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  • Author or Editor: Carl E. Sams x
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Members of the Allium genus are consumed for their culinary flavor attributes, but also contain antioxidant and anticarcinogenic phytochemicals. Bunching onions (Allium fistulosum L.) are commonly used in Asian cuisine, in which both leaves and pseudostems are consumed. Carotenoids and chlorophylls are important classes of phytochemicals gaining attention for their health attributes. The goal of our study was to characterize carotenoids and chlorophylls and identify possible genetic and environmental influences on carotenoid concentrations among A. fistulosum accessions. Twelve USDA-ARS accessions were field grown in Knoxville, TN, and Geneva, NY, during the summer of 2007. After harvest, carotenoid and chlorophyll pigments were evaluated in leaf and pseudostem tissues using high-performance liquid chromatography. We were able to identify the presence of antheraxanthin, β-carotene, chlorophyll a and b, lutein, neoxanthin, and violaxanthin in leaf tissues; however, pigments were not found in pseudostem tissues. Carotenoid and chlorophyll concentrations did not differ among accessions or between locations. It is possible that accessions evaluated in this study were a narrow genetic base or were selected based on flavor attributes and not leaf tissue pigmentation.

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`Golden Delicious' apples (Malus domestica Borkh) were dipped in either distilled water, methylene chloride, or one of the following surfactants: Brij 30, Tween 20, Tween 80, Tergitol 15-S-9, and Triton X-100. The fruit then were pressure-infiltrated with a 2% solution of CaCl2. Following 4 months storage at 0 °C, fruit were removed and flesh Ca concentration analyzed. The fruit surface was observed using low-temperature scanning electron microscopy, and fruit were rated for surface injury. Brij 30 altered the epicuticular wax the least and resulted in the smallest increase in flesh Ca concentration and the softest fruit. Triton X-100 altered the epicuticular wax the most and resulted in the highest fruit flesh Ca concentration and firmest of the surfactant-pretreated fruit. Methylene chloride removed some of the epicuticular wax, and fruit pretreated with this solvent had the highest flesh Ca concentration and greatest firmness. However, all of the fruit treated with methylene chloride were severely injured.

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Anaerobic soil disinfestation (ASD) is a biologically based, non-fumigant, pre-plant soil treatment developed to control soilborne plant pathogens and plant-parasitic nematodes in specialty crop production systems. Soil treatment by ASD includes the incorporation of a labile carbon (C) source, tarping with plastic, and irrigation of the topsoil to saturation (5 cm irrigation) to create conditions conducive to anaerobic decomposition of the added C source. A field study was implemented beginning in Fall 2010 and repeated in the same plot locations in Fall 2011 in Knoxville, TN, to evaluate ASD. Soil properties, weed and Rhizoctonia solani population dynamics, and crop performance were evaluated after ASD treatment with several potential C sources for ASD before production of fresh-market tomato (Solanum lycopersicum L. ‘Red Defender’) and red bell pepper (Capsicum annum L. ‘Red Knight X3R’). Treatments included: 1) untreated control; 2) mustard seed meal (biofumigant control); 3) ASD with dried molasses; 4) ASD with soil-incorporated Indian mustard (Brassica juncea L.), white mustard (Sinapis alba L.), and arugula (Eruca sativa Mill.) cover crop with molasses added at cover crop incorporation; 5) ASD with soil-incorporated Indian mustard, white mustard, and arugula cover crop; 6) ASD with soil-incorporated cereal rye (Secale cereale L.) cover crop with molasses added at cover crop incorporation; and 7) ASD with soil-incorporated cereal rye cover crop. Accumulated soil anaerobic conditions were significantly greater than the untreated control in all ASD treatments except the ASD mustard/arugula treatment. Although not related to accumulated anaerobic conditions, populations of R. solani were lowest and equivalent to the biofumigant control for ASD cereal rye and ASD mustard/arugula treatments. Differences in weed populations and soil inorganic nitrogen among treatments were limited. Yield of bell pepper and tomato did not differ among treatments, which may have been partly the result of the low pest pressure observed at the site over the 2 years of the study.

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Decay caused by Botrytis cinerea is significantly reduced by increasing the calcium concentration of apple fruit tissue. Electron microscope studies have revealed that cracks in the epicuticular wax may be an important pathway by which calcium penetrates into the fruit and increases the calcium concentration. In fruit inoculated with B. cinerea, the decay induced compositional changes in the cell walls of high-calcium fruit were smaller than those observed in the low calcium treatment. The effect of calcium in reducing decay is associated with maintaining cell wall structure by delaying chemical changes in cell wall composition. B. cinerea produced five polygalacturonase isozymes in vitro but only one in vivo. Among the cations studied-m was the most potent inhibitor of polygalacturonase activity in in vitro studies. Its mode of inhibition appears to involve the alteration of substrate availability for hydrolysis, rather than any direct effect on the active sites of the enzyme.

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Increasing the calcium content of apples with postharvest CaCl2, treatment has a beneficial effect on physiological and pathological storage problems. The optimal time after harvest during which the fruit can be successfully treated has not been investisated. This study examined the relationship between calcium uptake and the changes in surface cracking in the epicuticular wax of the fruit after various storage intervals. Apples were pressure infiltrated with 0, 2, or 4% CaCl, solutions at harvest or four or six months after storage at 0 C. Examination of the epicuticular wax with low temperature scanning electron microscopy revealed that as the storage duration increased, the numerous cracks on the fruit surface became deeper and wider, until, after six months storage, the cracking extended through the thickness of the cuticle. Calcium uptake in fruit pressure infiltrated with the CaCl2 solutions after six months storage was greater than fruit treated at previous storage intervals. As storage duration increased, epicuticular wax cracks became deeper and calcium uptake increased.

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Structural changes in the cuticle could be partially responsible for the differences in uptake of infiltrated Ca in apple fruit. We examined the relationship between the surface structure of epicuticular wax of `Golden Delicious' apple and Ca uptake by the fruit. Apples were nontreated or pressure infiltrated with distilled water, or with 0.14 or 0.27 mol·L-1 CaCl2 solutions 2 weeks before optimum harvest time, at optimum harvest, or after 2, 4, or 6 months of storage at 0 °C. Examination of the fruit surface with low-temperature scanning electron microscopy revealed that cracks in the epicuticular wax became wider and deeper as storage duration increased. After 6 months of storage, the cracks extended through the cuticle. Uptake of Ca by the infiltrated fruit was greater after 6 months of storage than after shorter storage intervals. These data indicate that as storage duration increased, epicuticular wax cracks became deeper and Ca uptake by the fruit increased.

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`Golden Delicious' apples (Malus domestica Borkh) were pressure-infiltrated at harvest with a 4% CaCl2 solution either without prior heat treatment or following 4 days at 38C. Examination of the apple surfaces from both treatments by low-temperature scanning electron microscopy revealed that heat treatment changed the pattern of epicuticular wax. The epicuticular wax of nonheated fruit exhibited numerous deep surface cracks that formed an interconnected network on the fruit surface. The epicuticular wax of heat-treated fruit did not exhibit a similar network of deep cracks. This apparent obstruction or elimination of deep cracks may limit the CaCl2 solutions from entering the fruit. The heated fruit contained significantly less Ca than the fruit that were pressure-infiltrated with CaCl2 solutions but not heated. These results indicate that cracks on the fruit surface may be an important pathway for the penetration of CaCl2 solutions.

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A pilot test was conducted over a 3-year period to determine the feasibility of using postharvest pressure infiltration of calcium into apples to maintain and/or improve the quality of fruit under commercial storage conditions. Fruits obtained from three different orchards were treated each year. `Golden Delicious' fruits were treated the first year, while `Delicious' fruits were treated the 2nd and 3rd years. In all treatments and years, there was a significant increase in calcium concentration of apples from all calcium chloride (CaCl2) treatments. In general, calcium concentration of treated fruit varied significantly among the three orchards. Firmness also varied among orchards, and was related to fruit calcium concentration. `Golden Delicious' apples were more susceptible to skin injury caused by CaCl2 treatment than were `Delicious' fruits. There was also an increase in infection as a result of some of the treatments, possibly due to injury caused to lenticels by the pressure applied or as a result of calcium injury.

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