Research Directions Based on the Current State of Pear Production and Rootstock Research RACHEL ELKINS', RICHARD BELL and TODD EINHORN3

153

Journal of the American Pomo logical Society 66(3): 153-163 2012 Needs Assessment for Future US Pear Rootstock Research Directions Based on the Current State of Pear Production and Rootstock Research RACHEL ELKINS', RICHARD BELL AND TODD EINHORN3

Abstract The area devoted to pear production in the United States (U.S.) is declining due to lack of precocity and high cost of production. The U.S. pear industry currently lacks "modern" orchard systems characterized by compact trees that produce early, high yields of large, high quality fruit. Tall, shaded canopies are not economically sustain- able and are at a competitive disadvantage for attracting and sustaining a labor supply. There is broad and deep consensus in the pear industry that developing size-controlling rootstocks isimperative to remain competitive nationally and globally. Currently employed rootstocks in the U.S. are Pyrus communis seedlings and clones, none of which achieve more than about a one-third size reduction, and P betulifolia seedlings. Quince (C. oblonga), used with interstems in Europe and South America, is utilized commercially (without interstems) in the U.S. only for 'Cornice' in southern Oregon and northern California. This is due primarily to a lack of cold hardiness needed in more northern production areas, a lack of graft-compatibility with the other major scion cultivars, fire blight and iron chlorosis susceptibility, and relative lack of productivity versus other rootstocks, especially in Califor- nia.Current evaluative trials rely on older U.S. and imported selections, and include the NC-140 Multistate Rootstock Research Project and several individual programs in California, New York, Oregon and Washington. A fundamental deficiency is the lack of a mature pear rootstock breeding program, despite access to the USDA- ARS National Clonal Germplasm Repository (NCGR), which holds a major worldwide collection of Pyrus and related genera. International breeding programs focus on increasing yield efficiency, but also graft compatibility, fruit quality and size, high soil pH tolerance, winter hardiness, warm climate/low chilling adaptation, drought and salt tolerance, and resistance to fire blight, pear decline, and pear scab. An intensive planning and implementation effort is needed to develop the necessary contacts, collaborations, explorations, and importation logistics to acquire the most promising clonal selections for propagation and testing. Basic research needs include effects of dwarfing rootstock on tree architecture and fruiting, the underlying mechanisms of dwarfing functional in pear, the inheritance of key traits, and selection criteria for breeding. Propagation and orchard systems have also been identified as major research needs. Introduction and Statement of Need descending order of acreage, are 'Bartlett', As of 2010, there were 22,800 hectares`D'Anjou', `Bost', 'Red D'Anjou' and other (57,000 acres) of commercially-grown pearsred skinned pears, 'Cornice', and 'Seeker. (Pyrus sp. L.) in the United States (U.S.),Only 'Bartlett' is grown for both the fresh with a total crop value of $382 million (48). and processing markets. The industry has Major pear producing states (hectares) arebeen stagnating due to declining consump- Washington (9,600), Oregon (6,480), andtion of processed pears and competition from California (5,600). New York (480), Michi-imported pears and other fruits, as reflected gan (320) and Pennsylvania (320) are mi-in the loss of 4,000 hectares (10,000 acres), nor production states (48). Total U.S. pearor 15%, since 2000. production includes Asian pears, which are The major factors contributing to acre- also grown in several Eastern states, main-age decline are lack of precocity and high ly for the direct market. Major cultivars, incost of production. Newly planted trees are

' University of California Cooperative Extension, Lakeport, CA 95453 2 USDA-ARS Appalachian Fruit Research Station, Kearneysville, WV 25430 'Department of Horticulture, Oregon State University, Mid-Columbia Agricultural Research and Extension Cen- ter, Hood River 97031 ' To whom reprint requests should be addressed. Email: [email protected] 154 JOURNAL OF THE AMERICAN POMOLOGICAL SOCIETY

slow to bear, discouraging orchard renewalcold, requiring a suite of superiorrootstocks (10,14,15). The U.S. pear industry currentlywhich are both efficient andpossess appro- lacks "modern" orchard systems character- priate traits for particular sites,as previously ized by compact trees that produce early, characterized (23). high yields of large, high-quality fruit. Ex- The U.S. pear orchard situation is incon- isting orchards comprise mature trees thattrast to European, and to a lesser extent, are large and widely spaced.Further, high- South American orchards, whichsuccess- density plantings on standard rootstocksare fully utilize dwarfing rootstock clonesof difficult to confine withoutaccess to vigorquince, with or withouta P communis L. management tools (i.e., acceptable dwarfinginterstem (13eurre Hardy', 'Old Home') for rootstocks or bio-regulators, neither of whichgraft-compatibility (49). Theuse of quince are presently available in the U.S.). Alterna-has enabled high-density plantings of3,000 tively, tighter in-row spacing betweenpearto greater than 10,000 trees per hectare,ver- trees on an array of commercially availablesus a maximum of about 500-1800 trees per Pyrus rootstock genotypes markedly im-hectare in the U.S. It is widely accepted that proved yield, and reduced tree size; however,high density orchards bear fruit andrepay fruit size was negatively related totree den-establishment costs sooner. Theycan also be sity (37). planted as narrow trellised Vor "wall" sys- Pear orchards are labor intensive;prun- tems which can be managed from the ground, ing, fruit thinning, and harvest of low den-platforms, stepstools, or short (0.6 to 1.8 m) sity plantings are time-consuming and costly. ladders. This creates a labor environment Eventually, these tall, shaded canopiespro-attractive to a wider pool of potential work- duce lower financial returns (7). Growers relyers. Pesticides can also be applied efficiently mainly on seasonal and largely immigrantwith less drift and wasted chemical andwa- (mainly Mexican, but also Central American)ter (12).There is broad and deepconsensus labor for pruning, thinning, and harvestoper- among all sectors of the U.S. pear industry, ations (26). However, pear plantings in closei.e. growers, nurseries, and academics, that proximity to apples, cherries andgrapes are developing efficient (precocious, good yield, at a competitive disadvantage for attracting,fruit size), size-controlling rootstocks is im- and sustaining a labor supply. In apple, size-perative for the pear industry to remaincom- controlling rootstocks produce shorter trees,petitive nationally and globally. which are more conducive to efficient and labor-friendly production practices. In thecase Currently Used Rootstocks of cherries, recent developments in dwarfing The main rootstocks currently employed rootstocks, pedestrian orchard systems andin the U.S. are Pyrus communis seedlings mechanization have markedly improved la-(e.g. 'Winter Nelis', 'Bartlett' seedling), P. bor efficiency (43). betulifolia seedlings on heavy clay soils, In addition to production and economicand more recently, several P communis demands, regulatory and social constraintshybrid clones, e.g. 'Old Homex Farming- now demand systems that offer a desir-dale (OHXF) 69', '0HxF 87', '0HxF 97', able environmental "footprint" (pesticides,`0HxF 217', '0HxF 333', and '0HxF 513'. water, nutrients and energy use). Pear treesOf these, '0HxF 87' and '0HxF 97'are the are inefficient and costly to spray, requiringmost widely utilized. Quince (Cydonia ob- ample spray volumes to displace air withinlonga L is used for commercial production large canopies. Varying growing sitesre- only for 'Cornice' (44). The most vigor- quire resistance to various biotic and abioticinducing selection, 13A29', is the preferred "stresses", i.e. fire blight, pear decline, dryor selection. Even with an interstem, quince has wet soils, low or high pH soil, and extremethus far been found to lack desirable horti- PEARS 155 cultural characteristics, e.g. cold hardiness in2-33' performance varies depending on the Pacific Northwest, long-term vigor andmacro- and microsite factors, scion cultivar, productivity in California, and tolerance toand management, though 'Bartlett' yield ef- fire blight and calcareous soils (51) . Nurser- ficiency on Tyro 2-33' was equivalent to ies and growers have also been reluctant toÒHxF 87' in Washington trials (Tim Smith, incur the added time and cost of grafting anpersonal communication). However, none of interstem needed for 'Bartlett', Beurre Bose'the P communis clonal stocks achieves more and `Beurre d'Anjou', and which may thenthan about a one-third size reduction versus a only provide incremental benefit. Further,"standard" tree grafted onto seedling P com- and irrespective of rootstock lineage, nurs- munis or P betulifolia (51) (Fig 1). eries demand a high survival rate, uniform and consistent performance (i.e. clonal root- Available Rootstocks for Dwarfing stocks), easy and efficient propagation, uni- Globally, there is a limited number of Py- versal graft-compatibility, good anchorage,rus rootstock cultivars and selectionswhich and minimal suckering (35). may be available for continuing or new tri- There are also limited commercial salesals in the U. S., for example, Tyriam' from of two German P communis rootstocks,INRA in France, the Fox series from the Tyrodwarf' (Òld Home' x 'Bonne LuisUniversity of Bologna in Italy, the 708 series d'Avranches', syn. `Rhenus1') and Pyro 2-33 from East Mailing Research in the U.K., and (Òld Home' x 'Bonne Luis d'Avranches',the Pi-BU series from Germany (Table 2). syn. Ithenus3') (16). 'Pyrodwarf' and TyroThere is a limited number of quince selec-

<40% 40-60% 61-70% 71-90% 91-100% >100%

Amelanchier Adams QuinceFox 11 OHxF 217 Bartlett sdlg. P. betulifolia sdlg. Brossier seriesBP10030 Fox 16 OHxF 220 BM2000 Sorbus Crataegus Homer 10 OHxF 267 Homer 4 W. B./M.26 Eline Quince OHxF 40 Winter Nelis sdlg. OHxF 51 OHxF 69 OHxF 97 Pi-Bu 3 OHxF 87 P. calleryana D6 Pyrodwarf OHxF 230 P. calleryana sdlg. QR517/9 OHxF 333 QR719-3 OHxF 513 Quince EMA Pi-BU 2 Quince BA29 Pyro 2-33 Quince EMC Quince C132 Quince EMH Sydo quince Fig 1. Relative size of pear trees on different rootstocks as a percentage of pear tree size on Pyrusseedling. Adapted from (51). W. B./M.26 = 'Winter Banana' apple grafted onto M.26 apple rootstock. 156 JOURNAL OF THE AMERICAN POMOLOGICAL SOCIETY tions in commercial use, namely 'Adams',org). The NC140 trials have provided much 13A29', 'EMC', 'EMH', and Sydo'. Theseof the database for decision making bynurs- are graft-incompatible with most commercial eries and growers thus far (2,11). pear cultivars without use of an interstem Continual evaluation of these trials, in ad- (35). There are several other quince root- dition to other replicated non-NC-140 field stocks which have been developed in Europe,evaluation trials in the U.S. have been, or are and which are deserving of trials in the U.S. being, performed at OSU-MCAREC (`Horn- er' series), OSU-Southern Oregon Research U.S. Breeding Programs and Extension Center (SORAC) (quince and A fundamental deficiency in the U.S. is theP communis), University of California Co- lack of an active pear rootstock breeding pro- operative Extension (ÒHxF' series), WSU gram. The '0HxF' clonal series was crossed CooperativeExtension(ÒHxF'series), by Oregon nurseryman Lyle Brooks in theand Cornell's New York State Geneva Ag- 1960s (52). The 'Horner' series, originallyricultural Experimental Station (NYSAES) crossed by Oregon nurseryman Dave Horner,(ÒHxF' series, Tyrodwarf', Tyro 2-33'). currently resides at Oregon State Univer-These trials have generally concluded that sity's Mid-Columbia Agricultural Researchthe 'OH xF' series and Tyro 2-33' are thus and Extension Center [MCAREC] (31);far the most promising of the currently however, pear breeding is not conducted atavailable P. communis rootstocks, particu- Oregon State University. There is a fledglinglarly '0HxF87',' 0HxF97', and in some breeding program at Washington State Uni- cases, '0HxF69' (10,11,45). While variable, versity (WSU) (Dr. Katherine Evans). The`0HxF87', '0HxF69', Tyro 2-33', and Ty- pear breeding program at the USDA-ARSrodwarr produce trees larger than quince, Appalachian Fruit Research Station in Ke-and '0HxF97' produces a nearly standard arneysville, West Virginia (Dr. Richard Bell) size, but more precocious, tree than P com- has made preliminary crosses of '0HxF' se-munis seedlings or P. betulifolia (Fig 1). lections and some ÙS' series fire blight re- These rootstocks, while more acceptable sistant scion selections which possess semi-than seedlings, do not provide sufficient size dwarf tree stature. Both of these programscontrol and precocity for ideal high density are now acquiring germplasm. orchard systems. Additionally, many clones are difficult to propagate, rendering them un- NC140 Multistate Rootstock Research desirable to nurseries (30, 33), despite pos- and Similar Trials sessing desirable traits. Other than these two incipient breeding programs, most U.S. pear rootstock research International Breeding and has focused on evaluating 1) commercially- Evaluation Programs available rootstock cultivars from the U.S. or Internationalbreedingprogramsand other countries, and 2) advanced selectionsgermplasm collections offer potential sourc- from international sources. Several repli-es of rootstocks to evaluate, as well as germ- cated, evaluation trials were established inplasm for breeding. There is considerable California, New York, Oregon, Washington,effort in Europe to evaluate new rootstocks, Chihuahua, Mexico, and Nova Scotia, Cana-for example the EUFRIN Rootstock Group da under the auspices of the NC140 Regionalwhich consists of 21 fruit research institu- Research Project in 1988, 2002, 2004, andtions from 16 countries, in which a total of 2005. Individual trials comprised a varying51 Pyrus and Cydonia rootstocks are under number of locations and scions (`Bartlett',evaluation (20). Tyrodwarr and Tyro 2-33' `Golden Russet Bose', 'Taylors Gold Corn-are examples of accessions from overseas ice', 'Concorde', 'D'Anjou') (http://nc140.(Germany) obtained privately and licensed to PEARS 157 commercial nurseries (16). While much lit-grams have been adequatelytested in the erature is in the language of origin, a cursory U.S., with the exception of, 'BU-2', 'BU- search, as well as personal knowledge (R.3', `BM2000', '708-36', 'Fox 11', 'Fox 16', Bell), revealed at least somewhat active and Tyrodwarf and Tyro 2-33' (refer to Table inactive breeding programs in Western Eu-2 for origin). Of those, only Tyro 2-33' and rope: France (41), Germany(13, 16), Greeceto a lesser extent, Tyrodwarf',which has (42), Italy (3, 21), UK (18), Spain (1, 38),a propensity for suckering, areconsidered and Netherlands. There are several programscommercial candidates.Performance data in Central and Eastern Europe: Belarus (19),for other selections indicate poor surviv- Czech Republic,Estonia, Hungary (46),ability, low or high vigor, expression of pear Lithuania (20), Poland (22), Romania (28),decline or decline-like symptoms, and/or Russia, and Ukraine (40). Rootstock evalu-poor compatibility as majorfactors limiting ation has been conducted in the Middle Eastadvancement (see reports http://nc140.org). (Egypt, Israel, Syria, Turkey), South America Several additional genotypes possess inter- (Brazil, Uruguay), and Africa (South Africa).esting traits, but are so far inaccessible to In Asia, rootstock breeding and evaluation isU.S. researchers due to logistical, financial, a major activity in China(17), and has re-diplomatic, or intellectual property issues, ceived attention in Japan (36, 47). There wasunderscoring the urgency of increased ex- one breeding program in Australia(24). Mostploration and collaboration. Additional geno- programs utilize P. communis, butothers uti-types may exist at the USDA-APHIS quar- lize other Pyrus species, Cydonia (quince), antine facility and the National Clean Plant Amelanchier, Sorbus, and the intergenericNetwork (NCPN) at the Washington State hybrid Pyronia (Table 2). University experiment station in Prosser, but Most breeding efforts focus on the pri- that information is proprietary. At the least it mary deficiency impedingindustry progressis imperative that interested parties network and profitability, i.e. yield efficiency (derivedand collaborate to hasten testing, propaga- from precocity, productivity, and dwarfing). tion, and distribution of potential rootstocks. Induction of precocious fruit bearing is a key An intensive planning and implementation trait, since the lack thereof inhibits replant-effort is needed to develop the necessary ing of existing cultivars in more profitablecontacts, collaborations, explorations, and higher-density systems, and likewise inhib-importation logistics for U.S. acquisition of its the adoption of new scion cultivars whichthe most promising selections for propaga- possess unique fruit qualityand other post- tion and testing. harvest traits desired by the consumer, the producer and others in the marketing chain. Current Research Using Other Genera Such traits may help to stimulate pear con- The USDA-ARS National Clonal Germ- sumption and reduce costs, contributing toplasm Repository (NCGR) inCorvallis, the economic sustainability of the industry.Oregon (http://www.ars-grin.gov/cor/pyrus/ In contrast to apple, for example, on 'Mailingpyrinfo.html) holds the major U.S. (and per- 9', it is rare for pear to bear fruit in the second haps the world) collection of Pyrus and relat- season of growth, or even thethird to fifth in ed genera, including Cydonia, Amelanchier many cases. Other major soughtafter traits(service berry) Pyronia (Pyrus x Cydonia), include graft compatibility, fruit quality andand Sorbus (mountain ash). A multi-year size, high soil pH tolerance, winter hardi-project tested 57 accessions of quince (2009- ness, warm climate/lowchilling adaptation,2011) for cold-hardiness, elucidating a group drought and salt tolerance, and resistance toof 24 that tolerated low temperatures of fire blight, pear decline and pear scab (5,50). -30°C with less than 50% oxidative brown- Few candidates from international pro-ing of phloem, cambium and xylem tissue 158 JOURNAL OF THE AMERICAN POMOLOGICAL SOCIETY

when fully dormant (9). This work iscon-this critical effort. Indeed, thepear decline tinuing and will result in new opportunitiescrisis could only be resolved and thepear in- for inclusion of quince in wider evaluationdustry saved from rapid and certain demise through NC-140 and other field trials. because research into alternative rootstocks In addition to evaluation of Cydonia, sev-was supported. While the current need for a eral selections of Amelanchier have beenrejuvenated effort is based more heavilyon privately imported into the U.S. andare cur-long-term economic factors, the need tore- rently being tested for graft-compatibilityinvest remains critical. Researchers incom- and propagation potential. Preliminary fieldbination with stakeholder input from both the evaluations of three Amelanchier rootstockPacific Northwest and California have identi- clones are underway in Oregon and Cali-fied a number of basic and applied research fornia (Einhorn and Elkins, unpublished). (and ultimately extension) needs. All three clones have been observed topos- Basic research needs include: a detailed sess high freeze-resistance (to -40°C; Ein- analysis of the effects of dwarfing rootstocks horn, unpublished).Besides Cydonia andon scion vis a vis tree architecture and fruit- Amelanchier, other Rosaceae genera mighting; underlying mechanisms of dwarfingex- have potential as pear rootstocks; Crataeguspressed inpear (i.e. graft-incompatibility, (hawthorn), Pyronia, and Sorbus. However,water relations, nutrient assimilation, pho- considerably less is known about pear per-tosynthate and carbohydrate synthesis and formance on these genera. Known graft-partitioning, phytohormone metabolism and compatibility between Pyrus and alternativetransport, etc.); inheritance studies of key genera is shown in Table 1. traits; molecular markers for these traits; selection criteria for breeding (e.g., is treear- Need for an Intensive Rootstock chitecture, or precocity, of self-rooted trees Research Effort a predictor of performance as a rootstock?). The dearth of research on pear rootstocks Two major applied rootstock research foci in the U.S. is long-term. There have beenhave been identified: propagation, andor- limited efforts since the pear decline crisischard systems. During stakeholder meetings of the 1960s, when it was learned that Pheld in 2010 and 2011, nursery representa- pyrifolia and P ussuriensis rootstocks weretives expressed clear preference forpropa- susceptible to infection and alternative root-gating Pyrus rootstocks from hardwoodor stocks were evaluated and planted. Notably, softwood cuttings versus micropropagated extensive federal funds were committed tomaterial. The authors are aware of interest and activity in stooling of quince rootstocks Table 1. Genus Graft-compatibility (35).However,micropropagationoffers Amelanchier Fair to good a means to improve survival and vigor of Aronia Poor clonal rootstock material, particularly those Chaenomeles Poor that are difficult to propagate with cuttings Cotoneaster Insufficient data due to declining juvenility or poor rooting Crataegus Poor to good ability. There are currently several industry- Cydomalus Insufficient data supported projects within USDA-ARS and at WSU focused on developing and improving Cydonia Poor to good micropropagation protocols that should be Docynia Insufficient data greatly expanded. Malus Generally poor Two other important areas of research are Plyonia Good? adventitious shoot regeneration and genetic Sorbopyrus Insufficient data transformation. Adventitious sh'oot regener- Sorbus Poor to good ation is a necessary component for isolation PEARS 159

Table 2. Compilation of active and inactive pear rootstock breeding programs and rootstocks.

Country Institution/Breeder Genus and species Primary Traits Rootstocks

Australia B. Morrison Pyrus communis Yield efficiency BM2000 Belarus Belorussian Res. Inst. Pyrus communis Yield efficiency Seedling rootstocks for fruit growing Brazil EMBRAPA Uva e Vinho Pyrus communis Climatic adaptation Seedling evaluation France INRA Pyrus communis Yield efficiency Pyriam Pyrus species High soil pH tolerance Interspecific hybrid selections GermanyFruit Genebank, Pyrus communis Yield efficiency Pi-Bu series Dresden-Pillnitz GermanyGeisenheim Research Institute Pyrus communis Dwarfing Pyrodwarf, Pyro 2-33 Italy CIV, Fen-era Pyrus communis Yield efficiency Many selections High soil pH tolerance Italy University of Bologna Pyrus communis High soil pH tolerance Fox series Poland Research Inst. of Horticulture Pyrus communis Elia, Belia, & Doria Poland Warsaw Agricultural Univ. Pyrus communis GK seedling series Russia Michurin All-Russia Pyrus communis No. 10, 3-21-32 Res. Inst. Hort. Sweden SLU, Balsgard Pyrus communis Yield efficiency BP 10030 UK East Mailing Research Pyrus communis Yield efficiency 708 series, 517-9 USA Oregon State University Pyrus communis Yield efficiency OHF series, Homer 4, Dwarfing Homer 10 Syria Damascus University Pyrus syriaca High soil pH tolerance Seedling evaluation Russia Vserossiyskij Sci. Res. Pyrus uss.' hybrids Cold hardiness 17-16, 218-2-2 Inst. Hort. China Several institutes and Asian Pyrus species Dwarfing Several selections universities Japan Gifu University P bet. & P Dwarfing SPRB & SPRC series Spain IRTA Pyrus species High soil pH tolerance Interspecific hybrid selections USA Washington State University Pyrus species Dwarfing Acquiring germplasm Yield efficiency USA USDA, ARS, AFRS Pyrus species Dwarfing US selections, Yield efficiency OHF 8US selections Armenia Cydonia Arm 21 Belarus Belorussian Institute of Cydonia 1/9, 1/22, 1/33 Fruit Growing Brazil EMBRAPA Uva e Vinho Cydonia Climatic adaptation Seedling evaluation Greece NAGREF, Pomology Cydonia High soil pH tolerance PII PI5, PI27 Institute Komorius seedlings Italy University of Pisa Cydonia Yield efficiency Ct.S series Lithuania LIH-Babtai Cydonia Yield efficiency K series NetherlandsFlueren Cydonia Yield efficiency Eline Poland Research Institute of Cydonia Cold hardiness Pigwa series: S-1, Horticulture S-2, S-3 Romania UASVM-Iasi Cydonia Yield efficiency BN-70 Russia Cydonia Anzherskaya, Peridskaya, Teplovskaya Turkey Ankara University Cydonia Yield efficiency S. 0. series Ukraine Ukrainian Academy of Cydonia Drought tolerance IS, SI, and R series Agrarian Sciences High soil pH tolerance 160 JOURNAL OF THE AMERICAN POMOLOGICAL SOCIETY

UK East Mailing Research Cydonia Yield efficiency C132, EMA, EMC, EMH Russia Pyronia VA2 Germany Bavarian Center for Ante !ambler Precocity, dwarfing Various selections Fruit Crops

' = undetermined. Some information is from secondary literature sources that do not mention the program or targeted traits. = Species abbreviations: P uss. = P ussuriensis; Pbet. = P betulifolia; P call. = P callegana. of useful somaclonal mutants and for geneticYork, and Washington that have provided transformation, and is a relatively unexploredbeneficial information. A new coordinated area of opportunity for many rootstocks. Pub-multi-state systems trial for 2013 includes lished results for rootstocks have been lim-California, Oregon, New York, and Wash- ited to `0HxF 333' (32, 53), BP10030 (53),ington. Stakeholders have expressed a clear Tyrodwarr (27) and quinces (4). However, desire for large systems trials. These can and research to optimize additional clones is on- should be conducted under the umbrella of going.Mutant 'Quince A' clones with in-NC-140. creased tolerance to high pH (6, 8) and NaC1 (25) have been recovered. Increased juvenil- Evaluation of the Corvallis USDA-ARS ity and consequent improved rooting ability NCGR Collection and Importation and may also result, but also with the potential Evaluation of Germplasm and Rootstocks for chimeras and genetic instability leading In depth evaluation of the Pyrus and re- to somaclonal mutants. lated genera collection for their specific suit- Genetic transformation, though controver- ability directly as pear rootstocks or as paren- sial at the marketing level, is a rapidly evolv-tal germplasm would be of great benefit. The ing and long-term strategy. At present onlyUSDA-ARS NCGR is one of the largest pear the rolB gene for improving rooting has beengermplasm collections in the world, a collec- inserted into `0HxF 333' (53) and Lithu-tion whose diversity must be exploited and anian quince selections (34). A techniquecharacterized using current molecular and known as cisgenics (39) presently exists forgenetic techniques. As previously discussed, manipulating genes without inserting genesthere are immediate opportunities for find- of differentspecies.Breeding programsing and accessing Pyrus and related genera should be actively increasing competence infrom other countries to expand the NCGR this area to take advantage of future opportu-and breeding program collections. Foreign nities and needs.Successful application ofcolleagues have expressed interest in collab- this approach depends on the identification oforating with U.S. counterparts (Bell and Dh- candidate genes that control tree architecture,ingra, personal communication). However, dwarfing and precocity. additional resources will be required to take The NC-140/Pacific Northwest regionaladvantage of these opportunities given the field trials are an excellent model for pre-current economic climate.Nursery stake- liminary evaluation of promising rootstocks.holders have also expressed willingness to Larger, more complex "systems" trials (i.e.work with researchers, and the Pyrus Crop rootstock x training system x spacing x scionGermplasmCommittee(http://www.ars- cultivar) under various site and managementgrin.gov/npgs/cgclist.html#Pyrus) has initi- scenarios are necessary for more advancedated efforts to collaborate with the private selections in order to gain "real-world" re-sector to hasten germplasm acquisition and sults and determine the most suitable role(s)advancement (field trialing through industry for different rootstocks. There are several ex-adoption), utilizing all available means, in- amples of individual trials in California, Newcluding NC-140. PEARS 161

Conclusion cal, cultural, and economic role. Given pear's New pear rootstocks are fundamental tounique adaptations to climates and soils in the modernization of an outdated and in-which other perennial orchard crops fail to do creasingly untenable U.S. pear productionwell, pear orchards are not easily replaced in culture. Pear consumption continues to de- some areas. Conversely, if recently proposed cline for a multitude of reasons, and grow-NIFA-SCRI and industry research efforts to ers face rapidly increasing costs while prof-improve fruit quality and increase consump- iting less from aged systems. Imports havetion succeed, producer opportunities will in- reduced market share, furthering the decline crease, provided growers can quickly recoup of both fresh and secondary markets such as establishment costs and remain profitable. canning, drying, and juice. In summary, itis imperative that size- While fruit quality, market strength, andcontrolling rootstocks are both developed consumption are critical issues, the abilityand rapidly transferred to industry in order to to farm competitively and profitably largely modernize U.S. pear production. It is not far- hinges on production issues. U.S. pear pro- fetched to conclude that if this fails to occur, duction is antiquated compared to apple pro- the U.S. pear industry will continue its induction systems. Although high-density appleevitable decline and become a minor orchard systems rely to a large extent on M.9, applecrop, while fresh and processed imports from growers have access to a wide range of root-Asia, Australia, Europe, New Zealand, South stock selections developed from a worldwideAmerica, and South Africa increasingly group of long-standing breeding programs, dominate the U.S. market. including two in the U.S. (USDA-ARS/Cor- nell University, New York), and now Wash-Acknowledgements ington State Universityat Wenatchee. The The authors thank the many individu- availability of size-controlling rootstocksals who contributed to this paper, particu- has enabled new training systems (e.g., talllarly those who actively participated in the spindle and vertical axe that allow fruiting in Root2Fruit Initiative stakeholder meetings the second season after planting), improved held in Provo, Utah, November 2, 2010, and laborconditions, more environmentally- Pasco,Washington, March 2, 2011. We also friendly pesticide and fertility practices, andthank the participants in the NC140 Regional efficient irrigation management (29). WhileResearch Project, the members of which have total apple acreage has decreased from 2000 diligently pursued this effort in rootstock tri- to 2010, the total number of individual apple als since 1988. trees had increased, reflecting the successful Mention of trade names or commercial adoption of efficient, high density orchards. products in this article is solely for the pur- In contrast, pear acreage and total number ofpose of providing specific information and individual pear trees both decreased, indicat-does not imply recommendation or endorse- ing a declining industry lacking the incentivement by the U.S. Department of Agriculture. or tools to modernize. USDA is an equal opportunity provider and The survival of the pear sector carries employer. societal significance as well. The U.S. pear industry, while much smaller than the apple Literature Cited industry ($382 million vs. $2.22 billion na- 1. Asin, L., I. Iglesias, R. Dolcet-Sanjuan, E. Clave- tionwide in 2010), is of major socio-econom- ria, P. Vilardell, J, Bonany, M.-H. Simard, and T. L. Robinson. 2011. INRA-IRTA pear rootstock ic importance where it exists. It is more con- breeding program: aiming for tolerance to iron centrated geographically in certain states and chlorosis. Acta Hort. 903:207-213. counties due to climactic adaptation, and in 2. Azarenko, A., E. Mielke, D. Sugar, F. Eady, B. those communities it plays a unique histori- Lay, G. Tehrani, A. Gus and C. Rom. 2002. Final 162 JOURNAL OF THE AMERICAN POMOLOGICAL SOCIETY

evaluation of the NC140 national rootstock trial. estimates of producing pears in the YakimaVal- Acta Hort 596:319-321. ley, Washington. Washington State University 3. Bassi, D., M. Tagliavini, A. d. Rombola, and Extension Fact Sheet FS034E. B. Marangoni. 1998. Il programma di selezioni 16.Jacob, H. 2002. New pear rootstocks from di portinnesti per it pero serie "Fox". Rivista di Geisenheim, Germany. Acta Hort: 337-344. Frutticoltura No. 4: 17-19. 17.Jiang, S., C. Chen, J. Jia, Z. Li, C. Fang, L. Ma, 4. Bell. R. L., and J. M. Leitdo. 2011. Cydonia. In: and B. Lu. 2006. A new dwarf rootstock of pear C. Kole (ed.), Wild Crop Relatives: genomic and `Zhong ai2'. Acta Hort. Sinica 33:1402. breeding Resources, Temperate Fruits. Springer- 18.Johnson, D., K. Evans, J. Spencer, T. Webster, -Verlag, Berlin. and S. Adam. 2005. Orchard comparison of new 5. Brewer, L. R., and J. W. Palmer. 2011. Global quince and Pyrus rootstock clones. Acta Hort. pear breeding programmes: Goals, trends and 671:201-208. progress for new cultivars and rootstocks. Acta 19.Kaziouskaya, Z. A., V. A. Samus, and T. L. Rob- Hort. 909:105-119. inson. 2011. Evaluation and selection of fruit 6. Bunnag, S., R. Dolcet-Sanjuan, D. W. S. Mok, rootstocks in Belarus. Acta Hort. 903:371-377. and M. Mok. 1996. Responses of two somaclonal 20.Kviklys, D. 2011. Fruit rootstock research in variants of quince (Cydonia oblonga Mill.) to Europe performed by EUFRIN rootstock group. iron deficiency in the greenhouse and field. J. Acta Hort. 903:349-353. Amer. Soc. Hort. Sci. 121:1054-1058. 21.Leis, M., and A. Martinelli. 2002. Selection pro- 7. DeJong, T. 2007. Canopy and light management. gramme of Pyrus communis rootstocks at CIV In: Pear Production and Handling Manual (Mit- Consorzio Italiana Vivaisti. Acta Hort. 596:357- cham and Elkins, eds.). Oakland: University of 361. California Division of Agriculture and Natural 22.Lewko, J., A. Sadowski, K. Scibisz, and D. Resources Publicaton 3483. Sterne. 2006. Growth of rootstocks for pears and 8. Dolcet-Sanjuan, D., D.W.S. Mok, and M. C. pear cultivars budded on them in the nursery. Mok. 1991. Plantlet regeneration from cultured Agronomijas vestis 2006(9):80-82. leaves of Cydonia oblonga L. (quince). Plant 23.Lombard, P.B. and M.N. Westwood. 1987. Pear Cell Rpts. 10:240-242. Rootstocks. In: R. Rom and R. Carlson (eds.). 9. Einhorn, T., C. Turner, D. Gibeaut and J.D. Post- Rootstocks for Fruit Crops. John Wiley & Sons, man. 2011. Characterization of cold hardiness New York. in quince: potential pear rootstock candidates 24.Manchester, B. 2002. `BM2000'. Plant Varieties for northern pear production regions. Acta Hort Journal 13(3):83-84. 909:137-151. 25.Marino, G., and L. Molendini. 2005. In vitro 10.Elkins, R., K. Klonsky, R. DeMoura and T.M. leaf-shoot regeneration and somaclone selection DeJong. 2008. Economic evaluation of high den- for sodium chloride tolerance in quince and pear. sity versus standard orchard configurations; case J. Hort. Sci. Biotechnol. 80:561-570. study using performance data for 'Golden Rus- 26.Martin, P. and J. Taylor. 2000. For California set' Bosc pears. Acta Hort 800:739-746. farmworkers, future holds little prospect for- 11. Elkins, R., S. Castagnoli, C. Embree, R. Parra- change. California Agriculture 54(1):19-25. -Quezada, T. Robinson, T. Smith and C. Ingels. 27.Martinelli, F., M. Busconi, C. Fogher, and L. Se- 2011a. Evaluation of potential rootstocks to im- bastiani. 2009. Development of an efficient pro- prove tree precocity and productivity. Acta Hort tocol for pear rootstock Pyrodwarf and assess- 909:184-194 ment of SSR variability in regenerating shoots. 12. Elkins, R., J. Meyers, V. Duraj, J. Miles, D. Teje- Caryologia 62:62-68. da, E. Mitcham, W.V. Biasi, L. Asin and J. Abreu. 28.Mazilu, C. 2002. Achievements in breeding of 2011b. Comparison of platform versus ladders Romanian clonal pear rootstocks. Acta Hort. for harvest in northern California pear orchards. 596: 345-349. Acta Hort 900:242-249. 29.Micke, W., R. Tyler, J. Foott, and J. Smith. 1976. 13.Fischer, M. 2007. New pear rootstocks from High density apple orchards offer many advan- Dresden-Pillnitz. Acta Hort. 732:239-245. tages. California Agriculture 30(9):8-11. 14.Galinato, S. and R.K. Gallardo. 2011a. 2010 cost 30.Mielke, E. and J. Turner. 2008. Difficult to prop- estimates for producing pears in North Central agate pear rootstocks: Will they work as inter- Washington. Washington State University Fact stems? Acta Hort. 800: 653-657. Sheet FS031E. 31.Mielke, E. and L. Smith. 2002. Evaluation of the 15.Galinato, S. and R.K. Gallardo. 2011b. 2010 cost Horner rootstocks. Acta Hort. 596: 325-330. PEARS 163

32.Nacheva, L. R., P. S. Gercheva, and V. T. Dzhu- 42.Sotiropoulos, T. E. 2006. Performance of the vinov. 2009. Efficient shoot regeneration of pear pear (Pyrus communis) cultivar William's Bon- rootstock OHF 333 (Pyrus communis L.) leaves. Cretien grafted on seven rootstocks. Australian J. Acta. Hort. 839:195-201. Exp. Agric. 46:701-705. 33.Neeas, T. and J. Kosina. 2006. Propagation of 43.Stern, R. 2011. A cherry revolution; mechanical promising pear rootstocks by hardwood cuttings. harvesting could affect every facet of the indus- International Conference of Perspectives in Eu- try. The Grower 44 (5):8 -9. ropean Fruit Growing on Horticulture Faculty in 44.Sugar, D. and S.R. Basile. 2011. Performance of Lednice. 140-143. `Cornice' pear on Quince rootstocks in Oregon, 34.Ralanskiene, A., G. Staniene, R. Rugienius, D. USA. Acta Hort. 909:215-218. Gelvonauskiene,I.Zalunskaite, J. Vinshiene, 45. Sugar, D., K. Powers, and S. Basile. 1999. Effect and V. Stanys. 2006. Transformation of quince of rootstock on fruit characteristics and tree pro- (Cydoniaoblonga) with the rolB gene-based ductivity in seven red-fruited pear cultivars. Fruit constructs under different promoters. J. Fruit and Varieties Journal 53(3):148-154. Ornam. Plant Res. 14 (Sppl. 1):95 -102. 46. Suranyi, D., and Z. Erdos. 2002. Wild pear 35.Reil, W. J. Ireland and R. Elkins. 2007. Propa- seedling rootstocks for pear scions. Acta Hort. gation and rootstock selection. In: Pear Produc- 596:331-335. tion and Handling Manual (B. Mitcham and R. 47.Tamura, F. 2012. Recent advances in research Elkins, eds.). Oakland: University of California on Japanese pear rootstocks. J. Japan. Soc. Hort. Division of Agriculture and Natural Resources Sci. 81:1-10. Publication 3483. 48.U.S. Department of Agriculture, National Ag- 36.Robbani, M., K. Banno, K. Yamaguchi, N. Fu- riculturalStatisticsService(USDA/NASS). jisawa, J. Y. Liu, and M. Kakegawa. 2006. Se- 2011 Non-citrus fruits and nuts 2010 summary. lection of dwarfing pear rootstock clones from USDA/NASS Crops and Plants website Pyrus beulaifolia and P calleryana seedlings. J. http ://usda01.1i brary. cornel 1 . edu/usda/c urrent/ Jap. Soc. Hort. Sci. 75:1-10. NoncFruiNu/NoncFruiNu-07-07-2011.pdf 37.Robinson, T.L. 2011. High Density Pear Pro- 49.Wertheim, S. 1998. Rootstock guide; apple, pear, duction with Pyrus communis Rootstocks. Acta cherry, European plum. Fruit Research Station Hort. 909: 259-269. Publication nr. 25, Wilhelminadorp, The Nether- 38.Rodriguez-Guisado, I., P. Melgarejo, F. Hernan- lands. dez, J. J. Martinez, R. Martinez-Font, P. Legua, 50.Wertheim, S. J. 2002. Rootstocks for European and A. I. ozgiiven. 2009. Characterisation of three pear: a review. Acta Hort. 596:299-307. quince clones (Cydonia oblonga Mill.) native to 51.Westwood, M. 1993. Temperate-zone pomology, Southeastern Spain. Acta Hort. 818:141-148. physiology and culture, Third Edition. Timber 39.Schouten, H. J., and E. Jacobsen. 2008. Cisgen- Press, Portland, Oregon. esis and intragenesis, sisters in innovative plant 52.Westwood, M., P. Lombard and H. Bjorstand. breeding. Trends in Plant Sci. 13:260-261. 1976. Performance of 'Bartlett' pear on standard 40.Sharko, L. V. 2005. Dwarf rootstocks of pear in and Old Home x Farmingdale clonal rootstocks. the south of Ukraine. Sadovodstvo vinogradarst- J. Amer. Soc. Hort. Sci. 101(2):161-164. vo 2005(1):11-13. 53.Zhu, L. H., and M. Welander. 2000. Adventitious 41.Simard, M.-H., J. C. Michelesi, and A. Maseron. shoot regeneration of two dwarfing per root- 2004. Pear rootstock breeding in France. Acta stocks and the development of a transformation Hort. 658:535-540. protocol. J. Hort. Sci. Biotechnol. 75:745-752.