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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.

Free access

Fruit color is a commercially important quality for sand pear ( Pyrus pyrifolia Nakai). Sand pear can be divided into russet, semi-russet, and green types based on the color of the peel, which is typically composed of a cuticle layer, an epidermis

Free access

Abstract

The age at which flowering began and the stem diameter at various ages were recorded for more than 9,000 pear seedlings planted in orchards at Beltsville. The juvenile period for individual seedlings varied from 2 to 10 years, with a number of seedlings still not flowering after 8 to 10 years. An overall negative correlation of stem diameter with length of the juvenile period was found. Within planting years, this relation was significant only in certain years; within progenies, the relation was significant less than half the time; within a specific cross repeated in different years, the relation varied considerably from year to year. Stem diameter can be successfully used as a preselection criterion for early flowering (short juvenile period) only when these two characteristics are significantly correlated. Since this condition does not exist in most crosses under the growing conditions at Beltsville, stem diameter is not a valid predictor of early flowering.

Open Access

Abstract

‘Flordahome’ pear was released by the University of Florida Agricultural Experiment Station in 1981 and fills the need for a pear with a low-chilling requirement that produces fruit which acquires a buttery, melting texture upon ripening. It is recommended for local use, but should be valuable germplasm for breeding pear cultivars with low chilling and resistance to fireblight and leafspot.

Open Access

Abstract

A computer program was written to allow fast tracing of pedigrees from a computer file of parentage records and which lists the pedigree of any requested individual or progeny in 2 forms. The first output format is a listing adapted to integration with another program which calculates inbreeding coefficients and coefficients of coancestry; the second output format is a family tree.

Open Access

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.

Free 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

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