George F. Antonious

Impact of Soil Management and Two Botanical Insecticides on Urease and Invertase Activity

Yard waste compost provides an organic amendment useful for improving soil structure and nutrient status. The activities of the enzymes hydrolyzing urea (urease) and sucrose (invertase) in the rhizosphere of potato plants were determined under field conditions. Soil urease and invertase activities were monitored in compost amended soil, grass buffer strips, and in adjacent bare soils during 35 d following soil treatment. Soil urease activity was increased by application of yard waste compost compared to untreated soil which provide evidence of increased soil microbial population following application of compost. Some transitional effects on urease activities were observed following Pyrethrins and Neemix‐4E application, these effects were neither drastic nor prolonged enough to be considered deleterious to the soil microorganisms and their activities important to soil fertility. No relationship was found between invertase activity and the three management practices or soil organic matter content. It is suggested that application of botanical insecticides like pyrethrins and Neemix‐4E may be useful in delaying urea fertilizer mineralization to maintain N in a form less leachable, so that the duration of N availability to plants is prolonged. The present study may also provide information on urease activity as a sensitive bioindicator of soil quality that reflects the effects of land management on soil quality and may assist land managers in monitoring long‐term productivity and sustainability of agricultural lands.

Residues and fate of endosulfan on field-grown pepper and tomato

Endosulfan (Thiodan 3 EC), a mixture of α- and β-isomers, was sprayed on 92-day-old field-grown pepper and tomato at the recommended rate of 0·61 kg AI ha-1. Plant tissue samples were collected at 1 h to 14 days after application and analysed to determine the content and dissipation rate of endosulfan isomers (α- and β-endosulfan) and the major metabolite, endosulfan sulfate. Analysis of samples was accomplished using gas chromatography-mass selective detection (GC-MSD). The results indicated the formation of endosulfan sulfate as a residue component on the plant tissues and also the relatively higher persistence of the β-isomer as compared to the α-isomer on pepper fruits. The initial total residues (α- and β-endosulfan isomers plus endosulfan sulfate) were higher on leaves than on fruits. On pepper fruits, the α-isomer, which is the more toxic to mammals, dissipated faster than the less toxic β-isomer. Total residues (α- and β-endosulfan isomers plus the sulfate metabolite) on tomato leaves revealed longer persistence (t1/2 4·6 days) compared to the total residues detected on pepper leaves (t1/2 2·0 days) 3–14 days following spraying. Persistence of the β-isomer on pepper fruits was high 3–14 days following spraying compared to on tomato fruits. This long persistence increases risk of exposure of the consumer. In addition, the longer persistence of the total residues on tomato foliage should be considered of importance for timing the safe entry of tomato harvesters due to the high mammalian toxicity of endosulfan.

Natural Products: Repellency and Toxicity of Wild Tomato Leaf Extracts to the Two-Spotted Spider Mite, Tetranychus urticae Koch

The potential of using phytochemicals from leaves of wild tomato for controlling the two-spotted spider mite, Tetranychus urticae Koch, is explored in this study as a promising alternative to the use of synthetic pesticides. Wild tomato accessions of Lycopersicon hirsutum plants that are not consumed by humans were planted under greenhouse conditions for mass production of leaves. Crude extracts from leaves of three accessions of L. hirsutum, six accessions of L. hirsutum f. glabratum, and one accession each of L. pennellii and L. pimpinellifolium were prepared in chloroform, ethanol and hexane. Two spider mite bioassays, one a measure of antibiosis and the other a measure of repellency, were utilized to determine the acaricidal performance of the crude extracts. The bioassay for antibiosis was a 6-h no-choice test. The bioassay for repellency utilized a ring bioassay. Chloroform leaf extracts of L. hirsutum f. glabratum accessions (PI-251304, PI-134417, PI-134418, and PI-126449) exhibited greatest antibiotic activity on two-spotted spider mites; the hexane extracts exhibited greatest repellency. Extracts from PI-251304, PI-126449, PI-134417, and PI-134418 were especially lethal (chloroform) or repellent (hexane). We investigated differences in chemical composition of the crude leaf extracts that may explain the observed differences in mortality and repellency among the different accessions. Major chemical compounds (α -curcumene, α -zingiberene, trans-caryophyllene, 2-undecanone, and 2-tridecanone) known to have pesticidal efficacy were detected and quantified in the crude leaf extracts using a gas chromatograph (GC) equipped with a mass spectrometer (GC/MS). Lethality of extracts was mainly associated with the presence of high concentrations of 2-tridecanone; repellency of extracts was mainly associated with the presence of trans-caryophyllene. Leaf extracts of L. hirsutum f. glabratum accessions that contain significant quantities of 2-tridecanone and/or trans-caryophyllene could be useful for managing populations of spider mites, which could reduce reliance on synthetic pesticides.

Antioxidants in Hot Pepper: Variation Among Accessions

The U.S. Department of Agriculture (USDA) pepper (Capsicum spp.) germplasm collection contains several thousand members or accessions. Many of these species and cultivars have not been analyzed for their concentrations of ascorbic acid, capsaicin, and total phenolic compounds, which are important antioxidants having a number of benefits for human health. The objective of this investigation was to select candidate accessions of hot pepper having high concentrations of ascorbic acid, capsaicin, free sugars, and total phenols for use as parents in breeding for these compounds. Seventeen accessions of pepper from the core Capsicum germplasm collection (four accessions of Capsicum chinense; five accessions of C. baccatum; six accessions of C. annuum; and two of C. frutescens) were field grown and their mature fruits were analyzed for their antioxidant composition. Concentrations of these compounds tended to be higher in C. chinense and C. baccatum, than in C. annuum and C. frutescens. Across all accessions the concentration of total phenols was correlated with ascorbic acid (r = 0.97) and free sugars (r = 0.80). Concentrations of total phenols (1.4, 1.3, and 1.3 mg g−1 fruit) and ascorbic acid (1.6, 1.2, and 1.3 mg g−1 fruit) were significantly greater in PI-633757, PI-387833, and PI-633754, respectively, compared to other accessions analyzed. Total capsaicinoids concentrations were greatest (1.3 mg g−1 fruit) in PI-438622 and lowest (0.002 mg g−1 fruit) in Grif-9320. The great variability within and among Capsicum species for these phytochemicals suggests that these selected accessions may be useful as parents in hybridization programs to produce fruits with value-added traits.

Screening Brassica species for glucosinolate content.

Glucosinolates (GSLs), a group of compounds found in Brassica plants, are toxic to some soil-borne plant pathogens because of the toxicity of their hydrolysis products, isothiocyanates. Other phytochemicals found in Brassica plants, such as phenols and ascorbic acid, may compliment the activity of GSLs. A survey of Brassica accessions from the national germplasm repository was conducted to identify potential cover crops that could be soil-incorporated for use as biofumigants. Ten Brassica accessions that demonstrated relative cold tolerance, rapid maturity, and superior biomass production were selected. The selected accessions were grown under three climatic conditions (fall greenhouse, winter high tunnel, and spring field) to investigate whether growing conditions affect their GSL, phenol, and ascorbic acid content. The selected accessions included seven accessions of Brassica juncea (Indian mustard), one of Brassica napus (oil seed rape), one of Brassica campestris (field mustard), and one of Eruca sativa (arugula). Separation of GSLs from the selected Brassica accessions was achieved using ion-exchange sephadex in disposable pipette tips. Quantification of total GSLs was based on inactivation of the endogenous thioglucosidase and liberation of the glucose moiety from the GSL molecule by addition of standardized thioglucosidase (myrosinase) and colorimetry. GSL concentration of greenhouse, high tunnel, and field-grown shoots (leaves and stems) averaged 24, 40 and 76 μ moles g− 1 fresh weight, respectively. Accessions of B. juncea generally had the highest GSL content. A comparison of accessions revealed that Ames 8887 of B. juncea contained the greatest GSL concentration, but had the lowest biomass yield and ascorbic acid concentration, in part because phytochemical concentration tended to be negatively correlated with biomass yield. More promising was B. juncea accession ‘Pacific Gold’ which coupled high biomass yield with above-average GSL production, but had low phenol and ascorbic acid concentration. We concluded that environmental stress on growing plants can increase the concentration of GSLs, ascorbic acid, and total phenols in Brassica shoots, but does not increase yields of these phytochemicals per unit area.

Accumulation of heavy metals in plants and potential phytoremediation of lead by potato, Solanum tuberosum L.

The use of sewage sludge as a source of nutrients in crop production is increasing in the United States and worldwide. A field study was conducted on a 10% slope at Kentucky State University Research Farm. Eighteen plots of 22 × 3.7 m each were separated using metal borders and the soil in six plots was mixed with sewage sludge, six plots were mixed with yard waste compost, and six unamended plots were used for comparison purposes. During a subsequent 3-year study, plots were planted with potato (year 1), pepper (year 2), and broccoli (year 3). The objectives of this investigation were to: (i) characterize chemical properties of soil-incorporated sewage sludge and yard waste compost; (ii) determine the concentration of seven heavy metals (Cd, Cr, Ni, Pb, Zn, Cu, and Mo) in sewage sludge and yard waste compost used for land farming; and (iii) monitor heavy metal concentrations in edible portions of plants at harvest. Concentrations of heavy metals in sewage sludge were below the U.S. EPA limits. Analysis of potato tubers, peppers, and broccoli grown in sludge-amended soil showed that Cd, Cr, Ni, and Pb were not significantly different from control plants. Concentrations of Zn, Cu, and Mo were significantly greater in tubers and peppers grown in sludge compared to their respective controls. Zn and Mo in broccoli heads were higher than their control plants. The ability of potato to accumulate lead needs additional investigation to optimize the phytoremediation of this pollutant element.

Light Reflected from Colored Mulches to Growing Turnip Leaves Affects Glucosinolate and Sugar Contents of Edible Roots

Abstract— Plastic mulches are widely used to conserve water and control weeds with less applied herbicides in production of food crops. Both yield and quality are important and can be affected by reflected blue (B), red (R) and far‐red (FR) light combinations received during growth and development. Photosynthate allocation among growing plant parts and flavor of edible roots were studied in turnip (Brassica rapa L.) grown in trickle‐irrigated field plots with blue, green and white mulches. The blue and green mulches reflected different amounts of B, but they both reflected FR/R ratios higher than the ratio in incoming sunlight. The white mulch reflected more photosyn‐thetic light and a lower FR/R ratio than the blue or green mulches. Plants grown with blue and green mulches did not differ significantly in leaf length, root size and shoot/ root biomass ratio. Those grown with white had shorter leaves and larger roots. Taste testers found that plants grown with blue mulch developed roots with a sharp flavor, and roots from plants grown with green mulch had a mild flavor. Those grown with white had a less distinct flavor. Roots grown with blue mulch had the greatest concentrations of total glucosinolates (GSL) and ascorbic acid. Reducing sugar concentrations were higher in roots grown with green than in those grown with blue mulches. The comparison of chemical composition of roots from plants grown with blue versus green mulches is important because the main difference was the amount of reflected B, suggesting that B influenced an enzyme involved in the pathway from glucose to GSL. We conclude that the spectrum of light reflected from mulch on the soil surface can influence not only shoot/root biomass ratio but also flavor‐related chemical composition of field‐grown food crop plants.

Enzyme activities and heavy metals concentration in soil amended with sewage sludge

Municipal sewage sludge (MSS) and yard waste compost (YWC) provide amendments useful for improving soil structure and nutrient status. However, soil amendments contain heavy metals that may potentially affect soil microbes and the enzymes they produce. A field study was conducted using three soil managemet practices (MSS, YWC, and native soil). Broccoli (Brassica oleracea L.) seedlings were planted, and the activities of the enzymes hydrolyzing urea (urease), sucrose (invertase), and p-nitrophenyl phosphate (acid and alkaline phosphatase) were determined in spring and fall agricultural soil. The greater soil urease and invertase activities in spring soil amended with MSS provided evidence of increased soil microbial population. On the contrary, the application of YWC in spring did not alter soil urease or invertase activities to any appreciable extent. Overall acid and alkaline phosphatase were stimulated in soil amended with YWC. Nickel, Zn, and Cu increased in soil amended with MSS while, concentration of Pb increased after addition of YWC to native soil. Nickel and Pb were taken up by broccoli plants grown in MSS amended soil, but their concentration in broccoli heads were below the Codex Commission Allowable Limits.

Residues and half-lives of pyrethrins on field-grown pepper and tomato.

Abstract The dried flower heads of Tanacetum cinerariifolium Trev. (Family: Compositae) contain insecticidal compounds collectively called “pyrethrins.” Pyrethrins are the subject of intense interest for use in crop protection because their toxicological properties permit control of certain insect species at application rates as low as 5–10 g AI acre−1. Seedlings of sweet pepper, Capsicum annuum L. cv. Bell Boy Hybrid and tomato, Lycopersicon esculentum Mill. cv. Mountain Spring F1 Hybrid were planted and sprayed with a Multi-Purpose Insecticide formulation that contains 0.2% pyrethrins, 1.0% piperonyl butoxide (PBO), 88% diatomaceous earth, and 10.8% inert ingredients. The formulation was sprayed on pepper and tomato foliage when tomato fruits became red ripe and pepper became mature green at the rate of 6 lbs of formulated product per acre (5.4 and 27.2 g AI of pyrethrins and PBO, respectively). Following spraying, pepper and tomato leaves and fruits were collected at different time intervals for residue analysis using a high performance liquid chromatograph (HPLC) equipped with a UV detector. Residues of pyrethrins and PBO were generally higher on the leaves than fruits. Initial deposits (1 h following spraying) of pyrethrins were significantly higher on pepper than tomato fruits. Half-life (T 1/2) values on pepper and tomato fruits did not exceed 2 h. Where concern exists over synthetic pesticide residues on treated crops and in the environment, pyrethrins are suitable alternatives that can be used to reduce the risk of exposure to synthetic pesticide residues.

Screening Capsicum Accessions for Capsaicinoids Content

Ninety Capsicum accessions selected from the USDA Capsicum germplasm collection were screened for their capsaicinoids content using gas hromatography with nitrogen phosphorus detection (GC/NPD). Fresh fruits of Capsicum chinense, C. frutescens, C. baccatum, C. annuum, and C. pubescens were extracted with methanol and analyzed for capsaicin, dihydrocapsaicin, and nordihydrocapsaicin. Mass spectrometry of the fruit crude extracts indicated that the molecular ions at m/z 305, 307, and 293, which correspond to capsaicin, dihydrocapsaicin, and nordihydrocapsaicin, respectively, have a common benzyl cation fragment at m/z 137 that can be used for monitoring capsaicinoids in pepper fruit extracts. Capsaicin and dihydrocapsaicin were the dominant capsaicinoids detected. Capsaicin concentrations were typically greater than dihydrocapsaicin. Concentrations of total capsaicinoids varied from not detectable to 11.2 mg fruit−1. Statistical analysis revealed that accession PI-441624 (C. chinense) had the highest capsaicin content (2.9 mg g−1 fresh fruit) and accession PI-497984 (C. frutescens) had the highest dihydrocapsaicin content (2.3 mg g−1 fresh fruit). Genebank accessions PI-439522 (C. frutescens) and PI-497984 contained the highest concentrations of total capsaicinoids.