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Jonathan D. Mahoney and Mark H. Brand

accession information for the plants used in this research is listed in Table 1 . Flowering shoots of Pyrus communis were sent from the US Department of Agriculture–Agricultural Research Service–National Clonal Germplasm Repository in Corvallis, OR, and

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Sokrith Sea, Cyril Rakovski, and Anuradha Prakash

The United States produced 407,000 t of ‘Bartlett’ pears ( Pyrus communis L.) in 2012 [ U.S. Department of Agriculture (USDA), 2013] . California produces ≈32% of all pears in the nation and exports between 20% and 30% of the fresh crop each year

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Gayle M. Volk, Christopher M. Richards, Adam D. Henk, Ann A. Reilley, Nahla V. Bassil, and Joseph D. Postman

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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Gayle Volk, Christopher Richards, Adam Henk, Ann Reilley, Nahla Bassil, and Joseph Postman

Edible European pears (Pyrus communis sp. communis L.) are thought to be derived from wild relatives native to the Caucasus Mountain region and eastern Europe. We collected genotype, phenotype, and geographic origin data for 145 P. communis individuals derived from seeds collected from wild relatives. These individuals are currently maintained in the USDA–ARS National Plant Germplasm System (NPGS) in Corvallis, Ore. Pear genotypes were obtained using 13 microsatellite markers. A Bayesian clustering method grouped the individual pear genotypes into 12 clusters. The subspecies of pears native to the Caucasus Mountains of Russia, Crimea, and Armenia could be genetically differentiated from the subspecies native to eastern European countries. Pears with large fruit clustered closely together and are most closely related to a group of genotypes that are intermediate to the other groups. Based on the high number of unique alleles and heterozygosity in each of the 12 clusters, we conclude that the genetic diversity of wild P. communis is not fully represented in the NPGS

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Richard L. Bell

Pear psyllids [ Cacopsylla pyri (L.), C. pyricola (Förster), and C. pyrisuga (Förster)] are major arthropod pests of pear ( Pyrus communis L.) throughout North America and Europe. Both adults and nymphs feed primarily in the vascular tissue of

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James P. Mattheis

disorders after removal from cold storage. Materials and Methods Plant material. ‘d’Anjou’ ( Pyrus communis L.) pear fruit were obtained from three commercial orchards in central Washington State. Pears determined to be commercially mature by the growers

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Peter C. Andersen, Brent V. Brodbeck, and Russell F. Mizell III

Diurnal variations in the chemical composition of xylem fluid have been established for many plant species exhibiting positive root pressure; similar patterns have not been well documented in transpiring plants. Diurnal changes in plant water status and xylem fluid chemistry were investigated for `Flordaking' peach [Prunus persica (L.) Batsch], `Suwannee' grape (Vitis hybrid), and `Flordahome' pear (Pyrus communis L.). Xylem tension was maximum at 1200 or 1600 hr and declined to <0.5 MPa before dawn. Xylem fluid osmolarity ranged from 10 to 27 mm and was not correlated with diurnal patterns of xylem tension. The combined concentration of amino acids and organic acids accounted for up to 70%, 45%, 55%, and 23% of total osmolarity for irrigated P. persica, nonirrigated P. persica, Vitis, and P. communis, respectively. The concentration of total organic compounds in xylem fluid was numerically greatest at 0800 or 0900 hr. For irrigated P. persica the osmolarity of xylem fluid was reduced by 45% from 0800 to 1200 hr, 1 h after irrigation, compared to only a 12% reduction from 0800 to 1200 hr for nonirrigated trees. Asparagine, aspartic acid, glutamine, and glutamic acid were mainly responsible for diurnal changes in the concentration of total amino acids and organic N for P. persica; the diurnal variation in organic N for Vitis was due to glutamine. Arginine, rather than the amides, was the primary source of organic N in xylem fluid of P. communis, and there was no consistent diurnal change in the concentration of amino acids or organic N. The predominant organic acids in all species examined were citric and malic acids. No consistent diurnal trend occurred in the concentration of organic acids or sugars in xylem fluid.

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R.S. Mueller, D.P. Murr, and L.J. Skog

1-Methylcyclopropene (1-MCP), a gaseous synthetic cyclic hydrocarbon, has been shown to have potential to become an important new tool in controlling the response of plants sensitive to ethylene. Due to its irreversible binding to the ethylene receptor(s) and its subsequent prevention of the physiological action of ethylene for extended periods, 1-MCP may prove also to have effective commercial application in the control of ethylene effects in detached organs such as fruit. Our objective was to investigate the effectiveness of 1-MCP in controlling ripening in pear. Two commercial cultivars (Bosc, Anjou) and one numbered cultivar from Agriculture and Agri-Food Canada's breeding program (Harrow 607) were harvested at commercial maturity. Immediately after harvest, fruit were exposed for 24 h at 20 °C to 1-MCP ranging from 0 to 100 μL•L-1 then placed in air at 0 °C and 90% relative humidity for 5 and 10 weeks. Following treatment and after 5 weeks storage plus a 7- or 14-day post-storage ripening period, fruit softening and ethylene evolution were inhibited and fruit volatile evolution was reduced significantly by exposure to 1-MCP at or above 1.0 μL•L-1 in all three cultivars. Concentrations exceeding 1.0 μL•L-1 were required to maintain initial firmness and inhibit ethylene production after 10 weeks storage in air. Evolution of alpha-farnesene and 6-methyl-5-hepten-2-one was related to low temperature stress and chlorophyll loss as a result of ripening, respectively, and were affected by 1-MCP exposure. The pattern of evolution and amounts of other volatiles was also affected by 1-MCP treatment. These results indicate a huge potential for commercial use and application of 1-MCP in controlling fruit ripening and senescence.

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Qiangsheng Wang, Yinping Shi, Qingrong Sun, and Yongsheng Yin

In the 1980' s, a Bartlett pear giant fruit sport was found in Pingdu, Shandong. The characteristics of mutation are larger fruit, thicker branch, shorter internode and much more spur. By grafting propagation, the clones began to bear fruit in 1990, and maintain the characteristics of variable mother plant.

From microspore formation to blossom and spreading pollen, the cytohistological observation of sport flowering organs indicates: in every phase of pollen development, the size of florets, anthers and pollen grains are similar to CK; their pollen types both belong to tricolporat, pollen grains are nearly equal in size. This indicates that sport sporogenous tissue do not mutate. The observation of shoot apex sections showes: for CK, the cells of three histogenic layers range regularly; the size of cells, nuclei, and nucleoli among LI, LII, LIII are similar. For sport, the cells of LI, LII are no difference from CK, but in LIII and inner tissue, cells, nuclei, nucleoli all become larger clearly. This indicates LIII had mutated. So this sport is a 2–2–4 type chimera.

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E. Lucienne Mansvelt and F.J. Calitz

`Packham's Triumph' (Pyrus communis L.) pear blossoms were inoculated with Pseudomonas syringae pv. syringae van Hall upon emasculation and then hand-pollinated at different times to assess the effects of bacterial colonization on fruit set. The pathogen significantly reduced fruit set by 24%. No lesions developed on pear flowers at any stage of the trials.