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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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Pear scab caused by Venturianashicolais one of the most important diseases of oriental pear. Breeding a variety resistant to scab can be improved through marker-assisted selection (MAS). Bulked segregant analysis (BSA) and amplified fragment length polymorphic (AFLP) analysis were performed to identify DNA markers linked to the scab-resistant gene (Vn) using a population from a cross between PS2-93-3-98 (resistant parent) and Yali (susceptible parent). A total of 480 EcoR I/MseI primer combinations were used to identify markers specific to PS2-93-3-98 and resistant pool. Three AFLP markers linked to Vn, E-AGT/M-CCA245, E-ATT/M-CCG300, and E-GGT/M-TCT225, were selected. Linkage analysis between the selected markers and Vn locus was conducted with 51 individual plants. The selected markers, E-AGT/M-CCA245, E-ATT/M-CCG300, and E-GGT/M-TCT225, were located at 3.9, 3.8, and 1.2 cm away from Vn, respectively. For practical application, we are currently converting selected markers to simple PCR-based markers. The markers could be used to increase selection efficiency in pear-breeding programs for scab resistance.

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Abstract

A survey of 18 pear species using the scanning electron microscope showed considerable variability in the size, shape and surface topography of both anthers and pollen grains. The size, shape and surface topography of anthers or anther cells did not vary directly with the size, shape and topography of pollen from the same species. The degree of similarity of individual features among species did not seem to coincide with their geographic distribution. However, the combination of pollen and anther features was unique for each species, indicating their value for taxonomic identification.

Open Access

Abstract

We rated 86 pear cultivars and selections for their grit content on an inverted scale of 9 to 1. Of these, 64% were rated 6, which we consider to be commercially acceptable, or higher. More than 2000 seedlings from 186 crosses with these cultivars and selections as parents were grouped on the basis of their parental mean grit rating. In each case where the parental mean was 5.0 or higher, the progeny mean was lower than the parental mean. Conversely, in each case where the parental mean was 4.5 or lower, the progeny mean was higher than the parental mean. Where the parental mean was 7.5 or higher, 84% of the seedlings had grit ratings of 6 or higher. Conversely, where the parental mean was 4.0 or lower, only 26% of the seedlings had grit ratings of 6 or higher. We can thus predict the percentage of seedlings in a progeny that can be expected to have a commercially acceptable grit rating. Grit cell development appears to be inherited quantitatively at a minimum of 4 loci. The genes appear to be additive in action rather than dominant.

Open Access

Abstract

At any stage of the ripeness of ‘Bartlett’ pear fruits, subsequent ripening was inhibited if the fruits were warmed to 40°C. Both production of, and sensitivity to, ethylene (C2H4) were almost totally suppressed. Even at 30°C, C2H4 production was greatly reduced in both early- and late-season fruit. Unless treated with C2H4, early-season fruit failed to ripen at 30°C although late-season fruit ripened spontaneously, presumably because of high internal concentrations of the gas. In both cases ripening was characterized by a watery breakdown of the floral end of the fruit.

At 40° and 50°C, respiratory rates declined progressively unless the fruits were treated with C2H4, whereupon a stimulation occurred although ripening was unaffected.

Gas exchange was not limiting at temperatures as high as 50°C, even when the ends of the fruits were sealed with paraffin wax. Maximum modification of the internal atmosphere of any individual fruit resulted in 15.7% O2 and 7.2% CO2. Ripening of fruits held at 20°C in that atmosphere was delayed about 3 days, presumably via mild competitive CO2 inhibition of C2H4 action.

We conclude that failure of ‘Bartlett’ pears to ripen at 40°C results from lack of C2H4 production and loss of sensitivity to the gas. The mechanisms are unknown.

Open Access

Abstract

The wide variability in ripeness frequent in ‘Bartlett’ pears at processing can be reduced by prompt, rapid, and uniform warming. Fruits with an initial core temperature of 0.25°C were uniformly warmed to 20° ± 2°C in 30 minutes when air at a rate of 2079 cc/sec/Kg (2 cfm/lb) of product was pulled over them by a modified forced-air tunnel bin warmer operating in a room with an air temperature of 45°C. These fruits ripened in precisely 4 days, with firmness differing between individual fruits by no more than 1.13 Kg (2.5 lb). Conversely, pears warmed at slower rates simulating current cannery procedures varied by as much as a week in time to ripeness.

Open Access

Abstract

Resistance to pear psylla (Psylla pyricola Forester) in trees having P. ussuriensis Maxim. (I-65) lineage is shown to be present, genetically transmissable, and not linked with the poor horticultural characteristics of small size, poor tree vigor, grittiness of the fruit, and poor quality. Since both susceptible and resistant backcross seedlings were originally selected for resistance to fire blight, it appears that fire blight resistance and pear psylla resistance are inherited independently.

Open Access
Authors: and

Many trials to supply germanium to fruit have been carried out since tests have confirmed germanium's role as a medical substance. Supplying germanium in orchards by soil and foliar application was not effective because of loss from rainfall. In order to increase germanium absorption by fruit, this study carried out tree trunk injections during the growing season. Two types of germanium, GeO (inorganic type) and Ge-132 (organic type), in concentrations of 5, 10, 25, and 50 mg·L–1 were supplied to `Niitaka' pear trees by trunk injection (1.5 L/tree), four times at 15-day intervals from June 2004. The treatment with 50 mg·L–1 GeO showed decreased fruit weight, but 50 mg·L–1 Ge-132 showed no difference to the control and other treatments. Fruit lenticels were increased in size by all of the Ge treatments in comparison to control fruit. Soluble solids as well as Hunter value `a' of the fruits of all Ge treatments were higher than that of the control. Flesh browning after peeling the fruit was delayed by the germanium treatment, and polyphenoloxidase (PPO) activities were lowered. Postharvest potentials were maintained at high levels for fruit firmness, physiological disorders, and decayed fruit during cold storage at 0 to 1 °C for 2 months.

Free access

Fruit maturity was hastened by 5 to 7 days with the application of GA3 and GA4+7 paste on petioles 4 weeks after full bloom and 3 to 4 days with the spray of both ethephon (1,000ppm) and dichroprop(30ppm) 62 days after full bloom. Fruit size was significantly increased by GAs treatment but there was a tendency of decreasing fruit size by ethephon and dichroprop treatments. Excessive softening of flesh was found in ethephon or dichroprop treated fruits while no significant difference was observed with GAs treatment until maturity. Calcium acetate partially prevented the enhancement of fruit softening and fruit size decrease induced by ethephon and dichroprop. Other fruit qualities such as soluble solids contents were not affected by the addition of calcium acetate except some delay in fruit maturity.

Free access

The aim of this study was to investigate the roles of spur characteristics and carbon partitioning in regulating cultivar differences in fruit size of two late-maturing japanese pear cultivars, `Atago' and `Shinkou'. The study of spur characteristics showed that the two cultivars displayed different patterns in leaf development, flower characteristics, fruit growth, and shoot type. In contrast to `Atago' with dramatically larger fruit, `Shinkou' is a heavily spurred cultivar with a higher total leaf area and leaf number per spur early in fruit growth, less vegetative shoots, and smaller fruit but larger core. No significant differences were obtained in specific leaf weight, leaf thickness, chlorophyll content, and net photosynthesis of mature leaves, and seed number per fruit between the two cultivars. The results of trace experiment with 13C revealed that on a spur basis, there were no significant differences in the amount of 13C assimilate produced by spur leaves on each labeling date except at 190 days after anthesis, however, there were highly significant differences in the amount of 13C allocated to fruit between cultivars. Moreover, a higher amount of 13C assimilates was allocated to `Atago' flesh (or fruit) than that in `Shinkou'. Analysis of relative sink strength (RSS) indicates that the sink strength of fruit was dominant over those of other organs in the spur measured in both cultivars except at the early stage of fruit growth. `Atago' exhibited a greater RSS of fruit and lower losses of 13C for respiration and export than `Shinkou'. These results suggest that the movement of photosynthates into the fruit was determined by sink strength of the fruit rather than the source strength in the two cultivars.

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