Malus Sylvestris Mill Research Articles

Effects of auxin and jasmonates on 1-aminocyclopropane-1-carboxylate (ACC) synthase and ACC oxidase gene expression during ripening of apple fruit

1-Aminocyclopropane-1-carboxylate (ACC) synthase and oxidase activities, their gene expression, and ethylene production in apple fruit [ Malus sylvestris (L.) Mill. Var. domestica (Borkh.) Mansf.] treated with a synthetic auxin 2,4-dichlorophenoxy-propionic acid (2,4-DP) and n-propyl dihydrojasmonate (PDJ), a jasmonic acid derivative, has been investigated to clarify the action of auxin and jasmonates on ethylene production. The fruit was harvested at 103 d after full bloom (preclimacteric). The expression of MdACS4 messenger RNA (mRNA) at 48 and 96 h after treatment was higher in fruit treated with 2,4-DP than in the untreated control, but those of MdACS1 and MdACO1 were not affected by treatment. The ethylene production in 2,4-DP-treated fruit increased at 96 h after treatment. In contrast, expression of mRNAs hybridized with MdACS1 and MdACO1 probes in the skin of PDJ-treated fruit were higher than those in the untreated control. In addition, ACC synthase activity and ethylene production also increased after treatment. These results show that the ethylene production rate may differ with the kind of genes which were stimulated by auxin or jasmonates.

Potential regulation of apple in vitro shoot growth via modulation of cellular polyamine contents

In the present research attempts were made to elucidate effects of d-arginine ( d-arg), a potential inhibitor of arginine decarboxylase (ADC) involved in polyamine biosynthesis, on growth and polyamine biosynthesis of apple [ Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] in vitro shoots. Growth of the shoots cultured on proliferation medium added with 1 or 5 mM d-arg was inhibited over a 3-week treatment, with 5 mM being more effective. Activity of ADC was slightly or remarkably inhibited by 1 and 5 mM d-arg, respectively, in line with change of free putrescine (Put) content in the treated shoots. Activity of ornithine decarboxylase (ODC) was only repressed by 5 mM d-arg. Application of exogenous Put at 1 mM slightly recovered the growth of impaired apple shoots, while exogenous Put at 5 mM could resume the growth to a level similar with the control. Addition of exogenous Put led to notable increase in endogenous free Put, coupled with corresponding recovery of ADC and ODC activities. Transcriptional levels of several key genes involved in polyamine biosynthesis were more or less repressed by 5 mM d-arg relative to the untreated shoots, which were otherwise up-regulated by exogenously applied Put. The data presented herein showed that it is possible to regulate apple shoot growth via modulation of cellular polyamine contents.

Antioxidant contents and activity of 1-methylcyclopropene (1-MCP)-treated ‘Empire’ apples in air and controlled atmosphere storage

The effect of 1-MCP on ripening and concentrations of total phenolics, flavonoids, anthocyanins and total antioxidant activity of ‘Empire’ apples ( Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.) was studied. Fruit were stored in air for up to 5 months, and in controlled atmosphere (CA) of 2 and 3 kPa O 2 (2 kPa CO 2) at 0.5 and 2.2 °C for 4.5 and 9 months. Ripening was delayed by 1-MCP treatment in both air and CA storage as indicated by lower internal ethylene concentrations and slower softening than in untreated fruit. Overall, total phenolic, flavonoid and anthocyanin concentrations as well as antioxidant activity were relatively stable during air and CA storage. In air-stored fruit, total phenolic concentrations were higher in the peel of 1-MCP treated fruit than in the control fruit, but slightly lower in the flesh of 1-MCP treated fruit. In CA-stored fruit, interactions between O 2 partial pressures, temperature and storage duration were detected but overall, few consistent trends were observed. However, flavonoid concentrations were higher in the flesh of 1-MCP treated than untreated fruit kept in 2 kPa O 2 while anthocyanin concentrations, only measured in the peel, were not affected by 1-MCP treatment. There were no correlations found between total phenolics and antioxidant activity. Ascorbic acid concentrations declined in both peel and flesh tissues of untreated and 1-MCP treated fruit stored in air, while changes of ascorbic acid concentrations in CA-stored fruit were inconsistent.

Surface Moisture Induces Microcracks in the Cuticle of ‘Golden Delicious’ Apple

Formation of microcracks in the cuticular membrane (CM) of epidermal segments (ES) of apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf., ‘Golden Delicious’, ‘Braeburn’, ‘Idared’, ‘Jonagold’, and ‘Topaz’; all grafted on ‘Malling.9’ rootstocks] fruit was studied after exposure of the surface of the ES to water. Potential strain of the CM on the ES was preserved by mounting a stainless steel washer on the fruit surface using an ethyl-cyanacrylate adhesive. Subsequently, ES were excised by tangentially cutting underneath the washer. The number of microcracks in the CM was established by light microscopy before and after a 48-h incubation period in deionized water. Within 48 h, the number of microcracks rapidly increased when the outer surface of ES of ‘Golden Delicious’ apple was exposed to water, but there was essentially no increase in microcracks when exposed to the ambient atmosphere. The occurrence of microcracks depended on the region of the fruit surface and increased from the rim of the pedicel cavity to the calyx. Increasing the relative humidity (greater than 75% relative humidity at 22 °C) above the outer surface of the ES exponentially increased the number of microcracks. Water-induced microcracking was not limited to ‘Golden Delicious’, but also occurred in ‘Braeburn’, ‘Jonagold’, ‘Topaz’, and, to a markedly smaller extent, in ‘Idared’ apple. The mechanism of formation of microcracks in the CM of apple fruit and their role in fruit russeting are discussed.

Annual Bloom-time Phosphorus Fertigation Affects Soil Phosphorus, Apple Tree Phosphorus Nutrition, Yield, and Fruit Quality

A randomized, complete block, split-plot experimental design with six replicates was established and maintained annually for the first five fruiting seasons (1999 to 2003) in a high-density apple [Malus sylvestris (L) Mill var. domestica (Borkh.) Mansf] orchard on M.9 rootstock planted in Apr. 1998. Main plot treatments involved eight different nutrient regimes, each containing three tree subplots of each of five different cultivars (Ambrosia, Cameo, Fuji, Gala, and Silken). This report compares a +phosphorus (P) treatment, involving annual fertigation at bloom time of 20 g P/tree as ammonium polyphosphate (10N–15P–0K), to a −P treatment. Both treatments also received nitrogen, potassium, and boron nutrients through fertigation. Drip fertigation of P increased 2 M KCl-extractable P to 0.4-m depth within 0.5-m distance of the drippers. Leaf and fruit P concentrations were consistently increased by the +P treatment with few differences among cultivars. P-fertigated trees also had a 20% increase in cumulative yield overall cultivars during the first five fruiting seasons. Standard fruit quality measurements, including fruit size, soluble solids concentration, titratable acidity, and red coloration were unaffected by P application. However, reductions in incidence of water core at harvest, increased resistance to browning, and elevated antioxidant content of harvested fruit measured in some years imply a role for P in apple membrane stability. The cumulative results indicate that applications of 20 g P as ammonium polyphosphate annually at bloom would be advantageous for apples receiving adequate fertigated applications of nitrogen, potassium, and boron. Best apple performance was associated with leaf P concentrations above 2.2 mg·g−1 dry weight and fruit P concentrations between 100 and 120 mg·kg−1 dry weight.

The Seasonal Changes in Endogenous Levels of Indole-3-Acetic Acid, Gibberellic Acid, Zeatin and Abscisic Acid in Stems of Some Apple Varieties (Malus sylvestris Miller)

Sivaci, A.; Department of Biology, Faculty of Sinop Art and Science, Sinop University, Sinop, Turkey

Organic Apple Systems: Constraints and Opportunities for Producers in Local and Global Markets: Introduction to the Colloquium

The global market for total organic product sales was $20 billion in 2005, continuing an annual growth rate of 20% to 35%. In the United States, there were 937,000 ha of certified organic land in 2003 with 5626 ha of organic apples [Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.]. Increases in organic fruit production have been associated with improved pest management methods, the use of disease-resistant cultivars, and organic-focused marketing schemes. Often constrained by lower apple yields and smaller fruit size compared with conventional counterparts, key challenges for organic growers include regulation of nutrient cycling processes to maintain crop yields while minimizing the need for external inputs. In local or regional organic markets, disease-resistant apple cultivars, such as ‘Enterprise’, ‘Liberty’, ‘Redfree’, and ‘Gold Rush’, have gained increased acceptance, whereas exporting countries have continued their use of cultivars susceptible to scab [Venturia inaequalis (Cooke)]. Integrated insect pest management approaches, including the use of kaolin clay, codling moth granulosis virus, and spinosad-based insecticides, have been successfully developed to comply with export standards and quarantines, and to meet market demand. Key pests, such as codling moth [Cydia pomonella (L.)], have been managed at damage levels less than 5% using these approaches. Future pest management strategies in organic apple production will focus on development of scab-resistant cultivars with enhanced storage capability and reduction in inputs associated with negative environmental and health effects.

Organic Apple Production in Two Humid Regions: Comparing Progress in Pest Management Strategies in Iowa and New Zealand

By 2003, organic apple [Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.] production had increased to 5626 ha in the United States and to 2964 ha in New Zealand by 2002. Common problems facing organic apple growers in the humid regions of New Zealand and the United States include effective management strategies for apple scab [Venturia inaequalis (Cooke)] and insect pests. Experiments conducted in Iowa in 2003–2004 demonstrated the effectiveness of a kaolin clay- and spinosad-based insecticide program in maintaining codling moth [Cydia pomonella (L.)] damage levels to less than 5% in the scab-resistant cultivars Enterprise, Liberty, Redfree, and Gold Rush. Similar pest management systems have been developed in New Zealand to comply with export standards and quarantines. The use of codling moth granulosis virus and a spinosad-based insecticide have led to reduced pest pressure and to an increase in organic exports with a 41% premium price over conventional apples. However, an association between spinosad use and woolly apple aphid [Eriosoma lanigerum (Hausmann)] population increase was observed in organic orchard surveys in 2006. An alternative to spinosad applications, insect disinfestation through controlled atmosphere (CA) treatment, was investigated to control quarantined pests and to extend the storage potential of scab-resistant cultivars. A CA treatment of 9 weeks of 2% O2 and 2% CO2 at 0.5 °C was determined to maintain firmness ratings to export standards in CA-stored, scab-resistant ‘Pinkie’ apples and to decrease internal ethylene concentration by 84% compared with apples stored in air. In addition, new scab-resistant cultivars with ‘Pinkie’ background under development in New Zealand show promise for organic production in humid regions. Few fruit quality differences were determined between ‘Pinkie’ fruits from integrated fruit production and organic production systems, although premium prices exist only for certified organic apples.

External carbon dioxide injury and 1-methylcyclopropene (1-MCP) in the ‘Empire’ apple

The effects of several factors on the susceptibility of untreated and 1-MCP-treated ‘Empire’ apple ( Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.) fruit to external CO 2 injury have been investigated. These factors include CO 2 partial pressure, the timing of elevated CO 2 exposure, delays between harvest and exposure to elevated CO 2, DPA concentration, and the timing of DPA treatment after exposure of fruit to 1-MCP. 1-MCP-treated fruit were more susceptible to external CO 2 injury than untreated fruit when stored in 5 kPa, but not 1 kPa, CO 2 (in 2 kPa O 2). 1-MCP did not increase the period of highest susceptibility to injury during controlled atmosphere storage. The greatest sensitivity to injury occurred 0–3 weeks after harvest. Sensitivity to injury decreased when untreated fruit were kept in air for up to 14 days before exposure to 5 kPa CO 2, but not for 1-MCP-treated fruit. DPA treatment prevented development of CO 2 injury even at a level as low as 250 μL L −1. DPA treatment could be delayed for 4 days after 1-MCP treatment while fruit were exposed to 5 kPa CO 2 in air without injury development. Overall the data indicate that 1-MCP enhances the risk of external CO 2 injury, but this injury can be prevented by treatment of fruit with DPA at harvest. In the absence of DPA treatment, handling procedures such as maintaining low CO 2 partial pressures in the storage atmosphere must be used.

Investigation of Changes in Phytohormone Levels Depending on Effects of Exogenous Indole-Butyric-Acid and Callus Formation in the Stem Cuttings of Some Apple Kinds (Malus sylvestris Miller)

Investigation of Changes in Phytohormone Levels Depending on Effects of Exogenous Indole-Butyric-Acid and Callus Formation in the Stem Cuttings of Some Apple Kinds (Malus sylvestris Miller)

Salt stress-mediated changes in free polyamine titers and expression of genes responsible for polyamine biosynthesis of apple in vitro shoots

In the present paper, changes in contents of free polyamines and expression of genes responsible for polyamine biosynthesis of apple [ Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] in vitro shoots exposed to 100 mM or 200 mM NaCl for 10 days were investigated. Salt stress led to severe growth retardation, based on electrolyte leakage (EL), net increase in fresh weight and shoot length. Na concentration in salt-treated shoots was significantly higher than that of the control, and K was unexpectedly enhanced, particularly by 100 mM NaCl. Three commonly occurring polyamines, putrescine (Put), spermidine (SPd) and spermine (Spm), were detected in the shoots, in which Spd and Spm were the most and the least abundant part, respectively. Both types of salt stress led to significant reduction of free Put, and Spm was significantly reduced by 100 mM NaCl, whereas Spd underwent negligible fluctuation. The genes encoding for polyamine biosynthetic enzymes showed diverse expression patterns in response to salt treatment. Salt stress led to induction of MdADC, MdSAMDC1, MdSPDS1 and MdSPMS, whereas it appreciably inhibited transcript level of MdACL5 in a concentration-dependent manner, indicating that the genes were differentially affected by salt stress. The data presented herein showed that salt stress led to conspicuous alteration of free polyamine contents and that mRNA levels of some genes involved in polyamine biosynthesis were strongly influenced. Mechanism underlying the decrease in free Put and gene expression patterns following long-term salt stress were discussed.

Polyamine biosynthesis of apple callus under salt stress: importance of the arginine decarboxylase pathway in stress response

To clarify the involvement of the arginine decarboxylase (ADC) pathway in the salt stress response, the polyamine titre, putrescine biosynthetic gene expression, and enzyme activities were investigated in apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] in vitro callus under salt stress, during recovery after stress, and when ADC was inhibited by D-arginine, an inhibitor of ADC. Salt stress (200 mM NaCl) caused an increase in thiobarbituric acid-reactive substances (TBARS) and electrolyte leakage (EL) of the callus, which was accompanied by an increase in free putrescine content, during 7 d of treatment. Conjugated putrescine was also increased, but this increase was limited to the early stage of salt stress. Accumulation of putrescine was in accordance with induction of ADC activity and expression of the apple ADC gene (MdADC). When callus that had been treated with 200 mM NaCl was transferred to fresh medium with (successive stress) or without (recovery) NaCl, TBARS and EL were significantly reduced in the recovery treatment, indicating promotion of formation of new callus cells, compared with the successive stress treatment. Meanwhile, MdADC expression and ADC activity were also decreased in the callus undergoing recovery, whereas those of the callus under successive stress were increased. Ornithine decarboxylase (ODC) activity showed a pattern opposite to that of ADC in these conditions. D-Arginine treatment led to more serious growth impairment than no treatment under salt stress. In addition, accumulation of putrescine, induction of MdADC, and activation of ADC in D-arginine-treated callus were not comparable with those of the untreated callus. Exogenous addition of putrescine could alleviate salt stress in terms of fresh weight increase and EL. All of these findings indicated that the ADC pathway was tightly involved in the salt stress response. Accumulation of putrescine under salt stress, the possible physiological role of putrescine in alleviating stress damage, and involvement of MdADC and ADC in response to salt stress are discussed.

AROMA VOLATILE BIOSYNTHESIS IN APPLES AT HARVEST OR AFTER HARVEST AFFECTED BY JASMONATES

Effects of jasmonates on production of aroma volatile compounds by 'Tsugaru' apples [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] at harvest, and by 'Delicious' apples after harvest were examined. Among volatiles classified as alcohols, esters, ketones, aldehydes, acetic acid, and α-farnesene, esters were the most prevalent compounds, followed by alcohols. Jasmonate treatment at pre-climacteric stage increased the production of esters (butyl propanoate, butyl butyrate, and propyl butyrate) and of anthocyanin. In addition, jasmonate treatment stimulated 1-aminocyclopropane-1-carboxylate oxidase 1 (ACO 1) mRNA transcript and thylene production at 3 days after treatment. This result suggests that jasmonates may influence ACC oxidase activity. The impact of jasmonate application after harvest on volatile production differed with cultivar. The combination of ethephon with jasmonates reduced volatile production by 'Delicious' compared with ethephon only. The effect of jasmonates on volatile production was related to the effect of jasmonates on internal ethylene concentration. The results show that the effect of jasmonates on aroma volatiles in apples may be mediated by ethylene. Furthermore, the effect of jasmonates on aroma volatiles may depend on the fruit development stage when treated with jasmonates.

Seasonal changes of total carbohydrate contents in three varieties of apple (Malus sylvestris Miller) stem cuttings

Abstract Stems of apple ( Malus sylvestris Miller) varieties ‘Golden delicious’, ‘Starkrimson delicious’ and ‘Misket delicious’ were taken at different times of the year and investigated to find out seasonal changes of their total carbohydrate concentrations. All investigated varieties exhibited seasonal differences in carbohydrate contents. Total carbohydrate contents of these varieties reached at the highest value in February but the lowest in May. For all the three varieties, soluble sugars and starch contents in stem tissues were found to be similar and also soluble sugars contents of stems to be higher than starch through all the sampling period (August–May).

Salicylic Acid, Ethephon, and Methyl Jasmonate Enhance Ester Regeneration in 1-MCP-Treated Apple Fruit after Long-Term Cold Storage

Volatile esters, primarily synthesized in peel tissues, are major aromatic components of apple fruits [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.]. The use of cold storage combined with 1-methylcyclopropene (1-MCP) treatment prolongs the life of apples but represses the regeneration of esters during poststorage ripening. In this study, the regeneration of total esters was significantly increased in apple fruits treated with salicylic acid (SA) and Ethephon (ETH) that had been treated once or twice with 1-MCP. However, methyl jasmonate (MeJA) treatment resulted in regeneration of total esters after a single 1-MCP treatment. To determine the mechanism by which SA, ETH, and MeJA regulate ester regeneration, the apple alcohol acyltransferase gene (MdAAT2) was investigated at the mRNA, protein, and enzyme activity levels. Genes associated with ethylene perception were also investigated by RT-PCR. The results suggest that MdAAT2 controls ester regeneration and that MdETR1 plays a key role in ethylene perception and regulation of downstream MdAAT2 gene expression during poststorage. Ester compounds and concentrations differed in peels treated with different signal molecules, indicating that regulation of the pathway upstream of straight-chain ester biosynthesis depended on the regulation of lipoxygenase (LOX) and alcohol dehydrogenase (ADH) activity by SA, ETH, and MeJA during poststorage ripening.

Spatial distribution of Malus root systems in irrigated, trellised orchards

SummaryRoot distribution was determined for apple trees [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf. ‘Fuji’/’M.26’ (syn. M. domestica Borkh. non Poir.)] 1, 2 and 3 years after planting in trellised orchards in central Texas. Using a soil-coring method, measurable differences were detected in root-length density (RLD; root length per unit volume of soil) by tree age, soil depth, radial distance from the tree, and spatial bearing within and across rows (P ≤ 0.05). For fine roots (root diameters < 1 mm), mean RLD values were 0.1028, 0.1139 and 0.2911 cm cm–3 for 1, 2 and 3 year-old plantings, respectively. For coarse roots (root diameters 1–5 mm), mean RLD values were 0.0006, 0.0009 and 0.0015 cm cm–3 for 1, 2 and 3 year-old plantings, respectively. Mean RLD values declined for both fine and coarse roots of all ages with increasing soil depth and radial distance from the trunk (P ≤ 0.05). Similar patterns were observed for the number of soil cores containing measurable roots. The percentage of samples with no roots increased with increasing soil depth and distance from the trunk (P ≤ 0.05). When examining fine roots by spatial bearing from the tree, the greatest RLD was found along the drip irrigation lines for the two youngest plantings and along drip irrigation lines and beneath shaded trellises for the oldest planting (P ≤ 0.05). For coarse roots, the greatest RLD was found along the drip irrigation lines for all plantings (P ≤ 0.05). This information is important for predicting the rates and locations of new root growth in orchards after transplanting, so that management techniques (e.g., fertilisation, irrigation, control of soilborne diseases) can be properly targeted and effectively implemented.

Effects of Delays between Harvest and 1-Methylcyclopropene Treatment, and Temperature during Treatment, on Ripening of Air-stored and Controlled-atmosphere-stored Apples

The effects of temperature during 1-MCP treatment, and the effects of delays of up to 8 d after harvest before treatment, have been investigated using `Cortland', `Delicious', `Jonagold', and `Empire' (normal and late harvest) apple [(Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] cultivars stored in air for 2 and 4 months and in controlled atmosphere (CA) storage for 4 and 8 months. Fruit were treated with 1 μL·L–1 1-MCP for 24 hours on the day of harvest (warm) or after 1, 2, 3, 4, 6, or 8 days at cold storage temperatures. CA storage was established by day 10. Little effect of temperature during treatment (warm fruit on the day of harvest compared with cold fruit after 24 hours of cooling) was detected. Major interactions among cultivars, handling protocols before 1-MCP treatment, storage type and length of storage were observed. Delays of up to 8 days before 1-MCP treatment either did not affect efficacy of treatment, or markedly reduced it, depending on cultivar, storage type and length of storage. The results indicate that, depending on cultivar, the importance of minimizing the treatment delay increases as storage periods increase.

Two types of spermine synthase gene: MdACL5 and MdSPMS are differentially involved in apple fruit development and cell growth

Three cDNAs with high homology to spermine (Spm) synthases in Arabidopsis were isolated from apple [ Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.]. MdACL5-1 and MdACL5-2 have high homology with ACL5 and MdSPMS has high homology with AtSPMS. The similarity of MdSPMS to spermidine synthases (SPDSs) was higher than that of MdACL5s, despite the fact that both are putative Spm synthases. However, MdSPMS could be discriminated from SPDSs by the presence of several characteristic amino acids, i.e., Val-149, Ser-161, Ala-205, and Val-235, in the decarboxylated S-adenosylmethionine (dcSAM)-binding motif of MdSPMS. Both MdACL5-1 and MdSPMS complemented Spm biosynthesis in a yeast mutant deficient in Spm synthase, and ectopic expression of MdACL5-1 in the Arabidopsis dwarf mutant acl5 allowed recovery of the normal phenotype. RNA gel blot analysis showed that MdACL5 and MdSPMS are differentially expressed in tissues and suspension cells. These results suggest that functional MdACL5 and MdSPMS are independently involved in apple fruit development and cell growth.

Response of Four Apple Cultivars to 1-Methylcyclopropene Treatment and Controlled Atmosphere Storage

Apples [Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf. (`Gala', `Delicious', `Granny Smith' and `Fuji')], pretreated or nontreated with 1-methylcyclopropene (1-MCP, 0.6 to 1.0 μL·L–1 for 18 hours at 20 °C), were stored in controlled atmosphere (CA, 1 to 1.5 kPa O2; 1 to 2 kPa CO2) or in regular atmosphere (RA) for up to 8 months at 1 °C. Firmness, titratable acidity (TA), soluble solids content (SSC), and volatile abundance were analyzed every month directly or after transfer to air at 20 °C for 1 week to determine effect of 1-MCP, storage atmosphere and storage time on apple quality immediately after cold storage and after simulated marketing conditions at 20 °C. The 1-MCP ± CA treatments delayed ripening and prolonged storage life as indicated by delayed loss of firmness and TA in all four cultivars during storage. The 1-MCP ± CA also slightly delayed loss of SSC for `Gala' but had no effect on SSC levels for the other cultivars. There were differences among treatments for firmness and TA content [(1-MCP + RA) &gt; CA] for `Gala', `Delicious', and `Granny Smith' apples, but not for `Fuji'. These differences were generally exacerbated after transfer of fruit to 20 °C for 1 week. A combination of 1-MCP + CA was generally best [(1-MCP + CA) &gt; (1-MCP + RA) or CA] for maintaining `Delicious' firmness and TA. However, the treatments that were most effective at retaining TA and firmness also retained the least volatiles. The results indicate that the efficacy of 1-MCP and CA in maintaining apple quality factors is cultivar dependent and that 1-MCP + RA may be a viable alternative to CA for optimal eating quality for some cultivars.

ETHANOL PRODUCTION AND CHLOROPHYLL FLUORESCENCE IN HEAT-STRESSED APPLE FRUIT DURING STORAGE

Ethanol concentration and chlorophyll fluorescence were measured as signs of heat stress in apple fruit [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.]. 'Mclntosh', 'Cortland', 'Jonagold', and 'Northern Spy' apples were held at 46°C for 0, 4, 8, or 12 h. Following treatments, fruit were stored at 0°C in air and evaluated after 0, 4, 8, or 12 weeks. Peel and flesh browning, headspace ethanol concentration, and chlorophyll fluorescence (Fv/Fm) were measured. Peel browning became apparent in all 4 cultivars 4 weeks after treatment and increased during storage. Exposure to 46°C for 12 h caused severe flesh browning in all cultivars. Severity of flesh browning increased with increasing heat treatment time and storage time. Headspace ethanol concentrations immediately following 12 h heat treatments increased and were 48-, 70-, 9-, and 170- fold higher in 'Mclntosh', 'Cortland', 'Jonagold', and 'Northern Spy' apples than in the controls, respectively. Ethanol concentrations also increased in fruit treated for 8 h but not in those treated for 4 h. Ethanol concentrations were maintained or increased during the 12 weeks of storage. Heat treatments reduced chlorophyll fluorescence (Fv/Fm). One day following treatment, fruit exposed to 46°C for 12 h had Fv/Fm values that were 36%, 59%, 63%, and 36% of the control values in 'Mclntosh', 'Cortland', 'Jonagold', and 'Northern Spy', respectively. The 8 h heat treatment also decreased Fv/Fm in treated fruit, but the 4 h treatment had no effect. Fv/Fm decreased in all treatments during storage. Correlations between flesh browning and ethanol concentration ranged from 0.87 to 0.78, and flesh browning and Fv/Fm ranged from -0.91 to -0.67 depending on cultivar. The increase in ethanol production and decrease in chlorophyll fluorescence were apparent before browning was visually apparent and have the potential to predict injury that develops during storage.