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  • Author or Editor: Donald J. Lee x
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This study was performed to characterize the physiological responses of tomato (Lycopersicon esculentum L.) fruit harvested at either 10% to 30% or 30% to 60% color change and treated with two forms of 1-methylcyclopropene (1-MCP). Tomato fruit were treated either by submersion for 1 min in 1-MCP aqueous solution at the ambient temperature or by exposure for 12 h at 20 °C in air with 1-MCP gas, then stored at 20 °C. The concentrations (1.0, 5.0, or 10.0 μL·L-1) in 1-MCP aqueous solution were achieved through addition of 0.5, 2.5, or 5.0 g of AFxRD-300 powder (2.0% formulation, Agro-Fresh, Inc.) to 10 L of the de-ionized water, following manufacturer's instructions. 1-MCP (0.5 μL·L-1) gas in a 174-L container was achieved through addition of 0.22 g of SmartFresh® powder (0.14% formulation, Agro-Fresh, Inc.) to 100 mL of tap water. Both forms of 1-MCP significantly delayed ripening of fruit at the two initial ripeness stages, as noted by a significant delay in fruit softening and peel color change. The firmness of 30% to 60% color change tomatoes was significantly retained in response to gaseous or aqueous 1-MCP. Control fruit softened rapidly and reached the minimum marketable firmness value (about 5 N) within 8 days of storage at 20 °C, whereas fruit treated with gaseous 1-MCP (0.5 μL·L-1) or aqueous 1-MCP (1.0 or 5.0 μL·L-1) reached the same stage after 16, 20, or 24 days, respectively. Firmness retention was also highly significant for 10% to 30% color change tomatoes treated with both forms of 1-MCP. The highest concentration of aqueous 1-MCP (10.0 μL·L-1) did not result in a further delay in ripening compared with treatment at 5.0 or 1.0 μL·L-1 1-MCP.

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Three experiments were performed to characterize the physiological responses of an Eastern United States shipper muskmelon (Cucumis melo L. var. reticulatus ‘Athena’) harvested preripe (¼ slip) and during ripening (half-slip, full-slip) to 1 μL·L−1 1-methylcyclopropene (1-MCP), a potent ethylene antagonist effective at significantly extending the time required for climacteric fruit to complete ripening. In the first experiment, preripe fruit were treated with 1-MCP (18 hour, 20 °C) before storage at 15 °C. Softening of preripe ‘Athena’ was significantly suppressed in response to 1-MCP, with firmness of control and 1-MCP–treated fruit declining ≈50% and ≈36% through 12 and 18 days of storage at 15 °C, respectively. By 21 days of storage, firmness of 1-MCP–treated remained near 70 N, minimally within the upper range of whole-fruit firmness values considered acceptable for consumption (50–75 N). Fruit treated with 1-MCP exhibited significantly lower ethylene production, respiratory rates, and electrolyte leakage throughout storage. In a second experiment, muskmelon were treated with 1-MCP (18 hours, 20 °C) at progressively advanced stages of ripening (half- and full-slip stages). Softening was significantly suppressed in half-slip fruit, declining ≈64% and ≈23% in control and 1-MCP–treated fruit, respectively, during 16 days of storage at 15 °C. Advanced-ripening, full-slip fruit were similarly affected, softening ≈60% and ≈25% in control and 1-MCP–treated fruit, respectively, during 10 days at 15 °C. In a third experiment designed to simulate possible commercial handling protocols, full-slip muskmelon were treated with 1-MCP (24 hours, 10 °C) and held at 10 °C for 5 days before transfer to 20 °C. Mesocarp firmness of 1-MCP and control fruit within 2 days of transfer to 20 °C had decreased ≈40% and ≈54%, respectively, compared with values at the start of the experiment. After an additional 2 days at 20 °C, the mesocarp tissue of the respective treatments had softened 42% and 70%. Fruit treated with the ethylene antagonist showed significantly delayed incidence of surface decay and sunken regions compared with control fruit.

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Roma tomatoes (`Sunoma') were hand-harvested at the mature-green color stage and treated with 100 μL·L-1 ethylene for 60 h at 20 °C and 90% RH. Tomatoes at breaker ripeness stage (<10% red coloration) were sorted by weight (about 100 g) and half of the fruits were treated with 1-methylcyclopropene (1-MCP; 1 μL·L-1 for 24 h at 22 °C). After 1-MCP treatment, individual fruits were subjected to double impacts over the marked locular surface with force equivalent to a 40-cm height drop using a pendulum impactor. In non-1-MCP treated fruit, impacts increased the maximum respiration rate by 27% (to 39.1 mL·kg-1 per h) and ethylene production by 24% (to 5.5 μL·kg-1 per h). Treatment with 1-MCP decreased relative production of both CO2 (56%) and ethylene (54%) over non-1-MCP treated fruit, while the ripening period (as measured by softening and color development) was extended 2.5 times, to about 8 d. Fruits treated with 1-MCP had increased TTA (about 40%; 0.58% citric acid equivalent), decreased pH (5%), and no difference in soluble solids content (3.7 °Brix); double impacts did not affect these values. Double impacts accelerated the onset of polygalacturonase (PG) activity by about 100% (to 99.8 mol·kg-1 per min*10-5 D-galacturonic acid) at day 6 over non-impacted control fruit. 1-MCP treatment delayed the onset of increased PG activity by 10 d over non-1-MCP treated fruit. Although 1-MCP alleviated the impact-induced increase in PG activity, PG activity recovered to rates similar to those of non-1-MCP treated fruit during the final 4 d of ripening.

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In this study, ripening characteristics, including color change and softening, were determined for tomato (Lycopersicon esculentum `Florida 47') fruit at immature-green through light red stages of development and subsequently treated with 1 μL·L–1 1-methylcyclopropene (1-MCP). Special attention was directed at comparing the responses of immature and mature-green fruit. Surface color and whole fruit firmness were measured every other day. 1-MCP delayed or slowed color changes and softening in fruit of every maturity class, with differences between control and treated fruit evident immediately following 1-MCP application for 24 h at 20 °C. Fruit treated with 1-MCP at early maturity stages (immature-green, mature-green, and breaker) exhibited an extended delay in external red pigment accumulation compared with control fruit. Fruit of all maturity classes developed acceptable final hue values (hue angle ≤55°), and the time required to reach these values declined with advancing fruit maturity. Immature-green fruit treated with 1-MCP did not attain an acceptable degree of softening during the specified storage periods examined before deteriorating due to shriveling and pathogen proliferation. 1-MCP-treated mature-green and breaker stage fruit did recover to acceptable firmness (5–10 N) and hue values but exhibited a severely reduced storage life thereafter compared with untreated fruit of equal maturity. Fruit at turning and more advanced stages exhibited reduced rates of softening and color development when treated with 1-MCP, yet they attained firmness and color values within the range of acceptability for commercial use. Fruit treated with 1-MCP at pink and light-red stages of ripening developed normal external color and exhibited significantly extended postharvest life due largely to a significant retention in firmness when compared to control fruit. Based on the studies described for `Florida 47' tomato fruit, 1-MCP would appear to be of little benefit and possibly detrimental if applied to early maturity fruit, most notably greens and breakers, due to irreversible limitations in the capacity of these fruit to soften to acceptable values. In sharp contrast, more advanced stage fruit, particularly pink and light red, responded to 1-MCP with significantly extended shelf-life due to retention of firmness.

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Roma tomatoes (‘BHN 467’) were hand-harvested at mature-green color stage and treated with ethylene (100 μL·L−1 at 20 °C and 90% relative humidity) until reaching breaker (<10% red), pink (30%–60% red), or light-red ripeness stage (60%–90% red). Individual fruit at each ripeness stage were subjected to double impacts over the locule using a pendulum-impact device with a force equivalent to two 40-cm drops, followed by ripening at 20 °C. Fruit exhibited most noticeable increases in respiration and ethylene production within 1 hour and 1 day after impact, respectively. After 24 hours, respiration rates increased 40%–60% regardless of ripeness stage, while ethylene production in impacted breaker-stage fruit increased 3-fold (to 6.7 μL·kg−1·h−1). Fruit impacted at breaker stage softened 2 days earlier compared with non-impacted breaker fruit. Fruit impacted at all ripeness stages had higher electrolyte leakage and polygalacturonase (PG) activity during ripening than non-impacted fruit. After 6 days, electrolyte leakage in fruit impacted at light-red ripeness stage was 23% higher than non-impacted fruit; PG activity in breaker fruit increased 40% at 10 days over non-impacted fruit. No changes were observed for soluble solids content, total titratable acidity, pH, or sugar/acid ratio from impacts, independent of ripeness stage.

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Hybridization and selection has been one of the methods used to generate turfgrass cultivars in buffalograss improvement. Three half-sib populations were developed by crossing three buffalograss female genotypes, NE 3296, NE 2768, and NE 2769, with NE 2871, a male genotype, to 1) investigate the pattern of genetic variability generated for turfgrass characteristics through hybridization; 2) assess the effect of parental change on the level of genetic variability generated in a buffalograss diploid population; and 3) predict the performance of a progeny generated from two heterozygous parents for turfgrass performance. The four parents and 20 random F1 progeny selected from each population were established in 2006 at the John Seaton Anderson Turfgrass Research Facility located near Mead, NE. A randomized complete block design (RCBD) was used with the progeny nested in the crosses. A visual rating scale of 1–9 was used to evaluate the population. Mean population lateral spread, genetic color, density, and turfgrass quality from early summer to fall ranged from 3.5 to 4.5, 7.1 to 7.9, 6.9 to 8.1, and 5.2 and 6.8, respectively. There were significant differences among the crosses and the parents for all the traits studied except quality in June and August. The progeny nested within crosses differed for turfgrass genetic color and quality. Best linear unbiased prediction (BLUP) indicated a high improvement potential for turfgrass lateral spread and spring density in NE 2768 × NE 2871 and for turfgrass genetic color in NE 3296 × NE 2871. From these findings, it can be concluded that hybridization breeding is a worthwhile approach for generating and identifying transgressive segregants for specific buffalograss traits.

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