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  • Author or Editor: A. Azarenko x
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Remobilization of reserve N and uptake of soil N in winter and spring were assessed in relation to the N status of trees. Ten-year-old `Newtown Pippin' apple trees on M.7A rootstock were fertilized to create moderately vigorous trees, trees with above-ground portions (tops) and roots relatively low in N (L/L), tops high in N and roots low in N (H/L), both tops and roots high in N (H/H), or tops low in N and roots high in N (L/H). Labeled (15N) fertilizers were used to tag the soil and frame and root N pools in the moderately vigorous trees prior to winter and spring remobilization. The level of 15N in the buds and new growth was monitored throughout winter and spring. Nitrogen stored in the aerial part of the tree was first to be remobilized to meet N requirements of the developing buds. Root and soil N reached the flower buds simultaneously. Trees of the L/H treatment transported labeled N upward to the bud as early as 9 Feb., even though average air temperature was close to 7°C, whereas L/L trees did not send any root-15N to the buds until 2.5 later. When trees received an abundance of N in the fall (H/H and L/H), their buds grew faster in the spring and they bloomed earlier compared with L/L and H/L trees. For root to shoot N translocation to start early (in winter), the bud needed to be low in N and the roots had to have adequate N reserves.

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`Lovell' peach seeds were stratified for 0 to 13 weeks at 4C under moist conditions. Heat of metabolism and CO2 evolution, measured by Differential Scanning Calorimetry, increased with stratification time. The calorespirometric ratio increased between 0 and 6 weeks and then remained constant until 13 weeks. Germination percentages paralleled this ratio and reached 80% only after 6 weeks of stratification.

After radicle emergence, seedlings from different stratification treatments were grown for 3 weeks. Increasing stratification time resulted in taller seedling growth. Calorimetrically measured CO2, evolution and the calorespirometric ratio of the apex (one cm) of the seedling increased with longer stratification time. Contrary to the observations of the seeds, metabolic heat rates decreased as stratification time increased. Yet, seedling sustained higher growth rates. These data suggest that the stratification treatment resulted in an improvement in metabolic efficiency.

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Fruit color of `Sensation' and `Max' Red Bartlett pears was analyzed once at mid-season and three times during later stages of fruit maturity with a Minolta CR-200b portable colorimeter. Color measurements were taken on sun-exposed and shaded fruit surfaces in three different growing locations in Oregon. Color change is nearly constant over time during fruit maturation. Both cultivars gained red and yellow on sun-exposed fruit surfaces, and lost red but gained yellow on shaded surfaces. `Sensation' gained red on sun-exposed surfaces to a greater extent than did `Max' at all locations. `Max' gained more yellow and lost more red on shaded surfaces than did `Sensation'. Differences between cultivars and locations were greater on shaded than on sun-exposed fruit surfaces. Greatest gain in both red and yellow on sun-exposed surfaces was associated with the warmest growing location. Visually perceived color change with maturity appears to be due both to loss of red on shaded surfaces and gain of yellow on all surfaces.

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Young bearing spur and standard type apple trees were given either 60 or 120 g actual N as ammonium nitrate depleted in 15N (0.01 atom percentage 15N) in Mar. 1992. The fertilizer was soil applied to 3 single replicate trees for each dose and each tree-type. Spur leaves had similar N contents for both types and both doses. The difference between the two types appeared to be related to differences in the relative number of spur leaves rather in their behavior. The percentage of N from the fertilizer in leaves from spur-type trees was 36% higher than those from standard type trees at low N rates, but 72% higher at high N rates. Doubling the N rate did not increase fruit N concentration in standard trees, but it did increase it in spur-type trees. The latter appeared to be more responsive to N management practices and more susceptible to deleterious effects on fruit quality of high N applications.

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Hazelnuts, (Corylus avellana L.), are wind-pollinated, monoecious, mostly dichogamous, and self-incompatible. About 90% of the cultivars studied are protandrous. Anthesis of the pistillate flower is temperature-dependent and occurs December through February, peaking in January. Stigmatic surfaces may remain receptive for up to 3 months. Four to 5 months separate pollination and fertilization of the ovule; the latter usually occurring between mid-May and the end of June in Oregon. A 10% pollinizer density has been the standard, with a recommended distance of 66 ft (20 m) or less between the main cultivar and the nearest pollinizer. Two or three different pollinizer cultivars, with different times of pollen shed, are recommended. The Oregon hazelnut industry is presently combating the fungal disease, eastern filbert blight, caused by Anisogramma anomala (Peck). Current management recommendations suggest reducing risk of infection are to reduce the most susceptible pollinizer cultivars to a density 5%, then gradually replace those left with immune or more resistant genotypes.

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Seven-year-old `Royal Ann' cherry trees were given a total of 244 g of actual N as ammonium nitrate depleted in 15N (0.01 atom % 15N) either in March (M), June (J), or both in March and June (Split). The fertilizer was soil-applied to eight single-replicate trees. The following August, leaves from the trees that had the M treatment had 15.3% of their N from the fertilizer compared to 9.6% for the split treatment. Trees that had a J application were not different from the control trees. Even though cherry trees are physiologically active during the late summer months, little N is translocated to the leaves once the crop is fully developed. The percentage of newly acquired N in the fruit is similar to that in the spur leaves. Leaves from the different treatments had similar N contents; therefore, labeled N is the tool of choice to assess the performance of different fertilization practices.

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Current N fertilization practices, where high spring applications are utilized, may lead to excessive vegetative growth. However, high rates may not be required to maximize fruit yield and quality. Therefore, alternative strategies to minimize shoot growth while still providing the N needs of the tree were investigated. Mature `Comice' and `Bosc' pear trees were given one of the following treatments: a spring soil (SS) application of NH4NO3 nitrate at 112.5 kg/ha rate, a similar application in the fall after harvest (FS), a fall foliar (FF) spray of a 7.5% urea solution after harvest (FF), or no N (Control). Trees that received a FF application had the same leaf and fruit N content as control trees, but they yielded more fruit The SS application gave more vigorous trees than FF application. Yield, however, was not different.

A 15N enriched urea solution was applied at harvest as either a foliar spray, soil application, or combination of both treatments to mature `Comice' trees. Flower buds from trees that previously received a foliar treatment had 37% of their N derived from the foliar N application. No labeled N was detected in buds from the soil treatment These results indicate that vegetative and reproductive N requirements of fruit trees may be managed separately.

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Although genetic studies have demonstrated that hazelnut (Corylus avellana L.) possesses sporophytic self-incompatibility, the pollen of this woody species is bicellular and potentially long-lived, a feature more typical of gametophytic self-incompatibility. Reports of the behavior of incompatible pollen on stigmatic surfaces conflict. Our objective was to better characterize pollen-stigma interactions in this species. Female flowers were left unpollinated, or pollinated with compatible or incompatible pollen, fixed at time intervals up to 24 hrs., and then examined using scanning electron microscopy. The stigmatic surface was of the “dry” type. Emerged styles were completely covered with elongate, rounded stigmatic papillae. Compatible pollen hydrated within 2 hrs. of pollination, and started to germinate after 4 hrs. Penetration of the stigma was intracellular in some cases. Although compatible pollen also hydrated within 2 hrs., many grains never germinated. When germination did occur, pollen tube emergence was delayed until at least 8 hrs. Incompatible pollen tubes were distorted and did not penetrate the stigmatic surface.

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Mature `Comice' pear trees were given 4 l of a 5% urea solution enriched in 15N (0.6 atom percentage 15N) either as a soil application (S), a foliar application with the ground covered to prevent soil contamination (F), or as a foliar application with the ground uncovered (F+S). The treatments were applied in mid-October 1990 to 6 single replicate trees each. The following spring, flower buds from trees that received either F or F+S had 38% of their N from the applied fertilizer. Trees from the S treatment had no label in their buds. In 1991, half of the trees were removed and their components analyzed for total and isotopical N to estimate N recovery. The relative enrichment of different tree parts in 15N was similar for the three modes of application. This suggests that unlike fall foliar applied N, reserve N is more uniformly distributed within the tree. N recovery depended more on tree biomass (r2 = 0.89, P = 0.001) than on the mode of fertilizer application. There was also a positive correlation between tree vigor and fruit N content.

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`Gala' apples were harvested at weekly intervals for 6 weeks, refrigerated at 0C, and evaluated by a consumer panel monthly over a 6 month period for overall liking, firmness, sweetness, tartness and flavor intensities. Firmness, titratable acidity and soluble solids concentration were also measured. Initial analysis of sensory data revealed multicollinearity for overall liking, sweetness, and flavor. The five descriptors explained 75 % of the dataset variation in the first two factors. An orthogonal rotation separated overall liking, flavor and sweetness, and firmness and tartness into two independent factors. The distribution of mean scores along these independent factors showed that panelists could perceive changes due to ripening and maturation. The multivariate factor analysis was better than univariate ANOVA at illustrating how apple maturity stages were apparent to untrained panelists. Firmness was the only instrumental variable correlated to firmness ratings in the sensory tests. None of the analytical measurements could explain overall liking.

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