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Brandon M. Hurr, Donald J. Huber, and Stephen T. Talcott

The present study was conducted to explore the process of watersoaking seen previously in beit alpha-type cucumber fruit treated with ethylene. Fruit were harvested at four levels of maturity: Immature (4 to 8 days after anthesis, DAA), Mature (10 to 14 DAA), Breaker (16 to 20 DAA), and Yellow (35 to 40 DAA). Fruit were then stored at 13 °C in the presence of air (control) or either 10 μL·L-1 ethylene or 1300 μL·L-1 propylene for up to 12 days. The physiological response to ethylene treatment varied with fruit maturity. Immature-stage fruit treated with ethylene for 9 days had mesocarp watersoaking, epidermal sloughing, and lower hue (118°, control 124°), endocarp pH (4.4, control 5.4), and whole fruit firmness (23 N, control 46 N). Mature-stage fruit behaved similarly to Immature-stage fruit, but lacked mesocarp watersoaking. In contrast, after 9 days of ethylene exposure, the Breaker- and Yellow-stage fruit exhibited no watersoaking, accumulated beta-carotene in peel tissue (13.6 μg·g-1 F.W, control 0.35 μg·g-1 F.W.) and had a “melon”-like aroma. Ethylene exposure for all maturities increased respiration rate and decay incidence compared to air-treated fruit. Ethylene evolution was only detectable in fruit with visible decay. Decay incidence in response to ethylene treatment was inversely proportional to maturity at harvest. Watersoaking, exhibited exclusively in Immature fruit, spread inward from the epidermis starting after about 6 days of ethylene treatment. Cells in watersoaked tissue stained negatively for viability with fluorescein diacetate and cells proximal to watersoaked cells stained weakly compared to air-treated controls. Current work is focused on identifying the mechanism of cell death.

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J.N. Sorensen, M. Edelenbos, and L. Wienberg

Yield and seed texture were studied in green peas (Pisum sativum L.) subjected to drought stress during flowering and pod filling. Field experiments were conducted with two cultivars on a sandy loam soil and drought conditions were obtained using movable rain shelters. The plants were harvested at three to five stages of maturity determined by tenderometer values and the concentration of alcohol-insoluble solids (AIS). Measured variables were related to the concentration of AIS in order to eliminate the influence of maturity when comparing between stress and nonstress conditions. Drought stress during flowering or pod filling reduced yield, but did not affect the size distribution consistently. To lessen the differences caused by variation in size distribution, all quality measurements were carried out on peas graded to 8.75 to 10.2 mm. Drought stress increased the concentration of sucrose at an AIS concentration of 140 g·kg-1. Besides the concentration of dry matter and starch the mean pea weight and testa weight did not reflect any consistency in relation to drought-stress conditions. The sensory scores for pea mealiness was not significantly increased in drought stress, and other sensory quality attributes were unaffected. In this study, the effect of drought stress on pea texture quality is weak and inconsistent when comparisons are made at the same stage of maturity. As texture quality is highly correlated to stage of maturity, the tenderometer value or AIS concentration is reliable when determining time of harvest for the production of high quality peas irrespective of drought-stress conditions during maturation.

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Marvin D. Butler and Robert E. Rush

Early maturity is of major importance to table grape producers in the Sonoran Desert. Prices are historically high at the beginning of the season, declining substantially over the first few days or weeks of harvest. Research was conducted in 1990 and 1991 at a commercial vineyard in southwest Arizona to determine the effect of bunch count per vine on yield and early maturity of fifth and sixth year flame seedless grapes. Vines were thinned to 15, 25 and 35 bunches in 1990, and 20, 30, 40, and 40 short bunches in 1991. The two-row, 0.2 acre plots were replicated four times using a randomized complete block design. Despite the large variation in crop load, there were no significant differences in total yield. There was an increase in percent soluble solids as bunch counts decreased. Berry weight followed the same trend. Small to moderate bunch counts produced a larger number of boxes and a greater percentage of the crop early in the season. By maintaining small to moderate bunch counts, early maturity is attainable without significantly reducing total yield.

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Ioannis P. Oikonomakos, Niels O. Maness, Donna Chrz, William McGlynn, and Penelope Perkins-Veazie

Lycopene from ground watermelon flesh can be segregated between filtrate and filter cake by coarse filtration. Low speed centrifugation of the filtrate can further segregate filtrate lycopene between an easily recoverable precipitated high lycopene pellet and a serum. Lycopene in watermelon flesh increases steadily during maturation and remains constant, or slightly decreases in overripe melons. This study was conducted to document the effect of melon maturity on lycopene segregation during filtration/centrifugal processing. Flesh of three seedless watermelon cultivars was ground and filtered through two layers of Miracloth. Filter cakes were rinsed with water and filtrates were centrifuged at 3500 g to precipitate lycopene. Centrifugal recovery of lycopene from filtrates was about the same for undermature and mature melons (50% to 70%), but was much lower for overripe melons (35% to 45%). This decline in recoverable lycopene from overripe melons could be negated if ground flesh was heated to 60 or 85 °C prior to filtration. Lycopene from preheated flesh segregated predominately into the filter cake for all three maturity groupings. The interaction between melon maturity and pre-filtration heating will be evaluated and integrated into a potential watermelon lycopene production system.

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R. Garca-Estrad, J. Siller-Cepeda, M. Bez, M. Muy, and E. Araiza

On Sinaloa State, tomato growers test new varieties every year looking high yield, better quality and long shelf life. However, few studies are done to know the resistance to postharvest diseases. The objective was to identify postharvest pathogens that infect this new tomato varieties with characteristics rin, nor or normals (BR84, S211, S69, and S121). Fruits in two stages of maturity (pink and red) were harvested and stored under simulated marketing conditions (20°C and 80% RH). Pathogens found were aisled on PDA and identified under microscope. Different chemicals were tested to control pathogens [NaOCl; Ca(OCl)2; Supersana; iodine; Citrucidal; Captan; and water]. Six fungus species—Alternaria alternata, Fusarium oxysporium, Rhizopus stolonifer, Colletotrichum sp., Rhyzoctonia sp, and Phomopsis sp—were found on all varieties. BR84 fruit (rin type) harvested on pink stage were more resistant than red ones. S69 fruit (nor type) were more susceptible at the pink than at the red stage. S121 fruits (normal type) were equally susceptible at both stages of maturity. Least resistant variety to fungus infection at both stages of maturity was S211 (rin type). Citrucidal and Ca(OCl)2 gave the best control.

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Nazir A. Mir, Najma Khan, and Randolf M. Beaudry

The effects of 1-MCP on ripening and shelf life in fruit of five classes of maturity (1, mature green; 2, turning; 3, half-ripe; 4, ripe; and 5, over-ripe) of `Plum' tomato (Lycopersicon × esculentum, Mill) at 22 °C were evaluated. 1-Methylcylopropene (1-MCP) reduced the rate of red color development in fruit of all maturity classes. However, the effect was more discernable in fruit with higher hue angle value. Single application of 1-MCP delayed the color development by 10 days. While a second application of 1-MCP at day 10 delayed color development by another 10 days for mature green tomatoes, it did not influence the color change in all other classes of maturity. The effects of 1-MCP on firmness loss were similar to color development. Compared to the control, 1-MCP reduced the ripening-related rate of respiration by approximately 40%. Contrary to this, ethylene production was not affected by 1-MCP application. Potential exists to use 1-MCP in tomato to reduce ethylene-associated changes in texture and color.

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Nadeem A. Abbasi, Mosbah M. Kushad, and Anton G. Endress

Superoxide dismutase (SOD: EC 1.1.15.1.1) and peroxidase (POD: EC 1.11.1.7) activities were evaluated during maturity, ripening, and senescence of `Red Spur Delicious' (Malus domestica Borkh.) apple fruits. SOD and POD activities did not exhibit uniform changes during fruit maturity; however, during fruit ripening, activities of both enzymes increased significantly. During fruit senescence, SOD activity continued to increase, while POD activity declined by 24% to 50%. Fruit maturity at harvest significantly affected SOD and POD activities during the progression of ripening and senescence. SOD activity was significantly higher during ripening and senescence of fruits that were harvested at full and over-mature stages than in fruits harvested at early mature stage. In contrast, POD activity was lower in fruits that were harvested at full and over-mature stages than in fruits harvested at early mature stage. Increase in SOD and POD activities during fruit ripening suggest that these enzymes are actively involved in scavenging free-radicals generated during this developmental stage. However, the decline in POD activity during fruit senescence suggest a possible disruption of the breakdown of H2O2 free-radicals. This disruption may have contributed to tissue senescence and the induction of a physiological disorder called senescence scald.

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Desmond R. Layne, Zhengwang Jiang, and James W. Rushing

Replicated trials were conducted in Summers 1998 and 1999 at two commercial orchards (A and B) to determine the influence of a metalized, high density polyethylene reflective film (SonocoRF) and aminoethoxyvinylglycine (ReTain), on fruit red skin coloration and maturity of `Gala' apples (Malus sylvestris var. domestica). There were four experimental treatments: 1) nontreated control; 2) reflective film (RF); 3) ReTain; and 4) RF + ReTain. RF was applied 4 weeks before anticipated start of harvest by laying a 5-ft-wide (150-cm) strip on each side of the tree row in the row middle. ReTain was applied 4 weeks before harvest at the commercial rate in one orchard and at 60% of the commercial rate in a second test. ReTain delayed fruit maturity. Fruit from RF trees had a significantly greater percent surface red color than fruit from trees not treated with RF. Fruit from RF + ReTain were significantly redder and had higher soluble solids concentration (SSC) than fruit from trees treated with ReTain alone. There were no differences in size, fruit firmness or starch content between fruit from RF and RF + Retain. RF appears to be a method to increase red skin coloration in `Gala' apples treated with ReTain without adversely impacting maturity.

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I.L. Goldman

Plant Breeding and Whole-system Crop Physiology. Improving Adaptation, Maturity, and Yield. D.H. Wallace and W. Yan. 1998. CAB International. Available from Oxford University Press, 198 Madison Ave., New York, NY 10016. 390 p. $100

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Laura Lehman-Salada

Three apple (Malus domestica Borkh.) cultivars of various maturity levels and flesh firmness were used to compare firmness readings obtained by three trained operators using Magness-Taylor (MT), Effegi (EF), and Electronic Pressure Tester (EPT) penetrometers. For all cultivars and operators, use of the MT resulted in the lowest mean readings, while use of the EPT operated in the MT testing mode resulted in the highest readings. Operator differences were observed for all instruments except when the electronic tester was used in the default mode. Comparisons between instruments and modes resulted in significantly different firmness readings across operators, except for the comparison of EF vs. EPT in default mode. For most comparisons, firmness variance due to instrument or mode was larger than the variance due to operator. Apple maturity did not significantly alter firmness trends due to instrument or operator. Thus, caution should be used to interpret apple firmness changes of a single lot of apples when several instruments and/or operators are used.