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Adriana Cibele de Mesquita Dantas, Adriano Nunes Nesi, Lilia Bender Machado, Janny Haerter, and Gerson Renan de Luces Fortes

The culture of meristems, shoot tips, and axillary buds leads to the method of in vitro multiplication that is easily used and safe to obtain uniform copies with no undesirable variations. This work aimed to propagate five in vitro pear cultivars: Housui, Carrick, Nijisseiki, Packham's Triumph, and Red Bartlett. The work was carried out in the Tissue Culture Laboratory at Embrapa Temperate Climate. The plants were sprayed with benomyl (1.0 mg./L) and agrimicine (2.4 mg/L) in the fields, 2 weeks before the shoots were collected. The shoots were then cut with two buds with no leaves and desinfested with alcohol 70% for 10 s and 1% sodium hypochloride for 20 min, 50 explants, 25 buds, and 25 meristems, were then transferred to test tubes containing MS salts and vitamins, myo-inositol (100.0 mg/L), sucrose (30.0 g/L), agar (6.0 g/L), added to in mg/L: BAP (1.0), GA3 (0.1), and NAA (0.01). Three pear cultivars were used for in vitro multiplication (`Nijisseiki', `Red Bartlett', and `Housui') by using the same basal salt with N reduced to strength, added to (in mg/L): BAP (1.6), NAA (0.16). The material was kept in growth room under 16-h photoperiod, 25 ± 2 °C and 19 μMol·m-2·s-1 of flux radiation. The in vitro contaminations were mainly due to bacteria derived from the bud material (71.5%). Higher oxidation for meristem material was observed for `Carrick' and `Packham`s Triumph'. `Red Bartlett' showed the best results for all the variable studied, although all cultivars in general presented low response.

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Abdelrahman S. Al-Wasel and Robert M. Skirvis

Variegated `Louise Bonne' (LB) pear is a periclinal chimera in which the LIII layer is albino. Chimeral shoots propagated in vitro segregate spontaneously into green, albino, pale, or rearranged chimeral types, making them difficult to maintain in culture. We investigated the role of growth regulators on chimeral stability and destability to find a combination that would maintain the chimera through repeated subcultures. 70 to 90% of shoots remained chimeral on Lepoivre (LP) medium supplemented with 8 μM BA or less. Only 36 to 58% of shoots grown at concentrations greater than 8 μM were stable. Shoots grown on LP with thidiazuron (TDZ) were very unstable (4 to 44%). NAA had no significant effect on chimeral stability. While shoots multiplied better on LP, the chimeral pattern was more obvious on MS, making it a good screening medium. Selection and subculturing chimeral shoots on a good medium (LP with 2 to 4 μM BA) increased the percentage of chimeral shoots from 26% at the 4th subculture to 84% at the 27th subculture.

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Andrew C. Bell, Thomas G. Ranney, Thomas A. Eaker, and Turner B. Sutton

Fire blight, caused by the bacterium Erwinia amylovora (Burrill) Winslow et al., is one of the most destructive diseases of plants in the Rosaceae subfamily Maloideae. Artificial inoculations, using E. amylovora strain E2002a, were conducted to determine levels of resistance to fire blight among taxa of flowering pears (Pyrus L. spp.) and quince (Chaenomeles Lindl. spp.). The level of resistance was measured as the length of the fire blight lesion as a percentage of overall shoot length. Considerable variation in resistance was observed among both pears and quince. Pyrus ussuriensis Maxim. `Prairie Gem' was highly resistant with a lesion length of 1% of the total shoot length. Pyrus calleryana Decne. `Bradford' was intermediate with a 50% lesion length while P. calleryana `Chanticleer' was significantly more resistant with a lesion length of 31%. Nine pear taxa were highly susceptible and did not differ significantly from 100% disease severity (total shoot death). Chaenomeles speciosa (Sweet) Nak. `Contorta' was highly resistant with a lesion length of 15%. Six quince taxa, including C. × superba (Frahm) Rehd. `Cameo', `Texas Scarlet', and `Jet Trail' were highly susceptible while nine other taxa showed intermediate resistance.

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Rayane Barcelos Bisi, Rafael Pio, Daniela da Hora Farias, Guilherme Locatelli, Caio Morais de Alcântara Barbosa, and Welison Andrade Pereira

The pear tree ( Pyrus spp.) is a temperate-climate fruit species, and its cultivation in subtropical regions was made possible by hybrid cultivars obtained from the cross Pyrus communis × Pyrus pyrifolia ( Curi et al., 2017 ). This cross

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R.L. Bell

Eight cultivars and wild seedlings of pear (Pyrus spp.) from Eastern Europe were evaluated for resistance to feeding by early instar pear psylla [Cacopsylla pyricola (Foerster)] in a 24-hour assay. All were compared to a susceptible control, `Bartlett' (P. communis L.), and to a moderately resistant control, NY10352 (P. communis × P. ussuriensis Maxim. BC hybrid). Three P. communis cultivars, Bartjarka (PI 483391), Lucele (PI 483402), and Kajzerka (PI 506387), and a wild seedling (PI 506381) of undetermined species, exhibited a high degree of host resistance, measured as reduced frequency of feeding and increased either mortality or movement off of the plants.

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R.L. Bell and L.C. Stuart

`Fifty-nine cultivars and wild seedlings of pear (Pyrus spp.) from Eastern Europe were evaluated for resistance to feeding by early instar pear psylla [Cacopsylla pyricola (Foerster)] in a 24-hour assay. `Bartlett' (P. communis L.) and NY 10352 (P. communis × P. ussuriensis Maxim. BC1 hybrid) were used as susceptible and resistant controls, respectively. A. high degree of resistance, measured as increased mortality and reduced frequency of feeding, was found in 11 plant introductions: `Erabasma' (PI 483370), `Krupan Burnusus' (PI 483387), `Topka' (PI 484489), `Zelinka' (PI 483393), `Mednik' (PI 483399), `Karamanlika' (PI 502165), `Katman' (PI 502172), `Smokvarka' (PI 502176), `Obican Vodenac' (PI 502177), a clone thought to be `Smiljerka' (PI 502178), and an unnamed seedling (PI 506382).

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Richard L. Bell and L. Claire Stuart

Four genotypes of pear (Pyrus spp.) of East European origin, a susceptible control, `Bartlett' (P. communis L.), and a moderately resistant control, NY 10352 (P. ussuriensis Maxim. × P. communis B C1 hybrid), were artificially infested with pear psylla (Cacopsyll a pyricol a Foerster) nymphs in the laboratory. Ten neonate first instars were placed on each of the two youngest leaves of four small trees per genotype. On PI 506381 and PI 506382, wild seedlings of P. nivalis Jacq., all nymphs died within 5 days. Mortality and development of nymphs on PI 502173, a wild P. communis seedling, was similar to that observed on `Bartlett', with 43% and 45% of the nymphs surviving to adulthood, respectively. On `Karamanlika' (PI 502165) and NY 10352, 15% of the nymphs developed into adults. Increased mortality and delayed development of nymphs was associated with feeding inhibition. The mode of host plant resistance to pear psylla nymphs in these accessions of East European pear is, therefore, similar to that previously characterized for NY 10352, in which the resistance is derived from germplasm of East Asian origin.

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Jeong Hwan Hwang, Yong Uk Shin, Daeil Kim, Seong Heo, and Seong Sig Hong

( Pyrus spp.) Korea Univ., Seoul Korea PhD Diss. The International Union for the Protection of New Varieties of Plants (UPOV). 2005. Guidelines for the conduct of tests for distinctness, uniformity, and stability.

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Graham H. Barry and Smit le Roux

–calcium [ProCa; BAS-125W (3-oxido-4propionyl-5-oxo-3-cyclohexene-carboxylate)] sold as Regalis® and Apogee® and developed by BASF (Limburgerhof, Germany) is used on pome fruit trees ( Malus and Pyrus spp.) to reduce and control vegetative growth ( Miller, 2002

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Katie Ellis, Tara Auxt Baugher, and Karen Lewis

.). Fresh apple acreage dominated the totals, followed by processing apples, pears ( Pyrus spp.), and peaches and nectarines ( Prunus persica ). Most operations grew fairly diverse arrays of tree fruit crops, with half of all eastern growers producing five