Postharvest Pathogens Of Fruits Research Articles

Exploring the Bioprotective Potential of Halophilic Bacteria against Major Postharvest Fungal Pathogens of Citrus Fruit Penicillium digitatum and Penicillium italicum

Citrus fruits are vulnerable to green mold (caused by Penicillium digitatum) and blue mold (caused by Penicillium italicum) during storage, posing significant challenges to the industry. Therefore, biological control utilizing antagonistic bacteria has emerged as a dependable strategy for managing postharvest diseases. In this study, halophilic bacterial isolates were carefully selected from diverse saline ecosystems, including the Dead Sea, the Agadir Sea, the Rabat Sea, saline soil, and water of the Amassine Oued in Taounate, based on rigorous in vitro and in vivo antagonism bioassays. Out of 21 bacteria from different saline environments, 10 were chosen for further characterization based on the 16S rDNA gene. Notably, the EAM1 isolate demonstrated exceptional inhibitory effects, reaching a 90% inhibition rate against P. digitatum, while the ER2 isolate closely followed with an 89% inhibition rate against P. italicum. Furthermore, in bacterial supernatant experiments, six bacterial isolates effectively curbed the growth of P. digitatum, and three demonstrated efficacy against P. italicum development. In an in vivo trial spanning ten days of incubation, three highly effective isolates against P. digitatum displayed zero severity, and two of these isolates also demonstrated zero severity against P. italicum. Interestingly, a comparison of bacterial filtrates revealed that all isolates exhibited a severity level of over 50% against the pathogen causing green rot (P. digitatum), while the severity was lower than 50% for the supernatants of the two isolates used against P. italicum. In conclusion, this study highlights the promising role of halophilic bacteria, specifically Bacillus amyloliquefaciens EAM1 and B. amyloliquefaciens ER2, in controlling postharvest fruit pathogens. The findings shed light on the potential of utilizing these bioprotective agents to address the challenges posed by green and blue citrus molds, providing valuable insights for the citrus industry.

Biocontrol efficacy of Meyerozyma guilliermondii LMA-Cp01 against post-harvest pathogens of fruits

This work aimed to broaden the spectrum biocontrol activity of Meyerozyma guilliermondii LMA-Cp01. Inhibition of postharvest pathogens, viz., Alternaria alternata, Penicillium italicum, P. digitatum, P. expansum, Botrytis cinerea, and Rhizopus stolonifer was tested on persimmon, oranges, apples, and pears. The effect of spraying or dipping application of the actinomycete for the phytopathogens biocontrol was evaluated. LMA-Cp01 reduced 30 and 50% (R. stolonifer), 53 and 67% (B. cinerea), and 55 and 67% (P. expansum) the disease incidence and severity on apples, respectively. Regarding pears, reductions of 44 and 71% (R. stolonifer) and 65 and 85% (P. expansum) of incidence and severity were respectively achieved. P. italicum and P. digitatum incidence on oranges was reduced by 70 and 72%, respectively, and the severity was also reduced by 85%. The LMA-Cp01 efficacy on apples and oranges was higher by spraying application. LMA-Cp01 is a promising broad-spectrum biocontrol agent against diseases on different hosts.

Efficacy of the cyclolipopeptides fengycin and iturin A against postharvest pome fruit pathogens

Botrytis cinerea (gray mold) and Penicillium expansum (blue mold), are major pome fruit postharvest pathogens and their control relies heavily on the use of one postharvest fungicide (fludioxonil). This study aimed to evaluate the efficacy of the cyclolipopeptides (CLPs), in the form of fengycin and iturin A, in crude metabolite extracts from Bacillus amyloliquefaciens as an alternative biofungicide. The crude extract containing CLPs was applied with an edible coating (i.e., zein as a carrier) as a postharvest treatment against B. cinerea on “Packham’s Triumph” pears and P. expansum on “Cripps Pink” apples. Treatments were applied either as dips in combination with a zein edible coating at pH 2.0 or pH 8.0, or as sprays with a zein edible coating at pH 2.0 or pH 8.0. The efficacy of CLP applications was measured in comparison to the standard registered synthetic fungicide fludioxonil at a concentration of 299.0 mg/L. Treatments were applied to the fruit either preventatively (as sprays) or curatively (as dips or sprays). The lowest mean blue mold incidence (68.6%) was achieved when the edible coating containing the crude extract of B. amyloliquefaciens (CLP at pH 2.0) was applied as a curative dip treatment. B. cinerea infection was reduced by 92.6%, resulting in a 5.7% gray mold incidence for the curative application of CLPs at pH 2.0. This result was not significantly different from the inhibitory action of the fungicide fludioxonil. These results indicate that CLPs are an effective alternative biofungicide that can be used for the control of B. cinerea on pome fruit, especially if their formulation and application are improved and optimized.

Biofumigation by Mustard Plants as an Application for Controlling Postharvest Gray Mold in Apple Fruits

Gray mold caused by Botrytis cinerea is a critical disease that results in severe postharvest losses for the apple industry. In recent years, biological control has become an increasingly effective approach for controlling postharvest diseases in fruits. Brassica plants contain abundant natural compounds with known antimicrobial activity against numerous plant pathogens. In this study, a large-scale screening of 90 mustard cultivars was conducted to evaluate their biofumigation effects against B. cinerea. Among these, one mustard cultivar named Dilong-1, displayed the highest inhibitory effect against B. cinerea, and was able to completely inhibit mycelial growth. Further investigations showed that fumigation with Dilong-1 inhibited mycelial growth, sporulation, and spore germination of B. cinerea in vitro. In addition, fumigation using Dilong-1 showed a wide antifungal spectrum, including other fruit postharvest pathogens such as Phytophthora litchii. Furthermore, apple gray mold disease severity was significantly reduced by biofumigation using Dilong-1. Importantly, fumigation with Dilong-1 did not negatively impact final apple qualities, including weight loss, firmness, and total soluble solids. These results suggested that Dilong-1 significantly inhibited gray mold decay caused by B. cinerea without affecting the quality of apple fruits. In conclusion, biological fumigation of apple fruits with the mustard cultivar Dilong-1 is a promising eco-friendly approach for controlling apple gray mold during storage and shipment.

Microbial Intervention: An Approach to Combat the Postharvest Pathogens of Fruits.

Plants host diverse microbial communities, which undergo a complex interaction with each other. Plant-associated microbial communities provide various benefits to the host directly or indirectly, viz. nutrient acquisition, protection from pathogen invaders, mitigation from different biotic and abiotic stress. Presently, plant-associated microbial strains are frequently utilized as biofertilizers, biostimulants and biocontrol agents in greenhouse and field conditions and have shown satisfactory results. Nowadays, the plant/fruit microbiome has been employed to control postharvest pathogens and postharvest decay, and to maintain the quality or shelf life of fruits. In this context, the intervention of the natural fruit microbiome or the creation of synthetic microbial communities to modulate the functional attributes of the natural microbiome is an emerging aspect. In this regard, we discuss the community behavior of microbes in natural conditions and how the microbiome intervention plays a crucial role in the postharvest management of fruits.

Effects of developed thyme and oregano essential oil formulations on Monilinia laxa and Monilinia fructicola

Essential oils have been well-known for their antimicrobial properties for a very long time. Some of them have been effectively used in human medicine for decades. Our earlier investigation revealed a great potential of thyme and oregano essential oils as crop protectants against some postharvest fruit pathogens. The effects of formulated thyme and oregano essential oils on Monilinia laxa and Monilinia fructicola were studied in vitro and in vivo. In vitro antagonistic assays were performed on solidified PDA medium using a slightly modified agar overlay technique, while in vivo experiments were conducted on inoculated apple fruits. In vitro essays showed that the developed formulations (emulsifiable concentrates - EC) significantly inhibited the mycelial growth of Monilinia spp. Experiments in vivo, performed on inoculated apple fruits, revealed that the developed formulations provided a significant level of Monilinia spp. suppression. To our knowledge, another EC formulation of oregano essential oil intended for use in Monilinia spp. control has never been developed before. The presented results are initial findings and evaluation of the activity of the developed products should therefore proceed under field conditions to determine their efficacy and activity spectrum, and to estimate economic aspects of their use.

RNA sequencing-based transcriptome analysis of mature strawberry fruit infected by necrotrophic fungal pathogen Botrytis cinerea

Botrytis cinerea, the causal agent of gray mold disease, is regarded as the most impactful postharvest fungal pathogen, as it causes serious losses in fresh fruits, ornamentals, and vegetables worldwide. To understand the molecular defense mechanisms of the affected plants, we analyzed transcriptome using RNA sequencing (RNA-seq) of mature strawberry fruit that were infected by B. cinerea at 12, 24, and 48 h. Overall, 18 cDNA libraries were produced generating 923,482,642,150 base pair reads. A total of 1459 differentially expressed genes (DEGs) were identified (≥2.0-fold change and FDR ≤ 0.05), among which only 26 were down-regulated. The majority of changes in gene expression occurred 24 h after inoculation, before significant lesion development, suggesting that this is an important stage during B. cinerea infection. Further analysis revealed that the DEGs were predominately involved in pathogen recognition (pattern recognition receptors), signaling transduction (MAPK cascades, CDPKs), defense response (transcription factors, secondary metabolism biosynthesis, pathogenis-related), as well as different sorts of transporter encoding genes. These data provided a global insight into mature strawberry fruit-B. cinerea interaction and might be used for fruit postharvest pathogens and diseases management.

Molecular characterization of the two postharvest biological control agents Aureobasidium pullulans L1 and L8

L1 and L8 are Aureobasidium pullulans strains previously shown to effectively act as biocontrol agents (BCA) against fruit postharvest pathogens. Here, L1 and L8 strains were tested in vivo against Monilinia laxa of peaches showing the ability to reduce the brown rot incidence by 95% and by 80% respectively. To develop future bioformulation and allow commercial use of these biocontrol agents (BCAs) it is necessary to develop specific identification tools. Since A. pullulans strains share very similar morphological features and are not distinguishable by visual analysis, the RAPD (Random Amplified Polymorphic DNA) technique was applied to genomic DNA of L1 and L8 and of other 40 different A. pullulans strains, and SCAR markers were developed from a L1 and L8 specific RAPD fragment of 984 bp. These primers amplify a fragment of 137 bp exclusively in L1 and L8, and can be used to distinguish the two yeasts strains from other A. pullulans strains with high specificity. The droplet digital PCR, used to determine the precise limit of detection (LOD), showed that these markers allow to detect up to 43 and 215 cells of L1 and L8 respectively.

Effect of Cinnamaldehyde and Citral Combination on Transcriptional Profile, Growth, Oxidative Damage and Patulin Biosynthesis of Penicillium expansum.

Penicillium expansum, as a main postharvest pathogen of fruits, can secrete patulin (PAT), causing fruit decay and health problems. In this study, the antifungal test, SEM (scanning electron microscope) observation, transcriptional profile, PAT biosynthesis, and physiological characters of P. expansum exposed to cinnamaldehyde and citral combination (Cin/Cit) were evaluated. Cin/Cit could inhibit the mycelial growth and spore germination of P. expansum in a dose-dependent manner. Besides, Cin/Cit caused spores and mycelia wrinkled and depressed by SEM observation. Gene expression profiles of P. expansum were conducted by RNA sequencing (RNA-seq) in the presence or absence of Cin/Cit treatment. A total of 1713 differentially expressed genes (DEGs) were obtained, including 793 down-regulated and 920 up-regulated genes. Most of the DEGs participated in the biosynthesis of secondary metabolites, amino acid metabolism, and oxidation-reduction process, etc. Cin/Cit induced the dysfunction of the mitochondrial membrane, causing the potential influence on energy metabolism and reactive oxidative species production. The changes of superoxide dismutase (SOD) and catalase (CAT) activities combing with the increase of hydrogen peroxide content indicated the oxidative stress on P. expansum induced by Cin/Cit, which corresponded well with the transcriptional results. Moreover, both the RNA-seq data and the qRT-PCR showed the remarkable down-regulation of genes included in the PAT biosynthetic pathway under the Cin/Cit treatment. These findings provided more useful information about the antifungal mechanism of Cin/Cit against P. expansum at molecular and gene levels and suggested that Cin/Cit is a potential candidate to control P. expansum.

An insight on the ethylene biosynthetic pathway of two major fruit postharvest pathogens with different host specificity: Penicillium digitatum and Penicillium expansum

Although several studies have reported the stress-induced ethylene burst occurring in fruit in response to pathogen attack, relatively little is known about the role of this hormone in the fungal metabolism of many postharvest pathogens. To gain further knowledge, we investigated the ethylene production capacity and which ethylene biosynthetic pathways (including the 1-aminocyclopropane-1-carboxylic acid (ACC), the 2-oxoglutarate (OXO) and the 2-keto-4-methylthiobutyric acid (KMBA) pathways) were used under different in vitro conditions by Penicillium digitatum and Penicillium expansum. Both pathogens were capable of producing ethylene in vitro using different pathways but were dependant on the growing conditions. For instance, both the KMBA and the OXO pathways seemed to be responsible for ethylene biosynthesis in P. digitatum when grown in more stressful conditions (limited surface and nutrient availability as in PDA tubes), while only the KMBA pathway seemed to be activated under other culture conditions (i.e. on PDA plates) or when the fungal mycelium was placed within aqueous solutions containing ethylene precursors. In contrast, the KMBA appeared to be the exclusive pathway responsible for ethylene production by P. expansum yet only when the fungal mycelium was in contact with aqueous solutions containing ethylene precursors. In both pathogens, ethylene production seemed to be synchronized with certain stages of fungal growth rather than conidiation, suggesting a putative role of this hormone in fungal metabolism.

Antifungal effect of volatile organic compounds produced by Bacillus amyloliquefaciens CPA-8 against fruit pathogen decays of cherry

The present work focuses on the antifungal effect of volatile organic compounds (VOCs) produced by Bacillus amyloliquefaciens CPA-8 against Monilinia laxa, M. fructicola and Botrytis cinera, three postharvest fruit pathogens of sweet cherry fruit. VOCs were evaluated with a double petri dish assay against mycelial and colony growth of target pathogens. For this purpose, CPA-8 was grown on different media and cultured for 24 and 48 h at 30 °C before assays. Data showed that mycelial growth inhibition was higher when CPA-8 was grown on Tryptone Soya Agar (TSA) while no differences were generally observed when CPA-8 was cultured for either, 24 and 48 h. Moreover, no effects were observed on colony growth. The main volatile compounds emitted by CPA-8 were identified by solid-phase microextraction (SPME)-gas chromatography as 1,3 pentadiene, acetoin (3-hydroxy-2-butanone) and thiophene. Pure compounds were also tested in vitro on mycelial growth inhibition and their EC50 values against the three pathogens were estimated. Thiophene was the most effective VOC, showing more than 82% suppression of mycelial growth at the highest concentration (1.35 μL/mL headspace) and EC50 values ranging from 0.06 to 6.67 μL/mL headspace. Finally, the effectiveness of thiophene and CPA-8 VOCs was evaluated against artificially inoculated cherry fruits. Among the target pathogens, M. fructicola was clearly controlled by CPA-8 with less than 25% of rotten fruits compared to the control (65% disease incidence) and for all pathogens, less than 37.5% of CPA-8 treated decayed fruits produced spores (disease sporulation). Otherwise, pure thiophene showed no effect against any pathogen on disease incidence and disease sporulation. The results indicated that VOCs produced by B. amyloliquefaciens CPA-8 could develop an additive antifungal effect against postharvest fruit pathogens on stone fruit.

Evaluation of Alternaria mycotoxins in strawberries: quantification and storage condition

ABSTRACTAlternariol (AOH), alternariol methyl ether (AME) and tentoxin (TEN) are Alternaria mycotoxins produced by the most common post-harvest pathogens of fruits. The production of these metabolites depends on several environmental factors, mainly temperature, water activity, pH and the technological treatments that have been applied to the product. In this study, the occurrence of AOH, AME and TEN was evaluated in strawberries samples stored at different temperatures ranges (at 22 ± 2 or 6 ± 2°C) and different periods (up to 1 month) simulating the current practice of consumer’s storage conditions. Sample extraction was performed using a liquid–liquid extraction method prior to LC-MS/MS analysis. AOH was the most prevalent mycotoxins with a 42% at strawberries stored at (22 ± 2)°C and 37% stored at (6 ± 2)°C. The highest AOH levels were found in samples conserved at (22 ± 2)°C ranging between 26 and 752 ng g–1. AME levels ranged between 11 and 137 ng g–1, which were found mainly in stored samples at (6 ± 2)°C for more than 28 days. None sample presented levels of TEN in either of the studied conditions.

Conyza canadensis: Green Extraction Method of Bioactive Compounds and Evaluation of Their Antifungal Activity

Synthetic fungicides are a common treatment for post-harvest diseases in fruits, although demand is increasing for alternatives such as biopesticides. The aim of this work was to investigate the presence of naturally occurring antifungal compounds in Brazilian specimens of the weed Conyza canadensis. Two compounds [(4Z)-lachnophyllum lactone and (4Z,8Z)-matricaria lactone] were isolated and their antifungal activities were evaluated against eight postharvest disease fungi. Aspergillus niger, Cladosporium sp., and Penicillium digitatum proved susceptible to the treatment (minimum inhibitory concentrations varying from 32 to 64 µg mL-1). These fungi are common postharvest pathogens of fruits and vegetables, causing rots and secreting mycotoxins. A green and sustainable extraction method employing pressurized hot water was developed and optimized (100 °C, 4 × 1 min cycles). Yields of 1.46 and 0.24 mg g-1 were obtained for (4Z)-lachnophyllum lactone and (4Z,8Z)-matricaria lactone, respectively. The extract could be applied directly to fruits and vegetables in postharvest treatments.

Postharvest application of a novel chitinase cloned from Metschnikowia fructicola and overexpressed in Pichia pastoris to control brown rot of peaches

Metschnikowia fructicola strain AP47 is a yeast antagonist against postharvest pathogens of fruits. The yeast was able to produce chitinase enzymes in the presence of pathogen cell wall. A novel chitinase gene MfChi (GenBank accession number HQ113461) was amplified from the genomic DNA of Metschnikowia fructicola AP47. Sequence analysis showed lack of introns, an open reading frame (ORF) of 1098bp encoding a 365 amino acid protein with a calculated molecular weight of 40.9kDa and a predicted pI of 5.27. MfChi was highly induced in Metschnikowia fructicola after interaction with Monilinia fructicola cell wall, suggesting a primary role of MfChi chitinase in the antagonistic activity of the yeast. The MfChi gene overexpressed in the heterologous expression system of Pichia pastoris KM71 and the recombinant chitinase showed high endochitinase activity towards 4-Nitrophenyl β-d-N,N′,N″-triacetylchitotriose substrate. The antifungal activity of the recombinant chitinase was investigated against Monilinia fructicola and Monilinia laxa in vitro and on peaches. The chitinase significantly controlled the spore germination and the germ tube length of the tested pathogens in PDB medium and the mycelium diameter in PDA. The enzyme, when applied on peaches cv. Redhaven, successfully reduced brown rot severity. This work shows that the chitinase MfChi could be developed as a postharvest treatment with antimicrobial activity for fruit undergoing a short shelf life, and confirms that P. pastoris KM71 is a suitable microorganism for cost-effective large-scale production of recombinant chitinases.

Production of volatile organic compounds by Aureobasidium pullulans as a potential mechanism of action against postharvest fruit pathogens

Two Aureobasidium pullulans strains (L1 and L8), effective against some fruit postharvest pathogens were evaluated for VOCs production as a part of their modes of action towards five pathogens (Botrytis cinerea, Colletotrichum acutatum, Penicillium expansum, Penicilliumdigitatum and Penicilliumitalicum). The VOCs were assayed with a double petri dish assay against conidia germination of target pathogens. Results obtained showed that the VOCs generated by the antagonists inhibited significantly the conidia germination of all pathogens compared to the control. In particular, the conidia germination of all Penicillium was completely inhibited by VOCs produced by L1 and L8. In in vivo tests, apples and oranges were artificially inoculated with pathogen conidia and then biofumigated with VOCs emitted by both antagonists. The antagonistic treatment controlled significantly pathogen infection, confirming the results obtained in vitro tests. The best L1 and L8 VOCs activity was observed on apple inoculated with B. cinerea where the lesion diameter reduction observed was greater than the 88%. The compounds emitted by L1 and L8 strains were identified with the solid-phase microextraction (SPME)–gas chromatographic technique. Compounds as 2-phenyl, 1-butanol-3-methyl, 1-butanol-2-methyl and 1-propanol-2-methyl belonging to the group of alcohols were mainly produced for both strains, in the first 96h of growth. These compounds were confirmed by comparison with standards. The pure compounds of VOCs cited above were used to determine the EC50 values for conidia germination of pathogens. The 1-propanol-2-methyl was the VOC least active against all tested fungi, with the EC50 values over 0.8μlml−1, while the 2-phenethyl alcohol was the most active with EC50 values lower than 0.8μlml−1, except for the C. acutatum (1.97μlml−1). The present study demonstrated, for the first time, that the production of VOCs could play an essential role in the antagonistic activity of two A. pullulans strains against five fruit postharvest pathogens.

Biocontrol activity of an alkaline serine protease from Aureobasidium pullulans expressed in Pichia pastoris against four postharvest pathogens on apple

The yeast-like fungus Aureobasidium pullulans PL5 is a microbial antagonist against postharvest pathogens of fruits. The strain is able to produce hydrolases, including glucanases, chitinases and proteases. The alkaline serine protease gene ALP5 from A. pullulans was cloned, inserted into the vector pPIC9 to construct pPIC9/ALP5, and then expressed in Pichia pastoris strain KM71. ALP5 had a molecular mass of 42.9kDa after 5days growth with 1% methanol induction at 28°C. The recombinant protease expressed in P. pastoris showed its highest activity under alkaline conditions (at pH10) and a temperature of 50°C. The antifungal activity of the recombinant protease was investigated against Penicillium expansum, Botrytis cinerea, Monilinia fructicola and Alternaria alternata in vitro and on apple. The recombinant protease reduced significantly the spore germination and the germ tube length of the tested pathogens in PDB medium. The highest level of protease efficacy was observed against M. fructicola and B. cinerea, whereas a lower efficacy was observed against P. expansum and A. alternata indicating a possible effect of the pathogen cell wall composition on the proteolytic activity of the recombinant protease. The presence of protease was able to cause the swelling of the hyphae of B. cinerea, under an optical microscope. The recombinant protease expressed in P. pastoris was more active against the pathogens in vitro than the same enzyme expressed in E. coli in previous studies. The efficacy of ALP5 was also evaluated against the pathogens in vivo on cv Golden Delicious apples. The protease was more efficient in controlling M. fructicola, B. cinerea and P. expansum than A. alternata. However, the extent of the activity was dependent on the enzyme concentration and the length of fruit storage. This study demonstrated the capacity of the alkaline serine protease to keep its enzymatic activity for some days in the unfavorable environment of the fruit wounds. The alkaline serine protease could be developed as a postharvest treatment with antimicrobial activity for fruit undergoing a short storage period.

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

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

Antagonismo in vitro de aislados bacterianos de fresa comercial y silvestre vs. Botrytis cinerea y Rhizopus stolonifer

La fresa es una fruta no climatérica, con una vida postcosecha muy corta. La pérdida de calidad del fruto puede deberse, entre otros factores a daños ocasionados por fitopatógenos. Entre los más comunes se encuentran los hongos causantes del moho gris (Botrytis cinerea), y podredumbre blanca (Rhizopus stolonifer) dos fitopatógenos de gran impacto por su velocidad de crecimiento la cual les permite colonizar la superficie de los mismos ocasionado importantes pérdidas económicas. Una alternativa para el control de los daños por patógenos en frutos postcosecha es el uso de antagonistas microbianos que pueden estar presentes en la planta o el fruto pero en densidades bajas. En este estudio se aislaron bacterias de tejido foliar y frutos de fresa silvestre (Duchesnea indica Andr. Fock) y comercial. Se seleccionaron aquellos aislados que presentaron los mayores porcentajes de inhibición del crecimiento micelial de ambos fitopatógenos in vitro. Se aislaron un total de 32 cepas de las cuales 15 provinieron de fresa silvestre y 24 de fresa comercial. Se obtuvieron solo nueve cepas con potencial biocontrolador para uno o ambos patógenos. Los mayores porcentajes de inhibición del crecimiento micelial oscilaron entre 67.1% y 81.7% para Botrytis cinerea y 45.5% a 73.2% para Rhizopus stolonifer. Estos fueron obtenidos por cuatro aislados dos obtenidos de fresa silvestre y dos de comercial, todos ellos con capacidad para controlar a ambos fitopatógenos

Efficacy of the antagonist Aureobasidium pullulans PL5 against postharvest pathogens of peach, apple and plum and its modes of action

The efficacy of Aureobasidium pullulans PL5 against different postharvest pathogens of fruits ( Monilinia laxa on plums and peaches, Botrytis cinerea and Penicillium expansum on apples) were evaluated under storage conditions when applied at 10 8 cells ml −1 and their interactions were studied in vitro and in vivo to discover the possible modes of action. Under 1.2 °C and 95% relative humidity (RH) for 28 days, the efficacy of PL5 against M. laxa on plums was 45%, reducing disease incidence from 78% to 43%. Under 1 °C and 95% RH for 21 days, the efficacy against M. laxa on peaches was 63%, reducing disease incidence from 79% to 29%. Under 4 °C and 95% RH for 45 days, the efficacy against B. cinerea and P. expansum on apples was 56% and 46%, respectively. In Lilly–Barnett minimal salt medium with the fungal cell walls of pathogens as sole carbon source, PL5 produced β-1,3-glucanase, exo-chitinase and endo-chitinase. Nutrient concentrations had significant effect on pathogen growth reduction by PL5. No attachment was observed in antagonist–pathogen interactions in vitro or in vivo. PL5 completely inhibited pathogen spore germination in PDB at 10 8 cells ml −1, whereas at 10 6 cells ml −1 the efficacy was significantly decreased. However, inactivated cells and culture filtrate of PL5 had no effect on pathogen spore germination and germ tube elongation. Our results showed that A. pullulans PL5 could be introduced in commercial formulations to control postharvest pathogens on fruits and its activity was based on secretion of lytic enzymes and competition for nutrients.

Antagonistic effects of volatiles generated by Bacillus subtilis on spore germination and hyphal growth of the plant pathogen, Botrytis cinerea

Botrytis cinerea is one of the most serious post-harvest pathogens of fruits and vegetables. Volatiles generated by Bacillus subtilis JA significantly inhibited both spore germination and elongation of germ tubes in Botrytis cinerea using a two-compartment agar-plate assay. The volatiles caused protoplasm retraction from the hyphal tips to the spores.