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  • Author or Editor: J. Kays x
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While we tend to think of postharvest volatiles as nitrogen, oxygen, carbon dioxide and ethylene, harvested products are actually exposed to thousands of volatile compounds. These volatiles are derived from both organic and inorganic sources, evolving from storage room walls, insulation, wrapping materials, combusted products, plants, animals, and a myriad of other sources. Plants alone manufacture a diverse array of secondary metabolizes (estimated to be as many as 400,000) of which many display some degree of volatility. We tend to be cognizant of volatiles when they represent distinct odors. A number of volatiles, however, have significant biological activity, and under appropriate conditions may effect postharvest quality. An overview of biologically active volatile compounds and their relation to postharvest quality will be presented.

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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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Levels of incident photosynthetic photon flux density (PPFD), net photosynthetic rate (Pn), and stomatal conductance (g) were monitored on individual intact kiwifruit (Actinidia chinensis Planch.) leaves at well-exposed and densely shaded canopy positions. Diurnal fluctuations of Pn and g closely paralleled changes in PPFD for exposed leaves. PPFD reaching shaded leaves were extremely low throughout the day; Pn and g were correspondingly low. Pn ranged between 10 and 12 µmol CO2·m-2s-1 when exposed leaves were light-saturated at PPFD between 500 and 700 µmol·m-2s -1. Exposed and shaded leaves had similar chlorophyll concentrations, though the former had significantly higher chlorophyll a:b ratios. Implications relative to leaf canopy design and management are discussed.

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Abstract

Levels of incident photosynthetic photon flux density (PPFD), net photosynthetic rate (Pn), and stomatal conductance (g) were monitored on individual intact kiwifruit (Actinidia chinensis Planch.) leaves at well-exposed and densely shaded canopy positions. Diurnal fluctuations of Pn and g closely paralleled changes in PPFD for exposed leaves. PPFD reaching shaded leaves were extremely low throughout the day; Pn and g were correspondingly low. Pn ranged between 10 and 12 µmol CO2·m-2s-1 when exposed leaves were light-saturated at PPFD between 500 and 700 µmol·m-2s -1. Exposed and shaded leaves had similar chlorophyll concentrations, though the former had significantly higher chlorophyll a:b ratios. Implications relative to leaf canopy design and management are discussed.

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Abstract

Autoradiographs of girdled and non-girdled almond seedlings treated with 14C-Alar revealed that the growth retardant moved readily from the phloem to the xylem. Autoradiographs of comparable seedlings treated with 14C-sucrose, with and without Alar pretreatment, showed that Alar induced greater leakage of radioactive material from the symplast to the apoplast indicating that the material lowered membrane integrity. This effect of Alar on cytoplasmic permeability was examined by immersing dormant stems, leaf discs, and beet root tissue in solutions of Alar and water. In all tissues, the compound induced greater leakage of cellular contents than water, which is attributed to the ability of Alar to depress utilization of respiratory energy necessary for the retention of solutes in the vacuole.

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Treatment of ‘Marianna 2624’ plum cuttings for 7 days with 1-14C-IAA with or without a pretreatment with 4000 ppm indolebutyric acid (IBA) for 5 sec revealed that the synthetic hormone inhibited IAA oxidase activity as measured by the decreased rate of 14CO2 evolution. KOH hydrolysis of different radioactive zones on paper chromatograms derived from alcoholic extractives of cuttings yielded presumptive IAA upon re-chromatography. Likewise, KOH and peptidase treatment of the alcohol insoluble residue yielded a radioactive substance with chromatographic properties characteristic of IAA. The presence of presumptive IAA and ninhydrin-positive substances in the peptidase hydrolyzate indicate that IAA was bound to protein(s). Appreciable radioactivity still remained in the alcohol insoluble residue after protein hydrolysis.

Open Access

Jerusalem artichokes are one of a small number of crops that store carbon predominately in the form of inulin, a straight chain fructosan. There has been a tremendous increase in interest in inulin due to its dietary health benefits for humans and calorie replacement potential in processed foods. We measured the allocation of dry matter within the crop (cv. Sunckoke) during an entire growth cycle by harvesting plants over a 40-week period (2-week intervals) from initial planting through field storage. Plant characters assessed were: no. of basal stems, leaves, branches, flowers, and tubers; the dry weight of leaves, branches, flowers, tubers, and fibrous roots; and date of flowering. Total dry weight of above-ground plant parts increased until 18 weeks after planting (22 Aug.) and then progressively decreased thereafter. Tuber dry weight began to increase rapidly ≈4 weeks (19 Sept.) after the peak in above-ground dry weight, suggesting that dry matter within the aerial portion of the plant was being recycled into the storage organs. Tuber dry weight continued to increase during the latter part of the growing season, even after the first frost. Final tuber yield was 13.6 MT of dry matter/ha.

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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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