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  • Author or Editor: Carl Sams x
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Isothiocyanates are volatile chemicals produced by damaged tissues of Brassica species. Allyl isothiocyanate (AITC), the predominant isothiocyanate in Indian mustard (B. juncea), has been shown to control pest in laboratory and field experiments. We investigated the effectiveness of AITC against the germination of sclerotia of Sclerotium rolfsii Saccardo, a common soilborne pathogen of tomato. Sclerotium rolfsii was cultured on PDA from a field isolate. Mature sclerotia were collected and placed in polyester mesh bags. Culture tubes (16 × 150 mm) were packed with 18 g clay loam soil. A sclerotia-bag was placed in each tube and covered with an additional 5 g soil. Soil was maintained at 60% field capacity for the duration of the experiment. AITC was injected into each tube through a septum. Treatments consisted of 0, 5.6, 11.2, 22.4, and 44.8 μmol AITC/L of atmosphere and an ethanol control. AITC in each tube was sampled using SPME and analyzed on GC-MS. Tubes remained sealed for 42 h at 30 °C. Sclerotia were then removed from tubes and bags and plated on PDA to determine viability. Radial growth was measured to determine the effects of AITC. Mycelial growth was negatively correlated to AITC concentration (P < 0.01). The highest concentration of AITC resulted in a 40.3% reduction in mycelial growth. Although the AITC concentrations used in this study did not kill sclerotia of S. rolfsii, they did suppress mycelial growth from germinating sclerotia. At higher concentrations, or mixed with other chemicals, AITC may prove to be an affective control for this pathogen.

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There has been significant interest in the glucosinolate-myrosinase system in plants of the Brassicaceae due to accumulating evidence that some glucosinolate degradation products are anticarcinogenic and/or suppressive to plant pathogens. Because glucosinolate hydrolysis is catalyzed by endogenous myrosinase, characterization of myrosinase activity is important for elucidating the potential bioactivity of crop glucosinolates. We measured the specific activity in citrate-phosphate buffer extracts across the pH range 4.5–6.5 of two cultivars each of five Brassica groups grown during two fall and two spring seasons. Specific activity in two kale cultivars was highly variable, but tended to have highest activity from pH 5.0–6.0. In both cauliflower cultivars from Fall 2000, Fall 2001, and Spring 2002, optimal pH was around pH 6.0. In Spring 2000, however, specific activity was highest at pH 5.0. Maximum specific activity in both cabbage cultivars occurred in the pH range 5.5–6.0 in Fall 2000, Fall 2001, and Spring 2002. In Spring 2000, specific activity in `Red Acre' cabbage was uniform across the range pH 4.5–5.5 and maximum specific activity was at pH 5.0 for `Early Round Dutch' cabbage. Both brussels sprouts cultivars had pH maxima around pH 5.5–6.0 and significantly lower activity at pH 4.5. Specific activity in broccoli was much like that of cauliflower in that highest activity occurred around pH 5.5–6.0 in Fall 2000, Fall 2001, and Spring 2002, but in Spring 2000, maximum activity was at pH 5.0. These results indicate that in most cases, pH optima were in the range 5.5–6.0, but varied somewhat with season and genotype.

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Two experiments were conducted in a greenhouse to evaluate soy-bean oil (SO) formulations for effects on powdery mildew (PM) and photosynthesis of dogwood trees. In the first experiment, one-year-old potted trees were sprayed with different formulations of 2% SO one day before exposure to PM. The formulations were emulsified with: teric/termul, lauriciden, lecithin, lecithin/MD 1, lecithin/MD 2, or Latron B-1956. A commercial formulation of Golden Natur'l was also used. The trees were arranged in a completely randomized design with six replications and eight treatments. In the second experiment, trees were sprayed 4 days after initial exposure to PM with the same treatments and arranged in a similar experimental design. The severity of PM infection was rated using the scale: 1 = 0%, 2 = 1% to 3%, 3 = 4% to 6%, 4 = 7% to 12%, 5 = 13% to 25%, 6 = 26% to 50%, 7 = 51% to 87%, and 8 = 88% to 100% of leaves visually displaying PM. The net photosynthetic (Pn) rates were measured using an infrared gas analyzer. In the first experiment, trees sprayed pre-inoculation with Golden Natur'l, lecithin, lecithin/MD 1, or Latron B-1956 formulation had less PM than control trees at 19 and 24 days after spraying (DAS). Pn of leaves sprayed with lecithin or Latron B-1956 formulations had 68% and 40% lower Pn rates, respectively, of the control leaves at one DAS. However, by 11 DAS, none of the SO formulations significantly affected Pn rates. Leaves of plants (expt. 2) sprayed with teric/termul, lauriciden, lecithin, and lecithin/MD 2 formulations had less PM than control trees at 28 DAS. All formulations reduced Pn rates at 6 DAS, with only Golden Natur'l treated leaves recovering to rates similar to control leaves by 15 DAS.

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Abstract

(2-Chloroethyl)phosphonic acid (ethephon) increased the pistillate flowers and decreased the staminate flowers of summer squash, Cucurbita pepo L. Hermaphroditic flowers appeared when the effects of ethephon were declining. Ethephon-treated plants produced more pistillate flowers but also had more aborted flowers. No direct relationship of carbohydrate or other nutrient accumulations and flowering were established.

Open Access

Foliar sprays of increasing concentrations (0, 75, 150, 300, 600, and 1200 mg·liter-1) of paclobutrazol were applied to `Cardinal' strawberry plants (Fragaria × ananassa Duch.) 35 days after transplanting. The plants were established in August in cultivated plots for measurement of paclobutrazol effects on first year growth or in a double-row hill system on black polyethylene-covered raised beds for 2nd year measurements. Increasing the paclobutrazol concentration reduced the number of runners, decreased runner length, and limited biomass partitioned into daughter plants. By the end of the first growing season, paclobutrazol had increased lateral crown development but reduced leaf area per treated plant. Root growth was reduced by concentrations >600 mg·liter-1. Treatment with 75 to 300 mg·liter-1 increased total plant dry weight by 33% to 46%. The following spring, plant growth was decreased by ≥ 300 mg·liter-1. Yield was increased by all treatments, except 1200 mg·liter-1. Leaf net photosynthesis increased within 12 days after treatment with paclobutrazol and was higher than in the controls the next summer. Leaf stomata1 conductance also increased the first year and was significantly higher the 2nd year after treatment. The optimum concentration of paclobutrazol for strawberries appears to be between 150 and 300 mg·liter-1.

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`Golden Delicious' apples were pressure-infiltrated (34 kPa) at harvest with 0, 20, 35, or 50 g·L–1 solutions of CaCl2 followed without and with a water rinse, a wax or shellac emulsion treatment, or a shrink-wrap packaging, and stored at 0°C. The CaCl2 treatments delayed senescent breakdown, but also caused superficial injury to the fruit. A water rinse in combination with a wax- or shellac-based coating or shrink wrap packaging reduced the appearance of superficial injury in fruit treated with 35 or 50 g·L–1 solutions of CaCl2 and eliminated it in fruit treated with a 20 g·L–1 solution of CaCl2. While reducing the risk of calcium-related injury to the fruit, the coating and film treatments maintained the beneficial effects of calcium on apples and reduced weight loss of the fruit during cold storage.

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Calcium has been linked to disease resistance in fruits and vegetables. The effects of calcium nutrition on six hydroponically grown tomato cultivars (`Switch', `Match', `Blitz', `Caruso', `Trust', and `Celebrity') were evaluated in the fall of 1996. Disease resistance and yield were measured for plants grown in either perlite or pine bark mulch. Plants were fertilized with a 5N–11P–26K water-soluble fertilizer solution containing micronutrients and either 60, 120, or 185 mg·L–1 calcium. Disease resistance was determined by measuring disease lesion diameters on mature green harvested fruit 3 to 5 days after inoculating with Botrytis cinerea Pers.: Fr. There was no significant difference in disease when evaluated by medium, cultivar, or calcium treatment. Foliar analysis by Inductively Coupled Argon Plasma Atomic Emission Spectrophotometer (ICAP) indicated that leaf calcium content ranged from 27,000 to 54,000 μg·g–1 dry weight (leaf above fifth flower cluster), but was not significantly different when analyzed by medium, cultivar, or calcium treatment. There was no significant difference in marketable yield due to medium or calcium treatment. Among cultivars, `Trust' had the highest marketable yield at 2.7 kg per plant, which was significantly different from `Celebrity' at 1.6 kg per plant. This experiment suggests that a cheaper medium (pine bark) and lower calcium levels can be utilized in fall tomato production.

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Vegetable crops can be significant sources of nutritionally important dietary carotenoids and Brassica vegetables are sources that also exhibit antioxidant and anticarcinogenic activity. The family Brassicaceae contains a diverse group of plant species commercially important in many parts of the world. The six economically important Brassica species are closely related genetically. Three diploid species (B. nigra, B. rapa, and B. oleracea) are the natural progenitors of the allotetraploid species (B. juncea, B. napus, and B. carinata). The objective of this study was to characterize the accumulation of important dietary carotenoid pigments among the genetically related Brassica species. The HPLC quantification revealed significant differences in carotenoid and chlorophyll pigment accumulation among the Brassica species. Brassica nigra accumulated the highest concentrations of lutein, 5,6-epoxy lutein, violaxanthin, and neoxanthin. The highest concentrations of beta-carotene and total chlorophyll were found in B. juncea. Brassica rapa accumulated the highest concentrations of zeaxanthin and antheraxanthin. For each of the pigments analyzed, the diploid Brassica species accumulated higher concentrations, on average, than the amphidiploid species. Brassicas convey unique health attributes when consumed in the diet. Identification of genetic relationships among the Brassica species would be beneficial information for improvement programs designed to increase carotenoid values.

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Field-grown dogwood trees in a commercial nursery were sprayed with 0%, 1%, or 2% soybean oil emulsified with Latron B-1956 at 2-week intervals from 10 June until 19 Aug. 1998. In 1999, dogwood trees were sprayed with 0%, 1%, 1.5%, 2%, or 2.5% emulsified soybean oil at 2-week intervals from 22 June until 26 Aug. The trials had treatments arranged in randomized complete-block designs with eight trees per block and six and four replications in 1998 and 1999, respectively. Disease severity of powdery mildew was estimated using the following scale: 0 = healthy, 1 < 2%, 2 < 10%, 3 < 25%, 4 < 50%, 5 > 50%, and 6 = 100% of foliage with symptoms or signs of powdery mildew. In 1998, trees sprayed with soybean oil had higher net photosynthesis rates and more caliper and height growth than control trees. Untreated trees and ≈25% of foliage infected with powdery mildew on 8 July, while trees sprayed with 1% or 2% soybean oil had about 2% of leaves infected. In 1999, the powdery mildew was already present on foliage (wet spring) when the first application of oil was made. Repeated sprays of soybean oil did not reduce the incidence of powdery mildew. Thus, soybean oil appeared to provide protective control of powdery mildew but not curative control of a heavy infestation of the fungi. Photosynthesis was increased by soybean oil for the first month of spraying in 1999, but did not differ after that. Repeated applications of even the high rates of oil did not cause phytotoxicity.

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