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Abbreviations: FMP, fruit maturation period; SFM, shortened fruit maturation. 1 Graduate Research Assistant. 2 Professor. Current address: Mountain Horticultural Crops Research Center, 2016 Fanning Bridge Rd. Fletcher, NC 28732-9629. This research

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Rootstock influence on bloom date and fruit maturation of `Redhaven' peach [Prunus persica (L.) Batsch] was studied over a 3-year period. Rootstock included seedlings (Lovell, Halford, Bailey, and Siberian C) and cuttings (GF677, GF655.2, Damas 1869, and `Redhaven'). Bloom dates of the various combinations differed in all 3 years, with a range of 3.6, 9.1, and 7.3 days in 1988, 1989, and 1990, respectively. Fruit development period differed each year with a range of 3.9, 5.8, and 4.4 days in 1988, 1989, and 1990, respectively. `Weighted-average harvest date also differed with a range of 3.6,2.9, and 5.6 days in 1988, 1989, and 1990, respectively. `Redhaven'/Lovell was the latest blooming and maturing combination in all 3 years of the study.

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Endogenous abscisic acid (ABA), its 2-trans isomer (trans-ABA), phaseic acid (PA), and dihydrophaseic acid (DPA) concentrations were quantified in the peel, aril, and seed of mangosteen (Garcinia mangostana L.). Changes in carbon dioxide (CO2) and ethylene (C2H4) production and 1-aminocyclopropane-1-carboxylic acid (ACC) concentration in the peel and aril were also examined. ACC concentration and CO2 and C2H4 production were high at the beginning of fruit development and gradually decreased toward harvest, which confirms that mangosteen is a nonclimacteric fruit. In the peel and aril, the increase in ABA concentration preceded the decrease in peel firmness and coloring of the peel. This suggests that ABA may induce the maturation of mangosteens. The state of ABA metabolism varied with the part of fruit. In the peel, PA and DPA were not considered to be predominant metabolites of ABA because their concentrations were low compared to ABA throughout fruit development. In contrast, in the aril and seed, it is possible that the PA-DPA pathway may be a main pathway of ABA metabolism because the concentrations of DPA in the aril and of PA in the seed directly coincided with the concentrations of ABA. The differences in the ABA metabolites between aril and seed may be caused by the rate of ABA metabolism. The concentrations of ABA and its metabolite in the seed decreased toward harvest.

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Abstract

Mesocarp development of peach [Prunus persica (L.) Batsch cv. Redhaven] as measured by fresh weight and size increase, progressed along a double sigmoid curve which was reflected in the activity of extractable wall-associated α- and β-nitrophenylgalactosidases. Enzyme activities, both on protein and dry weight basis, rose rapidly during early fruit development, leveled off, then again rose rapidly at maturation. There was more α-nitrophenylgalactosidase activity than β-nitrophenylgalactosidase activity throughout development. Increases in both galactosidases followed rather than preceded increases in size. The final increases were, however, well correlated with fruit maturation.

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Abstract

Fruit samples of grape (Vitis labrusca L., cv. Concord) from 6 vineyard locations were collected at 7 to 10-day intervals beginning prior to veraison and continuing through development of 16% soluble solids for a period of 19 years. The 19-year average date for peak bloom in these vineyards was May 19, for 8% soluble solids development was July 27 (69 days from peak bloom), and for 16% soluble solids development was August 23 (96 days from peak bloom). Heat unit summations were more closely related to development of soluble solids than to changes in either titratable acidity or color. Using degree-day accumulations and effective heat unit summations did not prove to be methods superior to use of the number of calendar days for predicting grape maturation. Predictions from 8 to 16% soluble solids development were more accurate than predicting from peak bloom (when 50% of clusters showed bloom). Variations between years and between vineyard locations within a given year prevented accurate predictions from the 3 methods. Other deterrents observed in predicting development of soluble solids included the cultural variables of fruit load and soil moisture.

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Abstract

Temperatures for several post-bloom periods were correlated with days from full bloom to ‘Bartlett’ pear maturity. Date of maturity based on pressure test showed a high negative correlation (r = -.88) with mean temp above 40°F for the 36 days following bloom. The peak thermal period occurred 26-30 days after bloom, with the highest correlation on the 28th day. Days to maturity had a higher correlation with accumulated mean temp above 45°F than with degree hr above 45°F for the same periods. Base temp of 38.5°F to 50°F gave r values greater than -.85 in this prediction method. Mean temp between 41.5°F and 68.5°F on the 28th day had a linear correlation r of -.71 with days to maturity. Equal temp increments were more effective at min levels than at max levels for accelerating maturity. The post-bloom thermal period affecting maturation coincides with the stage of cell division and most effective time for application of chemical thinning sprays.

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Changes in the physical and chemical properties of the plasma membrane from hypodermal mesocarp tissue of netted muskmelon (Cucumis melo L. var. reticulatus Naud.) fruit were compared in relation to the permeability changes of the same tissue during fruit maturation and storage at 4 or 24C. As muskmelon fruit progress from immaturity to maturity, and with storage of mature fruit at 4 or 24C, increased permeability of the hypodermal-mesocarp tissue occurs coincident with an increase in the saturation index of the plasma membrane phospholipids. Buoyant density of the plasma membrane from hypodermal mesocarp tissue increased from 1.13 to 1.14 g·cm-3 during fruit maturation. Vanadate-sensitive ATPase (EC 3.6.1.35) activity was highest in mature fruit at harvest. After 10 days of storage, vanadate-sensitive ATPase activity was much lower in fruit kept at 24C than in those kept at 4C. The decrease in vanadate-sensitive ATPase activity in fruit stored at 24C was correlated with increased hypodermal-mesocarp membrane permeability. We suggest that biochemical changes affecting the lipid matrix of the plasma membrane influence fruit membrane permeability and possibly muskmelon storage life.

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An invertase gene was isolated and its mRNA activity and protein levels were determined during papaya (Carica papaya L.) fruit development. A complete invertase cDNA (AF420223) and a partial sucrose synthase cDNA (AF420224) were isolated from papaya fruit cDNA libraries. The invertase cDNA encoded a predicted polypeptide of 582 residues (MW 65,537 Da), and was 68% and 45% identical with carrot apoplastic and vacuolar invertases, respectively. Key amino acids indicative of an apoplastic invertase were conserved. A full-length gene corresponding to the putative apoplastic invertase cDNA was isolated and was organized into seven exons and six introns. Exon 2 (9 bp long) encoded part of a highly conserved region (NDPNG/A). Invertase mRNA and activity levels increased during fruit maturation and sugar accumulation just before ripening. In contrast, sucrose synthase mRNA levels were high during early fruit growth and low during the fruit sugar accumulation stage. A 73-kDa cell wall extractable protein that cross-reacted with carrot apoplastic invertase antisera substantially increased during papaya fruit maturation and declined in full ripe fruit. The increase in invertase protein levels occurred 2 to 4 weeks before maturity and was markedly higher than the overall increase in enzyme activity at this stage. Subsequently, the increase in enzyme activity was higher than the increase in protein levels between 2 weeks before maturity and fully ripe. The results suggested that mRNA level and invertase activity were related to maturity. The data suggested that the invertase was apoplastic, and that post-translational control of enzyme activity occurred, in which a significant accumulation of invertase occurred before the peak of enzymes activity.

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Ethylene synthesis and sensitivity, and their relation to germination at supraoptimal temperatures, were investigated in lettuce (Lactuca sativa L.) seeds matured at 30/20 °C [12-h day/night, high temperature matured (HTM)] or 20/10 °C [12-h day/night, low temperature matured (LTM)]. HTM seeds of both thermosensitive `Dark Green Boston' (DGB) and thermotolerant `Everglades' (EVE) had greater germination at a supraoptimal temperature (36 °C), in both light or dark, than LTM seeds of DGB and EVE. HTM seeds of DGB and EVE produced more ethylene during germination than LTM seeds, regardless of imbibition conditions. The ethylene action inhibitor, silver thiosulfate, led to reduced germination in both cultivars. The ethylene precursor, 1-aminocyclopropane-1-carboxylic acid at 10 mm increased germination of both cultivars at supraoptimal temperatures, whereas germination of HTM seeds was greater than that of LTM seeds. No differences in ethylene perception were detected between HTM and LTM germinating seeds using a triple response bioassay. This study demonstrated that at least one method through which seed maturation temperature influences lettuce germination is by affecting ethylene production.

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External color, length, diameter, fresh weight, C02 production, internal C2HA concentration, flesh firmness, soluble solids concentration (SSC), flesh color, and seed cavity diameter were measured during fruit growth and maturation of seven melon cultivars (Cucumis melo L., Inodorus Group, Naud. cv. `Amarelo', `Golden Beauty Casaba', `Honey Dew', `Honey Loupe', `Juan Canary', `Paceco', and `Santa Claus Casaba') of known age. There was no increase in C02 production either during ripening (e.g., loss of firmness and increased SSC) or with increasing C2H4 levels in fruit from any of the seven cultivars. There was a significant decline in respiration only at the second sampling date, which ranged from 14 to 18 days after anthesis. Respiration measured 1 week later was substantially higher and was followed by a general decline. This post 14- to 18-day rise in respiration was not a climacteric since it occurred well in advance of other ripening characteristics, e.g., loss of firmness, increase in SSC, or rise in internal C2H4. The increase in internal C2H4. coincided with or followed attainment of full fruit size, while flesh softening and the rapid rise in SSC preceded the rise in internal C2H4, concentration. Respiration declined from 67 to 18 ml CO2/kg per hour by day 43 in all cultivars, except `Honey Dew' and `Honey Loupe'. Respiration in `Honey Loupe' remained above 23 ml CO2/kg per hour and showed a rise to 32 ml/kg per hour on day 53. Respiration in `Honey Dew' did not fall below 18 ml CO2/kg per hour until day 53. As with internal C2H4 levels, there was no correlation between changes in and any marked change in the other signs of ripening that were measured.

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