Acquiring Cherry Germplasm from Central and Eastern Europe Amy F. Iezzoni1 Department of Horticulture, Michigan State University, East Lansing, MI 48824 Additional index words. Prunus cerasus, Prunus avium, Prunus fruticosa Abstract. The sour cherry (Prunus cerasus L.) industry in the United States is a monoculture of a 400-year-old cultivar from France named ‘Montmorency’. To provide a solid germplasm base to breed alternatives to ‘Montmorency’, cherry germplasm was systematically collected over a 15-year period from its ancestral home in Central and Eastern Europe and introduced to the U.S. The strategy of germplasm collection using pollen, seed and budwood importation of highly quarantined species is discussed. Germplasm resulting from this effort is highlighted as well as an example of commercial success. Finally, the “recycling” of this immense germplasm collection to search for dwarfi ng precocious rootstocks for sweet cherry is described. The sour cherry (Prunus cerasus L., syn. variation from its native habitat, Central and in the warmer areas of Europe, that they have tart cherry) industry in the U.S. provides an Eastern Europe (Iezzoni et al., 1990; Vavilov, been given their own common name, Duke example of an agricultural crop with extreme 1951). Also targeted for collection were the cherries (Hedrick, 1914). genetic vulnerability to disasters caused by progenitor species of sour cherry, sweet cherry Sour cherry cultivars have further been pests, diseases and unfavorable weather con- (P. avium L.) and ground cherry (P. fruticosa classifi ed into two groups based upon fl esh ditions. Two factors which contribute to the Pall.). In particular, sweet cherries were tar- and juice color (Hedrick, 1914). The amarelle potential vulnerability of agricultural crops geted, as it is a major fruit crop in the U.S., types, of which ‘Montmorency’ is a member, are typifi ed by sour cherry production: genetic and its current production is also dominated have red skin but nearly colorless juice and uniformity and geographical concentration. by a few old cultivars. In addition, a minimal fl esh. Morello types, which have skin, fl esh The entire sour cherry industry in the U.S. is number of sweet cherry accessions (~70) are and juice ranging from red to deep purple, are based on one cultivar ‘Montmorency’ (Iez- maintained at the USDA–ARS National Clonal mainly grown in Europe. The darker pigmen- zoni, 1988); and Michigan produces 75% of Germplasm Repository for Tree Fruit/Nut tation of morello types reduces the need for the nation’s sour cherries. This monoculture Crops and Grapes, Davis, Calif. The strategies synthetic colorants in processing. In addition, provides an ideal environment for crop losses that were used to import cherry germplasm and morello fruit generally show less wind whip, due to unfavorable weather or to disease and some of the realized outcomes from this effort scald and bruising. Presumably the amarelle pest epidemics. Unfortunately, the vulnerabil- are described below. ‘Montmorency’ became the dominant U.S. ity of this monoculture was realized in 2002. sour cherry cultivar due to its productivity and Spring freeze damage reduced sour cherry Cherry Germplasm Collection adaptability to mechanical harvest and not due production to the lowest level recorded since to its clear juice characteristic, as red dye is 1945 (i.e., 2% of a normal crop) (Kleweno and Area of Origin and Genetic Diversity. There frequently used in ‘Montmorency’ products Matthews, 2003), with a devastating effect on are more than 30 species of cherries with most to enhance the red color. the industry and economy of the fruit-growing indigenous to Europe and Asia (Rehder, 1940). regions. For example, northwestern Michigan However, the main species grown for their fruit Implementation of Cherry Germplasm annually produces an average of approximately are in the Section Eucerasus which consists Collection Strategy 180 million pounds of sour cherries; yet, the of the sweet cherry, sour cherry, and ground 2002 production was only 3 million pounds cherry. Ground cherry is a low-growing bush Status of sour cherry germplasm in the U.S. (Kleweno and Matthews, 2003). cherry native to Russia but present throughout The Cherries of New York, published in 1914, In addition to the genetic vulnerability of much of Eastern Europe. Sweet cherry and describes more than 250 sour cherry cultivars the ‘Montmorency’ monoculture, this 400- ground cherry are presumably early deriva- that existed in U.S. collections at that time year-old cultivar has numerous shortcomings. tives of an ancestral Prunus (Watkins, 1976); (Hedrick, 1914). Most of the cultivars described These include poor fruit fi rmness, the necessity whereas, sour cherry is believed to have arisen are variants of ‘Montmorency’ or ‘English to add sugar and red coloring to the majority multiple times through natural hybridizations Morello’ (syn. ‘Schattenmorelle’), a common of processed products, and susceptibility to an between ground cherry and sweet cherry northern European sour cherry landrace, plus array of insects and diseases. The mission of (Beaver and Iezzoni, 1993; Brettin et al., selections of western European origins. A few the sour-cherry breeding program at Michigan 2000; Olden and Nybom, 1968). Since ground of the selections listed were of Russian origin; State University (MSU) is to increase the cherry is tetraploid (2n = 32) and sweet cherry however, there was a noticeable absence of profi tability and environmental sustainability is diploid (2n = 16), achieving tetraploid sour germplasm from regions likely to be replete of sour-cherry production by developing new, cherry and, therefore, fertile progeny requires with diversity, including Turkey, Hungary, cultivar-based opportunities. an unreduced gamete from the sweet cherry Romania, and the former Yugoslavia (Iezzoni Since sour cherry is not native to the U.S. parent. Unreduced pollen is present in sweet et al., 1990). Concurrent with the rise of the and little diversity was represented among cherry (Iezzoni and Hancock, 1984) supporting ‘Montmorency’ monoculture, most selections existing domestic collections, genetic improve- the theory that sexual polyploidization was the described in The Cherries of New York were ment required the acquisition and use of genetic likely mechanism of speciation. lost from U.S. collections in the half century As sour cherries spread throughout Europe, that followed its publication. The sour-cherry Received for publication20 May 2004. Accepted for ecotypes evolved that differed in cold hardi- breeding programs in North America located publication 27 June 2004. The fi nancial support from ness, tree habit and fruit and leaf characteristics in Ontario, New York, and Minnesota, also the Michigan Agricultural Experiment Station and (Kolesnikova, 1975). These ecotypes presum- had disappointing outcomes. The two cultivars the following grower organizations to support the ably arose in conjunction with continued gene bred at the University of Minnesota, ‘Northstar’ MSU cherry breeding and selection effort is grate- fl ow between sour cherry and its progenitor (Alderman et al., 1950), and ‘Meteor’ (Alder- fully acknowledged: Michigan Cherry Committee, species. For example, several cold-hardy man et al., 1952), and the one clone released Cherry Marketing Institute, Washington Tree Fruit sour-cherry cultivars grown in Russia and from the Cornell University program, ‘Surefi re’ Research Commission, and the Oregon Sweet Cherry Commission. The invaluable assistance of Renate Eastern Europe are hybrids between sour and (Andersen et al., 2000), gained only limited Karle with the Russian and Ukrainian collaborations ground cherry. These selections are common homeowner interest in the U.S. was greatly appreciated along with the technical in the cold northern ranges where sour and It was in this setting that the sour cherry assistance of Audrey Sebolt. ground cherry habitats overlap. Individual breeding program at MSU was initiated in the 1To whom reprint requests should be addressed; trees resulting from crosses between sweet spring of 1982. Present in the MSU collection at e-mail [email protected]. and sour cherry are so prevalent, particularly the time were a modest number of sour cherry 304 HORTSCIENCE VOL. 40(2) APRIL 2005 AAprilHSBook.indbprilHSBook.indb 330404 22/9/05/9/05 33:59:31:59:31 PPMM cultivars, most of which were from the ‘English observations would be limited to sampling generated with pollen collected in eastern Eu- Morello’ landrace and an ample number of processed fruit. However, the sour-cherry rope in 1983, were already fruiting and under ‘Montmorency’ clonal selections. That fi rst collection at MSU was so uninspiring that selection in the MSU breeding program. summer, evaluations of the fruits and trees were there was little reason to intermate the existing Targeted germplasm collection. The disappointing in that selections with fruit types selections. Therefore, the value of getting the previous cherry collection efforts in Europe signifi cantly superior to ‘Montmorency’ were pollen from superior germplasm to Michigan had the general objective of increasing the not identifi ed. This resulted in the conclusion in time for crossing took precedence. The genetic diversity available in the U.S. for that U.S. sour cherry breeding would not be hospitality and kindness of the breeders and cherry improvement. More recently, targeted successful without a rapid infusion of superior colleagues, who assisted with this effort, were germplasm collection trips were undertaken germplasm. overwhelming, and their kindness is acknowl- to address specifi c needs. “What this superior germplasm was and edged herein: Serbia, Asen Stancevic and M. The fi rst targeted trip was a joint Prunus where it would be found, I did not know. Nikolic; Bulgaria, Vassil Georgiev; Romania, and Malus collection trip to Russia funded However, the next spring, I set out to fi nd it Vasile Cociu and Titu Gozob; Hungary, Janos with a grant from the USDA–ARS, Plant Ex- and bring it to the U.S.” Apostol, Sandor Brózik, and Pal Maliga; and ploration Offi ce. One of the goals of this trip Goals.