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The relationship among the free amino acid content, the expression of genes related to branched-chain amino acid metabolism {branched-chain aminotransferase [BCAT], α-keto acid decarboxylase [pyruvate decarboxylase (PDC)], and threonine deaminase [TD]}, and the production of branched-chain (BC) esters during ripening and senescence in ‘Jonagold’ apple fruit (Malus ×domestica) was studied. Eighteen amino acids were measured by liquid chromatography coupled with tandem mass spectrometry. The content for all amino acids changed with developmental stage and some shared similar patterns of accumulation/diminution. The pattern for isoleucine differed from all other amino acids, increasing more than 20-fold during the ripening process. The onset of the increase was concomitant with the onset of increasing ethylene and BC ester production and the content remained elevated even during senescence. The elevated isoleucine levels are consistent with an increase in the flux through the pathway leading to the formation and degradation of the isoleucine precursor α-keto-β-methylvalerate, which is used for production of BC esters containing 2-methylbutanol and 2-methylbutanoate moieties. Unexpectedly, the content of threonine, the amino acid from which isoleucine is thought to be derived in plants, did not change in concert with isoleucine, but rather declined somewhat after ripening was well underway. Patterns in the expression of some, but not all, of the putative BCAT and PDC genes appeared to reflect the rise and fall in ester formation; however, the expression of putative TD genes did not change during ripening. The patterns in gene expression and amino acid content are interpreted to suggest that the synthesis of α-keto-β-methylvalerate and isoleucine during apple ripening may depend on an as yet uncharacterized pathway that bypasses threonine, similar to the citramalate pathway found in some bacteria.

Postharvest changes in flesh firmness, soluble solids concentration (SSC), and titratable acidity (TA) associated with increasing severity of sunburn browning of apples (Malus ×domestica Borkh.) were investigated over time in regular atmosphere cold storage. In 2005, ‘Gala’ apples were harvested at maturity and sorted into five classes ranging from no sunburn (Sb-0) to severe sunburn browning (Sb-4). Flesh firmness, SSC, and TA were measured on flesh tissue beneath the sunburned area of the apples at harvest and at monthly intervals for 6 months. In 2006, a similar protocol was used for ‘Gala’, ‘Golden Delicious’, ‘Jonagold’, ‘Granny Smith’, and ‘Fuji’ apples, except that these fruit quality traits were determined at harvest and after 3 and 6 months in regular atmosphere cold storage. Flesh firmness and SSC increased, but TA decreased both years in all cultivars as sunburn severity increased from Sb-1 to Sb-4. The patterns of higher firmness with more severe sunburn browning persisted during cold storage even though firmness in all classes of fruit decreased gradually with time in cold storage. The patterns of lower TA as severity of sunburn increased also persisted during cold storage, but TA declined more markedly in apples with more severe sunburn. The ratio of SSC to TA (SAR) increased as the severity of sunburn increased in all five cultivars. The SAR also increased dramatically from harvest to 3 and 6 months after harvest with ratios exceeding 200 in Sb-4 of some cultivars after 6 months storage. This occurred because TA declined very markedly as time in cold storage increased. Relative water concentration of tissue in sunburned areas of apples declined as the severity of sunburn increased, and helps to account for the higher SSC and firmness observed in sunburned apples.

The effect of 1-methylcyclopropene (1-MCP) on biosynthesis of volatiles and fruit ripening in apple (Malus ×domestica Borkh.) was investigated using `Golden Delicious', `Jonagold', and `Redchief Delicious' fruit. Application of 1-MCP to `Golden Delicious' at the preclimacteric stage effectively inhibited ripening as determined by decreased expression of genes for 1-amino-1-cyclopropane carboxylic acid (ACC) oxidase (ACO), and ACC synthase, ACO protein content, climacteric ethylene production, respiration, and volatile ester biosynthesis. Exogenous ethylene applied after 1-MCP treatment did not induce ethylene production, respiration, or volatile production. Activity for alcohol acyltransferase, which catalyzes the final step in ester formation, was demonstrable for 1-MCP-treated fruit, indicating no strict limitation on ester formation is imposed by this enzyme and that ester formation in 1-MCP-treated apple fruit is at least partially limited by reduced substrate synthesis. Once volatile ester formation had been suppressed by 1-MCP, the recovery of volatile synthesis required ≈3 weeks for `Jonagold' and 4 weeks for `Delicious' when held in air at 22 °C. For the first 2 months of storage at 0 °C in air, `Jonagold' and `Delicious' required ≈3 weeks holding at 22 °C for volatile biosynthesis to initiate; after 5 months in refrigerated storage, volatile formation was evident at the time of removal from cold storage. For `Jonagold' fruit held in controlled atmosphere (CA) storage for 2, 5, and 7 months at 0 °C, at least 3 weeks holding at 22 °C were required for volatile formation to begin to recover. The maximal amount of volatile formation was reduced 50% by 1-MCP relative to nontreated control fruit. CA storage had a similar impact on maximal volatile formation. The marketing of 1-MCP-treated fruit soon after treatment might result in the delivery of fruit to the consumer with little likelihood of recovery of volatile ester formation prior to consumption.

Volatile emissions and chlorophyll fluorescence were investigated as potential signals of heat injury for apple (Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.) fruit. 'McIntosh', 'Cortland', 'Jonagold', and 'Northern Spy' apples were exposed to 46 °C for 0, 4, 8, or 12 hours (heat treatments). Following treatments, fruit were kept at 20 °C and evaluated after 1, 2, 4, or 7 days. Heat treatments induced volatile production including ethanol and ethyl acetate. The 8 and 12 hours heat treatments increased ethanol and ethyl acetate production in all four cultivars by as much as 170- and 11-fold, respectively, 1 day after treatments. Heat treatments also reduced ethylene production and chlorophyll fluorescence. Heat for 12 hours caused serious flesh browning. Among the cultivars investigated, 'Northern Spy' and 'McIntosh' were most susceptible to heat stress based on the degree of flesh browning. Correlation coefficients of heat stress induced ethanol emission and chlorophyll fluorescence with flesh browning were 0.82 and -0.66, respectively. The nondestructive measurements of ethanol emission and chlorophyll fluorescence have potential to identify stressed fruit with reduced quality or compromised storage life. (Betula papyrifera Marsh.) seedlings exposed to SO2 exhibited increased production of ethylene, which can be a useful indicator of the onset of stress and/or the degree of stress that a plant is experiencing (Kimmerer and Kozlowski, 1982). However, the relationship between volatile emissions and fruit quality of differ- ent apple cultivars subjected to heat stress has not been reported. Chlorophyll fluorescence is also a useful indicator of several

Unlike cold-hardy apple germplasm, dormant vegetative buds from cold-tender accessions require stabilization of meristematic tissue to protect against injury during desiccation and cryopreservation. Dormant buds of six apple cultivars [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf. `Cox's Orange Pippin', `Einshemer', `Golden Delicious', `Jonagold', `K-14', and `Mutsu'] collected at specific intervals in 1993, 1994, and 1995 at Geneva, N.Y., were stabilized by encapsulation in 5% alginate, treated with step-wise imbibition of 0.5 to 1.0 m sucrose and 0.2 m raffinose solution, and desiccated with forced air at 0 °C. Sugar-alginate stabilization reduced injury during desiccation, increased cold-hardiness of the six cold-tender cultivars frozen to -30 °C, and improved recovery following cryopreservation of buds collected before optimal cold acclimation was attained. Sucrose tissue levels did not increase following stabilization treatment, but levels of glucose and fructose, and of an unknown disaccharide increased. This procedure used nontoxic cryoprotectants, and has potential to expand the scope of dormant bud cryopreservation to include cold-tender apple germplasm.

ADDITIONAL INDEX WORDS. fruit quality, firmness, ethylene, Malus sylvestris var. domestica, postharvest physiology, storage ABSTRACT. An ethylene action inhibitor, MCP, was applied to preclimacteric and climacteric apple ( Malus sylvestris L. (Mill.) var. domestica Borkh. Mansf.) fruit. Experiments were conducted in North Carolina and Washington State utilizing the following cultivars: Fuji, Gala, Ginger Gold, Jonagold, and Delicious. MCP inhibited loss of fruit firmness and titratable acidity when fruit were held in storage at 0 °C up to 6 months and when fruit were held at 20 to 24 °C for up to 60 days. For all cultivars except 'Fuji', differences in firmness between treated and nontreated fruit exceeded 10 N after 6 months storage. These beneficial effects were seen in both preclimacteric and climacteric fruit. Ethylene production and respiration were reduced substantially by MCP treatment. MCP-treated fruit had soluble solids equal to or greater than those in nontreated fruit. Storage and shelf life were extended for all cultivars tested. Chemical name used: 1-methylcyclopropene (MCP).

Hexanal vapor inhibited hyphae growth of Penicillium expansum and Botrytis cinerea on potato dextrose agar (PDA) and on apple (Malus domestica Borkh.) slices. After 48 hours exposure to 4.1 μmol·L-1 (100 ppm) hexanal, the hyphae growth of both fungi was about 50% that of untreated controls. At a concentration of 10.3 μmol·L-1 (250 ppm), neither fungus grew during the treatment period, however, some growth of both fungi occurred 120 hours after treatment. At concentrations of hexanal vapor of 18.6 μmol·L-1 (450 ppm) or more, the growth of both fungi ceased and the organisms were apparently killed, neither showing regrowth when moved to air. When fungi were allowed to germinate and grow for 48 hours in hexanal-free air, a subsequent 48-hour exposure to 10.3 μmol·L-1 hexanal slowed colony growth relative to controls for several days and a 48-hour exposure to 18.6 μmol·L-1 stopped growth completely. Concentrations of hexanal that inhibited fungal growth on PDA also retarded decay lesion development on `Golden Delicious' and on `Jonagold' apple slices. Hexanal was actively converted to aroma volatiles in `Jonagold' and `Golden Delicious' apple slices, with hexanol and hexylacetate production strongly enhanced after 20 to 30 hours treatment. A small amount of butylhexanoate and hexylhexanoate production was also noted. Within 16 hours after treatment, no hexanal could be detected emanating from treated fruit. Since hexanal was metabolized to aroma-related volatiles by the fruit slices, the possibility of hexanal being an essentially residue-less antifungal agent seems likely. The possibility of developing a system for treating apple slices with hexanal in modified-atmosphere packages was also examined. The permeability of low-density polyethylene (LDPE) film to hexanal and hexylacetate was, respectively, about 500- and 1000-fold higher than LDPE permeability to O2. The permeability of both compounds increased exponentially with temperature, with hexanal permeability increased 6-fold while hexylacetate increased only 2.5-fold between 0 and 30 °C.

Controlled atmosphere (CA) storage for 30 or 60 days reduced quality losses for 'Jonagold', 'Golden Delicious', 'Delicious', 'Granny Smith', and 'Fuji' apples ( Malus domestica Borkh.). After 30 days 'Jonagold' and 'Golden Delicious' from CA were firmer, had higher acidity, and were less yellow (more green) than apples from regular atmosphere (RA) storage. 'Delicious' and 'Granny Smith' were firmer after 60 days of CA storage than fruit from RA. In addition, 'Granny Smith' from CA had more acid and were greener than apples from RA. After 8 days of ambient storage, little loss in firmness and no loss in acid content occurred with 'Jonagold' or 'Golden Delicious' from CA compared to the significant loss in firmness and acid when stored in RA. After ambient storage for 8 days, 'Jonagold', 'Golden Delicious', and 'Granny Smith' retained a freshly harvested apple color with more green and less yellow development when stored in CA rather than RA. In 'Fuji', the treatments had no effect except for improved acid retention if stored in CA. A combination of 30 days CA followed by 30 days RA produced 'Jonagold', 'Golden Delicious', and 'Delicious' that were superior in quality to apples from 60 days RA. Present controlled atmosphere (CA) storage in Washington State (WAC, 1989), established in 1964, requires that before fruit can be certified as CA, apples must be stored for 90 days at 5% O 2 or less, and the O2, requirement must be met within 20 days after the room is sealed. Since these requirements were established, tech- nology has advanced and CA conditions can be at 1% O 2 in a matter of hours. There is no doubt that long-term storage in CA has enhanced the dessert quality of apples (Lidster et al., 1980; Mattheis and Olsen, 1989; Meheriuk, 1991; Meheriuk and Pruitt, 1973; Meheriuk, et al., 1984; Patterson and Nichols, 1988; Patterson and Workman, 1962; Olsen, 1969; Olsen and Schemer, 1964). If new technology of establishing very low O2 levels quickly is taken into consideration, there is good reason to believe that early storage quality advantages would be present. Some research (Couey and Olsen, 1975; Lau and Looney, 1978; Olsen and Barnum, 1978; Wang and Mellenthin, 1975) has been concerned with short-term changes in CA atmospheres, but after this short period of time, normal CA patterns were established for long-term storage. No research has been conducted on apple response to short-term (60 days or less) CA storage. with a computer-contr olled system (Technical Consulting Ser- vices, Chelan, Wash.). Nitrogen was supplied by a Generon Membrane Separation System (Generon, Houston). After 30 and 60 days of storage, apples were removed and quality comparisons made between RA and CA storage. A portion of the fruit was removed after 30 days from CA and stored an additional 30 days under RA. Fruit that had received a combination of CA and RA (30/ 30) storage were compared with fruit from 60 days of RA or CA storage alone. Analysis of 'Jonagold', 'Golden Delicious', 'Deli- cious', and 'Fuji' was determined immediately after removal from storage and after 8 days ambient temperature ( ≈ 21 C) storage and after 10 days ambient storage for 'Granny Smith'. Twenty fruit (storage type/storage time/rep) were used for quality analysis.

`Jonagold'/Mark apple (Malus domestica Borkh.) trees that were chip-budded in Washington and Illinois on 31 Aug. or 21 Sept. 1989 were sampled in Apr. 1990 to determine if magnetic resonance imaging (MRI) could be used to nondestructively examine vascular continuity or discontinuity between the rootstock and scion. Images could be placed into three categories based on signal intensity: 1) the rootstock, bud shield, and the bud or new scion growth had a high signal intensity; 2) the rootstock and the bud shield had a high signal intensity, but the scion had a low signal intensity; and 3) the rootstock had a high signal intensity, but the bud shield and scion had a low signal intensity. High signal intensity was associated with bound water in live tissue and the establishment of vascular continuity between the rootstock and scion. Azosulfamide staining and destructive sectioning confirmed that vascular continuity was established when the rootstock, bud shield, and scion had a high signal intensity in images, whereas budding failure occurred when the bud shield and/or the scion had a low signal intensity. Additional trees that had wilted or weak scion growth were collected from Illinois in June 1990. Parenchyma tissue was found in the scion adjacent to the bud shield that interrupted the vascular tissue. Poor scion growth on trees from the 21 Sept. budding in Washington may be attributed to insufficient growth of rootstock and/or scion tissues at the union in the fall.

Newly planted `Jonagold' and `McIntosh' apple (Malus domestica Borkh.) on M.26 fertigated with Ca(N03)2 showed increased early tree vigor and leaf Ca concentration but decreased leaf Mg and Mn compared to trees fertigated with urea or NH4N03. Fertigation with P increased early tree vigor, leaf and fruit P concentration, and decreased leaf Mn in the first year relative to a single planting hole application of granular P. Increased fruit Ca concentration in `Jonagold' in one year was associated with the use of Ca(N03)2 and fertigation of P. Fruit quality was generally unaffected by the experimental treatments.