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  • Author or Editor: S. J. Kays x
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The O2 and CO2 concentration between the shuck and shell and within the nut of individual pecans (Carya illinoensis (Wang.) K. Koch cv. Stuart) was monitored over a 4 week period from predehiscence to post-dehiscence. Internal O2 levels increased after dehiscence from initial concentrations of 16-17% to near that of the external environment after 3 weeks. Internal CO2 concentration, conversely, decreased substantially after dehiscence. Treatment of nuts over the same physiological stages of development with 2.5, 5.0, 10.0, 21.0 and 100% O2 had little effect on the induction and development of the kernel's normal pigmentation. Both high and low O2 levels did, however, produce some discoloration after 21 days of treatment. Changes in the internal nut O2 partial pressure are apparently not a significant factor in the induction and development of the normal complement of pecan kernel pigments during fruit maturation.

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Four high-yielding sweetpotato [Ipomoea batatas (L.) Lam.] cultivars displayed substantial leaf shedding, under typical field production conditions, that was not due to pathological or herbivory causes. Losses ranged from ≈ 45% to 60% of the total leaves formed by the normal harvest date during 2 years. There was a strong positive correlation between leaf shedding and the number of vines (r2 = 0.80) and nodes (r2 = 0.89) per plant. Likewise, positive correlations were found between leaf shedding and total dry weight (r2 = 0.67), root fresh weight (r2 = 0.65), root dry weight (r2 = 0.60), and vine dry weight (r2 = 0.68). Distinct differences were found among cultivars in dry-matter allocation within the plant. `Jewel' allocated a lower percentage of dry matter into vines and a higher percentage into storage roots. Estimated leaf dry matter losses due to leaf shedding ranged from 1.2 to 2.6 t·ha-1. High leaf losses appear to be closely related to vigorous vine growth and subsequent shading of older leaves but did not have a negative impact on storage root yield in the cultivars tested.

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Under typical field production conditions, four high-yielding sweetpotato cultivars (Centennial, Jewel, Regal and Resisto) were found to lose substantial amounts of leaves due to natural senescense rather than pathological or herbivory causes. Leaf loss by the normal harvest date ranged from 46 to 63% of the total leaves formed in 1991 and 48 to 59% in 1992. There was a strong positive correlation between leaves lost and the number of vines (r2 = 0.80) and nodes (r2 = 0.89) per plant. Positive correlations were also found between leaf loss and total dry weight of the plant (r2 = 0.67). root fresh weight (r2 = 0.65). root dry weight (r2 = 0.60), and vine dry weight (r2 = 0.68). Distinct differences were found among cultivars in dry matter allocation within the plant. Of the cultivars tested, 'Jewel' allotted a lower percentage of dry matter into vines and a greater percentage into storage roots. Estimated leaf dry matter losses due to leaf shedding ranged from 1.2 to 2.6 MT·ha-1. Amount of leaf loss appeared to be closely related to vigorous vine growth and subsequent shading of older leaves, though leaf loss did not have a negative impact on storage root yield in the cultivars tested.

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Mechanically harvested southernpeas (Vigna unguiculata (L.) Walp cv. Purple Hull Pink Eye lost substantial green color within 2 – 3 hours after harvest. Color loss was greater at higher temperature. Color changes were more closely related to O2, CO2, acetaldehyde and ethanol concentration in the load atmosphere than to endogenous ethylene concentrations. Solids and total sugar content decreased after harvest and were not affected by product temperature within the range studied. Flavor and off-flavor acceptability ratings were closely related to time from harvest, product temperature and load atmosphere O2 and CO2 concentrations, but were not closely associated with ethylene, acetaldehyde or ethanol concentrations.

Open Access
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Respiration of sweet potato roots was significantly depressed by low oxygen concentrations from 5 to 15% compared to 20% O2, but respiration at 2.5% O2 was high. Total sugar accumulated with low oxygen (2.5 and 5.0%) storage. Protopectin was low in roots stored at low O2 concentrations but water soluble pectin was not significantly affected. Physical parameters Ew and δf the storage roots were high when stored at low O2 concentrations. Ey and Ef were not significantly affected. Ew was correlated with total sugar (r = 0.79).

Open Access
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Abstract

Several environmental and physical factors affect the kinetics of ethylene release from (2-chloroethyDphosphonic acid and (2-chloroethyl)methylbis(phenylmethoxy)silane. Target surface chemistry exerted a strong influence on the evolution of ethylene from both compounds. Ethylene release from (2-chloroethyl)methylbis(phenylmethoxy) silane was slowed by glass and hydrophobic substances such as wax, surfactants in the spray solution, and high concentrations of the parent molecule, but not by epicuticular waxes on leaves. Ethylene evolution from (2-chloroethyl)phosphonic acid was inhibited by glass and high levels of epicuticular waxes. The rate of ethylene release from both compounds was positively correlated with temperature; however, ethylene released from (2-chloroethyl)methylbis(phenylmethoxy)silane was much less affected by temperature increases. Increases in light intensity promoted the initial release of ethylene from (2-chloroethyl)methylbis(phenylmethoxy)silane, but decreased long-term yield. Light intensity had no effect on the breakdown of (2-chloroethyl)phosphonic acid.

Open Access
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Abstract

Patterns of deposition of [14C]-photosynthate in the storage roots of Ipomoea batatas (L.) Lam. at 3 stages of development (44, 74, 105 days from planting) were distinct for each labeling period. [14C] initially accumulates in the vascular cambial region after labeling (24 hours); however, all areas of the storage root show discernable activity. Label in this region is lost with time probably through cell division with the majority of the label ending up in bundle parenchyma. Deposition of [14C]-photosynthate appears to occur for more than 24 hours reflecting either continued transport from aerial portions of the plant or redistribution within the root. Roots labeled early in their development do not have a uniform distribution of [14C] in the central stele, possibly due to later development of anomalous cambium. [14C] in the cortical region does not appear to be redistributed inward during subsequent growth of the root. [14C] deposited early in the development of the storage root was concentrated at the distal end with longitudinal bulking proceeding toward the proximal end. Invaginations along the surface of the root giving a furrowed appearance appear to be due to differential rates of activity of the vascular cambium in those regions.

Open Access
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Breeding sweetpotatoes [Ipomoea batatas (L.) Lam.] for improved flavor would be greatly facilitated by understanding the flavor chemistry of the crop. To ascertain the chemical composition of the aroma, an aroma extract of baked `Jewel' sweetpotatoes was obtained using a cold solvent trap system and analyzed by gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS) and gas chromatography olfactometry (GCO) using aroma extract dilution analysis (AEDA). GC with a flame ionization detector (GC-FID) revealed ≈60 compounds presented in the aroma extract, of which 48 were identified. Olfactory evaluation of the eluted compounds using GC with a thermal conductivity detector (GC-TCD) indicated the presence of 37 odor-active peaks in the aroma extract. Three compounds, phenylacetaldehyde (perfume), maltol (caramel), and methyl geranate (2,6-octadienoic acid, 3,7-dimethyl-, methyl ester) (sweet candy) possessed the highest flavor dilution (FD) values (1500) via AEDA. 2-Acetyl furan (baked potato), 2-pentyl furan (floral), 2-acetyl pyrrole (sweet, caramel), geraniol (sweet floral), and β-ionone (violet) had FD values of 1000. These compounds are thought to be the most potent odorants in baked `Jewel' sweetpotatoes. Additionally, 1,2,4-trimethyl benzene, 2-furmethanol, benzaldehyde, 5-methyl-2-furfural, linalool, isopulegone, n-decanal, 2,4-decadienal, octyl ketone, α-copaene, 4-decanolide, and one unidentified compound were also contributors to the aroma. There was not a character impact compound that comprised the basic baked sweetpotato aroma. The aroma appeared to be made up of a relatively complex mixture of compounds. Maillard and/or caramelization reactions, Strecker degradation of phenylalanine, lipid and carotenoid degradation, and the thermal release of glycosidically bound terpenes appear to be involved in the formation of the characteristic aroma of baked `Jewel' sweetpotatoes.

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Latex is known to act as a natural defense system in some laticiferous plants against certain herbivores. The importance of latex produced by the sweetpotato, Ipomoea batatas, Lam., as a defense mechanism against the sweetpotato weevil, Cylas formicarius elegantulus (Summers) (Coleoptera: Curculionidae), was tested. Distinct genetic and environmental differences were found in latex production in a broad cross-section of sweetpotato germplasm (96 lines). Most lines produced 2.6 to 10 mg fwt-vine-1 of latex when the second internode from the apex was severed. Some lines, however, produced substantially more, the highest being 48.3 mg·vine-1. The percent dwt of the latex exudate ranged from 2.5 to 54, with most lines falling within the 10 to 22.5% range. The amount of latex (fwt) released varied (1.9X) with differing environmental conditions (primarily light intensity). Young vine material produced more latex and had less feeding by the weevil than in older more mature portions of the vine. Application of latex to the surface of root cores markedly reduced feeding (67%) and oviposition (92%) after 24 hours in choice and oviposition in no choice experiments. Addition of latex to a semi-artificial media also significantly reduced feeding. Leaf feeding location (veins) and direction (basipetal), however, were not indicative of a deterrent role for latex. Collectively, existing evidence does not support a significant deterrent role for latex with regard to the sweetpotato weevil, however, additional information is needed on latex chemistry and quantitative and qualitative variation in latex within the sweetpotato genepool.

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Centella asiatica, the Asiatic pennywort, is an herbaceous perennial indigenous to the southeastern United States. In some Asian countries, it is valued as an important vegetable and is widely cultivated. In addition, it is considered an important medicinal herb due primarily to the pentacyclic phytochemical, asiaticoside, which effectively treats a variety of skin diseases. Information on the botany, photochemistry, medicinal, nutritional value, and cultivation of the crop is reviewed. This species may warrant preliminary field and consumer acceptance tests as a speciality vegetable in the United States.

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