Influence of film wrapping and fludioxonil application on quality of pomegranate fruit

Pomegranates are sensitive to low temperatures. When fruit are exposed to temperatures below 5–6 °C chilling injury appears as pitting of the skin, browning of the white segments separating the arils and discoloration of the arils, and husk scald, which generally is more severe at temperatures of 6–10 °C. The main objective of this work was to assess the effectiveness of individual film packaging, applied as a stand alone treatment or in combination with fludioxonil, on reducing the occurrence of husk scald, weight loss and decay. Fruit were dipped in an aqueous mixture containing 600 mg L^?1 fludioxonil, wrapped or not wrapped with a polyolephinic heat-shrinkable film and stored at 8 °C and 90% RH for 6 or 12 weeks plus one additional week of simulated shelf-life at 20 °C and 65–70% RH. Respiration rate decreased both in cold storage and at 20 °C. Ethylene production was not detected during cold storage; its rate increased upon transfer to 20 °C, but results were inconsistent. Control fruit deteriorated at a very high rate, due to excessive weight loss, skin browning and decay. Film wrapping almost completely inhibited weight loss and husk scald and preserved fruit freshness for the whole storage time. There was no statistical difference in decay incidence between wrapped and control fruit after 6 or 12 weeks of storage and after the first shelf-life, while after the second shelf-life, wrapped fruit had significantly higher decay levels. By contrast, fludioxonil, both alone and in combination with wrapping, effectively controlled mold development, resulting in 50–67% less decay than control fruit after 12 weeks at 8 °C plus one week shelf-life. Control fruit showed minor changes in nutritional compounds as well as in total polyphenols, anthocyanins and antioxidant activity, while higher losses were detected in film-wrapped fruit during storage at 20 °C.     

Non-invasive assessment of glossiness and polishing of the wax bloom of European plum

A number of fruit including plums develop a pronounced conspicuous layer of epicuticular wax responsible for their attractive visual appearance. During harvest, packaging and transport, this protective layer may be damaged or removed. The resulting appearance generates the impression of poor fruit quality. The aim of this research was to analyse and compare the influence of this wax bloom on storability using a new non-invasive technology and three modifications of the fruit surface. Weight loss was recorded of plums with the natural wax layer, polished by hand or wax removed chemically and stored at 20 °C room temperature or in a refrigerator at 5 °C. With 9.2 mg epicuticular wax/fruit or 302 μg/cm² surface, European plums were classified as highly waxy, which contributed to for their conspicuous wax bloom. The disappearance of the wax bloom viz. increase in glossiness, measured non-destructively with a special sensor, was associated with a doubling of luster levels from 150–250 arbitrary units (a.u.) to 300–600 a.u. after polishing, simulating postharvest handling. Luster levels decreased with time with the polished surface, but not with the natural wax layer, confirming the concomitant greatest weight loss during the 20 days storage of polished fruit. Weight loss was lowest in plums with the natural wax layer, refrigerated at 5 °C, while those stored at 20 °C lost more weight irrespective of surface treatment. This case study explains the relatively short shelf-life and effects of water loss of the plums under different temperatures and surface conditions with wax, polish and chemically treated. This affordable compact light-weight sensor technology offers the opportunity to detect the degree of glossiness and may be used for sorting a number of affected fruit.     

Cold quarantine responses of ‘Tarocco’ oranges to short hot water and thiabendazole postharvest dip treatments

This study investigated the effects of brief hot water and thiabendazole (TBZ) postharvest dip treatments on ultrastructural changes of fruit epicuticular wax (ECW), TBZ residues, decay development and quality traits of ‘Tarocco’ oranges [Citrus sinensis (L.) Osbek] subjected to cold quarantine, subsequent simulated transport and shelf-life. Commercially mature fruit were submerged in water at 20 °C (control fruit) or TBZ at 1000 mg/L and 20 °C for 60 s, or in hot water without or with TBZ at 300 mg/L and 53, 56, or 59 °C for 60, 30, and 15 s respectively. Following treatments, fruit were stored for 3 weeks at 1 °C (simulated quarantine conditions for fruit disinfestations against Mediterranean fruit fly, Medfly), followed by 4 days at 3 °C (simulated long distance transport), and finally kept at 20 °C for 3 days (shelf-life, SL). Scanning electron microscopy (SEM) analysis of ‘Tarocco’ orange surface showed that the typical wax platelets, lifting around edges of wax plates and areas free of epicuticular wax (ECW), that disappeared after hot water dips at 53–59 °C for 60–15 s, become visible again after storage for 21 days at 1 °C (quarantine conditions), and changes involving the appearance of rough ultrastructure, presence large curled plates, fissured wax crusts, and areas with ECW deficiencies, became much more pronounced after shelf-life. These occurrences were related to the transient effect of hot water treatment in decay control. Conversely, treatments with 300 mg/L TBZ 53 °C for 60 s or 56 °C for 30 s effectively reduced decay after quarantine. These treatments were as effective as standard treatment with 1000 mg/L TBZ at 20 °C and produced similar TBZ residue levels in fruit, without impairing fruit quality traits such as visual appearance, weight loss, compression test, sensory attributes, juice color parameters (a*, b*, h, L*, and Chroma), and juice chemical characteristics (soluble solids content, titratable acidity, ascorbic acid, glucose, sucrose, citric acid, total phenols, total anthocyanins, and total antioxidant activity).     

Inhibition of green mold disease in mandarins by preventive applications of methyl jasmonate and antagonistic yeast Cryptococcus laurentii

The objective of this study was to evaluate the preventive activity of methyl jasmonate (MeJA) alone and in combination with antagonistic yeast in suppressing green mold decay in citrus fruit, and to explore the mechanisms involved. At 100 μmol/L, MeJA inhibited disease incidence and lesion diameter of mold decay compared with the control (P < 0.05) The preventive application of Cryptococcus laurentii at 1 × 10⁸ cells/mL combined with 100 μmol/L MeJA reduced green mold incidence compared to the control and the other treatment groups (P < 0.05) when tested in wounded citrus fruit inoculated with Penicillium digitatum. MeJA and C. laurentii induced higher activity of polyphenol oxidase, peroxidase and catalase than control. Moreover, treatment with MeJA and C. laurentii induced a rise in the mRNA expression level of PR5 (pathogenesis-related protein family 5), which was stronger than in the single-treatment groups and the control. In addition, 100 μmol/L MeJA improved the rapid proliferation of C. laurentii in citrus fruit wounds. This combined treatment can induce natural resistance and stimulate the proliferation of antagonistic yeast on the fruit surface.     

Chitosan applications pre- or postharvest prolong raspberry shelf-life quality

Raspberries are fruit with high metabolism that makes them very perishable, impairing their storage and shelf-life. Chitosan coatings have the potential to improve their postharvest life by reducing water loss, respiration rate and decay incidence. The purpose of this work was to study the effect of different concentrations of chitosan, applied pre- or postharvest, on the retention of quality attributes of fresh raspberries. The chitosan concentrations tested were 0 (control), 0.5, 1.0 or 2.0%. The postharvest treatment was applied immediately after harvest, dipping the fruit in the solutions for 5 min. The pre-harvest treatment was done with one hand-spray application per week for three weeks, starting when the fruit were just turning pink. In both experiments the fruit were stored at 0 °C and 90% RH. Pre- or postharvest use of chitosan at 1 or 2% was effective in maintaining titratable acidity and retarding respiration and ethylene production, weight loss and decay incidence. Application by both means resulted in the highest chitosan concentrations accelerating a reduction of ascorbic acid contents. Firmness was maintained only when the fruit were treated pre-harvest at 2%. Thus, application of chitosan at 1 or 2% postharvest and 2% pre-harvest was able to retain key raspberry quality attributes for 15 and 12 days, respectively.     

Rhodosporidium paludigenum induces resistance and defense-related responses against Penicillium digitatum in citrus fruit

Induced disease resistance against plant pathogens is a promising non-fungicidal decay control strategy. In this study, a potential biocontrol yeast, Rhodosporidium paludigenum, was investigated for its induction of disease resistance against Penicillium digitatum in citrus fruit. The results showed that R. paludigenum is the most effective yeast among three selected yeasts in stimulating the resistance of citrus fruit to green mold. When R. paludigenum was applied 48–72 h before inoculation with P. digitatum, disease incidence and disease severity in citrus fruit significantly decreased. Application of R. paludigenum at concentrations of 1 × 10⁸ and 1 × 10⁹ cells mL⁻¹ respectively resulted in 49.6% and 52.5% reductions in the percentage of infections. Induction of resistance to P. digitatum by R. paludigenum treatment significantly enhanced the activities of defense-related enzymes, including β-1,3-glucanase, phenylalanine ammonia-lyase, peroxidase, and polyphenoloxidase, which may be an important mechanism by which the biocontrol yeast reduces the fungal disease of citrus fruit caused by P. digitatum.     

Thiabendazole residue loading in dip,drench and wax coating applications to control green mould and chilling injury on citrus fruit

Green mould (caused by Penicillium digitatum) is a major cause of postharvest losses in citrus. Residue loading of thiabendazole (TBZ) with application methods typically used in South African packhouses and green mould control was studied. TBZ was applied curatively and protectively in dip, drench and wax coating treatments and fruit were inoculated with a TBZ-sensitive or a TBZ-resistant isolate of P. digitatum. The dip treatments consisted of TBZ concentrations of 0–2000 μg mL⁻¹; fruit were dipped for 60 s at 22 °C at a pH of 7. Residues differed between fruit batches and ranged from 0.5 to 1.7 μg g⁻¹ at 1000 μg mL⁻¹ TBZ. Curative dip treatments almost completely controlled green mould (>96% at 1000 μg mL⁻¹ TBZ). The residue level needed for 75% curative control ranged from 0.06 to 0.22 μg g⁻¹, depending on citrus type. Protective treatments were unreliable and control varied from 17% to 97.9% at 1000 μg mL⁻¹ TBZ between fruit batches. Drench treatments consisted of exposure times of 30, 60 and 90 s with 1000 or 2000 μg mL⁻¹ TBZ. Average TBZ residues were 2.14 μg g⁻¹ for Clementine mandarin fruit and 3.50 μg g⁻¹ for navel orange fruit. Green mould control on navel orange fruit resulted in 66–92%, 34–90% and 9–38% control for curative treatments after 6 and 24 h and protective treatments, respectively, depending on fruit batch. Wax with 4000 μg mL⁻¹ TBZ was applied at 0.6, 1.2 and 1.8 L wax ton⁻¹ fruit. Chilling injury was evaluated after fruit storage at −0.5 °C for 40 days. Average TBZ residues loaded was 1.3, 1.3 and 2.7 μg g⁻¹ at the recommended 1.2 L ton⁻¹ for Satsuma mandarin, Clementine mandarin and Valencia orange fruit, respectively. Protective treatments showed lower infection levels (14–20%) than curative treatments (27–40%) for Valencia orange fruit. The same trend was observed with Satsuma (92–95% curative; 87–90% protective) and Clementine mandarin fruit (82–90% curative; 59–88% protective), but control was relatively poor. TBZ application in wax exceeded 5 μg g⁻¹ at higher wax loads (1.2 and 1.8 L ton⁻¹). Wax treatments showed a significant reduction in chilling injury; TBZ had an additive effect. TBZ resistant isolates could not be controlled.     

Evaluation of curative and protective control of Penicillium digitatum following imazalil application in wax coating

Imazalil (IMZ) is widely used in citrus packhouses to manage green mould, caused by Penicillium digitatum. The aim of this study was to investigate green mould control efficacy of IMZ applied in a wax coating, and the combination of aqueous dip and coating IMZ applications. Single application of IMZ at 3000 μg mL⁻¹ in carnauba wax coating at rates of 0.6, 1.2 and 1.8 L tonne⁻¹ of fruit gave better protective (mean 13% infection) than curative (mean 70% infection) control of the sensitive isolate. Imazalil residue levels increased (0.85 to 1.75 μg g⁻¹) with increasing coating load. However, the resistant isolate could not be controlled (>74% infection). Dip only treatment (IMZ sulphate at 500 μg mL⁻¹ for 45 s and 90 s) gave good curative control (≈77%) of the sensitive isolate at residue loading of 0.12–0.73 μg g⁻¹. Wax coating only treatment (IMZ at 3000 μg mL⁻¹ at 1.8 L wax tonne⁻¹) gave good protective control and improved sporulation inhibition (≈80%) at residue loading of 1.32–7.09 μg g⁻¹. The MRL of 5 μg g⁻¹ was exceeded at higher wax loads on navels and clementines. Double application with dip (45 s in IMZ sulphate at 500 μg mL⁻¹) followed by 2000 μg mL⁻¹ IMZ in wax coating at 0.6, 1.2 and 1.8 L wax tonne⁻¹ resulted in residue loading of 1.42 to 2.83 μg g⁻¹, increased protective control (≈69%) as well as curative control (≈83%). In all treatments, poor curative and protective control of the resistant isolate was observed (<46% and <55%, respectively). Double application demonstrated superior green mould control by giving good curative and protective control and sporulation inhibition.     

Combination of hot water,Bacillus amyloliquefaciens HF-01 and sodium bicarbonate treatments to control postharvest decay of mandarin fruit

An antagonistic isolate Bacillus amyloliquefaciens HF-01, sodium bicarbonate (SBC) and hot water treatment (HW) were investigated individually and in combination against green and blue mold and sour rot caused by Penicillium digitatum, P. italicum and Geotrichum citri-aurantii respectively, in mandarin fruit. Populations of antagonists were stable in the presence of 1% or 2% SBC treatment, and spore germination of pathogens in potato dextrose broth was greatly controlled by the hot water treatment of 45 °C for 2 min. Individual application of sodium bicarbonate at low rates and hot water treatment, although reducing disease incidence after 8 weeks or 4 weeks of storage at 6 °C or 25 °C respectively, was not as effective as the fungicide treatment. The treatment comprising B. amyloliquefaciens combined with 2% SBC or/and HW (45 °C for 2 min) was as effective as the fungicide treatment and reduced decay to less than 80% compared to the control. B. amyloliquefaciens HF-01 alone or in combination with 2% SBC or/and HW significantly reduced postharvest decay without impairing fruit quality after storage at 25 °C for 4 weeks or at 6 °C for 8 weeks. These results suggest that the combination of B. amyloliquefaciens HF-01, SBC and HW could be a promising method for the control of postharvest decay on citrus while maintaining fruit quality after harvest.     

Combination of postharvest antifungal chemical treatments and controlled atmosphere storage to control gray mold and improve storability of ‘Wonderful’ pomegranates

Common food additives (sodium bicarbonate (SB), sodium carbonate (SC), and potassium sorbate (PS)) were compared to the fungicide fludioxonil for the control of gray mold on California-grown ‘Wonderful’ pomegranates artificially inoculated with Botrytis cinerea and stored at 7.2 °C in either air or controlled atmosphere (CA, 5 kPa O₂ + 15 kPa CO₂) conditions. Fludioxonil was superior to other treatments. PS was the most effective additive. Synergistic effects between antifungal treatments and CA storage were observed. After 15 weeks of storage at 7.2 °C, the combination of PS treatment (3 min dip in 3% solution at 21 °C) and CA storage was as effective as the combination of heated fludioxonil (30 s dip in 0.6 g L⁻¹ of active ingredient at 49 °C) and air storage. Mixtures of PS with SB or SC did not improve the efficacy of either treatment alone. In tests conducted in commercial facilities, decay development and external and internal fruit quality were assessed on naturally infected pomegranates stored in either air or CA after application of a selected postharvest antifungal combined treatment (CTrt) integrating PS, SB + chlorine, and fludioxonil. CTrt was effective in controlling natural gray mold after 6 weeks of storage at 8.9 °C, but lacked persistence and it was not effective after 14 weeks. CA storage greatly enhanced decay control ability of CTrt. Skin red color was better maintained in CA-stored than in air-stored fruit. Juice color and properties (SSC, TA, and pH) were not practically affected by either postharvest treatment or storage condition. The integration of PS treatments with CA storage could provide an alternative to synthetic fungicides for the management of pomegranate postharvest decay.     

Influence of self-produced CO2 on postharvest life of heat-treated strawberries

Strawberries cv. Selva (75 or 90% superficial red color) were packaged with films having different permeability properties, heat-treated in an air oven (45 °C, 3 h), stored at 0 °C for 0, 7 or 14 days and then transferred to 20 °C for 2 days. The percentage of CO₂ in the package atmosphere and the effect of heat treatment on the following parameters were recorded: weight loss, external color, lightness, anthocyanin content, firmness, titratable acidity, pH, total sugar, total phenol and fruit decay. The application of heat treatment alone reduced fungal decay and delayed red color development and fruit softening. When the treatment was performed on fruit in films that allowed retention of part of CO₂ produced during heating, the delay of fruit softening and color development and the reduction of decay were enhanced. The benefit for 90% red fruit was minimal and decay development was only delayed by 1 day. The results of this work indicate that the well-known benefits of heat treatment could be considerably improved by performing the treatment in the presence of low permeability films, with the aim of retaining the CO₂ produced by the temporary increase in fruit respiration during the heating.     

Hot water dipping treatments on Tarocco orange fruit and their effects on peel essential oil

The most common and serious diseases which affect citrus fruit after harvest in Italy are induced by Penicillium digitatum Sacc. and Penicillium italicum Weh., responsible respectively for green and blue mold rots. This paper deals with the effectiveness of hot water dipping (HWD) treatments as alternative means to control postharvest decay on Tarocco orange fruit [Citrus sinensis (L.) Osbeck], and their effect on fruit quality with special regard to peel essential oils. Selected treatments were HWD at 52 °C for 180 s and at 56 °C for 20 s. These treatments were compared with an effective fungicide standard treatment (Imazalil) and an untreated control. The results showed that HWD at 56 °C for 20 s was more effective in inhibiting P. digitatum spore germination than HWD at 52 °C for longer exposure time. In addition, HWD treatment at 56 °C significantly increased the level of alcohols, esters and aliphatic (fatty) aldehydes. Therefore, the lowest values of decay incidence recorded in HWD fruit treated at 56 °C may be due to the increase in oxygenated monoterpenes, esters and aldehydes. Finally, HWD treatments did not cause surface damage or color change and did not influence internal quality parameters.     

Effect of calcium dips and chitosan coatings on postharvest life of strawberries (Fragaria x ananassa)

Strawberries (Fragaria x ananassa Duch.) were treated either with 1% calcium gluconate dips, 1.5% chitosan coatings or with a coating formulation containing 1.5% chitosan + 1% calcium gluconate and stored at 20 °C for up to 4 days. The effectiveness of the treatments was assessed by evaluating their impact on the following parameters: fungal decay incidence, loss of weight, firmness, external color, pH, titratable acidity and soluble solids content. Calcium dips were effective in decreasing surface damage and delaying both fungal decay and loss of firmness compared to untreated fruit. No sign of fungal decay was observed in fruit coated with 1.5% chitosan which also reduced fruit weight loss. Chitosan coatings markedly slowed the ripening of strawberries as shown by their retention of firmness and delayed changes in their external color. To a lesser extent titratable acidity and pH were also affected by coatings. Whilst addition of calcium gluconate to the chitosan coating formulation did not further extend the shelf-life of the fruit, the amount of calcium retained by strawberries was greater than that obtained with calcium dips alone, thus resulting in increased nutritional value of the strawberries.     

Integrated control of citrus green and blue mold and sour rot by Bacillus amyloliquefaciens in combination with tea saponin

A strain of Bacillus amyloliquefaciens HF-01, isolated from citrus fruit surfaces, was screened for in vitro antagonism toward Penicillium digitatum and identified, based on Biolog identification and phylogenetic analysis of 16S rDNA sequences. The isolate was further evaluated alone, or in combination with tea saponin (TS) on artificially inoculated ‘Wuzishatangju’ mandarin fruit. The results showed that the isolate performed significantly better than the water control in reducing the incidence of green and blue mold and sour rot, but was not as effective as the fungicide treatment. Biocontrol activity of B. amyloliquefaciens HF-01 was significantly improved by addition of TS, which might influence the formation of a bacterial biofilm and stimulate the antagonist population in wounds. The treatment comprising HF-01 combined with 50 μg mL^?1 TS was as effective as the fungicide treatment, which gave more than 90% control of green and blue mold and sour rot. B. amyloliquefaciens HF-01 alone or in combination with a low dosage of TS significantly reduced postharvest decay without impairing any of the other fruit quality parameters. The combination of B. amyloliquefaciens HF-01 and TS could be an alternative to synthetic fungicides for the control of citrus postharvest diseases.     

Improvement of quality and shelf-life of strawberries with edible coatings enriched with chitosan

Strawberry fruit have a very short shelf-life and senescent period due to their high degree of perishability and infection caused by several pathogens that can rapidly reduce fruit quality. The aim of this study was to determine the efficacy of carboxymethyl cellulose (CMC), hydroxypropylmethyl cellulose (HPMC) and composites with chitosan (CH) coatings on the shelf-life and overall quality of strawberry fruit. Strawberry fruit dipped for 2 min in solutions of CMC (1%), HPMC (1%), CMC (1%) + CH (1%) and HPMC (1%) + CH (1%) were stored at 11 ± 1 °C, 70–75% RH, while the uncoated fruit served as controls. Fruit coated with edible coatings showed significant delays in the change of weight loss, decay percentage, titratable acidity (TA), pH, total soluble solids (TSS) and ascorbic acid content as compared to uncoated control fruit. In addition, the edible coatings had a positive effect on maintaining higher concentrations of total phenolics and total anthocyanins, which decreased in control fruit due to over-ripening and senescence processes. Compared to the controls, all the coatings had positive effects on the inhibition of cell wall degrading enzymes and among all the tested coatings, CMC + CH and HPMC + CH was superior in inhibiting enzyme activity. These findings suggest that the use of CMC 1% + CH 1% and HPMC 1% + CH 1% coatings are useful for extending the shelf-life and maintaing quality of strawberry fruit.     

Increasing strawberry shelf-life with carvacrol and methyl cinnamate antimicrobial vapors released from edible films

The effect of carvacrol and methyl cinnamate vapors incorporated into strawberry puree edible films on the postharvest quality of strawberry fruit (Fragaria × ananassa) was investigated. Fresh strawberries were packed in clamshells and kept at 10 °C for 10 days with 90% RH. Strawberry puree edible films, applied in the clamshell, served as carriers for the controlled release of natural antimicrobial compounds without direct contact with the fruit. Changes in weight loss, visible decay, firmness, surface color, total soluble solids content, total soluble phenolics content and antioxidant capacity of strawberries during storage were evaluated. A significant delay and reduction in the severity of visible decay was observed in fruit exposed to antimicrobial vapors. Carvacrol and methyl cinnamate vapors released from the films helped to maintain firmness and brightness of strawberries as compare to the untreated strawberries. The natural antimicrobial vapors also increased the total soluble phenolics content and antioxidant activity of fruit at the end of the storage period.     

Effects of X-ray irradiation and sodium carbonate treatments on postharvest Penicillium decay and quality attributes of clementine mandarins

The integration of sodium carbonate (SC; dips at 20 °C for 150 s in aqueous 3% SC solutions) treatments and X-ray irradiation (at doses of 510 and 875 Gy) was evaluated on artificially inoculated ‘Clemenules’ clementine mandarins for the control of postharvest green and blue molds, caused by Penicillium digitatum and Penicillium italicum, respectively. Although significant, the reduction of both disease incidence (number of infected fruit) and severity (lesion diameter) on fruit either incubated at 20 °C for 7 days or cold-stored at 5 °C for 21 days was not sufficient for satisfactory disease control under hypothetical commercial conditions. Therefore, the combined treatments could not be a substitute for conventional chemical fungicides. However, pathogen sporulation was greatly inhibited on infected clementines, thus X-irradiation could be of value for management of Penicillium resistant strains and to reduce inoculum levels in citrus packinghouses. X-ray irradiation at 195, 395, 510, and 875 Gy did not influence either decay incidence or the area under the disease progress curve (AUDPC) of lesions of green and blue molds on mandarins inoculated with the pathogens 2, 3, or 6 days after irradiation and incubated for 7 days at 20 °C. Therefore, X-ray treatment did not induce disease resistance in the rind of irradiated fruit. Although X-irradiation at doses up to 875 Gy followed by either 14 days at 20 °C or 60 days at 5 °C caused very slight rind pitting, minor decreases in fruit firmness, and modest increases in juice acetaldehyde and ethanol contents, these changes had no practical impact on fruit quality. Rind color, titratable acidity, soluble solids concentration, maturity index and juice yield were not influenced by irradiation. ‘Clemenules’ can be considered as a clementine cultivar highly tolerant to X-irradiation.     

Characterization of sensitivity of grove and packing house isolates of Penicillium digitatum to pyrimethanil

In most northeast Argentinean citrus packing houses, postharvest fungicide treatments are based on the use of thiabendazole and imazalil. However, these fungicides have been used in a manner highly conducive to the selection and proliferation of resistant biotypes of Penicillium digitatum, the main fruit decay fungus in the area. Recently, a new fungicide, pyrimethanil (PYR), was introduced to control molds. Aims of this study were to determine the baseline sensitivities for PYR against isolates of P. digitatum considering its use in the region is not yet widespread and to evaluate the control of the fungus in vivo. One hundred and nine (109) P. digitatum isolates were collected from diseased fruit within citrus groves (43 isolates) and packing houses (66 isolates). EC₅₀ was determined for each isolate by measuring colony diameters on different agar dilutions of the fungicide. The mean EC₅₀ value of the green mold isolates collected from the groves was 0.14 ± 0.03 mg L⁻¹ while the mean EC₅₀ of those collected from packing houses was 0.13 ± 0.05 mg L⁻¹. No resistant isolates were found in the field where the fungicide is not used, while one isolate originated from a packing house showed an EC₅₀ of 3.40 mg L⁻¹, 26-fold higher than the mean level. This isolate was collected from lemons stored in cool rooms of a packing house where PYR had not been used. Fruit decay by sensitive isolates was reduced approximately 80% by PYR applied at 500–600 mg L⁻¹ by immersion for 60 s at room temperature to inoculated oranges and mandarins. In contrast, the resistant isolate was not controlled by PYR applied at 1000 mg L⁻¹. Thus, the introduction of PYR applied into packing houses should be done carefully and control strategies should be implemented in order to minimize the development of resistant isolates.     

Effects of hot water treatment on anthracnose disease in papaya fruit and its possible mechanism

Harvested papaya fruit are perishable due to rapid ripening and softening and susceptibility to biotic or abiotic stresses. Hot water treatment (HWT) can preserve fruit quality by reducing decay. The present study investigated effects of HWT on controlling fungal pathogens of papaya fruit and the possible mechanism by which HWT induced disease resistance. HWT (54 °C, 4 min) of papaya fruit had a pronounced effect on reducing the carrier rate of Colletotrichum gloeosporioides (C. gloeosporioides) in fruit peel, significantly inhibited the incidence of anthracnose and stem-end rot, effectively delayed fruit softening, but slightly promoted the rate of fruit coloring. HWT reduced the anthracnose index and fruit ripeness to a certain extent and induced changes in the wax arrangement on the surface of treated fruit, causing the wax to melt. The cracks and most stomata appeared to be partially or completely plugged by the melted wax, thereby providing a mechanical barrier against wound pathogens. HWT induced the expression of CpPGIP and promptly induced the expression of CpNPR1, and then regulated the expression of the CpPR1 gene, which may enhance the resistance of the fruit to anthracnose disease and reduce the decay rate. Together, these results confirm that HWT could reduce disease incidence and induce resistance, and thus maintain postharvest quality during storage and prolong the shelf-life of papaya fruit.     

Ripening and sensory analysis of Guatemalan-West Indian hybrid avocado following ethylene pretreatment and/or exposure to gaseous or aqueous 1-methylcyclopropene

Previous reports showed that both gaseous and aqueous 1-methylcyclopropene (1-MCP) delay ripening of avocado (Persea americana Mill.), but there are no reports of the influence of 1-MCP on its sensory attributes. The objective of this study was to evaluate the effects of ethylene pretreatment and/or exposure to gaseous or aqueous 1-MCP on fruit ripening and sensory attributes of ‘Booth 7’ avocado, a Guatemalan-West Indian hybrid. Separate experiments were conducted during two seasons (2008 and 2009) with fruit harvested at preclimacteric stage in October (early season) and in November (late season). Fruit from Season 1 were exposed to ethylene (4.07 μmol L⁻¹) for 12 h at 20 °C, and stored for more 12 h at 20 °C in an ethylene-free (ethylene, <0.1 μL L⁻¹) room prior to treatment with either aqueous (1.39 or 2.77 μmol L⁻¹ a.i.) or gaseous (3.15 or 6.31 nmol L⁻¹ a.i.) 1-MCP. Ripening was monitored and firmness, respiration, ethylene production and weight loss were measured. Texture profile analysis and sensory analysis were performed on ripe fruit only (firmness, 10–15 N). Fruit from Season 2 were not exposed to ethylene pretreatment but treated only with aqueous 1-MCP 24 h after harvest. Fruit were assessed exclusively for sensory analysis when ripe (firmness, 10–15 N). Treatment with either 1-MCP formulation effectively delayed ripening from 4 to 10 d for early-season fruit, and from 4 to 6 d for late-season fruit. Higher concentrations of 1-MCP of either formulation had the greatest effect on selected pulp textural parameters of early-season fruit; the gaseous formulation had greater effect on late-season fruit quality than the aqueous formulation. In general, sensory panelists ratings of overall liking were not affected by 1-MCP treatment. Both aqueous and gaseous 1-MCP formulations delayed ripening of the Guatemalan-West Indian ‘Booth 7’ avocado without significant loss in appearance or in sensory attributes and, therefore, could be considered for use as a postharvest treatment for this hybrid.