Pear ( Pyrus spp.) is cultivated worldwide and it is one of the economically important fruit crops in Taiwan with ≈8300 ha of cultural areas, which account for cash value of 3.6 billion NT dollars in 2008, just next to citrus, pineapple, and
Pyrus communis L. germplasm came to North America with early settlers. Pyrus cultivars have markedly declined since the turn of the century when more than 2700 unique Pyrus cultivars and 10,000 cultivar synonyms were noted. In 1956, 844 Pyrus cultivars and selections were widely available. Fireblight, Erwinia amylovora (Burril) Winslow et al. 1923, and lack of cold hardiness were main causes of cultivated germplasm loss. During June through December 1989, I resurveyed 37 State Agricultural Experiment Stations which had pear collections in 1956, to determine the present extent of their collections. Only four had more than 100 cultivars; 12 had 10 to 100 cultivars; 21 had less than 10. Experiment stations have decreased their collections because of funding cuts and program redirection. The National Clonal Germplasm Repository at Corvallis, established in 1981, has a collection of 811 unique cultivars and representatives of 26 Pyrus species. About 194 cultivars published in 1908 are in the NCGR collection. At least 424 of those listed in 1956 still exist. Oriental species and other foreign selections not previously available are actively being acquired. About 80% of the clones in the NCGR collection are virus negative; about 10 % reside in backup in vitro storage. Fireblight damage has not been observed thus far. With continued federal support, Pyrus germplasm availability should remain more stable than the decline seen in the last 90 years.
Three plant exploration trips were made to Eastern Europe between 1976 and 1980 in search of domestic Pyrus germplasm in five countries between the Baltic and Adriatic Seas. This collection of pear (Pyrus spp.) germplasm in Romania, Poland, Hungary, and Czechoslovakia was preceded by 279 accessions from Yugoslavia (16). Descriptions of Pyrus spp., method of budwood collection and shipment, and the care and maintenance of the plant material at the U.S. Plant Introduction Station, Glenn Dale, Md. were covered in ref. 16. Trees were exposed to natural infection by fire blight [Erwinia amylovora (Burr.) Winsl. et al.], Fabraea leaf spot (Entomosporium maculatum Lev.), and pear psylla (Cocopsylla pyricola Foerst.). In addition, evaluation of fruit size and a preliminary assessment of quality are being carried out. The most interesting accessions are being indexed for virus disorders before release.
During 1976-1980, three plant exploration trips were made throughout eastern Europe in search of native Pyrus germplasm. A total of 384 accessions (231 from Yugoslavia, 86 from Romania, 43 from Poland, and 12 each from Hungary and Czechoslovakia) were collected as budwood and propagated at the National Plant Germplasm Quarantine Center in Glenn Dale, Md. Following 8 years of exposure to the fire blight bacterium [Erwinia amylovora (Burr.) Winsl. et al.], 17.49” of the accessions remained uninfected, 11.2% rated resistant, 6.8% moderately resistant, and 64.6% blighted severely (26% to 100% of tree blighted). Some of the superior accessions have been released for use in the pear breeding program.
Pear leaf spot, caused by the fungus Fabraea maculata Atk. (anamorph: Entomosporium mespili (DC.) Sacc.) occurs in most areas of the world where pears are grown. Most major cultivars of the european pear, P. communis L., for which data are available are susceptible. Ratings appearing in the literature are sometimes contradictory. This study evaluated resistance/susceptibility within a diverse collection of Pyrus cultivars and other germplasm in a randomized and replicated nursery plot using quantitative measures of disease incidence and severity. The least susceptible genotypes were the P. communis cultivars `Beurre Fouqueray' and `Bartlett', the P. pyrifolia cultivars `Imamura Aki', and the P. communis × P. ussuriensis hybrid NJ 477643275.
Deep supercooling was found in the stem tissues of all the Pyrus species studied. There was more than 1 low temperature exotherm resulting from the freezing of supercooled water in stem tissue, and these exotherms were associated with the tissue injury. The supercooled water in the stems of P. nivalis Jacq., P. cordata (Desv.) Schneider and P. elaeagrifolia Pall, was found in both xylem and bark tissues. The supercooling characteristics of vegetative and flower buds are also described. The hardiest and least hardy species found were P. caucasica Fed. and P. pashia D. Don., respectively.
Micropropagated shoots of 49 Pyrus species and cultivars and one selection of Pyronia veitchii (Trabut) Guillaumin were evaluated to test their responses to several in vitro rooting techniques. Auxin treatment was required for rooting in most cases. Eighteen of 50 accessions rooted ≥50% with a 15-second, 10-mm IBA dip followed by growth on medium with no growth regulators (NGR). Twelve accessions rooted on a medium with 10 μm IBA applied for 1 week followed by NGR medium for 3 weeks; NGR medium alone was effective for only two accessions. Twenty-eight accessions rooted poorly with IBA treatments; an additional treatment of a 15-second dip in 10 mm NAA followed by NGR medium produced ≥50% rooting for eight genotypes. Root production increased for 10 of 19 especially recalcitrant genotypes by 10 μm IAA treatments in darkness or at 30C and NAA dip treatments. Of rooted shoots, 73% survived acclimation in the greenhouse. Selections of Pyrus betulifolia Bunge, P. calleryana Decne., P. hondoensis Kikuchi and Nakai, P. koehnei C. Schneider, P. pashia Buch.-Ham. ex D. Don, P. pyrifolia (Burm.f.) Nakai cv. Shinseiki, P. regelii Rheder, P. ussuriensis Maxim., and the Pyronia veitchii selection failed to root in any of the treatments. Twenty-five of 32 P. communis L. cultivars and three other species rooted on at least one of the treatments. Chemical names used: 1-naphthaleneacetic acid (NAA), 1H-indole-3-butyric acid (IBA), 1H-indole-3-acetic acid (IAA).
Cultures of 49 Pyrus species and cultivars and one Pyronia (Pyrus × Cydonia hybrid) selection were screened in vitro to determine a rooting method suitable for a wide range of germplasm. Auxin treatment was required for rooting in most cases. Eighteen of the 50 accessions rooted with a 15 sec. 10 mM indole-3-butyric acid (IBA) dip followed by growth on medium with no growth regulators (NCR). Medium with 10 μM IBA for one week followed by NCR medium produced 12 rooted accessions, but NCR medium alone produced little or no rooting. A 15 sec. dip in 10 mM naphthaleneacetic acid (NAA) followed by NCR medium was tested on 29 accessions which rooted poorly on the other three treatments. Twice as many (28%) rooted on NAA as on either IBA treatment (14% each). Additional treatments combining IBA with darkness or higher temperature were also tested and were successful for some cultivars. P. calleryana, P. koehnei, P. pashia, P. hondoensis, P. ussuriensis, P. betulifolia, P. regelii, P. pyrifolia hybrid cv. Shinseiki and the Pyronia selection failed to root. Twenty two of the 32 P. communis cultivars rooted on at least one treatment.
Edible european pears (Pyrus communis L. ssp. communis) are derived from wild relatives native to the Caucasus Mountain region and eastern Europe. Microsatellite markers (13 loci) were used to determine the relationships among 145 wild and cultivated individuals of P. communis maintained in the National Plant Germplasm System (NPGS). A Bayesian clustering method grouped the individual pear genotypes into 12 clusters. Pyrus communis ssp. caucasica (Fed.) Browicz, native to the Caucasus Mountains of Russia, Crimea, and Armenia, can be genetically differentiated from P. communis ssp. pyraster L. native to eastern European countries. The domesticated pears cluster closely together and are most closely related to a group of genotypes that are intermediate to the P. communis ssp. pyraster and the P. communis ssp. caucasica groups. Based on the high number of unique alleles and heterozygosity in each of the 12 clusters, we conclude that genetic diversity of wild P. communis is not fully represented at the NPGS. Additional diversity may be present in seed accessions stored in the NPGS and more pear diversity could be captured through supplementary collection trips to eastern Europe, the Caucasus Mountains, and the surrounding countries.
Some factors that affect the in vitro conservation of wild pear (Pyrus syrica) microshoot cultures were studied. Sorbitol and mannitol at 0.2 to 4.0 M reduced growth significantly and extended the subculture intervals to 5 months when cultures where kept at 15°C. Increasing sucrose to 12% in the medium was not highly effective and the subculture intervals did not exceed 3.0 months. After 2 years of maintaining cultures on slow-growth medium, cultures grew slowly when transferred to fresh control medium. Shoots started to proliferate after three subcultures (6.0 weeks apart) on medium containing 1.0 mg/L BA and 0.1 mg/L NAA. New microshoots were rooted on medium containing 2.0 mg/L IBA and rooted microshoots gave 90% survival when acclimatized ex vitro under intermittent mist.