early autumn freezes, excessive cloudcover, excessive rain during pollination, anddrought. Different Carya species are welladapted to different environmental niches,potentially possessing genes that could beintroduced into pecan to produce cultivarsadapted to new abiotic environments. Thereis a need to develop pecan rootstocks adaptedto specific soil environments, such as ex-tremes in pH, salts, and essential nutrientelements.

Status of Plant Genetic Resources in theNPGS Available for Reducing Genetic

Vulnerabilities

Germplasm collections and in situreserves

Holdings. The USDA ARS Pecan Breed-ing and Genetics Program maintains twoworksites where ex situ collections of theNCGR-Carya are held. Both are in Texas: theBrownwood worksite in Brown County, andthe College Station worksite in BurlesonCounty. At each location, there are threegeneral categories of holdings: pecan cultivarcollections (accessions grafted onto pecanseedling rootstocks), pecan provenance col-lections (primarily seedlings growing ontheir own roots, grown from seed collectedfrom geographic populations), and speciescollections (collected directly fromwild treesand held as seedlings on their own roots,grafted to pecan rootstocks, or in some casesreceived as named cultivars from varioussources and grafted to pecan seedlingrootstocks).

Brownwood: The Brownwood worksite isthe original home of the USDA ARS PecanBreeding and Genetics Program, with a his-tory tracing back to 1930. The worksiteincludes a total of 96.7 ha, of which 62.7 haare owned by the City of Brownwood andmade available to USDA ARS under a mem-orandum of understanding. Almost 2 ha andall headquarters buildings located at 701Woodson Road were donated by the city toARS in 1973 (and accepted by USDA in1976). An additional 32 ha of land adjacent tothe station was purchased by ARS in 1978as a permanent site for the National ClonalGermplasm Repository which was officiallydesignated in 1984. Louis Romberg, the firstARS breeder, began grafting selected culti-vars at Brownwood in the early 1930s for useas parents in breeding. Those collectionswere the reason the site was designated in1984 as the NCGR-Carya (Postman et al.,2006). The National Plant Germplasm Sys-tem mandated that plants within the systembe ‘‘backed up’’ by additional inventories toavoid catastrophic loss of accessions. Collec-tions have been transferred from land ownedby the City of Brownwood onto ARS ownedland, and materials transferred from each

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worksite to the other. Grafted accessions ofthe NCGR-Carya at Brownwood are found asisolated, old trees all across the Old MainOrchard, but are concentrated in the RombergBlock and C-Pans of the City Orchards. Since1991, grafted accessions have been added tothe NCGR BWV orchard, now occupying 5.7of 22 ha available on ARS land contiguous tothe original orchards. The oldest inventoriesof grafted accessions at the Brownwoodorchard were used to develop molecularmethods for cultivar identity (Marquardet al., 1995) as well as for subsequent micro-satellite profiles, and are invaluable for theintegrity of cultivar verification.

There are 354 grafted accessions in theBrownwood orchards, including 96 that arenot present in College Station. Ninety-fivepercent of the grafted accessions at Brown-wood are pecan, with 5% being other speciesof Carya. A small provenance collection ismaintained at Brownwood, comprised ofonly 120 pecan seedlings growing on theirown roots, representing 63 mother trees from49 populations. The planting consists of self-rooted seedling trees in a low-maintenanceplanting of 2.9 ha (of 9.75 ha available).

College Station: The College Stationworksite was obtained by leasing 145.7 haof land from Texas A&M University. The99-year lease was initiated in 1987 and willexpire in 2086. Initially, primary use of thesite was as nurseries for the Pecan BreedingProgram and as test orchards in the NationalPecan Advanced Clone Testing System. Col-lege Station collections include 349 graftedaccessions, 91 of which are not present inBrownwood. The majority of Carya speciescollections are maintained at the CollegeStation worksite. The majority of provenanceorchards are maintained at the College Sta-tion worksite (over 2000 self-rooted treesgrowing on about 12 ha, representing nativepecan populations from Mexico to Missouri,with detailed collections from Arkansas andcoastal Louisiana). A small seedling popula-tion from a noteworthy putatively nativestand in Alabama is also maintained.

Associated collections: The SoutheasternFruit and Tree Nut Laboratory in Byron, GA,maintains significant collections of pecan cul-tivars, self-rooted hickory seedlings (Wood andGrauke, 2011), and an excellent pecan prove-nance collection (Bock et al., 2016; Graukeet al., 1989; R€uter et al., 1999, 2000; Woodet al., 1998). The pecan provenance orchard atByron, GA, was established before the estab-lishment of provenance orchards at the Col-lege Station worksite, from the same seedsources, and constitutes an exceptionally valu-able resource for the pecan industry. Pheno-typic evaluations of leaf area and nutrientcontent have been cooperatively reported(Grauke et al., 2003). Selected accessions wereevaluated for nut quality and genotyped usingmicrosatellites (Grauke et al., 2011).

Associated informationGenebank and/or crop-specific web site(s).

Accessions are listed on the GermplasmResources Information Network and the

program website at www.CGRU.usda.gov/Carya. Both are continuously updated.

Passport information. Summaries of pe-can cultivar origination records published byThompson and Young (1985) form the foun-dation of cultivar passport information andare available for most commercial cultivarson the program website (http://cgru.usda.gov/Carya/pecans/cvintro.htm). Accessionshave been georeferenced to provide estimatesof latitude and longitude based on detailsavailable in acquisition information. Mo-lecular profiling offers confirmation or cor-rection at all nomenclatural levels and isongoing.

Genotypic characterization data. About170 pecan cultivars were profiled for malatedehydrogenase, phosphoglucose isomerase,phosphoglucomutase, leucine aminopep-tidase, and diaphorase (Marquard et al.,1995). About 800 pecan seedlings fromprovenance collections at College Stationwere evaluated for the same isozymes(Grauke et al., 1995), and over 200 of thoseinventories still exist in provenance planta-tions in College Station and Brownwood.

Microsatellite profiles at 14 nuclear lociand 3 plastid loci have been developed forabout 180 inventory specific pecan cultivars,�260 pecan seedlings in provenance collec-tions at College Station, TX, and Byron, GA,and �180 hickory samples from repositorycollections (not all maintained as livingaccessions).

Several cases of ‘‘identity confusion’’have been resolved using microsatellitemarkers (Grauke et al., 2015). Profiles ofmost commercially important U.S. pecancultivars have been developed using micro-satellite markers. Existing SSR profiles pro-vide molecular verification of identity withinour collections. Those profiles have provenuseful in identifying unknown accessionssent for determination, since parentage canoften be inferred. Currently, no commerciallaboratories are using the pecan microsatel-lites, possibly because of the challenges ofconsistently scoring fragment-basedmarkers.Standard methods are needed to allow com-parison of results obtained from differentanalysis platforms.

Using inventories of accessions main-tained at the Southeastern USDA–ARS Fruitand Tree Nut Laboratory in Byron, GA,patterns of genetic diversity have been shownto vary with geographic distribution over therange of pecan, with markers on maternallyinherited plastids being more closely relatedto geographic distribution than nuclearmarkers (Grauke et al., 2011).

A Carya diversity panel with 50 entrieswas analyzed for single nucleotide polymor-phism (SNPs) on the Juglans SNP chip (Youet al., 2012) by colleagues working withwalnut at the NCGR-Davis and Universityof California, Davis. With the help of Dr.David Kuhn (USDA–ARS Miami), the re-sults of theCarya panel have been interpretedand used to generate an informative phylo-genetic tree. The most informative SNPswere identified and primers developed for

222 SNP loci. Those are being evaluated forpolymorphism using an eight-member diver-sity panel using Kompetitive Allele SpecificPCR.

Two accessions of pecan (‘Pawnee’ and87MX3-2.11) were selected to investigate thefeasibility of generating a pecan referencesequence. They were selected due to theextensive use of ‘Pawnee’ in current breedingprogenies, and the low level of polymor-phism observed in the 87MX3-2.11 acces-sion, based on microsatellite analysis.Isolated DNA was used by HudsonAlphaGenome Sequencing Center to produce adraft survey sequence for pecan (Jenkinset al., 2015). The draft assembly allows SNPdiscovery, provides a scaffold to which otherCarya genomic sequence may be aligned andhas formed the foundation for the develop-ment of a community strategy for furtherdevelopment of genomic tools for pecan. APowerStation Gx2 Starter computing platform(PSSCLabs,LakeForest,CA) running aLinux(Red Hat Enterprise, Raleigh, NC) operatingsystem and CLC Genomics Workstation soft-ware (CLC Bio, Waltham, MA) was obtainedto house and work with that data in 2013.Preliminary efforts at RAD-Seq by USDAARS in conjunction with Dr. P. Klein (TexasA&M University) have yielded sequence in-formation that has been aligned to the surveyscaffolds, and provided a large numbers ofSNPs and microsatellite loci for development,given sufficient resources. Mattison et al.(2013) measured transcript levels of threenut allergens from ‘Desirable’ and ‘Sumner’over the course of nut development usingreverse transcription quantitative polymer-ase chain reaction. Those transcripts havebeen shared with Dr. Jennifer Randall atNew Mexico State University, who is usingthe sequence information to annotate thedraft survey sequence (Barnes et al., 2016).

Phenotypic evaluation data. Extensivenut quality information (nut length, width,height, weight, volume, and percent kernel),typically from several seasons, is collectedfor fruiting accessions of NCGR-Carya col-lections. Those collections are represented bystandardized digital photographs of nuts andkernels. A small number of those images areavailable on the unit website. Extent ofdichogamy is known for most named pecancultivars and photographs of catkin andpistillate flowers are available for many ofthe College Station accessions. Leaf and nutscab ratings based on the Hunter-Robertsscale of worst expression have been accumu-lated over multiple seasons, but disease isoften not expressed under Texas’ climateconditions.

Analysis of broad pecan provenance col-lections has shown that leaf morphologyvaries in geographic patterns that might haveadaptive significance (Grauke et al., 2003;Sagaram et al., 2007, 2011). Current researchin provenance orchards (J. Bernal, unpub-lished data) confirms that leaf morphology,including leaf pubescence, varies betweenprovenances and may impact insect popula-tions on trees grown in a common garden.

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Open-pollinated seed stocks from reposi-tory collections were used in screening ef-forts to find resistance to nematodes. Sourcesof nematode resistance were not found. Seed-lings showed patterns of growth phenologyand vigor that varied between provenances oforigin. Seedlings from southern sources be-gan growth first, continued growth longest,and achieved greatest diameters and heights(Grauke and Starr, 2014).

Prospects and Future Developments

The U.S. pecan industry is regionallyfragmented, with management and produc-tion constraints based on climatic andedaphic variation across diverse growing re-gions, coupled with regional competition forlimited markets. It is also characterized bydivision between pecan producers and thenut shelling industry that has traditionallycontrolled marketing and is increasinglyimportant in the protection of food safety.International interest in the crop is increas-ing, as evidenced both by increased exportsof the U.S. crop and increased pecan pro-duction in other countries. In both the UnitedStates and other countries, commercial pro-duction relies on a small subset of selectedgenotypes. The USDA ARS Pecan Breedingand Genetics Program is responsible forbreeding and development of the pecan, aswell as for the collection, characterization,evaluation, maintenance, and internationaldistribution of Carya germplasm. The U.S.pecan producing industry is uniting towardthe goal of improving domestic and interna-tional marketing, but is apprehensive aboutthe distribution of improved pecan cultivarsto competitor nations. The U.S. pecan re-search community has been focused on localcrop production issues, and grant applicationattempts seeking broad cooperation on long-term strategic research have been unsuccess-ful (Stevenson, 2012).

The driving force for increasing knowl-edge about the genus Carya has been theeconomic value of the pecan nut productionindustry, which motivated the developmentof the USDA ARS Pecan Breeding Programin the early 1930s. Pecan cultivars collectedfor use in breeding became the foundation ofthe National Clonal Germplasm Repository,which was designated in the early 1980s(Postman et al., 2006). That collection hasexpanded to the current NCGR-Carya. Theprogram has experienced reductions in per-sonnel and budget, while the mandate tocollect from ‘‘worldwide sources of wildspecies and domestic cultivars to providefor maximum genetic diversity in each ge-nus’’ (Westwood, 1986) has not changed.The Carya Crop Germplasm Committee Re-port of 1997 (http://cgru.usda.gov/carya/cgc/cgc97.htm) noted admonitions from leadingbotanists to describe, inventory and mapbiotic diversity (Raven et al., 1992; Soule1990). That process is ongoing and is in-centivized by the recognition of the contri-butions of crop wild relatives to recentlyreleased U.S. pecan cultivars (Grauke et al.,

2015). Areas needing future attention includeisolated, relatively uncharacterized popula-tions of indigenous Carya species in MexicoandAsia. Themotivation to accomplish thoseinventories is increased by the distribution ofexotic germplasm into those areas, and theincreased recognition of the frequency ofinterspecific hybridizations that can impactindigenous populations. The rapid destruc-tion of local native pecan populations arguesin favor of continuing broad characterizationsof the distribution of genetic and geographicdiversity to better understand adaptation andfacilitate development of regional cultivars androotstocks.

National Plant Germplasm System col-lections are mandated to distribute germ-plasm to both domestic and internationalcooperators. The recognition of a pathogensuch as X. fastidiosa, which could be distrib-uted inadvertently along with germplasm,requires the development and refinement ofphytosanitary certification procedures rele-vant to both domestic and internationalcooperators.

Cooperative germplasm evaluation andexchange will benefit by the rapid develop-ment of improved analytical methods andphytosanitary protection. Increasing accessto the broad diversity of the genus shouldopen new opportunities for crop improve-ment through the application of genomicmethods applied to appropriate populationsthat have been well characterized phenotyp-ically (Ouborg et al., 2010). The motivationfor maintaining diversity within the NPGShas always been clear: human need (utility) isthe primary criterion for genetic conserva-tion. However, since the primary usersof genetic collections are crop breeders(Namkoong, 1991; Palmer, 1989), it is neces-sary to establish effective cooperation acrossregional breeding programs. The 29 pecancultivars that have been released over the85-year history of the USDA ARS PecanBreeding Program have all been distributedwithout charge to the U.S. pecan nurseryindustry for propagation. They represent di-verse parentage that inadvertently incorpo-rated genes from crop wild relatives. Mostwere released after cooperative testing acrossregions. The 14 cultivars released since 1984required an average of 35 years from theoriginal cross until release. Purposefully in-corporating crop wild relatives in breedingpopulations targeting advantageous traitssuch as reduced tree size, while avoidingdeleterious traits such as reduced productionand nut quality, will either greatly extend thetime required for cultivar development orwill require improved methods of genomicselection.

Conner (2015) noted several problemsfacing the pecan research community in thedevelopment of practical genomic tools foruse in breeding, with the first being the smallnumber of scientists involved in the effort.He outlined a strategy necessary for successthat called for development of a referencegenome sequence, development of betterphenotyping methods, and development of a

standardized segregating population repli-cated across regions. The standardized seg-regating population would require regionaland multi-institutional cooperation, wouldprovide means to analyze environmentaleffects on genetic expression, and wouldprovide a platform for development of im-proved phenotyping methods.

Existing ex situ collections of the NCGR-Carya should be cooperatively evaluatedusing available genomic methods. Coopera-tive strategic planning of appropriate con-trolled crosses for use as shared mappingpopulations, followed by aggressive phe-notypic screening and genomic evalua-tion, should produce demonstrably refinedmethods of progeny selection while furtherdeveloping the ‘‘road map’’ of progressivelyimproving genomic information. The fruit ofthose efforts will be accessible to futurestudents of the genus only if the informationlinking verified living inventories of acces-sions, the passport information describingtheir origination, and phenotypic character-izations already accumulated can be associ-ated with genomic characterizations. Pecancultivar development is necessarily multidis-ciplinary, increasingly international in scope,and will be facilitated by a central databaseserving the accumulated information. Al-though much of that information can beappropriately maintained within the GRIN-Global database, genomic and bioinformaticutilities will necessitate cooperative develop-ment with other scientists and industry usersthat is beyond the scope of existing programbudgets. We have access to a collection thatrepresents a global forest. As stewards of thatresource, we must now use it.

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