Control of blue mold of apple by combining controlled atmosphere,an antagonist mixture,and sodium bicarbonate

‘Golden Delicious’ apples were wound-inoculated with Penicillium expansum and treated with various combinations of sodium bicarbonate and two antagonists (Metschnikowia pulcherrima, Cryptococcus laurentii), and then stored in air or controlled atmosphere (CA = 1.4 kPa O₂ and 3 kPa CO₂) for 2 or 4 months at 1 °C. The antagonists survived and their populations increased during both air and CA storage. The antagonists alone reduced blue mold but were more effective when combined. Sodium bicarbonate tended to reduce lesion size when used with these antagonist, either when they were used alone or combined. Storage under CA conditions also increased the effectiveness of both antagonist, when used alone or in combination. The only treatment that completely eliminated P. expansum-incited decay was the combination of the two antagonists and sodium bicarbonate on fruit stored under CA conditions. The proper combination of alternative control measures can provide commercially acceptable long-term control of fruit decay and could help reduce our dependency on fungicides.     

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.     

Synergistic effect of Lentinula edodes and Pichia membranefaciens on inhibition of Penicillium expansum infections

The feasibility of using a lyophilized culture filtrate (LCF) from Lentinula edodes at different concentrations to improve the efficacy of Pichia membranefaciens in controlling postharvest blue mold decay in apple fruit was investigated. Application of LCF alone was effective in inhibiting the blue mold rot in apple fruit wounds in a dose-dependent manner. Moreover, the biocontrol activity of P. membranefaciens against blue mold caused by Penicillium expansum in apple fruit could be enhanced by addition of LCF. The combination of P. membranefaciens and LCF resulted in a more effective control than individual treatment of P. membranefaciens or LCF alone. The combined treatment induced higher phenolic accumulation and the upregulation of superoxide dismutase, catalase, ascorbate peroxidase, chitinase and β-1,3-glucanase activities in fruit than LCF or yeast alone, and resulted in a lower lesion diameter and disease incidence. The use of LCF may be an effective method to improve the biological activity of P. membranefaciens, and induced host defenses appear to contribute to the control mechanism of P. membranefaciens and LCF.     

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.     

Integration of biocontrol yeast and thiabendazole protects stored apples from fungicide sensitive and resistant isolates of Botrytis cinerea

Three selected biocontrol yeasts, known for their elevated antagonistic activity against several fungal pathogens, were tested in vitro for compatibility with common fungicides. The antagonists were resistant to several fungicides, but they were inhibited by triazoles and dithiocarbamates. The yeast isolate LS28 (Cryptococcus laurentii), which tolerated in vitro high rates of benzimidazoles, was tested, alone or in combination with a low dose (10% of the full label rate) of thiabendazole, against grey mould on stored apples. Wounded fruit were inoculated with thiabendazole resistant and sensitive isolates of Botrytis cinerea, applied separately or as a mixture. A more effective and prolonged control of fungal decay was always exerted by the biocontrol yeast applied together with thiabendazole at a low dose. This treatment provided synergistic effects and was markedly better than treatments applied separately, whereas the fungicide applied alone at the highest label dose was ineffective in the presence of the isolate of B. cinerea resistant to thiabendazole. The biocontrol yeast applied alone provided significant protection of apples stored for up to 12 days at 20 °C (from 39 to 81% less decay than untreated control), whereas the fungicide alone at low or high dose was always ineffective in the presence of the B. cinerea isolate resistant to benzimidazoles. The integrated treatment was highly effective and durable showing high reduction of decay (from 66 to 92%) even after 18 days of storage. This study suggests that the integration of a biocontrol agent with a low rate of fungicide may be a useful alternative strategy to manage both sensitive and resistant isolates of fungal pathogens efficiently and to reduce risks involved with extensive use of synthetic chemicals.     

Sensitivity of Penicillium expansum to diphenylamine and thiabendazole and postharvest control of blue mold with fludioxonil in ‘McIntosh’ apples

Penicillium expansum is one of the most important pathogens that cause blue mold in stored apples. Due to the development of resistance to the postharvest fungicide, thiabendazole (TBZ), an increase in blue mold has been observed in apple storages. The sensitivity of three TBZ-sensitive and three TBZ-resistant isolates of P. expansum to diphenylamine (DPA), scald inhibitor, was tested in vitro. Of the 94 isolates, collected later in the storage season, 41% were found resistant to both DPA and TBZ. To manage the fungicide resistance, a reduced-risk fungicide, fludioxonil, was tested against blue mold caused by TBZ-sensitive and -resistant P. expansum on ‘McIntosh’ apples treated with or without 1000 μg ml⁻¹ of diphenylamine. Fruit were assessed for disease and scald incidence during storage. Diphenylamine controlled scald in treated fruit. Higher disease incidence of blue mold was observed in apples treated with diphenylamine and low concentrations of fludioxonil (3, 5, and 75 μg ml⁻¹). DPA neither positively nor negatively affected the control of blue mold when DPA was applied together with 150, 300 and 600 μg ml⁻¹ of fludioxonil during 12 weeks of storage at 4 °C.     

Involvement of ethylene in browning development of controlled atmosphere-stored ‘Empire’ apple fruit

‘Empire’ apples [Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.] are susceptible to development of chilling injury, expressed as firm flesh browning, during controlled atmosphere (CA) storage. Because of this susceptibility, fruit are typically stored at 2–4 °C, but the incidence of flesh browning can be increased by 1-methylcyclopropene (1-MCP) treatment at these temperatures. In this study, flesh browning development has been investigated in relationship to ethylene production, internal ethylene concentration (IEC), flesh firmness, total phenolic concentrations, and the activities of polyphenol oxidase (PPO) and peroxidase (POX) in the flesh tissues. Fruit were harvested from two orchards, either untreated or 1-MCP treated, and then stored under CA conditions at either 0.5 or 4 °C. Fruit were removed from storage at 1.5-month intervals for 10.5 months. 1-MCP treated apples were firmer than those of untreated apples, and had lower IECs, at all removals. Flesh browning incidence and severity developed earlier in 1-MCP-treated apples than untreated apples stored at either temperature. Total phenolic concentrations differed by orchard, but no major differences in concentrations were detected between untreated and 1-MCP treated apples. However, PPO activities were higher in the flesh of 1-MCP treated apples than untreated apples from both orchards and at both storage temperatures. POX activity was not consistently affected by 1-MCP treatment or storage temperature. Overall, our results suggest that inhibited ethylene production, either as a result of storage at 0.5 °C, or by treatment with 1-MCP at either temperature, may cause stress and damage to cells and result in higher PPO activity that leads to progressive flesh browning development during CA storage.     

Application of low concentrations of ozone during the cold storage of table grapes

The control by ozone of postharvest decay of table grapes, caused by Botrytis cinerea and other pathogens, was evaluated in chambers and commercial storage facilities. Ozone at 0.100 μL/L or higher inhibited the spread of gray mold among stored grapes. Ozone diffusion into many types of commercial packaging was measured. Boxes made of uncoated paper corrugate inhibited diffusion more than those composed of coated paper corrugate, plastic corrugate, hard plastic, or expanded polystyrene. Internal packaging of hard plastic clamshell containers inhibited diffusion less than low density polyethylene cluster bags. Atmospheres of 0.100 μL/L ozone in the day and 0.300 μL/L at night reduced the natural incidence of gray mold by approximately 65% after 5–8 weeks of storage. Its effectiveness to control postharvest decay was compared to sulfur dioxide fumigation. After 68 days at 1 °C the incidence of gray mold among grapes stored in air, ozone, or with weekly sulfur dioxide fumigation was 38.8%, 2.1%, and 0.1%, respectively. However, decay by other fungi, such as Alternaria spp. and Penicillium spp., was controlled by sulfur dioxide, but not by ozone. In some tests, rachis appearance was moderately harmed by ozone. The combination of ozone use in storage following a single initial sulfur dioxide fumigation, or its use in between biweekly sulfur dioxide fumigations, controlled both gray mold and other pathogens and matched the commercial practice of initial and weekly sulfur dioxide fumigation. The use of both gases in this way reduced sulfur dioxide use greatly. Differences in flavor of grapes treated with ozone were not detectable compared to those stored in air, and grapes treated with ozone were preferred over those treated with sulfur dioxide.     

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.     

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.     

Effect of chitin on the antagonistic activity of Rhodosporidium paludigenum against Penicillium expansum in apple fruit

This study aimed to investigate the effect of chitin on the antagonistic activity of Rhodosporidium paludigenum against Penicillium expansum, the cause of blue mold in apple fruit, and the possible mechanisms involved. Our results showed that biocontrol efficacy and population growth of R. paludigenum were greatly enhanced when it was harvested from nutrient yeast dextrose with added chitin (NYCB) medium compared with that harvested from nutrient yeast dextrose (NYDB) medium. The ability of R. paludigenum produced in NYCB to induce resistance to blue mold in apple fruit was significantly enhanced. The enhanced disease control efficacy was correlated with higher levels of polyphenoloxidase (PPO) and superoxide dismutase (SOD) activities in apple fruit treated with R. paludigenum. Moreover, the SOD and catalase (CAT) activities of R. paludigenum were stimulated by cultivating in NYCB, while malondialdehyde (MDA) accumulation in the yeast cells was suppressed. These results indicated that adding chitin to normal media might be an effective method to improve the antagonistic activity of R. paludigenum and the active oxygen metabolism of R. paludigenum might be closely related to the biocontrol activity of the yeast.     

Integration of continuous biofumigation with Muscodor albus with pre-cooling fumigation with ozone or sulfur dioxide to control postharvest gray mold of table grapes

An integrated approach was evaluated that combined biological and chemical fumigation of table grapes to control postharvest gray mold caused by Botrytis cinerea. After fumigation of the grapes with ozone or sulfur dioxide during pre-cooling, the fruit were then exposed to continuous biofumigation by the volatile-producing fungus Muscodor albus during storage. Biofumigation was provided by in-package generators containing a live grain culture of the fungus. This grain formulation of M. albus survived the initial ozone or sulfur dioxide fumigation, but sulfur dioxide reduced its production of isobutyric acid, an indicator of the production of antifungal volatiles. Gray mold incidence was reduced among inoculated ‘Autumn Seedless’ grapes from 91.7 to 19.3% by 1 h fumigation with 5000 μL L^?1 ozone, and further reduced to 10.0% when ozone fumigation and M. albus biofumigation were combined. The natural incidence of gray mold among organically grown ‘Thompson Seedless’ grapes after 1 month of storage at 0.5 °C was 31.0%. Ozone fumigation and M. albus biofumigation reduced the incidence of gray mold to 9.7 and 4.4, respectively, while the combined treatment reduced gray mold incidence to 3.4%. The use of commercial sulfur dioxide pads reduced the incidence to 1.1%. The combination of ozone and M. albus controlled decay significantly, but was less effective than the standard sulfur dioxide treatments. Although less effective than sulfur dioxide treatment, ozone and M. albus controlled decay significantly, and could be alternatives to sulfur dioxide, particularly for growers complying with organic production requirements.     

Increasing maturity reduces wound response and lignification processes against Penicillium expansum (pathogen) and Penicillium digitatum (non-host pathogen) infection in apples

Penicillium expansum is the main postharvest pathogen of pome fruit and is a necrotrophic fungus that requires wounds to infect the fruit. Therefore, injuries caused during harvest and postharvest handling provide an optimal locus for infection. In this study, the effect of wound response in apples harvested at three different maturity stages and stored at two different temperatures (20 and 0 °C) infected with P. expansum (pathogen) and Penicillium digitatum (non-host pathogen) was evaluated. The effect of wounding and pathogen inoculation on lignin content was also quantified. At 20 °C, less decay incidence and severity were observed when time between wounding and inoculation increased, and these differences were more important in fruit from immature and commercial harvests. However, at 0 °C, wound response was too slow to prevent P. expansum infection. Lignin content was highest in fruit from the immature harvest. Our results indicated that maturity and storage temperature play an important role in apple wound response. This is the first report demonstrating that P. digitatum, a non-host pathogen, was able to develop rots in over-mature apples.     

A new strain of Metschnikowia fructicola for postharvest control of Penicillium expansum and patulin accumulation on four cultivars of apple

The efficacy of three antagonistic yeasts, Metschnikowia pulcherrima strain MACH1, M. pulcherrima strain GS9, and Metschnikowia fructicola strain AL27, against Penicillium expansum and patulin accumulation was evaluated on apples stored at room (22 ± 1 °C for 7 days) and cold temperatures (1 ± 1 °C for 56 days). To increase the potential range of application of the biocontrol agents (BCAs), their efficacy was evaluated on four cultivars of apple, i.e. ‘Golden Delicious’, ‘Granny Smith’, ‘Red Chief’ and ‘Royal Gala’. AL27 was more effective than MACH1 and GS9 in the control of blue mold rot and in the reduction of patulin accumulation. The efficacy of AL27 was in most cases similar to the chemical control used, making the antagonist as competitive as chemical fungicides. In vitro experiments showed that AL27 reduced the conidial germination and germ tube length of P. expansum more than the other strains. The three BCAs were more effective in the control of blue mold rot on ‘Golden Delicious’ apples than on the other tested cultivars.     

Upregulation of polyphenol-related genes prevents ‘skin burning’ of well-colored ‘Cameo’ apples stored under stressful controlled atmosphere conditions

‘Skin burning’ of ‘Cameo’ apples resulting in poorly colored fruit can occur in storage under high CO₂ condition. To elucidate possible reasons for this physiological disorder, we assessed the differential expression of polyphenol-related genes. Poorly colored and well-colored mature ‘Cameo’ apples were stored under either high (3%) or low (0.7%) CO₂ levels, both in combination with 1% O₂, and monitored for seven months for ‘skin burning’. Samples were obtained by the end of storage period, and qPCR analyses were conducted using gene specific primers. We found expression levels of chalcone synthase (MdCHS), chalcone isomerase (MdCHI), anthocyanidin synthase (MdANS), flavonol synthase (MdFLS), dihydroflavonolreductase (MdDFR), and leucoanthocyanidinreductase (MdLAR1) genes to be substantially higher in well-colored compared to poorly colored apples. The delay in establishing the stressful controlled atmosphere (CA) storage condition (3% CO₂ level) led to significantly higher expression levels of MdLAR1, MdCHI, anthocyanidinreductase (MdANR) and flavanone 3-hydroxylase (MdF3H), which may explain the lower incidence of ‘skin burning’ by delayed CA fruit. On the other hand, after seven months in storage, the expression levels of phenylalanine ammonia-lyase (MdPAL), MdCHS, MdCHI, MdDFR, MdFLS, and MdF3H, were significantly higher in poorly colored injured apples, which reflect a feedback mechanism to synthesize more polyphenols to counteract the stressful storage condition.     

Mechanisms of action and efficacy of four isolates of the yeast Metschnikowia pulcherrima active against postharvest pathogens on apples

The mechanisms of action and efficacy of four isolates (GS37, GS88, GA102, and BIO126) of the yeast Metschnikowia pulcherrima against Botrytis cinerea, Penicillium expansum, Alternaria sp., and Monilia sp., all postharvest pathogens of apple fruit, were studied in vitro and on apples, in controlled and semi-commercial conditions. An application of a cell suspension (10⁸ cells per ml) of the antagonists in artificial wounds of apples reduced growth of B. cinerea and P. expansum after storage at 23 °C. A complete suppression of the pathogen was obtained against Monilia sp., stored at 23 °C, and against B. cinerea and P. expansum, stored at 4 °C. The results against Alternaria sp. were more variable. Applications of culture filtrates and autoclaved cells of the isolates were ineffective in reducing the diameter of the lesions on the fruit, supporting the hypothesis that living cells are necessary for biocontrol. In experiments of antagonism in vitro, on different solid substrates, a reduction in the mycelium growth of the pathogens resulted, so that, at least in vitro, the antagonists could produce some diffusible toxic metabolites. In co-cultivation in vitro on a synthetic medium, B. cinerea spore (10⁵ ml⁻¹) germination was completely inhibited by the presence of 10⁸ cells of the antagonists, while culture filtrates and autoclaved suspensions were not able to reduce germination. Dipping boxes of apples cv. Golden delicious in a suspension of 10⁷ antagonist cells per ml and storing for 8 months in controlled atmosphere at 1 °C, showed levels of control against B. cinerea and P. expansum similar to those from thiabendazole.     

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.     

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.     

Integration of pre- and postharvest treatments for the control of black spot caused by Alternaria alternata in stored persimmon fruit

In Israel, black spot caused by Alternaria alternata is the main postharvest factor that impairs the quality and reduces the storability of persimmon fruit (Diospyros kaki cv. Triumph). The fungus infects the fruit in the orchard and remains quiescent until harvest. After harvest, the pathogen slowly colonizes the fruit during storage at 0 °C, which elicits black spot symptom development 2–3 months after storage entry. A commercial postharvest dip treatment in chlorine at 500 mg L^?1, released from sodium troclosene tablets, effectively controlled black spot in fruit stored for up to 2 months. However, decay incidence increased as the length of storage was extended beyond 2.5 months. The long incubation period that precedes black spot symptom development after harvest enabled the development of a series of integrative approaches for application at the pre- and postharvest stages, in combination with the commercial chlorine dip treatment, to improve the control of black spot disease. Preharvest treatments included treatment with the cytokinin-like N₁-(2-chloro-4-pyridyl)-N₃-phenylurea (CPPU) 30 d after fruit set, or a single spray with the curative fungicide polyoxin B 14 d before harvest, and when one of these was applied in combination with the postharvest chlorine dip treatment, the black spot infected area was reduced by 3 and 60%, respectively, compared with the chlorine dip alone. At the postharvest stage, fogging during storage, or post-storage on-line spraying with sodium troclosene, when applied in combination with the postharvest chlorine dip, improved the percentage of marketable fruit by 2 or 10%, respectively, compared with the chlorine dip alone. The results indicate that postharvest pathogens that show a slow colonization pattern might enable the integration of pre- and postharvest disease control methods to improve quality and reduce postharvest disease development.     

Effect of rhamnolipids on Rhodotorula glutinis biocontrol of Alternaria alternata infection in cherry tomato fruit

This study was conducted to evaluate the efficacy of the biocontrol yeast, Rhodotorula glutinis with a surfactant produced by Pseudomonas aeruginosa, rhamnolipids, on the inhibition of Alternaria alternata on cherry tomato fruit. A combination of R. glutinis with rhamnolipids at 500 μg/mL was more effective in suppressing A. alternata infection than application of R. glutinis or rhamnolipids alone. Moreover, integration of R. glutinis with rhamnolipids significantly stimulated peroxidase, polyphenoloxidase and phenylalanine ammonialyase activities of cherry tomato fruit, which were stronger than the single treatments. Rhamnolipids with reduced concentrations did not affect the growth of R. glutinis in vitro, but were utilized as carbon sources by yeasts under conditions of limited carbon sources. Moreover, rhamnolipids themselves reduced decay incidence of A. alternata on cherry tomato fruit and promoted the population growth of R. glutinis in vivo. This combined treatment could induce natural resistance as well as accelerate colonization of yeasts on the fruit surface, providing an effective and safe strategy to control postharvest diseases.