A preliminary study on the effect of metabolic stress disinfection and disinfestation (MSDD) on ripening physiology and quality of kiwifruit and apple

Metabolic stress disinfection and disinfestation (MSDD) is a relatively new quarantine treatment in which fruit are exposed to rapid decompression and compression cycles and high CO₂ atmosphere, followed by exposure to ethanol vapour under decompression. This study evaluated the ripening response of ‘Hayward’ kiwifruit (Actinidia deliciosa) and ‘Pink Lady’ apple (Malus x domestica) to MSDD treatment, which can control longtailed mealybug (Pseudococcus longispinus). Following the treatments, fruit were held at 20 °C for 7 d for shelf-life assessment, while the remainder were refrigerated at 0.5 °C for 16 weeks. Respiration rate, volatile (ethylene, ethanol and acetaldehyde) production rates, firmness and disorders were measured at regular time intervals. MSDD treatments did not affect the metabolic activities and quality of ‘Pink Lady’ apples. However, firmness was reduced by 4.9 N in non-refrigerated MSDD treated fruit. MSDD treatments did not control superficial scald disorder in refrigerated ‘Pink Lady’ apples. For ‘Hayward’ kiwifruit, treatments increased the respiration rate and ethylene production of short-term refrigerated fruit, promoted endogenous production of ethanol and acetaldehyde in both short-term and long-term refrigerated fruit. MSDD treatments also increased the incidence of rots in refrigerated ‘Hayward’ kiwifruit. MSDD treatments accelerated the softening of short-term refrigerated kiwifruit, but retarded the softening of ‘Hayward’ kiwifruit during the 16 weeks of refrigerated storage. MSDD could potentially be used as a quarantine treatment of apples. Further studies are required on the sensory effect of MSDD treatment.     

Cold pre-treatment is effective for 1-MCP efficacy in ‘Tsugaru’ apple fruit

1-Methylcyclopropene (1-MCP) treatment maintains apple fruit quality during storage, but its efficacy is dependent on a number of conditions. ‘Tsugaru’ apples are a major early season cultivar in Japan, but because ‘Tsugaru’ fruit produce abundant ethylene, they have a short shelf-life, and efficacy of 1-MCP is not as high with ‘Tsugaru’ as with other cultivars. To improve 1-MCP efficacy, ‘Tsugaru’ fruit were pre-cooled at −1 °C or −3 °C for 24 h before 1-MCP treatment. Ethylene production decreased with the cold treatment, resulting in better storage after 1-MCP treatment. Although ethylene production was low at the end of 24 h of the cold pre-treatment, expression of ACS1, the ethylene receptor genes ERS1, ETR1(a), ETR1b, ETR2 and ETR5, and the cell wall degradation-related gene PG1 all increased with a 24 h cold treatment. It is assumed that these elevated gene expression levels were not caused by ethylene, but more directly by cold stimulus. Thus, a short period of cold stimulus suppresses ethylene production, but induces expression of some genes. 1-MCP treatment was more effective with some initial fruit chilling.     

Ethanol vapor and saprophytic yeast treatments reduce decay and maintain quality of intact and fresh-cut sweet cherries

The objective of this study was to evaluate the use of an ethanol vapor release pad and a saprophytic yeast Cryptococcus infirmo-miniatum (CIM) to reduce decay and maintain postharvest quality of intact or fresh-cut sweet cherries (Prunus avium) cv. Lapins and Bing. Intact or fresh-cut fruit were packed in perforated clamshells (capacity 454 g) and stored at 1, 10 or 20 °C for up to 21, 14 and 8 d, respectively. For ethanol treatment, a pad made with silica gel powder containing 10 g ethanol and covered with perforated film, which allows ethanol vapor to diffuse gradually, was attached to the upper lid of the clamshells. Ethanol treatment caused accumulation of ethanol in the packaging headspace, about 10 μL L⁻¹ with little change within 14 d at 1 °C, 23 μL L⁻¹ at d 1 and decreased to 15 μL L⁻¹ at d 10 at 10 °C, and 26 μL L⁻¹ at d 1 and decreased to 13 μL L⁻¹ at d 3 at 20 °C. Ethanol content in fruit was less than 9 mg kg⁻¹ in all the control fruit, and increased to 16, 34 and 43 mg kg⁻¹ in ethanol-treated fruit at 1, 10 and 20 °C, respectively. Nonetheless, a sensory taste panel did not perceive any flavor difference from the ethanol treatment. The ethanol treatment retarded softening, darkening, and acid decrease in fruit as well as discoloration of the stems, and extended shelf-life of intact cherries. Ethanol reduced brown rot (Monilinia fructicola) in fresh-cut cherries stored at 20 °C, but not at 1 and 10 °C. A pre-packaging dip in CIM completely controlled brown rot in inoculated fresh-cut cherries stored at 1 °C, and in naturally infected cherries at 20 °C.     

Metabolite content of harvested Micro-Tom tomato (Solanum lycopersicum L.) fruit is altered by chilling and protective heat-shock treatments as shown by GC-MS metabolic profiling

The primary aim of this study was to identify metabolites associated with chilling tolerance that was engendered by a heat-shock treatment of tomato fruit pericarp (Solanum lycopersicum L. cv. Micro-Tom). Harvested mature-green fruit were immersed in 20 or 40 °C water for 7 min (‘Heat-Shock’) and then stored at 2.5 °C for 0 or 14 d (‘Chilled’). A reduction in chilling injury symptoms (i.e., slow or abnormal ripening, increased ion leakage, and increased respiration following chilling) was used to select this heat-shock treatment as optimal. Using GC-MS (Gas Chromatography-Mass Spectrometry) metabolite profiling, 363 analytes were detected in fruit pericarp of which 65 are identified metabolites. Principal Component Analysis of these data led to distinct groups among the samples based on their treatments; ‘Chilled’ and ‘Chilled + Heat-Shocked’ fruit were markedly different from each other, while the ‘Non-Chilled Control’ and ‘Heat-Shocked’ fruit were similar and grouped closer to the ‘Chilled + Heat-Shocked’ fruit. These results indicate that the heat treatment provided protection from chilling in part by altering levels of fruit metabolites. The levels of arabinose, fructose-6-phosphate, valine and shikimic acid appear to be associated with this heat-shock induced chilling tolerance since their levels were altered in the ‘Chilled’ samples (p < 0.05), relative to the control and the heat-shocked protected fruit. We also describe the metabolites we identified that could be further studied as being indicative of incipient chilling injury in mature-green tomato fruit.     

Maturity assessment at harvest and prediction of softening in a late maturing nectarine cultivar after cold storage

The absorption coefficient μ_a measured at 670 nm in fruit pulp at harvest by time-resolved reflectance spectroscopy (TRS) has been shown to be a good maturity index for early nectarine cultivars. By including individual fruit maturity as a biological shift factor (BSF) into a kinetic model for softening it is possible to select fruit with different shelf-life potential. The BSF approach combined with TRS measurement and kinetic modeling of firmness was applied to a late maturing nectarine cultivar (‘Morsiani 90’), ripened at 20 °C after harvest or after storage at 0 °C and 4 °C, the latter conditions inducing chilling injury. At harvest the absorption coefficient μ_a had low values and low variability, indicating advanced maturity, while firmness was similar to that of early cultivars. The softening model took into account these differences, showing parameters similar to those of the early cultivars with the exception of the softening rate which was 2-6 times lower, indicating a slower softening in ‘Morsiani 90’ fruit. Decay of μ_a at 20 °C was also slower. Softening continued during storage at 4 °C, but not at 0 °C. After storage at 0 °C softening was resumed similarly to non-stored fruit, but with much variability. Fruit stored at 4 °C, which showed chilling injury, had a softening rate at 20 °C significantly higher than that of 0 °C fruit. It is suggested that the same changes in cell wall metabolism which induce the appearance of chilling injury also affect firmness and increase softening rate.     

Fruit maturity affects the response of apples to heat stress

Quality changes of apple fruit at different maturity stages in response to heat stress were investigated. ‘Jonagold’ and ‘Cortland’ apples at immature (pre-climacteric), commercial harvest maturity (CHM) and post climacteric maturity (PCM, CHM plus 4 weeks) were harvested and held at 46 °C for 0, 4, 8, or 12 h. Following treatments, fruits were stored in air at 0 °C and evaluated after 0, 1, 2, or 3 months. Quality indices including peel and flesh browning, firmness, titratable acidity, soluble solids, chlorophyll fluorescence (CF), and ethanol production were measured. Results indicated that different cultivars and maturities affected the fruit's resistance to heat stress. ‘Jonagold’ was more resistant to heat stress than ‘Cortland’. Fruit at PCM were most sensitive to heat stress, followed by fruits at CHM and immature stages. When ‘Jonagold’ apples at immature and CHM stages were held at 46 °C for 12 h and then stored for 3 months, flesh browning ratings were negligible compared with 1.4 or 2.9, respectively in ‘Cortland’. Flesh browning rating increased to 1.4 or 4.5 in PCM ‘Jonagold’ held at 46 °C for 8 or 12 h and then stored for 3 months while it was 4.9 or 5.0, respectively, in ‘Cortland’. Heat treatment-induced flesh injury was associated with a decrease in CF. After fruit were exposure to 46 °C for 12 h and then stored for 3 months, Fv/Fm was reduced by 13%, 30%, and 55% in ‘Jonagold’ at immature maturity, CHM and PCM, respectively, while it was reduced by 51%, 58% and 75%, respectively, in ‘Cortland’. Heat stress also caused a decrease in fruit titratable acidity, but had no effect on soluble solids contents. The 8 or 12 h heat treatment resulted in an increase in ethanol production, which was greatest in PCM apples.     

Calcium salts and heat treatment for quality retention of fresh-cut ‘Galia’ melon

‘Galia’ melon is one of the most common cv produced in Spain destined for fresh consumption and/or for the fresh-cut processing industry. Nevertheless, fresh-cut melon is very susceptible to softening during storage, even under chilling and modified atmosphere packaging. This softening process is related to Ca levels in fruit tissue. After preparing trapezoidal shaped sections of ‘Galia’ melons, the pieces were dipped for 1 min a 60 °C in Ca chloride, citrate, lactate, ascorbate, tartrate, silicate, propionate or acetate using a Ca concentration equivalent to 0.4% (0.15 g g⁻¹) pure Ca chloride, combined with 50 mg L⁻¹ H₂O₂ for controlling microbial growth. Dipping in sterile distilled water (without Ca salt) at 60 °C for 1 min was used as a control treatment. Firmness, pectin methylesterase and polygalacturonase activity, Ca content, microbial growth, respiration rate, and sensory evaluation, were evaluated throughout 10 days of storage at 5 °C under a passive modified atmosphere reaching 4.5 kPa O₂ and 14.7 kPa CO₂. At the end of shelf life, Ca ascorbate, chloride and lactate provided melon pieces with a lower respiration rate, increased tissue total Ca content, and maintained a good firmness. In addition, those Ca salts reduced microbial growth. Sensory parameters, such as flavor perception, were kept above the upper limits for marketability. A considerable loss of flavor was found in all treatments except with Ca chlorine, lactate and ascorbate, the only treatments found acceptable from the consumer point of view.     

Effect of 1-methylcyclopropene (1-MCP) on reducing postharvest decay in tomatoes (Solanum lycopersicum L.)

1-Methylcyclopropene (1-MCP as SmartFresh™ technology), an ethylene antagonist, was evaluated for affecting postharvest decay caused by Alternaria alternata, Botrytis cinerea, and Fusarium spp. on ‘Quality 23’ and ‘Seminis 35’ tomatoes at green or pink stages. Fruit with natural or artificial infection were subjected to 1-MCP at 0.0 μL L⁻¹, 0.6 μL L⁻¹ for 12 h, and 1.0 μL L⁻¹ for 6 h. After 31-42 d storage, disease incidence and severity of individual diseases in 1-MCP treated fruit was significantly reduced compared with that of the untreated controls, except in one inoculated test for ‘Quality 23’ where severity of Alternaria rot in 1.0 μL L⁻¹ treated fruit were significantly higher than that of the untreated control. Fruit treated with 1-MCP at 1.0 L⁻¹ for 6 h also had significantly higher incidence of Alternaria rot in the inoculated ‘Quality 23’ and in the non-inoculated ‘Seminis 35’ compared with the fruit treated with 1-MCP at 0.6 μL L⁻¹ for 12 h. The results of this study indicate that 1-MCP can reduce postharvest decay within a certain storage period.     

Mode of action of nitric oxide in inhibiting ethylene biosynthesis and fruit softening during ripening and cool storage of ‘Kensington Pride’ mango

The mode of action of nitric oxide (NO) in inhibiting ethylene biosynthesis and fruit softening during ripening and cool storage of mango fruit was investigated. Hard mature green mango (Mangifera indica L. cv. ‘Kensington Pride’) fruit were fumigated with 20 μL L⁻¹ NO for 2 h at 21 °C and allowed to ripen at 21 ± 1 °C for 10 d, or stored at 13 ± 1 °C for 21 d. During ripening and cool storage, ethylene production and respiration rate from whole fruit were determined daily. The 1-aminocyclopropane-1-carboxylic acid (ACC) content, activities of ACC synthase (ACS), ACC oxidase (ACO), and fruit softening enzymes such as pectin esterase (PE), endo-1,4-β-d-glucanase (EGase), exo- and endo-polygalacturonase (exo-PG, endo-PG) as well as firmness and rheological properties of pulp were determined at two- and seven-day intervals during ripening and cool storage, respectively. NO fumigation inhibited ethylene biosynthesis and respiration rate, and maintained higher pulp firmness, springiness, cohesiveness, chewiness, adhesiveness, and stiffness. NO-fumigated fruit during cool storage and ripening had lower ACC contents through inhibiting the activities of both ACS and ACO in the fruit pulp. NO-fumigated fruit showed decreased activities of exo-PG, endo-PG, EGase, but maintained higher PE activity in pulp tissues during ripening and cool storage. In conclusion, NO fumigation inhibited ethylene biosynthesis through inhibition of ACS and ACO activities leading to reduced ACC content in the fruit pulp which consequently, reduced the activities of fruit softening enzymes during ripening and cool storage.     

Influence of exogenous ethylene during refrigerated storage on storability and quality of Actinidia chinensis (cv. Hort16A)

The kiwifruit industry was established on fruit of Actinidia deliciosa (‘Hayward’), which is known as a climacteric fruit with high sensitivity to ethylene. In recent times fruit from Actinidia chinensis have become a substantial component of the kiwifruit market. There is limited information about the sensitivity of A. chinensis to ethylene during refrigerated storage and hence current ethylene management practices for A. chinensis mimic those established for A. deliciosa. This research aimed to quantify the effect of ethylene during refrigerated storage on A. chinensis (‘Hort16A’) quality (firmness, colour and total soluble solids). Three grower lines were stored at 1.5 °C, 95% RH with ethylene in the range of 0.001-1 μL L⁻¹ applied to the environment after 3 weeks of storage for the remainder of storage (17 weeks). Fruit quality was assessed at regular intervals. Loss of firmness was found to be very sensitive to ethylene, with significant differences between fruit stored in 0.001 μL L⁻¹ (as a control) and 0.1 μL L⁻¹ occurring after 2 weeks of exposure. Fruit exposed to 1 μL L⁻¹ ethylene not only rapidly softened, but also increased in hue angle (greenness) and reduced in lightness (darkened) further reducing the quality of the yellow coloured kiwifruit cultivar. Total soluble solids were not heavily influenced by ethylene exposure, with grower differences being maintained throughout the experiment. This work demonstrates that A. chinensis (cv. Hort16A) fruit firmness and colour will be influenced by the ethylene conditions in a commercial storage environment by advancing ripening and senescence.     

Low oxygen and 1-MCP pretreatments delay superficial scald development by reducing reactive oxygen species (ROS) accumulation in stored ‘Granny Smith’ apples

‘Granny Smith’ apples are highly susceptible to superficial scald, a symptom of chilling injury. For many crops, low temperature storage results in oxidative stress and chilling injury, caused by increased production of superoxide anions which in turn leads to the generation of other dangerous reactive oxygen species (ROS). Application, prior to cold storage, of low oxygen (LO2, <0.5%) atmospheres, ethanol (<2% vapour) or 1-methylcyclopropene (1-MCP, 0.5 μL L⁻¹) at 20 °C, was effective in reducing superficial scald in fruit following 24 weeks of cold storage. ROS levels were measured by confocal laser-scanning microscopy of apple peel treated with the fluorescent probe 2′,7′-dichlorodihydrofluorescein diacetate. In control fruit, ROS levels increased during cold storage and shelf-life and were very high after only 8 weeks, whereas in 1-MCP-, ethanol- and LO2-treated fruit, ROS levels remained low throughout storage. Gene-expression levels of ROS-scavenging enzymes were induced by the various pretreatments: catalase (MdCAT) was induced by LO2 treatment, whereas Mn superoxide dismutase (MdMnSOD) was induced by 1-MCP treatment. Polyphenol oxidase (MdPPO) gene expression levels were associated with scald symptom development and were highest in control fruit. Ethylene levels and expression of ethylene biosynthesis genes were correlated with α-farnesene levels and <alpha>-farnesene synthase (MdAFS) gene expression in the variously treated fruit. Accumulation of the α-farnesene oxidation product, 6-methyl-5-hepten-2-one (MHO), was highest in control fruit after 8 weeks, in accordance with ROS accumulation. The LO2 pretreatment mechanism might involve production of anaerobic metabolites, causing a delay in ethylene and α-farnesene biosynthesis and oxidation; this is different from the mechansism of action of 1-MCP, even though both consequently reduce ROS accumulation and scald symptoms.     

The combination of curing with either chitosan or Bacillus subtilis CPA-8 to control brown rot infections caused by Monilinia fructicola

Recently, it has been reported that brown rot in peaches and nectarines can be effectively controlled by exposing fruit to 50 °C for 2 h and 95-99% relative humidity (RH). This treatment was effective at reducing infections that had become established in the field. However, it did not provide protection for further Monilinia fructicola infections, indicating that fruit was susceptible to subsequent infections after the treatment process and before cool storage. Chitosan and Bacillus subtilis (strain CPA-8) were evaluated for their ability to prevent M. fructicola infections and for their ability to complement the heat treatment. Two chitosan concentrations (0.5% or 1%) were applied at three temperatures (20, 40 or 50 °C) for 1 min to wounded and unwounded fruit that were artificially inoculated with M. fructicola. One percent chitosan applied at 20 °C had a preventive effect against further M. fructicola infections on heat-treated fruit that had been previously inoculated: brown rot incidence was reduced to 10%, in comparison with the control (73%). However, chitosan applied to wounded fruit had a poor preventive effect. The antagonist, B. subtilis CPA-8, had a preventive effect in controlling M. fructicola infections: the incidence of brown rot was reduced to less than 15% for both varieties evaluated (‘Baby Gold 9’ and ‘Andros’ peaches), in comparison with the control fruit (higher than 98%). In contrast, when fruit were stored at 0 °C, this preventive effect was not detected. These findings indicate that heat-treated fruit can be protected from subsequent fruit infection after heat treatment by use of chitosan or B. subtillis CPA-8, thereby providing packinghouses with an effective biologically based, combined approach to the management of postharvest brown rot.     

Molecular analysis of softening and ethylene synthesis and signaling pathways in a non-softening apple cultivar, ‘Honeycrisp’ and a rapidly softening cultivar, ‘McIntosh’

A feature of ‘Honeycrisp’ apples [Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.] is that they maintain flesh firmness over extended storage. The objective of this study was to elucidate molecular mechanisms that are responsible for slow softening of ‘Honeycrisp’ as compared with a rapidly softening cultivar, ‘McIntosh’. Fruit from both cultivars were picked during the normal harvest period and stored at 20 °C for 10 d. Internal ethylene concentrations (IECs) in ‘Honeycrisp’ fruit were lower than in ‘McIntosh’, but at climacteric levels of ethylene ‘Honeycrisp’ fruit maintained their firmness over this period, while ‘McIntosh’ softened rapidly. Concentrations of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) were higher in ‘Honeycrisp’ than in ‘McIntosh’ apples. qRT-PCR analysis was carried out for genes involved in ethylene biosynthesis, perception and signaling [ACC synthase (MdACS); ACC oxidase (MdACO); ethylene receptors (MdETR and MdERS); constitutive triple response (MdCTR); ethylene response factor (MdERF)], as well as those involved in cell wall metabolism [polygalacturonase (MdPG); xyloglucan endotransglucosylase (MdXTH); expansin (MdEXP); β-galactosidase (Md β-GS); arabinofuranosidase (MdAFase); pectate lyase (MdPL)]. At comparable IECs, the expression of genes involved in ethylene synthesis, ethylene perception and signal transduction was generally much higher in ‘Honeycrisp’ than in ‘McIntosh’ fruit. However, the expression of MdAFase and MdEXP3 was generally lower in ‘Honeycrisp’ than in ‘McIntosh’, while that of MdPG and MdPL was extremely low in ‘Honeycrisp’. Expression of MdPG1 was very low, even though IECs were at climacteric levels. Absence of fruit softening in ‘Honeycrisp’ is probably associated with restricted cell wall enzyme activity. The lower maximum IECs found in ‘Honeycrisp’ compared with ‘McIntosh’ do not appear to be related to expression of genes involved in ethylene biosynthesis.     

1-MCP extends the storage and shelf life of mangosteen (Garcinia mangostana L.) fruit

Mangosteen (Garcinia mangostana L.) fruit were harvested when the peel (pericarp) was light greenish yellow with scattered pinkish spots. Fruit were exposed to 1 μL L⁻¹ 1-methylcyclopropene (1-MCP) for 6 h at 25 °C and were then stored at 25 °C (control) or 15 °C. The 1-MCP treatment only temporarily delayed softening of the fruit flesh, during storage. Storage life, defined as the time until the pericarp was dark purple, was much longer in fruit stored at 15 °C than in fruit stored at 25 °C. It was also longer in 1-MCP treated fruit (storage life at 15 °C: control 18 d, 1-MCP-treated fruit 27 d). The 1-MCP treatment also increased the length of shelf life, defined as the time until the pericarp turned blackish purple or showed calyx wilting, at 25 °C. 1-MCP treatment reduced ethylene production. It also reduced pericarp levels of 1-aminocyclopropane-1-carboxylic acid (ACC), and the pericarp activities of ACC synthase (ACS) and ACC oxidase (ACO). In the fruit flesh, in contrast, 1-MCP did not affect ACC levels and ACS activity, but the treatment reduced ACO activity. Taken together, both the storage life and the shelf life of the fruit were extended by the 1-MCP treatment. A decrease in ACO activity largely accounted for the effects of the 1-MCP on ethylene production in the pericarp.     

Importance of storage temperatures in maintaining flavor and quality of mandarins

Mandarins suffer from short ‘flavor-life’ compared with other citrus species. The recommended minimum safe temperature for mandarin storage is 5-8 °C. However, because of continuing reductions in permitted chemical residues and increasing concern regarding decay development, mandarins are often shipped at much lower temperatures of 3-4 °C. In the last few years we noticed wide differences in responsiveness of mandarin varieties to chilling, and that the earliest indication of damage was a decrease in flavor acceptability. In the present study, we evaluated changes in flavor and quality of chilling-tolerant ‘Or’ and chilling-sensitive ‘Odem’ mandarins after 4 weeks of storage at 2, 5, or 8 °C followed by 3 days at 20 °C. Low storage temperatures resulted in loss of orange peel color in fruit of both varieties, which became paler and yellowish. The flavor of ‘Or’ mandarins was not affected by different storage temperatures, whereas ‘Odem’ showed severe flavor loss at low storage temperatures. GC-MS analysis of aroma volatiles revealed that changes of storage temperatures had no major effects on aroma volatile contents in ‘Or’ mandarins. However, in ‘Odem’ mandarins, storage at 2 °C caused accumulation of 13 volatiles, mainly terpenes and their derivates, whereas storage at 8 °C resulted in decreases of six volatiles, comprising five terpenes and one terpene derivative. Overall, we conclude that storage temperature is a fundamental factor affecting color and flavor of mandarins, and therefore it is crucial to define the optimal minimum safe temperature for each mandarin variety. Furthermore, massive accumulation of terpenes is most likely the cause for the decrease in flavor acceptability of ‘Odem’ mandarins after storage at low chilling temperatures.     

Effect of penetration speed on flesh firmness measured on stored kiwifruit

The effect of penetration speed on flesh firmness (FF) measurement by motorised penetrometer was examined for ‘Hayward’ (Actinidia deliciosa var. deliciosa) and ‘Hort16A’ (Actinidia chinensis Planch. var. chinensis) kiwifruit. Data was collected for penetration speeds varying from 4 to 40 mm s⁻¹ using stored fruit of FF ∼10 N; a typical minimum FF threshold for export from New Zealand. Measurements were made on a number of instruments (Instron, GUSS FTA, HortPlus, TA.XTplus), using fruit from different orchards and in each of two different seasons. As expected, FF values increased with increasing penetration speed. A firmness-speed model was developed, based on the Maxwell rheological model for viscoelastic materials, which proved adequate in describing the FF data in terms of the effect of penetration speed. The effect of penetration speed was not adversely influenced by cultivar, season or instrument type. Within the range of fruit firmness examined - stored fruit below 20 N - it was concluded that the firmness-speed model could be successfully used to compare firmness values generated using instruments operating at different penetration speeds.     

Ethylene biosynthesis in apricot: Identification of a ripening-related 1-aminocyclopropane-1-carboxylic acid synthase (ACS) gene

Apricots are climacteric fruits with a high susceptibility to flesh softening and loss of flavor during postharvest storage, and most of the ripening processes are regulated by ethylene, which also has an effect on its own biosynthesis. To understand this process in apricot, inhibition of ethylene biosynthesis and perception was performed for studying key genes involved in the ethylene biosynthetic pathway. Apricots, cv. “Patterson”, were harvested with yellow-green ground color and immediately treated with either the ethylene perception inhibitor 1-methyl cyclopropene (1-MCP) at 10 μL L⁻¹ or the ethylene biosynthesis inhibitor aminoethoxyvinylglycine (AVG) at 1 g L⁻¹. After treatment, quality and physiological attributes such as firmness, color, total soluble solids, acidity, fruit weight, ethylene production and respiration rates were evaluated every 2 d until they ripened at 20 °C. Gene expression analysis was performed by quantitative polymerase chain reaction (qPCR). Both ethylene inhibitors were effective in reducing ethylene production, respiration rate and fruit softening. Three 1-aminocyclopropane-1-carboxylic-acid synthase (ACS) genes were characterized, but only the expression of ACS2 was highly reduced by ethylene inhibition, suggesting a key role in ethylene synthesis at ripening. Contrarily, ACS1 and ACS3 showed a higher expression under ethylene inhibition suggesting that the corresponding genes are individually regulated in a specific mode as observed in other climacteric fruits. Finally, changes in 1-aminocyclopropane-1-carboxylic-acid oxidase genes did not show a consistent pattern of ethylene modulation.     

Effects of ethylene, pollination, and ethylene inhibitor treatments on flower senescence of gentians

Flower senescence of the potted gentian (Gentiana scabra) ‘Shinbisei’ was investigated in relation to ethylene sensitivity and production. ‘Shinbisei’ flowers were used for all experiments except for those with inflorescences. Exposure to ethylene at 0.5 μL L⁻¹ or higher concentrations for 24 h markedly accelerated flower senescence, indicating that G. scabra flowers are highly sensitive to ethylene. Treatment with 0.2 or 0.5 mM silver thiosulfate complex (STS) and 2 μL L⁻¹ 1-methylcyclopropene (1-MCP), ethylene action inhibitors, and 50 mM α-aminoisobutyric acid, an inhibitor of 1-aminocyclopropane-1-carboxylate (ACC) oxidase, did not delay flower senescence. However, treatment with 1 mM l-α-(2-aminoethoxyvinyl) glycine, an inhibitor of ACC synthase, slightly delayed flower senescence. Pollination significantly accelerated petal senescence of G. scabra flowers. Ethylene production of petals, gynoecium, and stamens in unpollinated flowers slightly increased during senescence. Pollination significantly increased ethylene production of petals, gynoecium and stamens 1 day after pollination. To clarify whether 1-MCP delays senescence of cut gentian inflorescences, cut G. scabra ‘Yuki-hotaru’, G. scabra × Gentiana triflora ‘Aoi-kaze’, and G. triflora ‘Koharu’ inflorescences with various stages of flowers, including buds with colored petals, were treated with 2 μL L⁻¹ 1-MCP for 24 h. 1-MCP treatment delayed flower wilting of cut inflorescences of ‘Aoi-kaze’ and ‘Yuki-hotaru’ more than that of ‘Koharu’, suggesting that there is species variation in the effect of 1-MCP in delaying flower senescence of cut gentian inflorescences.     

Structural and physiological changes associated with the skin spot disorder in apple

Skin spot is an important physiological disorder of ‘Elstar’ apples (Malus × domestica Borkh.) that occurs after fruit have been removed from controlled atmosphere storage. Skin spots are irregular patches of small, round, brown blemishes. Cross-sections reveal a browning of protoplasts (coagulated) and of cell walls that extends into the hypodermis. Skin spots are always associated with linear, gaping and non-gaping microcracks in the cuticle. Staining of apple skin with calcofluor white usually results in white fluorescence of cell walls but, within a skin spot, the white fluorescence is weak or absent. Cell walls within, and in the immediate vicinity of skin spots stain with phloroglucin/HCl indicating the presence of lignin. The area of skin affected by skin spots was positively and linearly correlated with the area of the non-blush fruit surface infiltrated by acridine orange. In general, skin spots were limited to the non-blush fruit surface and occurred more frequently near the stem-end than the calyx region of the fruit. Skin spot areas were correlated with a 2.5-fold increase in water vapour permeability compared with unaffected areas (23.8 ± 4.0 m s⁻¹ with skin spots, 9.6 ± 2.1 × 10⁻⁵ m s⁻¹ without skin spots). Strips of the fruit skin from regions with skin spots had an increased maximum force and modulus of elasticity. Dipping fruit in ascorbic acid (0.1 or 0.3 mM for 10 min) before storage decreased the area affected by skin spots. There was no effect of dipping in ethanol/water (70%, v/v, 15 min) or in solutions of captan (1.5 g L⁻¹, 10 min) or trifloxystrobin (0.1 g L⁻¹, 10 min). In contrast, prestorage treatment with 1-methylcyclopropene (630 nL L⁻¹ for 24 h) or poststorage incubation in H₂O₂ (10% for 2, 6, 10 and 16 h) increased skin spots. Our data are consistent with a typical cell response to an oxidative burst that seems to be focussed on particular regions of the ‘Elstar’ fruit surface by concentrations of cuticular microcracks, and that is possibly caused by reoxygenation injury upon removal from CA storage.