Apple Blue Mold Research Articles

Residue levels and performance of potassium sorbate and thiabendazole and their co-application against blue mold of apples when applied as water dip treatments at 20 or 53 °C

The efficacy of potassium sorbate (K-sorb) as an antifungal, alone or combined with thiabendazole (TBZ), and hot water at 53°C, was studied against blue mold on apples. Results demonstrated the fungistatic effect of K-sorb: 2000mgL−1 significantly reduced Penicillium expansum growth, and a 24h delay in fungi development was observed in the amended liquid culture. K-sorb at 1% significantly diminished decay incidence, especially when applied at 53°C. The performance of TBZ was not improved by the co-application of K-sorb. Treatments efficacy was related to K-sorb distribution on fruit surface. ESEM and X-ray qualitative spectra analyses revealed an irregular distribution of K-sorb over the fruit surface and areas with salt accumulation. K-sorb residues remained quite unchanged until 3 d of storage then they declined progressively. Their degradation was influenced by water temperature: it was faster on fruit treated at 53°C. An inverse relation between P. expansum growth and K-sorb concentration was observed. After 72h of incubation, P. expansum depleted 99% of K-sorb from liquid culture media.The low efficacy of K-sorb treatments against blue mold decay on apple fruit may be ascribed to the low persistence of K-sorb residues, to the irregular spatial distribution of the salt on the fruit surface, and the ability of P. expansum to degrade the salt.

Efficacy of Non-Chemical Alternatives on Blue Mold of Apple under Controlled Cold Storage Conditions

Fruits of three apple cultivars; Golden Delicious, Granny Smith and Fuji were inoculated with blue mold, Penicillium expansum , and kept under cold storage conditions for 75 days after treatment with non-chemical alternatives and the fungicide Topsin as a standard. This aimed at providing new postharvest methods for the control of blue mold incidence and severity in apple fruits. Granny Smith showed lower sensitivity to blue mold disease than Golden Delicious but Fuji was the most sensitive to the disease in relation to fruit firmness and total soluble solid content (TSS). Dipping apple fruits in yeast ( Saccharomyces cerevisiae ) solution at a concentration of 1 g L -1 or in hot water at 50 °C for 1 or 5 min., or exposing them to microwave for 10 s resulted in an effective control of blue mold disease under controlled cold storage conditions. Calcium nitrate at 1 or 8 g L -1 did not result in an effective control of blue mold but increased the storability of apple fruits. Therefore, a combination of two or more of the alternatives may provide a long-lasting effective control of post-harvest blue mold affecting apple fruits.

POST-HARVEST CONTROL OF APPLE BLUE MOLD UNDER COLD STORAGE CONDITIONS

To control blue mold of apples caused by Penicillium expansum after harvest and during commercial cold storage, microwave exposure was investigated as a p hysical measure and compared with the use of calciu m chloride and the systemic fungicide, carbendazime. Microwave exposure of Golden Delicious and Royal Gala apples at 2450 Mhz for 10, 30 and 45s was effe ctive as 4% CaCl 2 and carbendazime on significantly reducing the disease incidence %. Calcium chloride was more effective at 8% than 4% or at 1% and was as effective as carbendazime in reducing the mold seve rity and incidence. Microwave exposure for 10, 30 a nd 45s was as effective as 8% CaCl 2 and carbendazime on controlling blue mold caused b y P. expansum stored under the conditions of commercial cold storage. Di fferent apple cultivars have different degrees of susceptibility to the blue mold. Granny Smith and R ed Delicious were relatively more tolerant than Gol den Delicious, Starking or Royal Gala. However, sight v ariations were found in their responses to differen t treatments. Therefore, 10-45s microwave exposure of apple fruits before cold storage alone or in a combination with other methods can be an environmental safe physical alternative to chemical fungicide s for controlling P. expansum infections during cold storage.

Acid adaptation and biocontrol efficacy of antagonistic marine yeast Rhodosporidium paludigenum

The objectives of this work were to assess the optimum conditions for induction of acid tolerance in the marine yeast Rhodosporidium paludigenum and evaluate the biocontrol activity of non-adapted and acid-adapted yeasts in controlling apple blue mold caused by Penicillium expansum. R. paludigenum grown in malic and lactic acid treatments were stimulated after 12 h incubation. Moreover, medium modified with malic and lactic acid significantly enhanced the acid tolerance of R. paludigenum (p < 0.05). In acid tolerance response test, the highest viability of R. paludigenum was obtained at initial pH of 5.5 in the NYDB medium modified with malic acid (91.6 %). In addition, all R. paludigenum treatments significantly reduced the disease incidences and lesion diameters of blue mold in apples. Furthermore, there was no significant difference between acid-adapted and unadapted yeasts in the apple wounds after 48 h dynamics. Acid stress improved R. paludigenum viability under acidic conditions. However, there was no significant difference between acid-adapted and unadapted yeasts in controlling P. expansum on apple fruit (p < 0.05). These results indicate the potential for maintaining the survival level of biocontrol agents by physiological inducement strategy.

Effect of Metschnikowia pulcherrima and methyl jasmonate on apple blue mold disease and the possible mechanisms involved

Metschnikowia pulcherrima alone and in combination with methyl jasmonate [MeJA] was applied for control of blue mold of apple caused by Penicillium expansum. In vitro, MeJA at different concentrations had no direct effect on the pathogen. In vivo, both M. pulcherrima (1×108 cell ml-1) and MeJA, as a stand-alone treatment, significantly reduced the lesion area of blue mold decay in apple. The combination of MeJA at 100 μmol l-1 and antagonistic yeast (1×108 cell ml-1) was a more effective approach to reduce the lesion diameter of blue mold decay of apples than the application of MeJA or M. pulcherrima separately after incubation for 15 and 50 days at 20°C and 4°C, respectively. In addition, MeJA increased the population of M. pulcherrima in the wounds of the apple fruit. The activity of the defense enzyme peroxidase was enhanced by MeJA and yeast treatments, and the level of total phenolic content in MeJA and yeast-treated fruit was also higher than that in control fruit. These results suggest that MeJA was effective in reducing decay and might enhance disease resistance in apple fruit by increasing defense enzyme activity and levels of antimicrobial phenolic compounds.

Molecular characterization and a multiplex allele-specific PCR method for detection of thiabendazole resistance in Penicillium expansum from apple

Thiabendazole (TBZ) is commonly used as a postharvest treatment for control of blue mold in apples caused by Penicillium expansum. Different point mutations in the β-tubulin gene conferring benzimidazole resistance have been reported in plant pathogens, but molecular mechanisms of TBZ resistance in P. expansum from apple in Washington State are unknown. Determination of TBZ resistance level showed that all 102 TBZ-resistant (TBZ-R) isolates were highly resistant. Sequencing of the majority of the β-tubulin gene showed that 76 TBZ-R isolates harboured the E198V mutation and 26 harboured the F167Y mutation, and all the sensitive isolates did not possess any of the mutations, indicating that these two point mutations in the β-tubulin gene were correlated with TBZ resistance in P. expansum from apple in Washington State. There was no association between levels of TBZ resistance and types of point mutations (E198V or F167Y) in the β-tubulin gene. A multiplex allele-specific PCR assay was developed to detect these two mutations simultaneously. Microsatellite-primed PCR derived presence-absence matrix used to assess the genetic relationship among 56 isolates suggested that the resistance mutations originated several times independently and that there was no correlation between the types of point mutation and the genetic background of the isolates.

In vitro and in vivo antifungal activity of natural inhibitors against Penicillium expansum

Penicillium expansum is the causative agent of apple blue mold. The inhibitory effects of the capsaicin derived from Capsicum spp. fruits and yeast Hansenula wingei against P. expansum were evaluated in an in vitro and in in vivo assay using Fuji apples. The minimum inhibitory concentration of capsaicin determined using the broth micro-dilution method was 122.16 µg mL-1. Capsaicin did not reduce blue mold incidence in apples. However, it was able to delay fungal growth in the first 14 days of the in vivo assay. The in vivo effect of the yeast Hansenula wingei AM2(-2), alone and combined with thiabendazole at low dosage (40 µg mL-1), on the incidence of apple diseases caused by P. expansum was also described. H. wingei AM2(-2) combined with a low fungicide dosage (10% of the dosage recommended by the manufacturer) showed the best efficacy (100%) up to 7 days of storage at 21 oC, later showing a non-statistically different decrease (p > 0.05) after 14 (80.45%) and 21 days (72.13%), respectively. These results contribute providing new options for using antifungal agents against Penicillium expansum.

Inhibition of Penicillium expansum by an oxidative treatment

Several oxidizing compounds such as sodium hypochlorite (NaClO) and hydrogen peroxide (H2O2) are used to control postharvest decay in fresh fruit due to their antimicrobial effects. Here, we applied these compounds in vitro, in the presence of CuSO4, against Penicillium expansum, causal agent of apple blue mold. MICs were 50 mg L−1 and 400 mmol L−1 for NaClO and H2O2, respectively, when these compounds were individually applied to conidia suspensions during 2 min. A combined oxidative treatment (OT) consisting on an incubation with 1 mg L−1 NaClO and 200 mmol L−1 H2O2, in the presence of 6 mmol L−1 CuSO4, inhibited growth, conidial germination and fungal infectivity on apple. The fractional inhibitory concentration index for the interaction between NaClO and H2O2 in the OT was 0.52 indicating a synergistic effect of the oxidizing compounds. These results suggest that the OT could be an interesting alternative for apple diseases postharvest control.

Biocontrol of blue mold of apple by Candida membranifaciens in combination with silicon

In this study, antagonistic yeast Candida membranifaciens was combined with different concentrations of silicon (Si; 0, 0.1, 0.3 and 0.5% wt/vol) to evaluate the control of blue mold of apple in storage at 20°C and 5°C. Preliminary studies showed that Si at 0.6% or above inhibited mycelial growth of pathogens significantly in vitro. In vitro studies showed that Si at 0.1% had lower effect on yeast growth. In vivo studies showed that combination of different concentrations of Si with C. membranifaciens improved the efficacy of yeast in control of disease better than Si and yeast alone (P < 0.05). Our result showed that the effective concentration of Si is varied based on pathogen isolates and temperature, so that the most effective concentration of Si was 0.5% for isolate P2 at 20°C and 0.5% and 0.1% for isolates P1 and P2 at 5°C.

Control of apple blue mold by Pichia pastoris recombinant strains expressing cecropin A

Recombinant Pichia pastoris yeasts expressing cecropin A (GS115/CEC), was evaluated for the control of the blue mold of apple caused by Penicillium expansum due to cecropin A peptide's effective antimicrobial effects on P. expansum spores by the thiazolyl blue (MTT) assay. Then, the protein concentration was determined and it was expressed at high levels up to 14.2 mg/L in the culture medium. Meanwhile, the population growth was assayed in vivo. The population growth of recombinant strain GS115/CEC was higher than that of non-transformed strain GS115 in red Fuji apples wounds. Recombinant yeast strains GS115/CEC significantly inhibited growth of germinated P. expansum spores in vitro and inhibited decay development caused by P. expansum in apple fruits in vivo when compared with apple fruits inoculated with sterile water or the yeast strain GS115/pPIC (plasmid pPIC9k transformed in GS115). This study demonstrated the potential of expression of the antifungal peptide in yeast for the control of postharvest blue mold infections on pome fruits.

Evaluation of different formulations of potential biocontrol yeast isolates efficacy on apple blue mold at storage condition

Post-harvest pathogens cause major losses in apple production. Biological control by using epiphytic yeasts against Penicillium expansum has been considered as an alternative method for controlling the post-harvest decays. The yeast isolates Rhodotorula mucilaginosa, Pichia guilliermondii, which showed high biocontrol efficacy against P. expansum, were selected for formulation tests. Formulation is an important step in developing a biocontrol product. The successful delivery of biocontrol agents, shelf life, stability and effectiveness in commercial conditions depend on the formulation. In the formulation, the carrier is the primary material used to allow a bioproduct to be dispersed effectively. Yeast isolates were grown in a cane molasses-based medium. Harvested yeast cells were combined with inorganic (talk, kaolin) and organic (Rice bran, wheat bran) carriers. Viability of the yeast cells in formulations stored at 4°C and 24°C was determined each month during 6 months storage. After 6 months storage to evaluate efficacy of formulations, all formulations were tested on apple to control blue mold in storage condition. High stability of antagonistic yeasts was achieved by using organic and inorganic carriers. Rice bran and wheat bran stimulated the germination of the yeasts cells during storage period. Both of the yeasts had significantly highest viable yeast cell content over 6 months in formulation containing wheat bran as a carrier. P.guillermondii in all formulations had significantly higher shelf life and was effective than R. mucilaginosa.

Control of Apple Blue Mold by the Antagonistic Yeast Pichia anomala Strain K: Screening of UV Protectants for Preharvest Application.

When applied preharvest, antagonistic yeasts that act as biocontrol agents of postharvest fruit diseases must survive the environmental conditions in the field. In particular, UV-B radiation (280 to 320 nm) can greatly reduce their survival and effectiveness. The influence of artificial UV-B radiation on Pichia anomala strain K, an antagonistic yeast with potential for control of postharvest fruit diseases, was evaluated in vitro and in vivo. The in vitro 50 and 90% lethal dose values were 0.89 and 1.6 Kj/m2, respectively, whereas lethal values in vivo were 3.2 and 5.76 Kj/m2, respectively. UV protectants tested in combination with strain K included congo red, tryptophan, riboflavin, lignin, casein, gelatine, folic acid, tyrosine, and four mixtures. Riboflavin, folic acid, and the mixtures 1% folic acid + 0.5% tyrosine + 0.5% riboflavin (formula 2), 0.5% folic acid + 1% tyrosine + 0.5% riboflavin (formula 3), and 0.5% folic acid + 0.5% tyrosine + 1% riboflavin (formula 4) reduced yeast mortality caused by UV-B radiation in petri dish assays. Riboflavin, folic acid, gelatine, lignin, and tyrosine reduced yeast mortality caused by UV-B radiation on apple fruit surfaces. With the exception of lignin and folic acid, none of the compounds or mixtures increased significantly the ability of strain K to control the postharvest pathogen Penicillium expansum on wounded apple fruit. In contrast, casein, gelatine, tyrosine, congo red, riboflavin, and formulas 1 to 4 significantly reduced the effectiveness of strain K. Further investigations are justified to verify a potential benefit of lignin and folic acid for UV protection of strain K in preharvest applications.

Biological control agents and chemical inducers of resistance for postharvest control of Penicillium expansum Link. on apple fruit

Penicillium expansum Link. is the causal agent of apple blue mold, and it can cause severe loss of stored fruit. The use of fungicides is still the major means for postharvest control of this disease. In the present study, we investigated the effectiveness of biological control agents (BCAs) and/or induction of resistance for postharvest control of blue mold on apple ( Malus domestica L. cv Golden Delicious). The BCAs and chemical inducers of resistance tested had direct effects against P. expansum, significantly reducing the percentages of infection and/or lesion sizes when applied directly against this pathogen. The antifungal activities of acibenzolar-S-methyl, β-aminobutyric acid and methyl jasmonate were also confirmed in vitro against P. expansum and Trichoderma atroviride P1. Treatments with BCAs and chemical inducers of resistance did not control infection on the untreated wounds that were made 1 cm from the original treated wounds. However, reverse-transcription PCR showed that treatments with Pseudomonas syringae pv. syringae 1,3S and acibenzolar-S-methyl induced significant increases in the levels of gene transcripts of the pathogenesis-related proteins PR-1a, PR-2, PR-5 and PR-8 in apple peel, as compared to controls. Moreover, immunoblotting showed an accumulation of PR-2 and PR-5 proteins in treated samples. These data indicate that these treatments trigger resistance responses in the apple fruit, although these responses do not limit the infection. Thus, biological control is confirmed as one of the most promising alternatives for postharvest control of blue mold on apple, while the induction of resistance does not appear to be a useful approach here.

First Morphomolecular Identification of Penicillium griseofulvum and Penicillium aurantiogriseum Toxicogenic Isolates Associated with Blue Mold on Apple

Postharvest blue mold decay caused by Penicillium spp. is the most important disease of fresh apple fruit in the world, which extend from the field to the store. Two new Penicillium spp. responsible for apple fruit decay were recovered. The morphological and molecular features of Penicillium griseofulvum and Penicillium aurantiogriseum isolated from apple fruits were characterized morphologically and molecularly. Pathogenicity test exhibited that both P. griseofulvum and P. aurantiogriseum were responsible for blue mold decay in storage apple fruits. Lesion diameter indicated that P. aurantiogriseum was more aggressive than P. griseofulvum. All tested isolates were able to synthesize citrinin in addition to patulin. Not all of the isolates belonging to the same species showed the same profile of secondary metabolites. Microsatellite-primed polymerase chain reaction was able to differentiate these isolates at the species level and divided the analyzed isolates into two genetically different groups. Little intraspecific variability was evident. Microsatellite-primed polymerase chain reaction analysis proved to be an objective, rapid, and reliable tool to identify Penicillium spp. involved in blue mold of apple. This is the first report of occurrence of P. griseofulvum and P. aurantiogriseum on imported apple fruits in Saudi Arabia.

Preharvest Application of a Boscalid and Pyraclostrobin Mixture to Control Postharvest Gray Mold and Blue Mold in Apples.

After harvest, apples (Malus × domestica) may be kept in cold storage for up to 12 months prior to packing. Gray mold caused by Botrytis cinerea and blue mold caused by Penicillium expansum are common postharvest fruit rot diseases affecting apples and are controlled commonly by applications of fungicides after harvest. To search for an alternative strategy, Pristine (a premixed formulation of boscalid and pyraclostrobin) as a preharvest treatment was evaluated for control of postharvest gray mold and blue mold in cultivars Fuji and Red Delicious apples during 2004 to 2006. Pristine (0.36 g per liter of water) was applied 1, 7, or 14 days before harvest. For comparison, thiram (2.04 g per liter of water) was applied 7 days before harvest and ziram (2.4 g per liter of water) was applied 14 days before harvest, to Fuji and Red Delicious, respectively. Fruit were harvested at commercial maturity, wounded with a finishing nail head, inoculated with conidial suspensions of either B. cinerea or P. expansum, stored in air at 0°C, and evaluated for decay after 8 or 12 weeks. In 2004 and 2005, Pristine was equally effective when applied to Fuji 1 or 7 days before harvest, reducing gray mold incidence by 93 to 99% and blue mold incidence by 78 to 94% compared with the nontreated control. Thiram reduced gray mold incidence by 38 to 85%. Thiram reduced blue mold incidence by 22% in 2004 but not in 2005. On Red Delicious, Pristine was equally effective when applied 7 or 14 days before harvest and reduced gray mold incidence by 69 to 85% and blue mold incidence by 41 to 70%. Ziram applied 2 weeks before harvest reduced gray mold incidence by 97 and 94% in 2005 and 2006, respectively, but it did not reduce blue mold incidence. The results indicate that Pristine applied within 2 weeks before harvest may be an effective alternative to postharvest fungicides for control of postharvest gray mold and blue mold in Fuji and Red Delicious apples.

Biological Control of Apples Blue Mold by Isolates of Saccharomyces Cerevisiae

Yeasts (52, 51, 69, and 04) were received from Biotechnology Center of Karaj and Penicillium expansum isolates P 11 and P 12 iso- lated from Golden Delicious. Isolates were evaluated as a potential biological control agents of apple blue mold caused by P. expansum. Dual culture, cell free metabolites and volatile test were used in vitro assay. All tested of yeast isolates inhibited growth of P. expansum. The inhibition varied among isolates of yeasts and ranged from 19.81% to 40.73%, in dual culture, from 43.16% to 66.44% in volatile metabolite and from 22.16% to 50.23% in cell free metabolite test. Apple fruit wounds were inoculated with 40 µl of yeast cell suspension (10 7 cell/ml) followed 48 h later by P. expansum (10 5 conidia/ ml). The apples were then incubated at 25°C. Four isolates of Saccharomyces cerevisiae reduced, the decay area from 13.46 to 24.92 cm 2

Production of mycotoxins by Penicillium expansum inoculated into apples.

We investigated the production of mycotoxins in apple fruits inoculated with spores of 40 strains of apple blue mold, Penicillium expansum. Patulin and citrinin contents in the extracts from apples stored at 25 degrees C for 12 days after inoculation were determined by high-performance liquid chromatography (HPLC) analysis with UV and fluorescence detection. Patulin and citrinin were produced by 90% (36) and 80% (32) of the 40 strains, indicating that P. expansum is a consistent producer of these mycotoxins. The patulin content in the extracts was substantially higher than the citrinin content. Other mycotoxins whose production in pure culture has been reported were simultaneously detected with high-resolution liquid chromatography-mass spectrometry (LC-MS) analysis with the positive ion mode of electrospray ionization. Along with patulin and citrinin, expansolides A and B were identified based on the HPLC and LC-MS spectral data and detected in 88% (35) of the extracts. The results indicate that P. expansum is a consistent producer of expansolides A and B in rotten areas of apple fruits. The findings raise the possibility that products from decayed apples might contain expansolides A and B in addition to patulin and citrinin.

Control of blue mold decay of apple during commercial controlled atmosphere storage with yeast antagonists and sodium bicarbonate

A mixture of two yeast antagonists, Metschnikowia pulcherrima and Cryptococcus laurentii, originally isolated from apples and exhibiting greater biocontrol activity against blue mold of apple than either yeast applied alone, were used in combination with sodium bicarbonate (SBC) in a pilot test in which treated fruit were stored under commercial controlled atmosphere (CA) storage conditions. Conidia of Penicillium expansum, antagonists cells and SBC were added to the drench solution. The treatments were applied to apples by drenching entire bins filled with apples containing 100 wounded fruit evenly distributed among five positions in each bin. The treated fruit were stored in commercial CA storages for approximately six months in the 2005–2006 and 2006–2007 storage seasons and then evaluated for incidence of decay. In both years, the treatments with the antagonist alone or in combination with SBC were equally effective and reduced blue mold incidence by 84–97% in 2005–2006 and 73–82% in 2006–2007. SBC alone significantly reduced blue mold incidence compared to the non-treated control but was less effective than the antagonist alone or in combination with SBC. This pilot test showed that the combination of these two antagonists and SBC can be an effective decay control method under commercial CA conditions, confirming results from our earlier laboratory studies using similarly treated fruit stored under CA conditions.

Preliminary Evaluation of Apple Germplasm from Kazakhstan for Resistance to Postharvest Blue Mold in Fruit Caused by Penicillium expansum

Blue mold of apples, incited by Penicillium expansum, causes extensive losses on stored apples worldwide. Despite the severity of this problem, apple breeders do not evaluate their crosses for resistance to this disease, because there has been little resistance to blue mold in the gene pool of the germplasm used. A new apple germplasm collection from the center of origin in Kazakhstan, maintained in Geneva, NY, and representing a much broader gene pool, was evaluated for resistance to blue mold. Apples were harvested from the Elite collection trees that were clonally propagated from budwood collected in Kazakhstan and from seedling trees originating from seeds of the same trees as the Elite budwood or from other wild seedling trees in Kazakhstan. Fruit from 83 such accessions were harvested at the preclimacteric to climacteric stage, wound-inoculated with P. expansum at 103, 104, and 105 mL−1 conidial suspension, incubated for 5 d at 24 °C, and evaluated for decay incidence and severity. Two accessions were classified as immune (no decay at 103 and 104 mL−1), four as resistant (no decay at 103 mL−1), 53 as moderately resistant (lesions less than 10 mm at 103 mL−1), and 24 as susceptible. There were positive correlations (r = 0.92, 0.86, and 0.91) between decay severity and all three inoculum levels. Our results indicate a greater genetic diversity among the Kazak apple collection than among cultivated apples as evidenced by their broad range of fruit maturity, quality, and disease resistance patterns. The immune and resistant accessions may serve as a source of resistance in breeding programs and can be useful in explaining the mechanism of resistance to blue mold in apples.

In vitro and in situ study of postharvest apple blue mold biocontrol by Aureobasidium pullulans: Evidence for the involvement of competition for nutrients

Aureobasidium pullulans strain Ach1-1 was selected for its effectiveness against blue mold caused by Penicillium expansum on stored apple fruit. The possible involvement of competition for nutrients in the biocontrol activity of this antagonistic strain was investigated both in vitro and in situ. For in vitro assays, the effect of strain Ach1-1 on germination percentages of P. expansum conidia was evaluated after a 24 h incubation period in the presence of increasing apple juice concentrations (0–5%) using a system allowing the physical separation of both agents. In the absence of strain Ach1-1, conidial germination was strongly promoted by apple juice whatever the concentration. However, germination was significantly reduced by the presence of strain Ach1-1 except at the highest juice concentration. For conidia previously inhibited at 0.5% juice, germination after 24 h of incubation was partially recovered in the presence of strain Ach1-1 when fresh juice was added to a final concentration of 5%, and completely restored at both 0.5 and 5% juice concentrations in the absence of strain Ach1-1. For in situ assays, strain Ach1-1 was very protective against P. expansum on postharvest wounded apples. However, the application of high concentrations of exogenous sugars, vitamins and most particularly amino acids, significantly reduced such protection. Time-course analysis of apple amino acids at the wound site revealed that these compounds were more depleted in wounds treated with strain Ach1-1 alone and especially in those treated with both agents (strain Ach1-1 and P. expansum) compared to wounds treated with P. expansum alone or to untreated ones. Exogenous amino acids, applied at high concentrations on apple wounds as a mixture of specific amino acid groups or as individuals, significantly decreased strain Ach1-1 efficacy against P. expansum. The present study provides in vitro and in situ evidence that competition for apple nutrients, most particularly amino acids, may be a main mechanism of the biocontrol activity of A. pullulans strain Ach1-1 against blue mold caused by P. expansum on harvested apple fruit.