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
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
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.
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
Respiration of flower-buds of Pyrus communis L., a late blooming species, and P. calleryana, an early blooming species, was investigated throughout the winter. Respiration of P. calleryana Decne at 5°C was twice as high as that of P. communis, whereas the respiration rates were similar at 25°. A large portion (60–70%) of the respiration at 5° was cyanide resistant in P. calleryana and much less in P. communis. The combination of inhibitors, cyanide (KCN) and salicylhydroxamic acid (SHAM), still only partially inhibited respiration. The residual respiration was much higher for P. calleryana than for P. communis. The nature of the residual respiration is not known.
Factors influencing the foliar penetration of naphthaleneacetamide (NAAm) were established by following penetration from a glass vial into pear leaf discs (Pyrus communis L. cv. Bartlett). Penetration through the upper surface was linear for 96 hr, whereas, through the lower surface there was rapid penetration for 48 hr followed by a reduced rate. Uptake of NAAm was proportional to the concentration applied. Penetration was not influenced by pH of treatment solutions ranging from 3.0 to 7.0. Increasing temperature from 5–35°C caused a marked increase in penetration with Q10 values ranging between 1.59 to 5.46. Increasing light intensity resulted in increased penetration through the lower surface up to about 300 ft-c, but had no effect on NAAm penetration through the upper surface. Penetration was greater through the upper than lower surface in expanding leaves, but the reverse was true when leaves were fully expanded. Tween 20 and Triton B-1956 (0.1%) increased NAAm penetration through the lower surface, but to a lesser degree than X-77 (0.1%). No surfactant studied enhanced penetration through the upper surface. Penetration from microdroplets was similar to that from solutions in glass cylinders until the droplets dried. Droplet drying resulted in an immediate increase in penetration.
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
Shoot tips of ‘Almey’ crabapple [Malus baccata (L.) Borkh. × M. pumila var. niedzwetzkyana (Dieck) Schneid.] and ‘Secke!’ pear (Pyrus communis L.) were cultured on Murashige and Skoog medium supplemented with 2 mg/liter 6-benzylamino purine and agar levels ranging from 0 to 1.2%. The greatest shoot proliferation and shoot growth in ‘Almey’ occurred on medium containing 0.3% agar. Higher agar concentrations decreased both shoot proliferation and shoot growth. Increasing agar concentrations resulted in decreased shoot growth in ‘Seckel’, but shoot proliferation was significantly greater at concentrations of 0.6% and higher as compared to 0.3% or lower. Autoclaving caused an acidification of the medium. The addition of agar reduced media acidification. This pH variation does not explain the effect of agar on shoot proliferation and growth.
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
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.