Bruce Schaffer

The avocado: botany, production and uses.

History and distribution of avocado botany and taxonomy climate and soil, ecophysiology genetics, breeding and biotechnology cultivars and rootstocks, propagation flowering, pollination, fruit set and development orchard design and management pests and diseases harvesting, postharvest technology.

Cadmium, Copper, Lead, Nickel and Zinc Concentrations In Tomato and Squash Grown In MSW Compost-amended Calcareous Soil

Vegetables grown in compost containing cadmium, copper, lead, nickel, and zinc in low concentrations should be safe for human consumption unless the crop acts as a bioaccumulator. The effects of amending soil with compost products made from municipal solid waste (MSW) on cadmium, copper, lead, nickel, and zinc concentrations in tomato and squash were investigated. For each crop, three inorganic nitrogen treatments were applied 1) 72, 2) 143, or 221 kg N ha−1 for tomato 1991 and 1992 and 40, 80, or 120 kg N. ha−1 for squash 1991 and 1992. Each fertilizer treatment was subdivided into three MSW compost treatments. For the compost treatments, the following products were incorporated into calcareous limestone soil at rates suggested by the manufacturers: 1) Agrisoil compost, a processed MSW, at 48 t. ha−1, 2) Eweson co-composted MSW and biosolids at 24 t. ha−1, or 3) no MSW compost. The experimental design, strip-split plot with four replications was conducted in 1991 and repeated in 1992. Compost treatments ...

Citrus leafminer (Lepidoptera: Gracillariidae) in lime: Assessment of leaf damage and effects on photosynthesis

Abstract Studies were conducted to quantify leaf area damage to ‘Tahiti’ lime by citrus leafminer (CLM) (Phyllocnistis citrella Stainton) and to relate leaf damage to larval density and the length of time mining per leaf. Visual estimates of leaf damage were similar among five evaluators and were positively correlated with image analysis determinations. The number of CLM larvae per leaf and the number of days of mining were positively correlated with visual estimates of leaf damage and negatively correlated with net photosynthesis. Leaf damage by CLM was negatively correlated with net photosynthesis of potted trees and trees in an orchard. The data indicate that visual estimation is an accurate and rapid technique to assess leaf damage by CLM, and that leaf area damage and reductions in net photosynthesis due to CLM are related to the number of larvae per leaf as well as to mining duration.

Leaf gas exchange, chlorophyll fluorescence and pigment indexes of Eugenia uniflora L. in response to changes in light intensity and soil flooding

The interactive effects of changing light intensity and soil flooding on the photosynthetic performance of Eugenia uniflora L. (Myrtaceae) seedlings in containers were examined. Two hypotheses were tested: (i) the photosynthetic apparatus of shade-adapted leaves can be rapidly acclimated to high light after transfer from shade to full sun, and (ii) photosynthetic acclimation to changing light intensity may be influenced by soil flooding. Seedlings cultivated in a shade house (40% of full sun, approximately 12 mol m(-)(2) day(-)(1)) for 6 months were transferred to full sun (20-40 mol m(-2) day(-1)) or shade (30% of full sun, approximately 8 mol m(-2) day(-1)) and subjected to soil flooding for 23 days or not flooded. Chlorophyll content index (CCI), chlorophyll fluorescence, leaf weight per area (LWA), photosynthetic light-response curves and leaf reflectance indexes were measured during soil flooding and after plants were unflooded. The CCI values increased throughout the experiment in leaves of shaded plants and decreased in leaves of plants transferred to full sun. There were no significant interactions between light intensity and flooding treatments for most of the variables analyzed, with the exception of Fv/Fm 22 days after plants were flooded and 5 days after flooded plants were unflooded. The light environment significantly affected LWA, and light environment and soil flooding significantly affected the light-saturated gross CO(2) assimilation rate expressed on area and dry weight bases (A(max-area) and A(max-wt), respectively), stomatal conductance of water vapor (g(ssat)) and intrinsic water use efficiency (A/g(s)). Five days after flooded plants were unflooded, the normalized difference vegetation index (NDVI) and the scaled photochemical reflectance index (sPRI) were significantly higher in shade than in sun leaves. Thirty days after transferring plants from the shade house to the light treatment, LWA was 30% higher in sun than in shade leaves, and A(max)(-area) and g(ssat) were 59% and 99% higher, respectively, in shade than in sun leaves. Changes in CCI, NDVI and sPRI in leaves of E. uniflora seedlings transferred from shade to full sun appear to be associated with changes in pigment composition and protective mechanisms against excess light.

Citrus Leafminer (Lepidoptera: Gracillariidae) Density: Effect on Yield of ‘Tahiti’ Lime

Abstract The relationship between damage by citrus leafminer , Phyllocnistis citrella Stainton, and ‘Tahiti’ lime yield were investigated in a 15-yr-old and a 5-yr-old lime orchard. Citrus leafminer population densities were controlled by insecticide applications of abamectin plus FC 435 oil, abamectin plus FC435 oil plus imidacloprid, and methomyl. The control was not treated. To ensure adequate citrus leafminer densities, adult citrus leafminer were periodically released in the experimental plots during fall and winter. For the 15-yr-old trees, the least amount of leaf area damage occurred in the abamectin plus FC 435 oil plus imidacloprid (1.9%) and the abamectin plus FC435 oil (2.3%) treatments compared with the control treatment (10–21%). In the 5-yr-old orchard, the least amount of leaf area damaged occurred in the abamectin plus FC 435 oil plus imidacloprid (0.4%) and the imidacloprid (0.1%) treatments compared with the control (20.85%). The percentage of leaf area damaged was linearly correlated with the average number of mines per leaf, average mine days, and cumulative mine days in both orchards. In both orchards, the percentage of leaf area damaged and cumulative mine days was linearly correlated with the number of fruit per tree and total fruit weight per tree. Calculating the economic injury levels indicated that 16–23% and 18–85% of leaf area damaged caused significant yield reductions in 15-yr-old and 5-yr-old trees, respectively.

Electrical signaling, stomatal conductance, ABA and Ethylene content in avocado trees in response to root hypoxia

Avocado (Persea americana Mill.) trees are among the most sensitive of fruit tree species to root hypoxia as a result of flooded or poorly drained soil. Similar to drought stress, an early physiological response to root hypoxia in avocado is a reduction of stomatal conductance. It has been previously determined in avocado trees that an extracellular electrical signal between the base of stem and leaves is produced and related to reductions in stomatal conductance in response to drought stress. The current study was designed to determine if changes in the extracellular electrical potential between the base of the stem and leaves in avocado trees could also be detected in response to short-term (min) or long-term (days) root hypoxia, and if these signals could be related to stomatal conductance (gs), root and leaf ABA and ACC concentrations, ethylene emission from leaves and leaf abscission. In contrast to previous observations for drought-stressed trees, short-term or long-term root hypoxia did not stimulate an electrical potential difference between the base of the stem and leaves. Short-term hypoxia did not result in a significant decrease in gs compared with plants in the control treatment, and no differences in ABA concentration were found between plants subjected to hypoxia and control plants. Long-term hypoxia in the root zone resulted in a significant decrease in gs, increased leaf ethylene and increased leaf abscission. The results indicate that for avocado trees exposed to root hypoxia, electrical signals do not appear to be the primary root-to-shoot communication mechanism involved in signaling for stomatal closure as a result of hypoxia in the root zone.

Polyamines in adventitious and somatic embryogenesis in mango (Mangifera indica L.)

Summary Polyamines were measured in nucelli, embryogenic and non-embryogenic nucellar calli, adventitious nucellar embryos, nucellar somatic embryos and zygotic embryos of monoembryonic and polyembryonic mango types. In vitro conditions caused a 50-fold increase in putrescine concentration in non-embryogenic nucellar callus of monoembryonic mango. Polyamine concentrations were greater in nucellar calli from monoembryonic mangos than from polyembryonic mangos, and were greater in non-embryogenic than in embryogenic calli. Polyamines added to the culture medium generally had no effect on callus initiation or somatic embryogenesis from nucellar explants except spermidine, which suppressed callus formation from the monoembryonic «Keitt». Callus induction was enhanced by the presence of 2,4-D, although somatic embryogenesis was not affected by this phytohormone.

Use of a SPAD meter to estimate chlorophyll content in Eugenia uniflora L. leaves as affected by contrasting light environments and soil flooding

In three separate experiments, the effectiveness of a SPAD-502 portable chlorophyll (Chl) meter was evaluated for estimating Chl content in leaves of Eugenia uniflora seedlings in different light environments and subjected to soil flooding. In the first experiment, plants were grown in partial or full sunlight. In the second experiment plants were grown in full sunlight for six months and then transferred to partial sunlight or kept in full sunlight. In the third experiment plants were grown in a shade house (40% of full sunlight) for six months and then transferred to partial shade (25–30% of full sunlight) or full sunlight. In each experiment, plants in each light environment were either flooded or not flooded. Non-linear regression models were used to relate SPAD values to leaf Chl content using a combination of the data obtained from all three experiments. There were no significant effects of flooding treatments or interactions between light and flooding treatments on any variable analyzed. Light environment significantly affected SPAD values, chlorophyll a (Chl a), chlorophyll b (Chl b), and total chlorophyll [Chl (a+b)] contents in Experiment I (p≤0.01) and Experiment III (p≤0.05). The relationships between SPAD values and Chl contents were very similar among the three experiments and did not appear to be influenced by light or flooding treatments. There were high positive exponential relationships between SPAD values and Chl (a+b), Chl a, and Chl b contents.

Characterization of soil-water retention of a very gravelly loam soil varied with determination method

Soil-water characteristic curves were determined for Krome calcareous very gravelly loam soil in the laboratory and in situ in an orchard. In the laboratory, soil-water retention was determined with a pressure plate and pressure Tempe cells for soil collected from vegetable fields. In the orchard, soil-water suction measured with tensiometers was compared to volumetric soil-water content (&thgr;) determined with neutron or multi-sensor capacitance probes. Before field measurements, calibration equations were developed for neutron and multi-sensor capacitance probes for this soil. Krome calcareous gravelly loam soil was found to have two distinct solid fractions with 51% coarse particles and 49% loam particles that resulted in a peculiar soil-moisture retention pattern. Two soil-moisture retention regions were identified, each corresponding to one of the soil solid fractions. As shown by a large number of observations, rapid drainage occurs in the gravel fraction corresponding to soil-water suction less than 75 cm. In an orchard, suction values rarely exceeded 125 cm even when there was no rainfall and irrigation was withheld for three weeks. In the orchard, &thgr; measured with a capacitance probe was considerably more variable and less correlated with soil suction than &thgr; measured with a neutron probe. In very gravelly loam soils such as Krome, results from capacitance sensors may be too variable and inconsistent for reliable monitoring of soil-water content.

Inoculation with arbuscular mycorrhizal fungi enhances growth of Litchi chinensis Sonn. trees after propagation by air-layering

Lychee (Litchi chinensis Sonn.) is typically propagated by air-layering mature tree branches which are potted in fertilized, soil-free media after cutting. The size of these branches, low phosphorus retention by pot substrates, and fertilization all might combine to preclude benefits of arbuscular mycorrhizas to lychee. In order to examine the potential of lychee to benefit from arbuscular mycorrhizas in an agriculturally realistic context, lychee air-layers were grown for 469 days in ca. 95-l pots of soil-free substrate inoculated with field-collected arbuscular mycorrhizal roots or not at two different levels of phosphorus fertilization. High phosphorus fertilization (a one-time addition of ca. 1.32 g l−1 slow-release triple-superphosphate) had no detectable effects on mycorrhiza formation, lychee survival, net CO2 assimilation, or growth. Inoculation with indigenous South Florida arbuscular mycorrhizal fungi improved leaflet expansion as early as 120 days after inoculation, and subsequently enhanced height growth and leaf production but did not affect stem diameter growth, net CO2 assimilation, or survival. At harvest, although mycorrhizal colonization was low (average 7.4% colonized root length), mycorrhizal plants had 39% higher above-ground dry weight than control plants. Below-ground dry weights did not differ, but inoculated plants had lower fine root to leaf dry weight ratios than control plants. Leaflets of inoculated plants had higher concentrations of P, K, Cu, and Zn, and lower concentrations of Ca, Mg, and Mn than those of control plants, but total Kjeldahl nitrogen and iron concentrations did not differ significantly 10 months after inoculation. Mycorrhiza enhancement of lychee growth occurred even though phosphorus clearly was not limiting for growth. Our observations suggest that in this soil-free medium, arbuscular mycorrhizal fungus enhancement of copper and iron nutrition improved lychee growth.