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  • Author or Editor: Bruce Schaffer x
  • Journal of the American Society for Horticultural Science x
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Abstract

Fruit number and weight per tree were recorded for 3 years for 2 avocado (Persea americana M.) cultivars—‘Booth 8’ and ‘Peterson’. Sample variances were used to determine the number of years per experiment and trees per treatment required to detect differences in yield among treatments at the 5% and 10% significance levels for each cultivar. Yearly variability was greater than variability among trees for both cultivars. Yearly variability for total fruit weight was greater for ‘Booth 8’ than for ‘Peterson’. Fifteen trees per treatment were required to detect a 10–20% difference in total fruit weight per treatment at the 5% level of significance. Each additional tree per treatment decreased the percentage of detectable difference only slightly. Increasing the number of years per experiment decreased the percentage of detectable difference. However, after 3 years, additional years decreased the percentage of detectable difference only slightly for both an alternate- and a nonalternate-bearing cultivar. Efficient designs for avocado yield experiments for the cultivars tested should consist of 10 to 15 trees per treatment and should be conducted for at least 3 years.

Open Access

The effects of atmospheric CO2 enrichment and root restriction on net CO2 assimilation (A), dry mass partitioning, and leaf mineral element concentrations in `Kensington' and `Tommy Atkins' mango (Mangifera indica L.) were investigated. Trees were grown in controlled-environment glasshouse rooms at ambient CO2 concentrations of 350 or 700 μmol·mol-1. At each CO2 concentration, trees were grown in 8-L containers, which restricted root growth, or grown aeroponically in 200-L root mist chambers, which did not restrict root growth. Trees grown in 350 μmol·mol-1 CO2 were more efficient at assimilating CO2 than trees grown in 700 μmol·mol-1 CO2. However, total plant and organ dry mass was generally higher for plants grown at 700 μmol·mol-1 CO2 due to increased A as a result of a greater internal partial pressure of CO2 (Ci) in leaves of plants in the CO2 enriched environment. Root restriction reduced A resulting in decreased organ and plant dry mass. In root-restricted plants, reduced A and dry matter accumulation offset the increases in these variables resulting from atmospheric CO2 enrichment. Atmospheric CO2 enrichment and root restriction did not affect dry mass partitioning. Leaf mineral element concentrations were generally lower for trees grown at the higher ambient CO2 concentration, presumably due to a dilution effect from an increased growth rate.

Free access

Leaf gas exchange of avocado (Persea americana Mill.) and mango (Mangifera indica L.) trees in containers and in an orchard (field-grown trees) was measured over a range of photosynthetic photon fluxes (PPF) and ambient CO2 concentrations (Ca ). Net CO2 assimilation (A) and intercellular partial pressure of CO2 (Ci) were determined for all trees in early autumn (noncold-stressed leaves) when minimum daily temperatures were ≥14 °C, and for field-grown trees in winter (cold-stressed leaves) when minimum daily temperatures were ≤10 °C. Cold-stressed trees of both species had lower maximum CO2 assimilation rates (Amax ), light saturation points (QA ), CO2 saturation points (CaSAT ) and quantum yields than leaves of noncold-stressed, field-grown trees. The ratio of variable to maximum fluorescence (Fv/Fm ) was ≈50% lower for leaves of cold-stressed, field-grown trees than for leaves of nonstressed, field-grown trees, indicating chill-induced photoinhibition of leaves had occurred in winter. The data indicate that chill-induced photoinhibition of A and/or sink limitations caused by root restriction in container-grown trees can limit carbon assimilation in avocado and mango trees.

Free access

Cocoyam was grown in 100%, 50%, or 30% daylight to determine the effect of light intensity on growth characteristics at various stages of plant development. Beginning ≈ 2 months after planting, growth was monitored at three or four monthly intervals. Plants grown in shade had more petiole and leaf lamina growth and extension, as well as increased top: corm plus cormel ratio (dry-weight basis), than plants grown in 100% daylight. Shade-grown plants had a higher leaf area index and specific leaf area than sun-grown plants. Sun-grown plants had a higher net assimilation rate and specific leaf density than shade-grown plants. Linear equations were developed to predict lamina area through measurements of leaf lamina width and length, petiole length, and lamina dry weight.

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Growth and leaf physiology responses of container-grown `Arkin' carambola (Averrhoa carambola L.) trees to long-term exposure of ≈25%, ≈50%, or 100% sunlight were studied in four experiments in Guam and Florida. Shading increased rachis length and leaflet area, and decreased leaflet thickness. Shaded trees also had a more horizontal branch orientation. Shading reduced dark respiration (Rd) and light compensation and saturation points but increased chlorophyll concentration and N-use efficiency. Light-saturated net CO2 assimilation (A) was not affected by developmental light level. Trees in full sun had smaller total leaf area, canopy diameter, and shoot: root ratio and exhibited leaflet movement to avoid direct solar radiation. Also, trees grown in 100% sunlight had a more vertical branch orientation and greater stomatal density than shaded trees. The ratio of variable to maximum fluorescence (Fv/Fm) declined during midday in 100% sunlight trees. This pattern was accompanied by a midday suppression of A in 100% sunlight-grown trees in Guam. `Arkin' carambola trees exposed to ≈25%, ≈50%, or 100% sunlight for up to 39 weeks exhibited physiological and morphological adaptations that resulted in similar growth. These results indicate that carambola efficiently adapts to different developmental light intensities.

Free access

The effect of flooding on container-grown `Tommy Atkins' mango (Mangifera indica L.) trees on two rootstock, and on container-grown seedling `Peach' mango trees, was investigated by evaluating vegetative growth, net gas exchange, and leaf water potential. In general, flooding simultaneously reduced net CO2 assimilation (A) and stomatal conductance (gs) after 2 to 3 days. However, flooding did not affect leaf water potential, shoot extension growth, or shoot dry weight, but stem radial growth and root dry weight were reduced, resulting in larger shoot: root ratios for flooded trees. Mortality of flooded trees ranged from 0% to 45% and was not related to-rootstock scion combination. Hypertrophied lenticels were observed on trees that survived flooding but not on trees that died. The reductions in gas exchange, vegetative growth, and the variable tree mortality indicate that mango is not highly flood-tolerant but appears to possess certain adaptations to flooded soil conditions.

Free access

The effects of shade during leaf development on photosynthetic activity of cocoyam [Xanthosoma sagittifolium (L.) Schott] were investigated. Net gas exchange and N and chlorophyll concentrations were determined for cocoyam leaves growing in 30%, 50%, or 100% sunlight. Net CO2 assimilation (A) and water use efficiency (WUE) were greater for plants grown in 100% sunlight than for plants grown in less sunlight. Substomatal CO2 concentration increased with increased shading. Stomatal conductance (gs) and transpiration (E) did not vary significantly among treatments. Diurnal paterns for A were positively correlated with gs, lamina temperature, relative humidity, and photosynthetic photon flux (PPF). Lamina N concentrations, determined on lamina dry weight and lamina area bases, increased with increased PPF. Shade plants (30% and 50% sunlight) had greater chlorophyll: N ratios (dry-weight basis) and greater lamina area: lamina dry weight ratios than 100% sunlight-grown plants, which indicates increased photosynthate and N allocation to leaves of shade plants and maximization of light interception.

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Net gas exchange and growth were determined for cocoyam [Xanthosoma sagittifolium (L.) Schott] growing in 30%, 50%, and 100% sunlight and fertilized with 0 or 475 mg N/kg nutrient solution. Interactions between N and shade were observed for lamina area per plant, top : corm ratio, corm weight, transpiration (E), stomatal conductance (g,), and lamina N and chlorophyll concentrations. When N treatments were pooled, shade-grown plants (30% and 50% sunlight) had greater lamina areas, lamina and petiole biomass, top: corm (fresh weight) ratios, and corm fresh weights than plants grown in full sunlight. All of these criteria also had higher values for plants that received the N-fertilizer solution (+ N) than for plants that received the N-free solution (- N), when shade treatments were pooled. When N treatments were pooled, 100%-sunlight plants had greater net CO2assimilation (A) rates than shade plants. Water-use efficiency (WUE), A, g., and E for 100%-sunlight-grown plants were higher for + N than for - N plants. For shade plants, however, A and E were similar between N treatments. When N treatments were pooled, shade plants had a greater lamina chlorophyll concentration on a dry-weight basis than 100%-sunlight plants, whereas content on an area basis was similar among shade treatments. Among shade treatments, chlorophyll contents on an area and dry-weight basis were higher for + N than for - N plants. Plants grown in 100% sunlight had higher lamina N concentrations (area and dry-weight bases) than shade plants. The interactions between N and shade showed that cocoyam response to N depends on incident photosynthetic photon fluxes during growth.

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Abstract

Studies were conducted during five winter cropping periods in the Everglades, near Belle Glade, Fla., to determine effects of shade applied at various times throughout the growing period on the growth and yield of lettuce (Lactuca sativa L.). Ancillary studies also were conducted in a greenhouse to determine effects of shade on the light response of lettuce with respect to net CO2 assimilation. The maximum net CO2 assimilation rate (Pn) for lettuce decreased as the irradiance at which the plants were grown decreased. Continuous shading from thinning to harvest reduced crop growth approximately in direct proportion to the reduction in irradiance. Lettuce was most sensitive to reductions in radiation when growth and development were most rapid. These data suggest that lettuce growth from planting through the eight-leaf stage is not affected by small reductions in radiation that might occur in nature, but appears to be largely influenced by temperature. This observation is consistent with data collected during greenhouse experiments that showed that Pn at this early growth stage was low regardless of the shade treatment. Lettuce growth from the eight-leaf through the preheading stage was reduced by low shade levels (75% of prevailing solar radiation). Lettuce yield, however, generally was not affected by low shade levels through the preheading stage. Shading, regardless of the degree, reduced growth and yield during the heading stage of development. Results from greenhouse experiments indicated that the light saturation point of lettuce for photosynthesis during this latter growth stage could reach 800 μmol·s−1·m−2. This light level is higher than prevailing light that often exists during fall and winter growing seasons in southern Florida.

Open Access

`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.

Free access