Near-Harvest Applications of Metschnikowia fructicola, Ethanol, and Sodium Bicarbonate to Control Postharvest Diseases of Grape in Central California

Recent advances in biocontrol and other alternative strategies for the management of postharvest decay in table grapes

During postharvest, table grapes are often spoiled by molds. Aspergillus sp., Alternaria sp., Botrytis sp., Cladosporium sp. and Penicillium sp. are different mold genera frequently related to table grape rot. Fungal spoilage affects nutritional value and organoleptic properties while also producing health hazards, such as mycotoxins. Traditionally, synthetic fungicides have been employed to control fungal diseases. However, possible negative effects on health and the environment are a serious concern for consumers and government entities. This review summarized data on innovative strategies proposed to diminish postharvest losses and extend table grape shelf life. Among physical, chemical, and biological strategies, either alone or in combination, the integrated management of fungal diseases is a sustainable alternative to synthetic fungicides. However, to date, only a few alternative technologies have succeeded on a commercial scale. Recent research aimed at increasing the competitiveness of alternative technologies has led to the development of integrated management strategies to prevent postharvest decay and increase the safety and quality of table grapes.

Biocontrol of Alternaria alternata in cold-stored table grapes using psychrotrophic yeasts and bioactive compounds of natural sources

Alternaria alternata is a common fungal pathogen causing postharvest decay in table grapes. This study addressed the potential of autochthonous yeasts and bioactive compounds of natural sources to act as biocontrol agents (BCAs) against A. alternata in cold-stored table grapes. With this purpose, 19 yeast capable of growing at 0-1 °C were isolated from the surface of Red Globe table grapes. These isolates, along with the pre-isolated strain Metschnikowia pulcherrima RCM2, were evaluated as BCAs in wounded berries. From these results, six yeast isolates were pre-selected to be combined with bioactive compounds of natural sources, like phenolic compounds (PCs) of side streams of wine industry, including bunch stem extract (BSE) (5-25 %), and cane extract (CE) (5-25 %), and functional polysaccharides from shrimp waste such as chitosan (CH) (0.5 %). Then, the biocontrol efficacy of combined treatments beyond individual ones was compared. The results revealed that 4 yeast isolates, namely M. pulcherrima RCM2 and ULA146, and Aureobasidium pullulans FUL14 and FUL18, were the most effective. However, when combined with the natural bioactive compounds, their efficacy against A. alternata did not increase significantly. Notably, ULA146 and FUL18 demonstrated a biocontrol efficacy of 36-37 %, comparable to that of the treatment with commercial doses of SO2, which only showed a 27 % reduction in the lesion diameter. These findings highlight the potential of using psychrotrophic yeasts as BCAs against A. alternata in cold-stored table grapes. Combining these yeast strains with BSE, CE and CH did not increase BCAs efficacy against this pathogen at the concentrations tested. The development of effective biocontrol strategies for A. alternata could contribute to reducing reliance on chemically synthesized fungicides, promoting sustainable practices, aiming to improve the quality and safety of cold-stored table grapes.

Biocontrol Efficacy of Metschnikowia spp. Yeasts in Organic Vineyards against Major Airborne Diseases of Table Grapes in the Field and in Postharvest

The aim of this work was to evaluate the efficacy of two antagonistic yeasts, Metschnikowia pulcherrima strain MPR3 and M. fructicola strain NRRL Y-27328 (commercial product NOLI), applied in addition to the "on-farm biological treatments" (BIO) carried out during the production season, for the containment of powdery mildew and grey mould diseases on organic table grapes 'Italia'. The yeast strains were applied in the field three times, and their efficacy was evaluated during the production season and under postharvest conditions. Overall, M. pulcherrima MPR3 combined with BIO treatments reduced disease incidence caused by Erysiphe necator and disease incidence and severity caused by Botrytis cinerea with values between 67.8% and 86.2%, showing higher efficacy than BIO treatments applied alone and in combination with NOLI. Field treatments based on BIO+MPR3 maintained their performance also during fruit storage, protecting grape berries from grey mould development to a greater extent than the other treatments (disease reduction of about 98%). Thus, the presence of M. pulcherrima MPR3 seems to improve disease management both in the field and in postharvest environments, without negative impacts on grape microbial communities. These findings highlight the potential of M. pulcherrima MPR3 as a promising alternative strategy for disease control in organic vineyards and in postharvest, providing sustainable solutions to improve food quality and safety.

Evaluating Food Additives Based on Organic and Inorganic Salts as Antifungal Agents against Monilinia fructigena and Maintaining Postharvest Quality of Apple Fruit

A set of commonly used food additives was evaluated for their antifungal activity against the brown rot disease of fruits caused by the fungal pathogen Monilinia fructigena, which is one of the most economically important agents, causing important damage to pome fruits, such as pears and apples. The radial mycelial growth of the fungal pathogen was assessed in PDA amended with different concentrations (0.5, 2, 2.5, and 5%) of each additive. The results underlined that most of the additives displayed a significant inhibition of mycelial growth, with the extent of inhibition varying depending on the specific additive and concentration used. Five food additives showed high inhibition rates (above 88%), of which sodium bicarbonate, sodium carbonate, copper sulphate, and sodium hydroxide were the most effective, whereas ammonium carbonate, magnesium chlorite, and citric acid were the least effective. Interestingly, the coatings containing sodium bicarbonate, copper sulphate, and ammonium bicarbonate significantly reduced the incidence of brown rot disease in apples, but other additives were not effective, such as ammonium carbonate and magnesium sulphate. The anhydrous sodium sulphate used at a concentration of 2%, was found to be one of the least effective additives, with a reduction rate of 20%. Subsequently, food additives showing good growth inhibition rates and reduction in disease severity were then tested in semi-commercial trials at temperatures of 4 °C and 22 °C. The results indicated that these additives demonstrate effectiveness in controlling M. fructigena at specific concentrations, and lower temperatures (4 °C) can improve the efficiency of the control measures. In addition, the selected food additives exhibited significant antimicrobial activity against M. fructigena, suggesting their application as a promising alternative for managing brown rot disease in apple fruits.

Evaluation of a novel water-soluble decanoic acid formulation as a fruit sanitizer

Fruits irrigated with contaminated water can transmit various pathogens. High sugar content in fruits such as black cherry (BC) fruit encourages microbial proliferation. A novel water-soluble decanoic acid (WSDA) was evaluated as a fruit sanitizer and compared with other traditional fruit sanitizers such as ethanol, bleach, or dishwasher surfactants. WSDA sanitizer killed yeasts, molds and bacteria including E. coli microbes effectively as other sanitizers with (4 log cycle reduction) of microbial load. Furthermore, the bacterial sanitization mechanism i.e. bactericidal or bacteriostatic was evaluated for alcohol, bleaching and WASDA solutions. E. coli was selected as the model pathogen used for such comparison. Results indicated that the mechanism of action for the three sanitizer solutions against E. coli was bactericidal. The problem with most used fruit sanitizers is their negative influence on fruit quality in terms of physical, mechanical and taste properties. In addition, some led to toxicological and ecological concerns. Thus, studies were conducted to explore the changes in the exocarp cell structure of BC fruit upon exposure to WSDA and other sanitizers using microscopic investigation. WSDA could have a very mild or gentle effect on the BC fruit cells compared to other sanitizers. Alcohol, bleaching and dishwasher surfactant changed the cellular structures and the intercellular spaces. Sanitizers may also affect fruit swelling. WSDA showed an increase in percent weight gain but it was significantly (p < 0.05) much lower than dishwasher surfactant and bleaching solution. BC Fruit flesh firmness and hardness were investigated upon exposure to different sanitizer solutions. BC fruit treated with WSDA showed the highest firmness values. Some liquid sanitizers could affect fruit quality in terms of fruit taste. Sensory evaluation in terms of the sanitizer's smell, texture and hedonic of BC fruit after soaking in different sanitizers was carried out. All sensory parameters of BC fruit soaked with WSDA were similar with insignificant differences (p > 0.05) compared to BC fruit soaked in tap water. However, the sensory parameters were significantly different (p < 0.05) when compared with alcohol, bleach and dishwasher surfactant. This ensures that WSDA was superior to other evaluated sanitizers in terms of physical, mechanical and fruit quality.

Epiphitic Microbiome of Alvarinho Wine Grapes from Different Geographic Regions in Portugal

Geographic location and, particularly, soil and climate exert influence on the typicality of a wine from a specific region, which is often justified by the terroir, and these factors also influence the epiphytic flora associated with the surface of the grape berries. In the present study, the microbiome associated with the surface of berries obtained from ten vineyards of the Alvarinho variety located in different geographical locations in mainland Portugal was determined and analyzed. The removal of microbial flora from the surface of the berries was carried out by washing and sonication, after which the extraction and purification of the respective DNA was carried out. High-throughput short amplicon sequencing of the fungal ITS region and the bacterial 16S region was performed, allowing for the determination of the microbial consortium associated with Alvarinho wine grapes. Analysis of α-diversity demonstrated that parcels from the Monção and Melgaço sub-region present a significantly (p < 0.05) lower fungal diversity and species richness when compared to the plots analyzed from other regions/sub-regions. The ubiquitous presence of Metschnikowia spp., a yeast with enologic potential interest in all parcels from Monção and Melgaço, was also observed.

Starmerella bacillaris Released in Vineyards at Different Concentrations Influences Wine Glycerol Content Depending on the Vinification Protocols

Starmerella bacillaris is a non-Saccharomyces yeast proposed for must fermentation together with Saccharomyces cerevisiae because of its high glycerol and moderate volatile acidity production. Furthermore, it was demonstrated that the same S. bacillaris strains that possess interesting technological properties exhibited antifungal activity against Botrytis cinerea, suggesting the release of this yeast in the vineyard. To obtain a positive effect during the following winemaking process, the maintenance of suitable concentrations of S. bacillaris is essential. Therefore, to obtain information on the survival of S. bacillaris, a small-scale field trial was performed. One week before the harvest, two different concentrations of S. bacillaris (10⁶ and 10⁷ cells/mL) were sprayed on Pinot grigio bunches, and the strain concentration was monitored by means of qPCR during the subsequent fermentation process. In addition, the combined effect of different winemaking techniques was evaluated, i.e., the vinification of juice, juice with marc and cryomaceration treatment. Results demonstrated that, under the tested conditions, S. bacillaris released in the vineyard remained viable for one week on grape bunches and increased glycerol content during the subsequent fermentation process. Different vinification protocols influenced cell concentrations. In particular, the cryomaceration treatment, due to the use of low temperature, supported S. bacillaris growth due to its cryotolerant aptitude. The collected data open new perspectives on the control of alcoholic fermentation, involving both vineyard and cellar management.

Combination of Sodium Bicarbonate (SBC) with Bacterial Antagonists for the Control of Brown Rot Disease of Fruit

Simultaneous treatment with antagonistic bacteria Bacillus amylolquefaciens (SF14), Alcaligenes faecalis (ACBC1), and the food additive sodium bicarbonate (SBC) to control post-harvest brown rot disease caused by Monilinia fructigena, and their effect on the post-harvest quality of nectarines were evaluated. Four concentrations of SBC (0.5, 2, 3.5, and 5%) were tested. Results showed that bacterial antagonists displayed remarkable compatibility with different concentrations of SBC and that their viability was not affected. The results obtained in vitro and in vivo bioassays showed a strong inhibitory effect of all treatments. The combination of each bacterial antagonist with SBC revealed a significant improvement in their biocontrol efficacies. The inhibition rates of mycelial growth ranged from 60.97 to 100%. These results also indicated that bacterial antagonists (SF14 or ACBC1) used at 1 × 10⁸ CFU/ mL in combination with 2, 3.5, or 5% SBC significantly improved the control of M. fructigina by inhibiting the germination of spores. Interestingly, disease incidence and lesion diameter in fruits treated with SF14, ACBC1 alone, or in combination with SBC were significantly lower than those in the untreated fruits. In vivo results showed a significant reduction in disease severity ranging from 9.27 to 64.83% compared to the untreated control, while maintaining the appearance, firmness, total soluble solids (TSS), and titratable acidity (TA) of fruits. These results suggested that the improved disease control by the two antagonistic bacteria was more likely due to the additional inhibitory effects of SBC on the mycelial growth and spore germination of the pathogenic fungus. Overall, the combination of both bacteria with SBC provided better control of brown rot disease. Therefore, a mixture of different management strategies can effectively control brown rot decay on fruits.

Microbial-based Biocontrol Solutions for Fruits and Vegetables: Recent Insight, Patents, and Innovative Trends

BACKGROUND

Fruits and vegetables are susceptible to colonisation by undesired microflora, which, in pre- and post-harvest conditions, negatively impact the quality of these products, leading to a reduction of yield, shelf-life, and marketability. In the few last years, the use of microbial Biological Control Agents (BCAs) has assumed international relevance in order to control harmful microorganisms, as a promising alternative to chemical interventions.

OBJECTIVE

The purpose of this review is to discuss the microbial-based solutions applicable for the biocontrol of the main microbial spoilers, phytopathogens, and human food-borne pathogens affecting fruits and vegetables during their production and storage.

RESULTS

A comprehensive overview of the scientific literature investigating the effectiveness of BCA-based products available on the market is provided, as well as of the most recent patents protecting biotechnological applications in this field. Innovative trends are discussed, with a particular focus on the integration of BCAs to minimise spoilage phenomena and microbiological risks adopting combined approaches.

CONCLUSION

This study underlines the growing interest about biocontrol strategies to counteract the growth of spoilage and/or pathogenic microorganisms indicating that in the next years a considerable increase of commercial products and patents will be developed worldwide to exploit innovative biotechnological solutions in the sector.

Resistance against phomopsis leaf blight disease induced by potassium salts in strawberry plants

Background

Growing interest of strawberry cultivation in Egypt necessitates more efforts towards its severe phomopsis leaf blight disease caused byPhomopsis obscurans. Synthetic fungicides could control this fungus but due to their critical impact on human beings and the environment, we are in dire need of safe alternatives for its control. Therefore, the leverage of the potassium bicarbonate and dipotassium phosphate onP. obscuranssuppression on strawberry plants was examined.

Results

Full inhibition of the fungal linear growth was achieved at the highest concentration (2%) of the two salts. Under field conditions, 87.5, 81.3, and 81.3% were the best decreases in disease severity gained by the two salts at 2% of both salts and the fungicide Amstar, respectively. Potassium bicarbonate at 1.5% reduced severity by 68.8%. Concentrations 1, 1.5, and 2% of each salt considerably enhanced strawberry yield. The increases were 66.7 and 61.7%, at 2% concentration by the two salts, respectively. Increments by 126.7 and 150% of peroxidase activity in plant leaves and by 140 and 148% of chitinase activity were noted by the two salts, respectively, at 2%.

Conclusions

The examined bicarbonate and phosphate salts could suppressP. obscuransgrowth and spread. The more the used salt concentration, the better it suppresses the fungal growth with consequent effect on the plants which apparently promoted their field yield. Potential implications of the two salts on enhancing activities of the two enzymes reflected their role in suppressing the disease. Further research is needed to integrate these salts in management strategies ofP. obscuransin Egypt to foster strawberry yield utilizing ecofriendly approaches.

Microbial Resources as a Tool for Enhancing Sustainability in Winemaking

In agriculture, the wine sector is one of the industries most affected by the sustainability issue. It is responsible for about 0.3% of annual global greenhouse gas emissions from anthropogenic activities. Sustainability in vitiviniculture was firstly linked to vineyard management, where the use of fertilizers, pesticides and heavy metals is a major concern. More recently, the contribution of winemaking, from grape harvest to bottling, has also been considered. Several cellar processes could be improved for reducing the environmental impact of the whole chain, including microbe-driven transformations. This paper reviews the potential of microorganisms and interactions thereof as a natural, environmentally friendly tool to improve the sustainability aspects of winemaking, all along the production chain. The main phases identified as potentially interesting for exploiting microbial activities to lower inputs are: (i) pre-fermentative stages, (ii) alcoholic fermentation, (iii) stage between alcoholic and malolactic fermentation, (iv) malolactic fermentation, (v) stabilization and spoilage risk management, and (vi) by-products and wastewater treatment. The presence of proper yeast or bacterial strains, the management and timing of inoculation of starter cultures, and some appropriate technological modifications that favor selected microbial activities can lead to several positive effects, including (among other) energy savings, reduction of chemical additives such as sulfites, and reuse of certain residues.

Biocontrol yeasts: mechanisms and applications

Yeasts occur in all environments and have been described as potent antagonists of various plant pathogens. Due to their antagonistic ability, undemanding cultivation requirements, and limited biosafety concerns, many of these unicellular fungi have been considered for biocontrol applications. Here, we review the fundamental research on the mechanisms (e.g., competition, enzyme secretion, toxin production, volatiles, mycoparasitism, induction of resistance) by which biocontrol yeasts exert their activity as plant protection agents. In a second part, we focus on five yeast species (Candida oleophila, Aureobasidium pullulans, Metschnikowia fructicola, Cryptococcus albidus, Saccharomyces cerevisiae) that are or have been registered for the application as biocontrol products. These examples demonstrate the potential of yeasts for commercial biocontrol usage, but this review also highlights the scarcity of fundamental studies on yeast biocontrol mechanisms and of registered yeast-based biocontrol products. Yeast biocontrol mechanisms thus represent a largely unexplored field of research and plentiful opportunities for the development of commercial, yeast-based applications for plant protection exist.

Genome Sequence, Assembly and Characterization of Two Metschnikowia fructicola Strains Used as Biocontrol Agents of Postharvest Diseases

The yeast Metschnikowia fructicola was reported as an efficient biological control agent of postharvest diseases of fruits and vegetables, and it is the bases of the commercial formulated product "Shemer." Several mechanisms of action by which M. fructicola inhibits postharvest pathogens were suggested including iron-binding compounds, induction of defense signaling genes, production of fungal cell wall degrading enzymes and relatively high amounts of superoxide anions. We assembled the whole genome sequence of two strains of M. fructicola using PacBio and Illumina shotgun sequencing technologies. Using the PacBio, a high-quality draft genome consisting of 93 contigs, with an estimated genome size of approximately 26 Mb, was obtained. Comparative analysis of M. fructicola proteins with the other three available closely related genomes revealed a shared core of homologous proteins coded by 5,776 genes. Comparing the genomes of the two M. fructicola strains using a SNP calling approach resulted in the identification of 564,302 homologous SNPs with 2,004 predicted high impact mutations. The size of the genome is exceptionally high when compared with those of available closely related organisms, and the high rate of homology among M. fructicola genes points toward a recent whole-genome duplication event as the cause of this large genome. Based on the assembled genome, sequences were annotated with a gene description and gene ontology (GO term) and clustered in functional groups. Analysis of CAZymes family genes revealed 1,145 putative genes, and transcriptomic analysis of CAZyme expression levels in M. fructicola during its interaction with either grapefruit peel tissue or Penicillium digitatum revealed a high level of CAZyme gene expression when the yeast was placed in wounded fruit tissue.

Edible coating composed of chitosan and Salvia fruticosa Mill. extract for the control of grey mould of table grapes

BACKGROUND

Consumer concerns regarding high-quality produce, free of pesticide residues, direct research towards disease management strategies that minimise or even exclude the use of synthetic chemistries in crop production. The efficacy of a chitosan-based edible coating combined with the acetonic extract of Salvia fruticosa Mill. (ASF) was assessed against the grey mould of table grapes.

RESULTS

HPLC-SPE-NMR and q-NMR analyses defined major constituents of ASF to be the flavonoids hispidulin, salvigenin and cirsimaritin and the diterpenes carnosic acid, carnosol and the 12-methoxycarnosic acid. The extract was found to be efficacious in reducing spore germination and mycelial growth of Botrytis cinerea in vitro at 10 and 25 °C. However, the combination of the ASF with chitosan 1% (w/v; CHIT) significantly improved fungal inhibition. Similarly, in fruit inoculation trials at 10 °C, the efficacy of the combined application of the ASF at 500 mg L^-1 with CHIT against grey mould was statistically equal to the synthetic fungicide thiabendazole, ranging from 98.4% to 92.7% at 12 and 21 days post-inoculation, respectively. Furthermore, chitosan coating alone and in combination with ASF decreased the rate of fruit weight loss during cold storage, while preserved soluble solids content and titratable acidity. Chitosan-based coatings did not affect quality attributes and the bioactive compounds in table grapes.

CONCLUSION

The combined application of the ASF in the form of an edible coating with chitosan could effectively control B. cinerea without deteriorating quality and physico-chemical properties of grapes. © 2016 Society of Chemical Industry.

Efficiency of Artemisia nilagirica (Clarke) Pamp. essential oil as a mycotoxicant against postharvest mycobiota of table grapes

BACKGROUND

In order to get a potent botanical fungicide for the management of fungal decay of table grapes, an experiment was conducted in which 20 essential oils of higher plants were screened at 0.33 µL mL(-1) against dominant fungi causing decay of table grapes, including Aspergillus flavus, A. niger and A. ochraceus. Furthermore, the minimum inhibitory/fungicidal concentration, fungitoxic spectrum and mycotoxin inhibition activity of the most potent oil were determined. The efficacy of the most potent oil in preservation of table grapes, along with organoleptic evaluation, was also carried out by storing 1 kg of grapes in the oil vapour.

RESULTS

Artemisia nilagirica oil was found to be most toxic, exhibiting 100% mycelia inhibition of all test fungi. Moreover, 0.29 µL mL(-1) A. nilagirica oil was fungistatic and 0.58 µL mL(-1) was fungicidal for all tested species of Aspergillus. The oil exhibited a broad range of fungitoxicity against other grape berry-rotting fungi. Artemisia nilagirica oil completely suppressed the growth and mycotoxin (AFB1 and OTA) secretion of aflatoxigenic and ochratoxigenic strains of Aspergillus at 1.6 µL mL(-1) . During the in vivo experiment, fumigation of 1 kg of table grapes with 200 and 300 µL dosage of A. nilagirica oil enhanced the shelf life for up to 9 days. The oil did not show any phytotoxic effect. Besides, oil application did not substantively change the sensory properties of the fruits.

CONCLUSION

Artemisia nilagirica oil can be used as an alternative botanical fungicide for the control of fruit-rotting fungi of stored grapes.

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 1098 bp encoding a 365 amino acid protein with a calculated molecular weight of 40.9 kDa 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.

Influence of Temperature, Inoculation Interval, and Dosage on Biofumigation with Muscodor albus to Control Postharvest Gray Mold on Grapes

Control of postharvest gray mold, caused by Botrytis cinerea, on Thompson Seedless grape by biofumigation with a rye grain formulation of Muscodor albus, a fungus that produces volatiles lethal to many microorganisms, was evaluated. The influences of temperature, biofumigant dosage, and interval between inoculation and treatment on disease incidence and severity on detached single berries were assessed. When biofumigation began within 24 h after inoculation, higher M. albus dosages (≥50 g of the M. albus grain formulation per kilogram of grapes at 20°C or 100 g/kg at 5°C) stopped infections and control persisted after M. albus removal. Biofumigation was more effective at 20 than 5°C. Among inoculated clusters inside clamshell boxes incubated for 7 days at 15°C, gray mold incidence was reduced from 20.2% among untreated grape fruit to less than 1%, when ≥5 g of the formulation per kilogram of grapes was added. Among grape berries commercially packaged in ventilated polyethylene cluster bags incubated for 7 days at 15°C, gray mold incidence was 40.5% among untreated fruit and 11.1 or 6.7% when the formulation at 5 or 20 g/kg, respectively, had been added. In the same packaging, among grape berries incubated for 28 days at 0.5°C, gray mold incidence was 42.8% among untreated fruit and 4.8 or 4.0% when the formulation at 5 or 10 g/kg, respectively, had been added. Lower dosages (≤20 g/kg) suppressed disease development while M. albus was present; however, after their removal, B. cinerea resumed growth and gray mold incidence increased. Placement of M. albus inside grape packages significantly controlled gray mold and may be a feasible approach to manage postharvest decay of table grape.

Combination of antagonistic yeasts with two food additives for control of brown rot caused by Monilinia fructicola on sweet cherry fruit

AIMS

To evaluate beneficial effect of two food additives, ammonium molybdate (NH4-Mo) and sodium bicarbonate (NaBi), on antagonistic yeasts for control of brown rot caused by Monilinia fructicola in sweet cherry fruit under various storage conditions. The mechanisms of action by which food additives enhance the efficacy of antagonistic yeasts were also evaluated.

METHODS AND RESULTS

Biocontrol activity of Pichia membranefaciens and Cryptococcus laurentii against brown rot in sweet cherry fruit was improved by addition of 5 mmol l(-1) NH4-Mo or 2% NaBi when stored in air at 20 and 0 degrees C, and in controlled atmosphere (CA) storage with 10% O2 + 10% CO2 at 0 degrees C. Population dynamics of P. membranefaciens in the wounds of fruit were inhibited by NH4-Mo at 20 degrees C after 1 day of incubation and growth of C. laurentii was inhibited by NH4-Mo at 0 degrees C in CA storage after 60 days. In contrast, NaBi did not significantly influence growth of the two yeasts in fruit wounds under various storage conditions except that the growth of P. membranefaciens was stimulated after storage for 45 days at 0 degrees C in CA storage. When used alone, the two additives showed effective control of brown rot in sweet cherry fruit and the efficacy was closely correlated with the concentrations used. The result of in vitro indicated that growth of M. fructicola was significantly inhibited by NH4-Mo and NaBi.

CONCLUSION

Application of additives improved biocontrol of brown rot on sweet cherry fruit under various storage conditions. It is postulated that the enhancement of disease control is directly because of the inhibitory effects of additives on pathogen growth, and indirectly because of the relatively little influence of additives on the growth of antagonistic yeasts.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results obtained in this study suggest that an integration of NH4-Mo or NaBi with biocontrol agents has great potential in commercial management of postharvest diseases of fruit.

Impact of Postharvest Hot Water or Ethanol Treatment of Table Grapes on Gray Mold Incidence, Quality, and Ethanol Content

The influence of brief immersion of grape berries in water or ethanol at ambient or higher temperatures on the postharvest incidence of gray mold (caused by Botrytis cinerea) was evaluated. The incidence of gray mold among grape berries that were untreated, or immersed for 1 min in ethanol (35% vol/vol) at 25 or 50°C, was 78.7, 26.2, and 3.4 berries/kg, respectively, after 1 month of storage at 0.5°C and 2 days at 25°C. Heated ethanol was effective up to 24 h after inoculation, but less effective when berry pedicels were removed before inoculation. Rachis appearance, epicuticular wax content and appearance, and berry shatter were unchanged by heated ethanol treatments, whereas berry color changed slightly and treated grape berries were more susceptible to subsequent infection. Ethanol and acetaldehyde contents of grape berries were determined 1, 7, and 14 days after storage at 0.5°C following treatment for 30 or 90 s at 30, 40, or 50°C with water, or 35% ethanol. Highest residues (377 μg/g of ethanol and 13.3 μg/g of acetaldehyde) were in berries immersed for 90 s at 50°C in ethanol. Among ethanol-treated grape berries, the ethanol content declined during storage, whereas acetaldehyde content was unchanged or increased. Untreated grape berries initially contained ethanol at 62 μg/g, which then declined. Acetaldehyde content was 0.6 μg/g initially and changed little during storage.

Commercialization and implementation of biocontrol

Although the number of biocontrol products is increasing, these products still represent only about 1% of agricultural chemical sales. Yet these are important contributions because biocontrol agents offer disease management alternatives with different mechanisms of action than chemical pesticides. Trends in research include the increased use of biorational screening processes to identify microorganisms with potential for biocontrol, increased testing under semicommercial and commercial production conditions, increased emphasis on combining biocontrol strains with each other and with other control methods, integrating biocontrol into an overall system.