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Chris Watkins* and William B. Miller

The discovery and subsequent commercialization of 1-MCP has resulted in intense research interest around the world. A web site (http://www.hort.cornell.edu/mcp/) has been developed which provides a summary of the effects of 1-MCP on climacteric (18 species) and non-climacteric (6) fruits, vegetables (13), fresh cut produce (5), cut flowers and pot plants (more than 50 species has been created. The site is updated on a regular basis. For edible crops, most citations are available for apple (32 citations) and banana (21 citations). The ornamental literature is much less concentrated, and most crops are represented by a single citation. For all commodities, the majority of research has been focused on quality responses of the various products to 1-MCP, although increasingly 1-MCP is being used to investigate physiological and biochemical events associated with development, ripening and/or senescence.

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Rao V. Mulpuri and Chris B. Watkins

Apple fruits are highly susceptible to superficial scald, which is currently controlled by both chemical- and non-chemical-based technologies. The possible threat of withdrawal of diphenylamine (DPA) for the control of superficial scald has prompted us to investigate the biochemical and molecular aspects of scald resistance. We have selected genetic populations of a cross between `White Angel' and `Rome Beauty' that are resistant and susceptible to scald, and investigated whether the resistance of scald in these populations is due to the higher antioxidant-based defense systems. Cortical tissue of fruits (0–3 cm) was peeled and analyzed for conjugated trienes, H2O2, carbonyl groups, and antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), and peroxidases (POX). Scald-resistant fruits at harvest had higher antioxidant enzymes and low levels of conjugated trienes, carbonyl compounds, and H2O2 levels compared to fruits that are susceptible to scald. Further, H2O2 levels rose in scald-susceptible fruits stored under low temperature with a concomitant increase in the production of conjugated trienes and carbonyl compounds, while no major changes were observed in scald-resistant fruits. Enhanced levels of H2O2 in scald-susceptible populations could be related to enhanced SOD activities and decreased activities of H2O2 degrading enzymes, suggesting that an imbalance between \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{O}_{2}^{-}{/}\mathrm{H}_{2}\mathrm{O}_{2}\) \end{document} may have occurred. These results indicate that a coordination between SOD and H2O2 degrading enzymes in scald resistant populations may have minimized the influence of AOS on the oxidation of α-farnesene, protein, and, thereby, on scald. Hence, we have hypothesized that enhancing the potential of apple fruit to metabolize AOS develops resistance to superficial scald. [Supported in part by USDA Specific Cooperative Agreement 58-1931-5-017.]

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Robert E. Paull and Chris B. Watkins

Production of heat shock proteins (HSP) in response to high temperatures are a highly recognizable feature of plant and animal systems. It is thought that such proteins play a critical role in survival under supraoptimal temperature conditions. The use of heat treatments has been examined extensively, especially for disinfestation of fruit and disease control. Heat treatments can affect physiological responses, such as ethylene production, softening, and other ripening factors, as well as reducing physiological disorders, including chilling injury. HSPs have been implicated in a number of stress responses, but the extent that they are involved, especially in amelioration of chilling injury, is a subject of debate. In a number of cases, heat shock proteins do not appear to be involved, and HSPs do not explain long-term adaptation to heat; other systems for which we do not have models may be at work. Resolution of these issues may require the use of transgenic plants with modified heat shock responses.

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Chris B. Watkins* and Jacqueline F. Nock

Most information about the effects of 1-methylcyclopropene (1-MCP) on apple fruit that is available in the literature involves its application immediately after harvest. However, depending on the storage facility, fruit may be treated within a few days of harvest, especially if destined for rapid CA storage, or after longer time periods. We have investigated the effects of: 1) 1, 2, 3, 4, 6, and 8 d delays before 1-MCP treatment on `McIntosh', `Cortland', `Jonagold', `Empire' and `Delicious' apple quality stored in air for 2 and 4 months, and in CA for 4 and 8 months; and 2) 1, 7, 14, and 21 d delays on `Cortland', `Jonagold', `Empire' and `Delicious' apple quality stored in CA for 5 months. `McIntosh' and `Empire' apples were harvested at two maturities. Our data show that responses of apple cultivars to 1-MCP can be affected by delay treatments, but that within each cultivar, these effects vary according to harvest maturity, storage type, and length of storage.

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James M. Wargo and Chris B. Watkins

`Honeycrisp' apples (Malus × domestica) were harvested over 3-week periods in 2001 and 2002. Maturity and quality indices were determined at harvest. Fruit quality was evaluated after air storage [0.0 to 2.2 °C (32 to 36 °F), 95% relative humidity] for 10-13 weeks and 15-18 weeks for the 2001 and 2002 harvests, respectively. Internal ethylene concentrations (IEC), starch indices (1-8 scale), firmness and soluble solids content (SSC) did not show consistent patterns of change over time. Starch hydrolysis was advanced on all harvest dates, but it is suggested that a starch index of 7 is a useful guide for timing harvest of fruit in western New York. After storage, firmness closely followed that observed immediately after harvest, and softening during storage was slow. No change in SSC was observed during storage in either year. Incidence of bitter pit and soft scald was generally low and was not affected consistently by harvest date. The incidence of stem punctures averaged 18.5% over both years, but was not affected by harvest date. Development of stem end cracking in both years, and rot development in one year, increased with later harvest dates. A panel of storage operators, packers, growers, and fruit extension specialists evaluated the samples for appearance and eating quality after storage, and results suggested that a 2-week harvest window is optimal for `Honeycrisp' apples that are spot picked to select the most mature fruit at each harvest.

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Susan S. Liou, Chris B. Watkins, and William B. Miller

During transport and the subsequent storage of tulip bulbs, inadvertent failure in ventilation and/or high contamination of Fusarium-infected bulbs may expose healthy bulbs to high concentrations of ethylene. Ethylene is known to cause many detrimental effects on forcing quality, including gummosis, increased respiration, flower bud abortion, bulb splitting and poor rooting. In this work, exposure duration and timing as well as the post-stress storage temperatures were evaluated for their potential effects on ethylene sensitivity in bulbs of four tulip cultivars. Degree of damage in sensitive cultivars `Apeldoorn' and `World's Favourite' increased with days at about 10 ppm ethylene starting at 9 and 16 days respectively. This effect strongly depended on timing of ethylene stress, as late treated bulbs showed more severe responses to ethylene treatment than early treated bulbs. Additionally, bulbs that were cooled immediately after ethylene stress, compared with those stored at 17 °C after stress, have significantly higher flowering quality in all attributes measured. This response was also strongly dependent on timing of ethylene stress and cultivar. Implications of the potential cold reversal of ethylene damage as well as effects of ethylene exposure duration and timing of stress on shipping and storage recommendations will be discussed.

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Chris B. Watkins, Juan-Pablo Fernández-Trujillo, and Jacqueline F. Nock

Susceptibility of apple fruit to CO2 can be affected by cultivar and postharvest treatment with diphenylamine (DPA). To study possible metabolic reasons for CO2 injury development, `Cortland' and `Law Rome' apple fruit were either untreated or treated with DPA at harvest, and then exposed to air or 45 kPa CO2 for up to 12 days. Fruit were sampled at 3-day intervals during treatment, and peel and flesh samples were taken for organic acid and fermentation product analysis. Additional fruit were removed to air and stored for 25 weeks for evaluation of injury. `Cortland' apple fruit had more external CO2 injury, but less internal CO2 injury than `Law Rome'. DPA treatment markedly reduced incidence of both external and internal injury. Fermentation products increased in peel and flesh of both cultivars with increasing exposure to CO2. However, acetaldehyde concentrations were ≈10 times higher in peel and flesh of `Law Rome' than `Cortland' apples. Ethanol concentrations in the flesh were similar in both cultivars, but were about twice as high in `Cortland' than `Law Rome' peel. Neither acetaldehyde nor ethanol concentrations were affected consistently by DPA treatment. Cultivar or DPA treatment did not affect accumulation of succinate, often regarded as the compound responsible for CO2 injury. These results do not indicate that acetaldehyde, ethanol, or succinate accumulation is responsible for CO2 injury in apple fruit.

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Adirek Rugkong, Jocelyn K.C. Rose, and Chris B. Watkins

Tomato fruit (Solanum lycopersicum L.) can develop mealiness and enhanced softening when exposed to chilling temperatures during storage, but the involvement of cell wall-associated enzymes in chilling injury development is not well understood. To study this aspect of injury development, we have exposed breaker-stage `Trust' tomato fruit to a chilling temperature of 3 °C for 0, 7, 14, and 21 days followed by storage at 20 °C for 12 days. Ethylene production was not affected by storage except after 21 days where production was greater at 20 °C. Exposure of fruit to chilling temperatures delayed the ripening-related color change (chroma and hue) and initially increased compression values, but percent extractable juice was not affected consistently. Increased polygalacturonase (PG) activity during ripening was reduced by about 50% after 7 days at 3 °C, and further inhibited with increasing storage periods. In contrast, the activities of pectin methylesterase (PME) and α-galactosidase were not significantly affected by the cold treatments. β-Galactosidase activity was greater in all chilled fruit compared with fruit ripened at harvest, whereas endo-β-1,4-glucanase activity was lower after 21 days at 3 °C. In chilled fruits, transcript accumulations for PG, PME (PME1.9), and expansin (Expt.1) were lower during storage at 20 °C compared with those of nonchilled fruits. Transcript accumulation for β-galactosidase (TBG4) was affected only at 14 days of cold storage, when transcript accumulation decreased. Cold treatment increased transcript accumulation of endo-β-1,4-glucanase (Cel1) after 12 days at 20 °C and decreased transcript accumulation after 7 days and 21 days at 21 °C. Cell wall analyses to investigate relationships among enzyme activities and cell wall disassembly are ongoing.

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Seok-Kyu Jung, Jacqueline F. Nock, and Chris B. Watkins

Late-harvested apple fruit generally are less responsive to 1-MCP than early harvested fruit, but the effect of harvest date on these responses can vary greatly by cultivar. Little is known about the relationships between internal ethylene concentration (IEC) and responses of fruit to 1-MCP. We have investigated the effects of 1-MCP on `McIntosh', `Cortland', and `Empire' apples in two experiments. In the first, fruit of each cultivar were picked three to five times during the normal harvest season, untreated or treated with 1 μL·L-1 1-MCP, and stored in air. Fruit IEC and firmness were then measured at monthly intervals for 4 months. In the second experiment, fruit were harvested several times during maturation, and, at each harvest, fruit were categorized into groups based on their IEC (<0.5, 0.5–1.0, 1–10, 10–50, 50–100; and >100 μL·L-1), treated with 1 μL·L-1 1-MCP for 24 hours at room temperature, and stored in air. The IEC and firmness of each fruit was then measured at set intervals during storage. Increasing IECs were associated with declining effectiveness of 1-MCP, but the individual fruit study showed that, even in high-IEC fruit, there was an initial inhibition of IEC values during storage before the IECs increased. A Lower IEC at harvest indicated a longer delay before the IEC ultimately increased. Collectively, the data show that it should be possible to determine the response of fruit to 1-MCP based on their IEC.