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Abstract

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.

Open Access

Abstract

Shoot tips of ‘Almey’ crabapple [Malus baccata (L.) Borkh. × M. pumila var. Niedzwetzkyana (Dieck) Schneid.] and ‘Seckel’ pear (Pyrus communis L.) were cultured on Murashige and Skoog (MS) medium containing 8.8 µm BA. Media were solidified with either Bacto-agar, Phytagar, or TC agar at concentrations varying from 0.3% to 1.2%. Explant nutrient levels were influenced both by agar brand and concentration. The trends in nutrient composition, although not identical, tended to be similar for both genera. Increasing agar concentrations resulted in increased P, Fe, Zn, and Al in the explant and reduced Ca, Mg, and Mn levels. Although striking variations in many elements occur both in agar brands and in explants cultured on media containing similar concentrations of different agar brands, variations in shoot proliferation and growth of explants cannot be explained on the basis of variations in individual elements. From the nutritional standpoint, the alterations in the elemental composition of the basal medium by the addition of specific agars best explain variations induced by different agar brands. Chemical names used: N-(phenylmethyl)-1H-purin-6-amine (BA).

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Abstract

High levels of decadienoate esters were found in the iso-octane soluble fraction extracted directly from pureed canned fruit of ‘Harvest Queen’, HW-606, ‘Bartlett’, 5 sports of ‘Bartlett’, ‘Surecrop’, and ‘Laxtons Progress’ pear (Pyrus communis L.). These cultivars, with the exception of ‘Surecrop’, had a Bartlett-like aroma. The decadienoate equivalents observed in 19 other cultivars ranged from none to one-half the high group. Higher levels of decadienoate esters were also detected by high pressure liquid chromatography (HPLC) in essences of canned fruit of ‘Bartlett’, ‘Harvest Queen’, and HW-606 with a Bartlett-like aroma than in canned fruit of 3 cultivars with aroma unlike ‘Bartlett’, including ‘Harrow Delight’, HW-607, and ‘Kieffer’. Cultivars with Bartlett-like aroma seem to be characterized by high decadienoate ester level, but high decadienoate ester levels are not necessarily indicative of Bartlett-like aroma. Decadienoate esters were not detected in essences extracted from actively growing or dormant shoots of ‘Bartlett’. Thus, early screening of seedlings for Bartlett-like aroma on basis of decadienoate extraction of the shoot or leaves cannot be effective.

Open Access

Abstract

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.

Open Access
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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.

Free access

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.

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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.

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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).

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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.

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One year old Asian pear scion cultivars were grafted onto Pyrus calleryana rootstock utilizing two grafting methods (whip grafting and splice side grafting). Percentage survival of grafted scions was 78 and 96 via the splice side graft and the whip graft, respectfully. Shoot length and caliper 80 days after grafting did not vary between cultivars. `Yakumo' and 'Chojuro' produced a greater number of branches as compared to the remaining cultivars. `Yakumo', `Chojuro', `Seuri' and `Hosui' produced the least amount of shoot growth. Branching angle was greatest for `Seigyoku', `Chojuro' and `Yakumo' with 60, 70, and 55 degrees, respectfully. As indicated by leaf area, `Seuri' and `Hosui' produced large leaves and `Yakumo' and `Chojuro' produced small leaves.

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