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Richard J. Campbell and Richard Marini

Light saturation curves were developed for detached, non-fruiting `Stayman' and `Delicious' spur leaves from interior, middle, and peripheral canopy positions throughout the season in 1989 and 1990, respectively. Be inning at bloom, measurements were made every 2 weeks for the first 8 weeks, and monthly thereafter. SLW was calculated simultaneously with photosynthetic measurements. MacArthur-Wilson saturation equations were used with non-linear regression to fit the saturation curves and SLW data, and curves were compared using indicator variables. Even at bloom, saturation curves and SLW differed among positions. The peripheral position bad a greater saturation point and equilibrium rate throughout the season, and the interior and middle positions were equivalent by about 6 weeks after bloom.

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Richard J. Campbell and Richard Marini

Light saturation curves were developed for detached, non-fruiting `Stayman' and `Delicious' spur leaves from interior, middle, and peripheral canopy positions throughout the season in 1989 and 1990, respectively. Be inning at bloom, measurements were made every 2 weeks for the first 8 weeks, and monthly thereafter. SLW was calculated simultaneously with photosynthetic measurements. MacArthur-Wilson saturation equations were used with non-linear regression to fit the saturation curves and SLW data, and curves were compared using indicator variables. Even at bloom, saturation curves and SLW differed among positions. The peripheral position bad a greater saturation point and equilibrium rate throughout the season, and the interior and middle positions were equivalent by about 6 weeks after bloom.

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Richard J. Campbell and Richard P. Marini

Integrative measurements of photosynthetically active radiation (PAR) were made at 30 `Delicious' canopy positions throughout the season to characterize the canopy light environment. Instantaneous measurements (IM) of PAR were made at the same positions with a quantum sensor on clear and overcast days and correlated with integrated seasonal PAR. Hourly (1100, 1200, 1300, and 1400 hrs) IM made on clear days were influenced b sunflecks and had variable relationships with integrated values (R2 = 0.52-0.90). This was improved by using the average of the four IM measured during the day (R2 = 0.92). Hourly IM on overcast days were consistent and highly correlated to integrated values (R2 = 0.97). IM from overcast days were reliable predictors of seasonal PAR and could be used to characterize the canopy light environment.

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Richard J. Campbell and Richard P. Marini

The interaction of N fertilization and European red mite (ERM) [Panonychus ulmi (Koch)] feeding on the physiology of greenhouse-grown `Imperial Delicious' apple (Malus domestica Borkh.) leaves was evaluated. Visual damage was noticeable with 75 mite days (MD) and was consistently greatest on the low-N leaves. Net photosynthesis (Pn) was decreased by mite feeding in all N treatments. However, with equal MD, the high-N treatment retained higher Pn than the low- or medium-N treatments. Transpiration, dark respiration, leaf N, and total chlorophyll increased with N and were reduced by mite feeding. Mite feeding increased dark transpiration at all N levels. Relative water content was unaffected by N and was reduced by mite feeding. Specific leaf weight increased with N and MD.

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Richard J. Campbell and Richard P. Marini

Photosynthetic photon flux density (PPFD), measured at various canopy positions throughout the growing season in 1989 and 1990, was used to explain variation in fruit characteristics of `Delicious' apples (Malus domestica Borkh.) harvested from these positions at 135, 145, 155, and 165 days after full bloom (DAFB). Hours above an average PPFD threshold of 250 μmol·m-2·s-1 (HR250) explained an average of only 2% more variation in fruit characteristics than other PPFD threshold levels or total cumulative photosynthetic photon density (PPD) in each year. Percent of red surface had a positive linear relationship with HR250 on all harvest dates in both years; intercepts increased on each successive harvest. The slopes and R 2 were highest at 135 DAFB and decreased on each successive harvest. Intensity of red pigmentation and soluble solids concentration also increased linearly with HR250, with equivalent slopes and increasing intercepts on each successive harvest. Fruit weight, flesh firmness, length: diameter ratio, and starch index were not consistently affected by any measure of canopy light levels. Except for intensity of redness, relationships developed between fruit characteristics and cumulative late-season PPD during the final 10 weeks before harvest (CPPDLS) had trends similar to the models for HR250 for all harvests in both years. Models developed with instantaneous light measurements were similar to those developed with the more detailed cumulative light measurements.

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Richard J. Campbell and Richard P. Marini

Percent instantaneous incident photosynthetic photon flux density (%INPPFD) was measured within an apple (Malus domestica Borkh.) canopy for various sky conditions and used to predict the percent cumulative incident photosynthetic photon density (PPD) for the last 10 weeks of the growing season (%CPPDLS) and the total growing season (%CPPDTS). Instantaneous measurements from overcast conditions were superior to measurements from clear or hazy conditions for the prediction of %CPPDLS in 1989 and 1990. A one-to-one relationship between %INPPFD and %CPPDLS was found for overcast conditions in both years, even though there was an 11% difference in total cumulative PPD between the years. The models had good predictive accuracy, with prediction coefficients of determination (R 2 Pred) >0.83 in both years (n = 30). %lNPPFD from overcast conditions also yielded accurate predictive models for %CPPDTS (R > 0.84, n = 30), which differed from the models for %CPPDLS. Predictive models (for both %CPPDLS and %CPPDTS) from %lNPPFD made before the canopy was fully developed differed from the models developed after canopy development was complete. The models still had good predictive accuracy, with R 2 Pred >0.76 (n = 30). Predictive models developed for cloudless conditions had inferior predictive accuracy (R 2 Pred = 0.49 to 0.80, n = 30) compared to models for overcast conditions. R 2 Pred were higher for hazy than for clear conditions. Time of day (1000 to 1400 hr) had no consistent effect on the development of predictive models for any weather condition. The most reliable models resulted from the average of several measurements within a day, particularly for cloudless conditions.

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Richard J. Campbell, Richard D. Fell and Richard P. Marini

Flowering spurs located at interior and exterior canopy positions of `Stay-man' and `Delicious' apple (Malus domestics Borkh.) trees were girdled and/or defoliated to determine the influence on nectar production and composition. Nectar volume was less at exterior than interior canopy positions for `Delicious', but not for `Stayman'. Girdling suppressed nectar production by 92% and reduced the sugar concentration of the remaining nectar. Defoliation of nongirdled spurs had no effect on nectar sugar concentration, but defoliation of girdled spurs reduced nectar sugar concentration by 24%. Relative percentages of sucrose, glucose, and fructose, and the sucrose: hexose ratio were unaffected by any treatment. Nectar production of nongirdled spurs did not depend on the presence of spur leaves.

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Richard J. Campbell, Randolph L. Grayson and Richard P. Marini

Scanning and transmission electron microscopy were used to investigate damage to strawberry (Fragaria ×ananassa Duch.) leaves caused by twospotted spider mite (Tetranychus urticae Koch.). Mites damaged epidermal cells on the lower leaf surface, but did not damage major vascular elements of the leaf. Mite-damaged spongy and palisade parenchyma cells had coagulated protoplasts, with some cells devoid of cellular contents. Mesophyll cells adjacent to damaged regions showed no ultrastructural distortion or disruption of chloroplasts.

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Richard J. Campbell, Kendrick N. Mobley and Richard P. Marini

The effect of growing conditions on the physiological damage caused by mite feeding was evaluated. Control and twospotted spider mite (Tetranychus urticae Koch)-infested `Imperial Delicious' apple (Malus domestica Borkh.) and `Redhaven' peach [Prunus persica L. (Batsch.)] trees were grown under winter and summer greenhouse conditions. Mite feeding reduced net photosynthesis (Pn) of apple in both winter and summer, with equivalent regression models (Pn on mite days). Total chlorophyll content (TCHL) was decreased, and specific leaf weight (SLW) was increased by mite feeding in both winter and summer. In peach, Pn was also reduced by mite feeding, with equivalent regression models in winter and summer. SLW was unaffected, and TCHL was reduced by mite feeding in both seasons. Transpiration (Tr) of apple and peach was inconsistently affected by mites in winter and summer. In another experiment, control and European red mite (ERM) [Panonychus ulmi (Koch)]-infested `Red-chief Delicious' apple trees were grown in the summer under both greenhouse and field conditions. ERM feeding negatively affected Pn in both the greenhouse and the field, but reductions were less under field conditions. Mites reduced Tr 28% in the greenhouse and 12% in the field. TCHL, SLW, and leaf N content (LFN) were reduced by 16%, 24%, and 26%, respectively, in the greenhouse. In the field, TCHL was not significantly reduced, and SLW and LFN were reduced by 6% and 13%, respectively.

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Richard J. Campbell, Richard P. Marini and Jeffrey B. Birch

Light response curves for gas exchange characteristics were developed for spur leaves of `Stayman' and `Delicious' apple (Malus domestica Borkh.) from interior, intermediate, and exterior canopy positions throughout the season. At full bloom (FB), before full leaf expansion, exterior leaves had higher maximum rates of net photosynthesis (Pn), and a statistically different Pn light response curve than the interior leaves. Intermediate leaves had intermediate Pn rates and light response curves. Pn light response curves for all three `Delicious' canopy positions differed from each other from FB + 6 weeks until the end of the season. Interior leaves had maximum Pn rates of only 50% to 60% of those for the exterior leaves from FB + 10 weeks until the end of the season. Light saturation levels were higher for the exterior leaves than for interior or intermediate leaves. Exterior leaves had a tendency throughout the season for higher quantum efficiency of Pn at subsaturating light levels than interior or intermediate leaves. Stomatal conductance was higher for the exterior than the interior or intermediate leaves of `Delicious' on all dates. Water-use efficiency was equivalent among all leaves. Exterior leaves had higher specific leaf weight, dark respiration rates, and incident light levels on all dates than interior or intermediate leaves.