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Javier Sanzol and Timothy P. Robbins

European pear, like other fruit species of the Rosaceae, is impaired in effecting self-fertilization by a gametophytic self-incompatibility (GSI) system ( Crane and Lewis, 1942 ). In the Rosaceae, GSI is inherited as a single multiallelic locus (S

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Richard L. Bell

Pear psyllids ( Cacopsylla spp., Hemiptera: Psyllidae) are major pests of European pear ( Pyrus communis L.) in orchards in most temperate regions where the crop is grown ( Berrada et al., 1995 ; Westigard et al., 1970 ). In North America, the

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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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Nele De Belie, Ian C. Hallett, F. Roger Harker, and Josse De Baerdemaeker

The tensile properties of european pear (Pyrus communis L. `Beurre Bosc') and asian pear (Pyrus pyrifolia Nakai `Choguro') were examined using a microscope-mounted apparatus that allowed direct observation and recording of cell and tissue changes during testing. To manipulate turgor potential, tissue slices from fruit of different firmness (ripeness) were incubated in sucrose solutions of differing water potential. Solution water potentials were adjusted for individual fruit, and varied between -2.5 and 1 MPa from the water potential of the expressed juice. Fruit firmness declined from 100 to 20 N and from 60 to 25 N during ripening of european and asian pears, respectively. For both european and asian pears the relationship between fruit firmness and tensile strength of tissue soaked in isotonic solutions was sigmoidal, with the major mechanism of tissue failure being cell wall failure and cell fracture at high firmness and intercellular debonding at low firmness. In the intermediate zone, where fruit firmness and tissue tensile strength decreased simultaneously, a mixture of cell wall rupture and intercellular debonding could be observed. Tissue and cell extension at maximum force both declined similarly as fruit softened. Tensile strength of tissue from firm pears (>50 N firmness, >0.8 N tensile strength) decreased by as much as 0.6 N during incubation in solutions that were more concentrated than the cell sap (hypertonic solutions). When similar tissue slices were incubated in solutions that were less concentrated than the cell sap (hypotonic solutions), the tensile strength increased by up to 0.4 N. This is interpreted as stress-hardening of the cell wall in response to an increase in cell turgor. Tensile strength of tissue from soft pears was not affected by osmotic changes, as the mechanism of tissue failure is cell-to-cell debonding rather than cell wall failure.

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Sabahudin Hadrović, Filip Jovanović, Sonja Braunović, Saša Eremija, Zoran Miletić, Snežana Stajić, and Igor Golić

Technologies, Inc., Warrenton, VA). Results and Discussion All species studied, except for the european pear ( Pyrus communis L.), had a greater N content and lesser C/N ratio in their bark than in wood; in all species, the C content was greater in

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Xingbin Xie, Congbing Fang, and Yan Wang

‘Bosc’ is the second most produced winter cultivar of european pear in the Pacific northwesten United States with annual production of about 61 million kilograms ( Northwest Horticultural Council, 2013 ). Although most european pears are normally

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Christopher S. Walsh, Julia M. Harshman, Anna E. Wallis, Amy Barton Williams, Michael J. Newell, and George R. (G.R.) Welsh

Production of european pears ( P. communis ) in the eastern United States is limited by a number of pathological and physiological problems, particularly fire blight, a disease caused by E. amylovora (Burr.) Winslow et al. This bacterium appears

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Caihong Wang, Yike Tian, Emily J. Buck, Susan E. Gardiner, Hongyi Dai, and Yanli Jia

al., 2009b ). The maps of japanese pear ‘Hosui’ ( Pyrus pyrifolia ) and european pear ‘Bartlett’ were successfully aligned to the apple consensus map using SSR markers, and all pear linkage groups corresponding to its basic chromosome number (x = 17

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Reut Niska, Martin Goldway, and Doron Schneider

European pears ( Pyrus communis ) ‘Abugo’ and ‘Ceremeno’ are self-compatible as a result of the absence of S21° -RNase protein in their styles ( Sanzol, 2009 ). From an agricultural point of view, self-compatibility provides an advantage in that an

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Yan Wang

‘Anjou’ is the most widely produced european pear cultivar in the Pacific northwestern United States with annual sales of ≈222 million kilograms ( Northwest Horticultural Council, 2013 ). Superficial scald, resulting from necrosis of the hypodermal