Combination of peracetic acid and hot water treatment to control postharvest brown rot on peaches and nectarines

Brown rot caused by Monilinia spp. is the most important postharvest disease of stone fruit. From preliminary studies, the combination of 0.25% hydrogen peroxide, 0.02% peracetic acid (PAA) and 0.075% acetic acid, corresponding to 300 mg L⁻¹ of PAA, was selected to control Monilinia fructicola. Brown rot control was similarly controlled when the same concentration of PAA was applied with a PAA-based commercial product. In order to reduce PAA concentration, combinations of different concentrations and temperatures were evaluated. A treatment of 200 mg L⁻¹ of PAA at 40 °C for 40 s was selected to control pre-existing and future infections, different inoculum concentrations of M. fructicola and to control brown rot on naturally infected fruit. Brown rot was completely controlled with the selected treatment when peaches and nectarines were inoculated 0 h before the treatment but it was not controlled when infection time was increased to 24, 48 and 72 h. Also, the treatment significantly controlled brown rot at all inoculum concentrations evaluated (10³, 10⁴, 10⁵ and 10⁶ conidia mL⁻¹) in both peaches and nectarines, but no protection against future infections was observed. In naturally infected fruit, brown rot incidence was slightly but significantly reduced to 61 and 36% in ‘Roig d’Albesa’ and ‘Placido’ peaches, respectively, but not in nectarines. Immersion for 40 s in 200 mg L⁻¹ of PAA at 40 °C provides an alternative treatment to control only recent infections of Monilinia spp. whatever their concentration without generally affecting fruit quality.     

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.     

Continuous microwave treatment to control postharvest brown rot in stone fruit

Monilinia spp. are the most important causes of brown rot in stone fruit and no chemical fungicides are allowed in the European Union to be applied to stone fruit after harvest. From preliminary studies, microwave (MW) treatments at 17.5 kW for 50 s and 10 kW for 95 s were selected as effective conditions to control brown rot. Both treatments were investigated to control Monilinia fructicola in fruit with different weights and maturity levels and in naturally infected fruit. Fruit weight only had a significant effect on microwave efficacy in ‘Placido’ peaches treated by MW at 10 kW for 95 s in which better brown rot control was observed in small than large fruit. Maturity level did not have a significant effect on efficacy of MW treatments in any of the varieties evaluated. When both MW treatments were studied in naturally infected peaches and nectarines, brown rot incidence was significantly reduced to less than 14% compared with untreated fruit where brown rot incidence was higher than 45%. The effect of both treatments on fruit quality was also evaluated. Fruit firmness was not negatively affected in the varieties tested and even a delay of fruit softening was observed. However, internal damage around the stone was observed, especially in the smallest fruit in which high temperature is achieved at the end of both MW treatments.     

Immersion of fruit in water to improve radio frequency treatment to control brown rot in stone fruit

Brown rot caused by Monilinia spp. is the most important postharvest disease of stone fruit. Currently, no chemical fungicides are allowed in the European Union to be applied to stone fruit after harvest, which has increased the need to develop alternative methods. Radio frequency (RF) treatment at 27.12 MHz with fruit immersed in water was studied to control brown rot in peaches and nectarines artificially inoculated with M. fructicola. Additionally, RF treatment in air was also investigated to evaluate the benefit of water immersion to reduce the effect of fruit size on treatment efficacy. RF treatment with fruit immersed in water at 20 °C applied for 9 min significantly reduced brown rot incidence in both peaches and nectarines and no significant differences in RF efficacy were observed depending on fruit size. However, when RF treatment was applied in air for 18 min, brown rot reduction was significantly higher in large fruit than in small fruit. Finally, the decrease in exposure time of radio frequency treatment with fruit immersed in water with increasing water temperature was also studied. Reduction of treatment time to 6 and 4.5 min was achieved by increasing water temperature at 35 and 40 °C, respectively, to control brown rot without adverse external and internal damage in both ‘Baby Gold 9’ peaches and ‘Autumn Free’ nectarines.     

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.     

Effect of host and Monilinia spp. variables on the efficacy of radio frequency treatment on peaches

Brown rot caused by Monilinia spp. is the most important postharvest disease of stone fruit. Currently, no chemical fungicides are allowed in the European Union to be applied to stone fruit after harvest. In previous work, radio frequency (RF) treatment for 4.5 min applied with fruit immersed in water at 40 °C was very promising for the control brown rot on peaches and nectarines. In the present study, the efficacy of this radio frequency treatment was studied employing different infection times, inoculum concentrations, fruit maturity levels and in naturally infected fruit. Generally, infection time and maturity level of fruit did not have a significant effect on the RF treatment efficacy and brown rot incidence was significantly reduced in fruit inoculated 0, 24 or 48 h before treatment and at all maturity levels evaluated in both peaches and nectarines. RF treatment significantly reduced brown rot incidence at all inoculum concentrations evaluated (10³, 10⁴, 10⁵ and 10⁶ conidia mL⁻¹). However, in peaches, the treatment efficacy was slightly less when the inoculum concentration was increased to 10⁵ or 10⁶ conidia mL⁻¹. In naturally infected fruit, brown rot incidence was significantly reduced from 92% among control fruit to less than 26% in peaches and complete brown rot control was achieved in nectarines. RF treatment did not have an effect on fruit firmness in the varieties tested, and even a delay of fruit softening was observed. Moreover, both external and internal fruit appearance was not affected by the treatment.     

Biocontrol of Botrytis cinerea in table grapes by non-pathogenic indigenous Saccharomyces cerevisiae yeasts isolated from viticultural environments in Argentina

Botrytis cinerea, the causal agent of gray mold, is an important disease of grapes. Yeasts are members of the epiphytic microbial community on surfaces of fruits and vegetables and because some yeasts inhibit fungi they are used as biocontrol agents. The major objective of the present work was to isolate yeasts from grapes, vineyard soil, and grape must and select them for their ability to prevent gray mold onset after harvest. Yeasts that were found effective against the fungus were also assayed for their possible pathogenicity in humans. Two antagonism experiments were performed to study the effect of yeasts on B. cinerea, an in vitro study with Czapeck Yeast Extract Agar and an in vivo study with grape berries at 2 °C and 25 °C; both experiments were conducted at different yeast concentrations (10⁵, 10⁶ and 10⁷ cfu/mL). Antagonists were subsequently assayed for their ability to colonize and grow in fruit wounds. The biocontrol yeasts were also examined for their possible pathogenicity in humans: phospholipase and proteolytic activity, growth at 37 °C and 42 °C, pseudohyphal formation and invasive growth. A total of 225 yeasts belonging to 41 species were isolated from must and grape berries and 65 of them, representing 15 species, exhibited in vitro inhibition of B. cinerea at 25 °C. These 65 biocontrol yeasts were subsequently assayed in vivo and 16 of them (15 Saccharomyces cerevisiae and 1 Schizosaccharomyces pombe) showed antagonistic properties against B. cinerea at 25 °C. Only one isolate (S. cerevisiae BSc68) was able to inhibit mycelial growth of B. cinerea on grape berries at both 2 °C and 25 °C. The biomass of this strain in grape wounds increased 221.5-fold at 25 °C after 3 d and 325.5-fold at 2 °C after 10 d of incubation. An increase in the concentration of certain yeasts significantly enhanced their antagonistic activity. All yeast isolates determined as biocontrol agents under in vivo conditions were isolated from fermenting musts. Twelve biocontrol agents (S. cerevisiae) revealed one or more phenotypical characteristics associated with pathogenicity in humans but none of them showed all characteristics together. The fact that there exist few reports on S. cerevisiae and none on Sch. pombe as biocontrol agents against B. cinerea makes our results even more relevant.     

The effect of metabolic stress disinfection and disinfestation (MSDD) on ‘Hass’ avocado fruit physiology and mortality of longtailed mealybug (Pseudococcus longispinus)

Metabolic stress disinfection and disinfestation (MSDD) is a potential quarantine treatment in which a combination of cycles of rapid decompression and compression are followed by exposure to ethanol vapour under decompression. The response of ‘Hass’ avocado (Persea americana Mill., cv. Hass) to MSDD treatment for control of longtailed mealybug (Pseudococcus longispinus) was investigated. The best treatment for the most resistant life stage (2nd/3rd instars) was 90-min MSDD treatment with 371 mg L⁻¹ ethanol. Early and late season ‘Hass’ avocados were subjected to MSDD treatments (with 371 mg L⁻¹ ethanol), or in air (control). Following the treatments, early season fruit were ripened at 20 °C and 25 °C. Half of the late season fruit were ripened at either 20 °C or 25 °C, and the remainder were stored at 5.5 °C for 6 weeks, then ripened at 20 °C. There were no significant difference in quality and rot incidence between non-treated controls and MSDD-treated fruit. The main disorders found were stem-end and body rots, vascular browning and flesh greying for the stored fruit. There were also no significant differences in fruit respiration rate or ethylene production. Thus, MSDD was shown to be a potentially ‘soft’ disinfestation treatment for surface pests of avocado.     

Culturable bacteria from plum fruit surfaces and their potential for controlling brown rot after harvest

Fruit microflora have been the richest source of antagonists against fruit decays and the active ingredient in all currently available commercial biocontrol products. A comprehensive evaluation of plum bacteria for biocontrol activity against Monilinia fructicola, which causes brown rot of stone fruit, is important for determining their biocontrol potential. Resident culturable bacterial microflora of plums from early fruit development until maturity were characterized. The most dominant genera were Curtobacterium (19.88%), Pseudomonas (15.06%), Microbacterium (13.86%), and Clavibacter (12.65%). These genera occurred at all four isolation times and accounted for 61.45% of all isolates. Microbacterium and Curtobacterium dominated at the early stage of fruit development while Pseudomonas and Clavibacter were dominant at the end of the season. Less prevalent genera were Enterobacter (5.42%), Chrysomonas (4.82%), and Pantoea (4.22%). Most frequently isolated species were Microbacterium lacticum, Clavibacter michiganensis, Curtobacterium flaccumfaciens, Enterobacter intermedius, and Chrysomonas luteola. The seasonal succession of genera was observed in both MANOVA and frequency analysis. Primary and secondary screening of plum-inhabiting bacteria for control of brown rot on wounded fruit resulted in selection of several antagonists among which Pantonea agglomerans and Citrobacter freundii were the most effective. These antagonists grew well in plum wounds and increased by four log units during first three days at 24 °C, and two log units after seven days at 4 °C. Results indicate that plum microflora are an excellent source of antagonists against brown rot decay originating from wounds after harvest.     

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.     

Chilling-injury of harvested tomato (Solanum lycopersicum L.) cv. Micro-Tom fruit is reduced by temperature pre-treatments

Heat-shocks were used to reduce the development of chilling injury symptoms during ripening of tomato fruit (Solanum lycopersicum L. cv. Micro-Tom). Mature green tomatoes were immersed in 30-50 °C water for 3-9 min before being chilled at 2.5 °C for 0, 0.5, 1, 2, 3, or 14 days, and then held at 20 °C for an additional 7-14 days. The affect of both heat-shock and chilling treatments were independent of fruit weight. Measured at 20 °C after 14 days of chilling, fruit exposed to 40 °C for 7 min exhibited reduced chilling injury symptoms, as measured by their advanced ripening score and decreased rate of ion leakage into an isotonic 0.2 M mannitol solution. Reduced rates of leakage from the symplastic compartment probably contributed to the 2-fold decrease in the amount of ions in the apoplastic space, when compared to the control. A subsequent paper will report the results of metabolic profiling of Micro-Tom tomato fruit subjected to treatments that significantly decreased their development of chilling injury symptoms.     

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.     

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.     

Control of Monilinia rots on fruit naturally infected by hot water treatment in commercial trials

In recent years, safer methods for the control of fruit postharvest pathogens have been investigated and heat treatment could represent an effective and safe approach for managing postharvest decay such as Monilinia rots. In the present study, the effect of hot water treatment (HWT) (60 °C for 30 and 60 s) on brown rot was investigated. More specifically, the influence of HWT was determined in in vitro trials on conidial germination of Monilinia laxa, Monilinia fructicola and Monilinia fructigena and in peach and nectarine fruit, naturally infected. The effect of hot water application on fruit quality was also assessed. M. fructicola showed a greater resistance to heat than M. laxa and M. fructigena, however conidia germination of all three species was completely inhibited by a dipping in hot water for 1 min at 55 °C. The results of a large scale experiment under commercial conditions and several pilot trials showed a good antifungal activity of HWT in naturally infected fruit. After 6 days at 0 °C and 3 days at 20 °C, in both semi-commercial and commercial trials, the inhibition of decay was higher than 78% in four trials out of six. In addition, the treated fruit showed an acceptable commercial quality and no visual damage was observed as a consequence of HWT. The results demonstrated that HWT is a promising method to control Monilinia rots of peach and nectarine, and is safe and readily available for conventional and organic production under commercial conditions.     

Control of fungal decay of apples and peaches by the biofumigant fungus Muscodor albus

The potential of the volatile-producing fungus Muscodor albus for controlling postharvest diseases of fresh fruit by biological fumigation was investigated. In vitro tests showed that M. albus volatiles inhibited and killed a wide range of storage pathogens belonging to species of Botrytis, Colletotrichum, Geotrichum, Monilinia, Penicillium and Rhizopus. Fumigation of apples for 7 days with culture of M. albus grown on autoclaved grain gave complete control of blue mold (Penicillium expansum) and gray mold (Botrytis cinerea) in wound-inoculated fruits. There was no direct contact between the fruit and the M. albus culture. Shorter fumigation times ranging between 24 and 72 h, applied immediately or 24 h after inoculation, also controlled blue mold and gray mold. In wound-inoculated peaches, 24–72 h fumigation with M. albus provided complete control of brown rot (Monilinia fructicola). The volatile profile of M. albus-colonized grain was measured by gas chromatograph connected to a flame ionization detector (GC-FID) and showed that 2-methyl-1-butanol and isobutyric acid were the major volatile compounds found in the headspace. Since M. albus is a sterile mycelium and does not require direct contact with the crops to be treated, it could be an attractive biological fumigant for controlling postharvest diseases.     

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 UV-C treatment on inactivation of Escherichia coli O157:H7, microbial loads, and quality of button mushrooms

This study investigated the effects of ultraviolet-C (UV-C) light applied to both sides of mushrooms on microbial loads and product quality during storage for 21 d at 4 °C. Microflora populations, color, antioxidant activity, total phenolics, and ascorbic acid were measured at 1, 7, 14 and 21 d of storage. Additionally, the inactivation of Escherichia coli O157:H7 by UV-C was determined. Results showed that UV-C doses of 0.45-3.15 kJ m⁻² resulted in 0.67-1.13 log CFU g⁻¹ reduction of E. coli O157:H7 inoculated on mushroom cap surfaces. UV-C radiation also reduced total aerobic plate counts by 0.63-0.89 log CFU g⁻¹ on the surface of mushrooms. Although mushrooms treated with UV-C had more severe browning with increasing dosage after initial treatment, the control mushrooms also browned as indicted by lower L* and higher a* values after 21 d of storage at 4 °C. In addition, the UV-C treatments apparently inhibited lesion development on the mushroom surface. During the first 7 d, irradiated mushrooms had lower antioxidant activity, total phenolics, and ascorbic acid content compared to non-radiated samples. However, irradiated mushrooms reached similar amounts of these nutrients as the control after 14 d of storage at 4 °C. In summary, UV-C radiation could potentially be used for sanitizing fresh button mushrooms and extending shelf-life.     

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.     

The frost tolerance of Miscanthus at the juvenile stage: Differences between clones are influenced by leaf-stage and acclimation

Miscanthus, a perennial, C₄ grass, has numerous advantages for biomass production, notably its high yield per hectare and low input requirements. However, establishment of this crop may be affected in Europe by frost damage when stem emergence occurs early in the year. The principal aim of this study was to quantify the impact of frost on young miscanthus shoots at different leaf-stages, and to characterise inter-species variations in frost tolerance. Four clones belonging to two species were tested at three leaf stages in a climate-controlled chamber simulating acclimation conditions and frost treatments. Frost tolerance was scored using a 0-6 visual assessment scale and analysed with nonparametric tests.We were thus able to show that more developed plants (6 or 7-leaf stage) were less frost tolerant than those at the 3 or 5-leaf stage. Plants at the 6 or 7-leaf stage also displayed differences in tolerance between clones. The leaf-stage of the plant is linked to apex height, and this appeared to play a role in frost tolerance. M. sinensis displayed variable frost tolerance (tolerance score of between 3.6 and 4.9), although the three clones observed were always more frost tolerant than M. x giganteus (with a score of 3). Moreover, the differences in frost tolerance were negatively correlated (r = −0.94) with the mean leaf surface area of clones at the time of frost exposure. Finally, we observed that acclimation at 12 °C under strong light intensity (600 μmol m⁻² s⁻¹) enabled an increase in the tolerance of young shoots in all the clones tested.