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Curt R. Rom and Bruce Barritt

The role of spur leaves in bud and fruit development on two spur-type `Delicious' apple strains (Malus domestica Borkh.) and factors affecting spur development were studied. Reducing spur leaf area on vegetative spurs in August reduced the number of spurs that flowered the following year but did not affect flower size. On spurs that did flower, leaf area reduction the previous year did not influence leaf number or area, but the bourse shoot leaf area was reduced. Spur bud diameter, leaf area, size, specific leaf weight (SLW), and leaf dry weight were larger on 2-year-old vegetative spurs than on 1- or 3-year-old spurs. Within each age section of a limb, spur leaf number, area, size, SLW, and bud diameter decreased from the apical to basal positions on the limb. Flower number did not vary within a limb section, but fruit set was lower on the most apical and basal spurs compared to midshoot spurs. Fruit size was largest at the apical end of each limb section and was smallest at basal positions. These relationships were not affected by strain, tree age, or orchard location. Summer pruning at 30 days after bloom tended to increase leaf number, area, size, and spur length compared to unpruned trees or pruning later in the season but did not influence spur bud diameter.

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Terence L. Robinson and Bruce H. Barritt

In unstressed apple seedlings (Malus domestics Borkh.), concentrations of free abscisic acid (ABA) decreased in order from apical stem sections, immature expanding leaves, mature stem sections, and mature leaves. PEG-induced water stress stimulated a 2- to 10-fold increase in free ABA concentrations 1 day after treatment, depending on the amount of stress and the tissue. By the 3rd day of stress, free ABA concentrations were nearly the same as the unstressed treatment and remained low for the remainder of the 21-day stress period. Bound ABA concentrations were an order of magnitude lower than free ABA and were not influenced dramatically by water stress. Shoot growth rate, leaf expansion rate, and leaf emergence rate were reduced by water stress in relation to the severity of the stress; this reduction was associated with the initial increase in ABA. However, there was no increase in shoot or leaf growth rates associated with the decline in ABA concentrations by day 3 as growth rates remained depressed on water-stressed plants throughout the 21-day stress period. Water stress reduced evapotranspiration rate and midshoot leaf water potential (ψW)after 1 day, but leaf osmotic potential (ψS) adjusted more slowly, resulting in a loss of leaf turgor. The reduction in leaf turgor pressure (ψP) was highly correlated with decreased shoot growth rate and increased ABA concentrations on day 1 after treatment. By the 3rd day of water stress, ψP bad recovered even in the most severe treatment, and the recovery of turgor was associated with the drop in ABA concentrations. However, the increase in midshoot ψP and the decline in ABA were not associated with any increase in shoot growth rate. The continued inhibition of shoot growth was probably not related to ABA or turgor pressure of mature leaves but may have been related to turgor pressure in the growing tip.

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Michele Warmund, Bruce Barritt and Karen Schaffer

`Mark' rootstock is a relatively new dwarfing rootstock that induces precocity in apple trees. While `Mark' has desirable horticultural characteristics, it has been difficult to propagate in some areas of the United States. To determine the optimum budding date at two climatically diverse locations, `Jonagold' buds were chip-budded onto `Mark' rootstock on 20 July, 10 Aug., 31 Aug. and 21 Sept. 1989 at Atlas, Illinois and Wenatchee, Washington. Prior to budbreak, unions were sampled from each budding date and the callus, bud plate and rootstock were measured and photographed. Trees budded and grown in Illinois had more callus growth than those budded in Washington. In Illinois, the callus of trees budded on 20 July averaged 3.2 mm., whereas those budded on 21 Sept. averaged 1.0 mm. Trees grown in Washington had 0.4 mm of callus at both budding dates. Callus growth will be correlated with union compatibility and strength in Nov. 1990.

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Bruce H. Barritt and Bonnie J. Schonberg

Vegetative (nonflowering) spur characteristics of `Granny Smith', `Lawspur Rome', and `Redchief Delicious' apples (Malus domestics Borkh.) at two canopy positions (1 and 2 m heights) were examined on eight dates throughout a growing season. `Granny Smith' had a greater leaf number/spur (LNO/SP) at each date than `Rome' and `Delicious'. Area/leaf (LA) and dry weight/leaf (LDW) for `Delicious' were substantially less than for `Granny Smith' and `Rome'. Area/leaf increased rapidly after full bloom (FB) until FB + 21 days for `Delicious', FB + 35 for `Granny Smith', and FB + 56 for `Rome', after which no further changes occurred. For each cultivar, leaf area/spur (LAMP) and leaf dry weight/spur (LDW/SP) increased rapidly from FB until FB + 35 days and then more gradually until FB + 104 days. From FB + 21 onward, `Granny Smith' had greater LA/SP and LDW/SP than `Rome', which, in turn, was greater than for `Delicious'. At harvest (FB + 160), LA/SP was 2.5-fold greater for `Granny Smith' and 1.7-fold greater for `Rome' than for `Delicious'. Cultivar differences for leaf dry weight/leaf area (LDW/LA) were small and canopy position differences were large. LDW/LA declined from 7 days before FB to FB + 7, then gradually increased to the end of the season. Dry weight of the vegetative spur buds (with leaves removed) was lower for `Delicious' than for `Rome' or `Granny Smith'. Total spur dry weight (bud + leaves) was, from FB + 21 onward, greatest for `Granny Smith', intermediate for `Rome', and lowest for `Delicious'.

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Kate Evans, Lisa Brutcher, Bonnie Konishi and Bruce Barritt

Selecting for crispness instrumentally in fruit from apple (Malus ×domestica) breeding programs is notoriously difficult. Most breeders rely on sensory assessment for this important characteristic. Following the 2009 harvest, we used a computerized penetrometer to assess firmness and texture of apple selections from the Washington State University's apple breeding program and 16 standard reference varieties. Data were compared with sensory data from the apple breeding team. In addition to the expected high correlations between the various firmness measures of the computerized penetrometer and the sensory firmness values, our data also show a significant correlation between the computerized penetrometer crispness value and the sensory crispness value, thus demonstrating the benefit from using this equipment rather than the industry standard Magness–Taylor penetrometer.

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Kate M. Evans, Bruce H. Barritt, Bonnie S. Konishi, Lisa J. Brutcher and Carolyn F. Ross

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Michele R. Warmund, Bruce H. Barritt, John M. Brown, Karen L. Schaffer and Byoung R. Jeong

`Jonagold'/Mark apple (Malus domestica Borkh.) trees that were chip-budded in Washington and Illinois on 31 Aug. or 21 Sept. 1989 were sampled in Apr. 1990 to determine if magnetic resonance imaging (MRI) could be used to nondestructively examine vascular continuity or discontinuity between the rootstock and scion. Images could be placed into three categories based on signal intensity: 1) the rootstock, bud shield, and the bud or new scion growth had a high signal intensity; 2) the rootstock and the bud shield had a high signal intensity, but the scion had a low signal intensity; and 3) the rootstock had a high signal intensity, but the bud shield and scion had a low signal intensity. High signal intensity was associated with bound water in live tissue and the establishment of vascular continuity between the rootstock and scion. Azosulfamide staining and destructive sectioning confirmed that vascular continuity was established when the rootstock, bud shield, and scion had a high signal intensity in images, whereas budding failure occurred when the bud shield and/or the scion had a low signal intensity. Additional trees that had wilted or weak scion growth were collected from Illinois in June 1990. Parenchyma tissue was found in the scion adjacent to the bud shield that interrupted the vascular tissue. Poor scion growth on trees from the 21 Sept. budding in Washington may be attributed to insufficient growth of rootstock and/or scion tissues at the union in the fall.

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Bruce H. Barritt, Curt R. Rom, Bonnie J. Konishi and Marc A. Dilley

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Kate M. Evans, Bruce H. Barritt, Bonnie S. Konishi, Marc A. Dilley, Lisa J. Brutcher and Cameron P. Peace

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Kate M. Evans, Bruce H. Barritt, Bonnie S. Konishi, Marc A. Dilley, Lisa J. Brutcher and Cameron P. Peace