Impact of mild heat treatments on induction of thermotolerance in the biocontrol yeast Candida sake CPA-1 and viability after spray-drying

Aims: The objective of this study was to examine the induction of thermotolerance in the biocontrol agent Candida sake CPA‐1 cells by mild heat treatments to enhanced survival of formulations using spray‐drying. The possible role of heat‐shock proteins (HSPs) biosynthesis in induced thermotolerance and the role of sugars and sugar alcohols were also determined. Methods and Results: Studies were conducted on C. sake cells grown in molasses medium and exposed to mild temperatures of 30 and 33°C during mid‐ (16 h), late‐exponential (24 h), early‐ (30 h) and mid‐stationary (36 h) growth phases. The effect on viability was determined both before and after spray‐drying. Cycloheximide and chloramphenicol were used to examine the role of HSPs and HPLC was used to analyse the accumulation of sugar and sugar alcohols. The results indicate that both temperatures induced thermotolerance in cells of C. sake. Mild heat‐adapted cells at 33°C in the early‐ or mid‐stationary phases had survival values after spray‐drying significantly higher (P ≤ 0·05) than nonadapted cells. However, viabilities were not high enough to be considered for commercial use with values up to 17%. HSPs were not implicated in thermotolerance acquired by mild heat‐adapted cells as similar viabilities were obtained in the presence of protein inhibitors. Little change was observed in sugar and sugar alcohols with an increase in glucose and arabitol in some treatments. Conclusions: This study suggests that it is possible to induce thermotolerance in biocontrol yeasts such as C. sake. However, this does not improve survival of cells exposed to spray‐drying sufficiently to consider this a suitable formulation method for this biocontrol agent. HSPs, sugars and sugar polyols were not directly responsible for induced thermotolerance in yeast cells. Significance and Impact of the Study: This type of information can be effectively applied to improve the viability of cells in the process of formulation.     

Liquid formulation of the biocontrol agent Candida sake by modifying water activity or adding protectants

AIMS: To evaluate the effect of modification of water activity (aw) and the addition of protective substances in the preservation medium of liquid formulations of the biocontrol agent Candida sake stored at 4 and 20 degrees C. METHODS AND RESULTS: The aw of the preservation medium of C. sake was modified from 0.72 to 0.95 by adding glycerol or polyethylene glycol (PEG). Moreover, several protectant substances at different concentrations were evaluated. Modification of lower aw-levels (0.721-0.901) with glycerol did not maintain the viability of the yeast cells. Higher aw-levels (0.93-0.95) with either glycerol or PEG improved the viability but not at acceptable viability levels. C. sake cells maintained viabilities >60% when sugars, such as trehalose, and polyols, such as glycerol and PEG were used as protectants in liquid formulations. Moreover, liquid formulations of C. sake stored at 4 degrees C showed higher number of viable counts than at 20 degrees C. When different sugars were tested, all of them, except 10% fructose, resulted in a viability higher than 50% of the C. sake formulations. Biocontrol of liquid formulation treatments was similar to fresh cells in controlling Penicillium expansum on wounded apples. CONCLUSIONS: Sugars such as lactose and trehalose could be considered as good protectants in order to obtain liquid formulations of C. sake cells as they maintain the viability >70% for 4 months at 4 degrees C. SIGNIFICANCE AND IMPACT OF STUDY: This study shows that a suitable liquid formulation for commercial application can be produced with high viability and conservation of biocontrol efficacy. Moreover, if 10% lactose is the protectant used in the formulation, the economic costs would not be limiting for industrial production.     

Stability of biocontrol products carrying Candida sake CPA-1 in starch derivatives as a function of water activity

The preservation and shelf-life of formulations of the biocontrol agent Candida sake CPA-1 and starch derivatives as a function of water activity (a_W) were studied in terms of the physical stability of the products and cell viability. Formulations of biocontrol products (BCPs), based on combinations of potato starch and pre-gelatinised potato starch (F1 and F2) or maltodextrines (MD) (F3) containing cell protectants, were obtained by fluidised-bed drying. The carriers and the formulated products were stored at 20°C under different a_W conditions. The water sorption and water plasticization behaviour of the different products were analysed through the water sorption isotherms and glass transition temperatures (T_g). Likewise, the viability of C. sake over time was determined as a function of the a_W. The solubility of the products was also assessed. Although formulations stored at 20°C and low a_W (≤?0.33) exhibited a better shelf-life, a significant decrease in cell survival ratio after 180 storage days was observed. Cold storage (5°C) was required to better maintain the cell viability, thus prolonging the shelf-life of BCPs. Formulations containing MD were the most effective at preserving cell viability and also exhibited the highest water solubility. All the formulations were physically stable at ambient temperature; therefore, the cell stability is the critical point at which to establish both the a_W levels and temperature during storage. Packaging the product using high water vapour barrier material and under cold storage would be necessary to ensure a high number of viable cells and an effective and competitive BCP.     

Formulation development of the biocontrol agent Bacillus subtilis strain CPA-8 by spray-drying

Aims: To prepare commercially acceptable formulations of Bacillus subtilis CPA‐8 by spray‐drying with long storage life and retained efficacy to control peach and nectarine brown rot caused by Monilinia spp. Methods and Results: CPA‐8 24‐h‐ and 72‐h‐old cultures were spray dried using 10% skimmed milk, 10% skimmed milk plus 10% MgSO₄, 10% MgSO₄ and 20% MgSO₄ as carriers/protectants. All carriers/protectants gave good percentages of powder recovery (28–38%) and moisture content (7–13%). CPA‐8 survival varied considerably among spray‐dried 24‐h‐ and 72‐h‐old cultures. Seventy‐two hours culture spray dried formulations showed the highest survival (28–32%) with final concentration products of 1·6–3·3 × 10⁹ CFU g^?1, while viability of 24‐h‐old formulations was lower than 1%. Spray‐dried 72‐h‐old formulations were selected to subsequent evaluation. Rehydration of cells with water provided a good recovery of CPA‐8 dried cells, similar to other complex rehydration media tested. Spray‐dried formulations stored at 4 ± 1 and 20 ± 1°C showed good shelf life during 6 months, and viability was maintained or slightly decreased by 0·2–0·3‐log. CPA‐8 formulations after 4‐ and 6 months storage were effective in controlling brown rot caused by Monilinia spp. on nectarines and peaches resulting in a 90–100% reduction in disease incidence. Conclusions: Stable and effective formulations of biocontrol agent B. subtilis CPA‐8 could be obtained by spray‐drying. Significance and Impact of the Study: New shelf‐stable and effective formulations of a biocontrol agent have been obtained by spray‐drying to control brown rot on peach.     

Optimization of growth conditions of the postharvest biocontrol agent Candida sake CPA-1 in a lab-scale fermenter

AIM: To maximize the growth (expressed as number of viable cells per millilitre) of the postharvest biocontrol agent Candida sake CPA(-1) at laboratory scale conditions. METHODS AND RESULTS: Growth conditons (aeration, agitation speed and inoculum size) were studied in batch conditions in a 5 l fermenter using molasses and urea as growth medium. Consumption of sugars and urea were analysed. Fed-batch studies were also carried out. Glucose and fructose were consumed during the exponential growth phase and were depleted after 18 h of growth. On the contrary, C. sake cells assimilated sucrose during the stationary phase. There was not growth improvement when fed-batch technology was used. Addition of an extra amount of glucose or molasses after 18 h of growth did not contribute to increase final population. CONCLUSIONS: Maximum growth (about 8 x 10(8 )CFU ml(-1)) was obtained at batch fermentation after 30 h growth at 400 rev min(-1), 150 l h(-1) of air and initial concentration of 106 CFU ml(-1). SIGNIFICANCE AND IMPACT OF THE STUDY: The results obtained in this study are an approach for further upscaling of C. sake production.     

Iturin A is the principal inhibitor in the biocontrol activity of Bacillus amyloliquefaciens PPCB004 against postharvest fungal pathogens

Aims: A Bacillus amyloliquefaciens strain, surviving epiphytically on the surface of fruit, was isolated while searching for naturally occurring biological control agents. This bacterial strain was characterized for its antifungal activity against seven selected fungal postharvest pathogens of citrus. Methods and Results: To understand the antifungal activity, seven postharvest fungal pathogens were screened for growth inhibition by B. amyloliquefaciens strain. Assays using B. amyloliquefaciens lipopeptide extracts showed a strong inhibitive activity. The inhibitory effect was observed in abnormal conidial germination and germ tube development when conidia were treated with different lipopeptide extract concentrations. Further analysis using PCR and chromatography confirmed the presence of fengycin, iturin and surfactine, of which iturin A showed the strongest and most common inhibitory effect. The results are supported by site‐directed mutagenesis analysis, targeted to suppress the biosynthesis of iturin A production. Fruit trials confirmed disease development inhibition when the antagonist was applied 1 day prior to or 1 day after fungal application. Conclusions: We conclude that the iturin family of lipopeptides are vital in the antagonism of B. amyloliquefaciens against the seven citrus postharvest pathogenic fungi tested. Significance and Impact of the Study: We elucidated the principal mechanism used by B. amyloliquefaciens PPCB004 to suppress postharvest disease development on stored fruits.     

Survival of the biocontrol yeast Pichia anomala after long-term storage in liquid formulations at different temperatures, assessed by flow cytometry

AIMS: Investigate the survival of liquid formulations of the biocontrol yeast Pichia anomala J121 at different temperatures, and develop a system for comparative studies of different storage conditions and formulations. METHODS AND RESULTS: The survival of P. anomala in liquid formulations with lactose, starch and trehalose amendments was measured during prolonged storage at temperatures ranging from -20 to +30 degrees C. The relative survival of the stored cells was rapidly estimated by flow cytometry. After 4 weeks incubation at 4 and 10 degrees C, 75-90% of the cells were viable, with no significant differences between the various formulations. Supplementing the storage buffer with lactose or trehalose increased the survival after longer incubations (8 and 12 weeks) at all temperatures (-20 to 30 degrees C). Trehalose was the most effective protectant at 20 and 30 degrees C (>20% viable cells after 12 weeks at 20 degrees C). The biocontrol activity was maintained after formulation and prolonged storage of P. anomala. CONCLUSIONS: The storage potential of liquid formulated P. anomala cells can be increased by supplementation with lactose or trehalose. The combination of a custom made incubation chamber and flow cytometry was suitable to evaluate stability of P. anomala formulations. SIGNIFICANCE AND IMPACT OF THE STUDY: Liquid formulated P. anomala have a long shelf life. The developed test system can be used to study different formulations of other biocontrol agents.     

Fluidised-bed spray-drying formulations of Candida sake CPA-1 by adding biodegradable coatings to enhance their survival under stress conditions

The biocontrol agent Candida sake CPA-1 has demonstrated to be effective against several diseases on fruit. However, for application of CPA-1 under field conditions, it was necessary to mix it with a food coating to improve survival under stress conditions, as well as adherence and distribution on fruit surfaces. The objective of this study was to obtain a more competitive formulation under field conditions to be applied independently of any product. To achieve this purpose, the drying process of CPA-1 by a fluidised-bed spray-drying system together with biodegradable coatings was optimised. This approach is novel for the drying system used and the formulation obtained which was able to form a film or coating on fruit surfaces. Several substances were tested as carriers and binders, and drying temperature was optimised. The addition of protective compounds was also tested to improve survival of CPA-1 during the dehydration process. Product shelf life, biocontrol efficacy on grapes against Botrytis cinerea, and the improvement of C. sake behaviour under stress conditions were tested. The optimal temperature of drying was 55 °C and two formulations that were able to develop a coating on fruit surfaces were obtained. One of the formulations was created by using a combination of native and pregelatinised potato starch; the other formulation was obtained using maltodextrin and by adding skimmed milk and sucrose as protectant compounds. The formulated products reduced the incidence and severity of B. cinerea, and CPA-1 survival rate was increased under stress conditions of temperature and humidity.

     

Enhancement of biocontrol activity of yeasts by adding sodium bicarbonate or ammonium molybdate to control postharvest disease of jujube fruits

AIMS: To assess the potential of sodium bicarbonate and ammonium molybdate as additives in enhancing the biocontrol efficacy of Rhodotorula glutinis and Cryptococcus laurentii against blue mould in jujube fruits. METHODS AND RESULTS: Two yeasts at a concentration of 107 CFU ml-1, in combination with 238 mmol l-1 sodium bicarbonate or 15 mmol l-1 ammonium molybdate, showed a significant inhibition effect on blue mould of jujube fruits stored at 20 degrees C for 5 days. The colonizing ability of the yeasts in wounded sites was significantly decreased in the presence of ammonium molybdate. CONCLUSIONS: Combining R. glutinis or C. laurentii with sodium bicarbonate or ammonium molybdate provided a more effective control of postharvest disease than using the antagonistic yeasts or the chemicals alone. SIGNIFICANCE AND IMPACT OF THE STUDY: The addition of sodium bicarbonate or ammonium molybdate reduced the number of antagonists required to efficiently control disease of postharvest fruits, which could result in the reduction of costs.     

Biological control of postharvest blue mold of oranges by <Emphasis Type="Italic">Cryptococcus laurentii </Emphasis>(Kufferath) Skinner

Cryptococcus laurentii (Kufferath) Skinner was evaluated for its activity in reducing postharvest blue mold decay of oranges caused by Penicillium italicum in vitro and in vivo. The results showed that washed cell suspensions of yeast provided control of blue mold decay better than yeast in culture broth. Autoclaved cell culture and cell-free culture filtrate failed to provide protection against the pathogen. The concentrations of antagonist had significant effects on biocontrol effectiveness. When the washed yeast cell suspension reached the concentration of 1 × 10⁹ CFU/ml, challenged with pathogen spore suspension at 1 × 10⁴ spores/ml, the blue mold decay was completely inhibited during 5 days of incubation at 20 °C. No complete control was obtained when oranges were stored at 4 °C for 30 days, but the decay was distinctly prevented. Efficacy of C. laurentii was maintained when applied simultaneously or prior to inoculation with P. italicum. Efficacy was reduced when C. laurentii was applied after inoculation. In drop-inoculated wounds of oranges, the populations of C. laurentii increased by approximately 50-fold during the first 24 h at 20 °C. The maximum yeast populations, approximately 250-fold over the initial populations, were reached 15 days after inoculation at 4 °C.     

Improving low water activity and desiccation tolerance of the biocontrol agent Pantoea agglomerans CPA-2 by osmotic treatments

AIMS: To study the improvement of tolerance to low water activity (aw) and desiccation during spray drying in Pantoea agglomerans cells subjected to mild osmotic stress during growth. METHODS AND RESULTS: The micro-organism was cultured in an unmodified liquid (control) or in aw-modified media, and viability of these cells was evaluated on unstressed (0.995) and 0.96 aw stressed solid media, in order to check total viability and aw stress tolerance respectively. Significant improvements in viability on unmodified medium were observed with cells grown for 24 h in NaCl 0.98 aw, glycerol 0.98 aw and 0.97 aw and for 48 h in NaCl 0.98 aw and 0.97 aw modified media. Both yield improvements and water stress tolerance were achieved with low aw media. Cells grown for 24 h in NaCl 0.98 aw or for 48 h in NaCl 0.98 aw, 0.97 aw and 0.96 aw, glucose 0.97 aw and glycerol 0.97 aw showed improved aw stress tolerance in comparison with control cells. The best results were obtained with NaCl treatments (0.98 aw and 0.97 aw) which also exhibited better survival rates than control cells during spray-drying process and maintained their efficacy against postharvest fungal pathogens in apples and oranges. CONCLUSIONS: NaCl treatments are very appropriate for improving P. agglomerans low aw tolerance obtaining high production levels and maintaining biocontrol efficacy. SIGNIFICANCE AND IMPACT OF THE STUDY: Improving stress tolerance of biocontrol agents could be an efficient way to obtain consistency and maintain efficacy of biological control under practical conditions.     

Effects of stabilizers on shelf-life of Epicoccum nigrum formulations and their relationship with biocontrol of postharvest brown rot by Monilinia of peaches

AIM: To find a formulation of Epicoccum nigrum conidia that maintains a high viability over time and which proves efficient to biocontrol peach rot caused by Monilinia spp. METHODS AND RESULTS: We tested the effect of stabilizers and desiccants on the shelf-life of Epicoccum nigrum conidia. Conidial samples were dried for 40 min at 40 degrees C in a fluidized bed-dryer to obtain moisture contents <15%. The toxicity of additives was tested by assaying production of conidia in fermentations and germinability of the produced conidia: 50% PEG300, 10%-5% KCl (stabilizers) and 95.24% Cl(2)Ca (desiccant) significantly (P = 0.05) reduced conidial germination. To enhance shelf-life of dried conidia, nontoxic stabilizers were added at the following different stages of the production-drying process: (i) to substrate contained in bags before production, (ii) to conidial centrifuge pellets obtained after production, before filtering and drying, (iii) to conidial centrifuge pellets obtained after production, before adding talc and drying, and (iv) to conidial centrifuge pellets obtained after production, before adding silica powder and drying. Conidial germinability was tested at 0, 180 and 365 days after storage at room temperature. Shelf-life of formulations retaining the highest viability were conidia produced with 1% KCl or 50% PEG 8000, conidia dried with 2.5% methylcellulose, and conidia dried with 1% KCl + silica powder. All these formulations improved the shelf-life of E. nigrum conidia and significantly reduced brown rot on peaches. CONCLUSIONS: Our results show that additives improve the shelf-life of E. nigrum and assist controlling brown rot on peaches. SIGNIFICANCE AND IMPACT OF THE STUDY: New improved formulations of a biocontrol agent have been obtained which will improve the control of Monilinia on peach.     

Control of postharvest decay on cherry tomatoes by marine yeast Rhodosporidium paludigenum and calcium chloride

Aims: In this study, the potential of calcium chloride (CaCl₂) application to improve the efficacy of the marine antagonist Rhodosporidium paludigenum in controlling postharvest diseases of cherry tomatoes was assessed. Methods and Results: CaCl₂ alone was found not to have any direct influence on the population growth of R. paludigenum in NYDB cultures or in cherry tomato wounds. However, the combined treatments with 1 × 10⁸ cells ml^?1R. paludigenum and CaCl₂ at the concentration from 0·5 to 2% showed high activities to reduce black rot caused by Alternaria alternata in cherry tomato wounds, significantly higher than those of R. paludigenum or CaCl₂ alone. Meanwhile, 0·5% CaCl₂ in combination with 1 × 10⁸ cells ml^?1R. paludigenum greatly inhibited the natural decay of cherry tomatoes in 21 days’ storage at 25°C. Conclusions: The combination of R. paludigenum and CaCl₂ enhances the inhibition of black rot and natural decay of postharvest cherry tomatoes. The results from this study provide a new way to improve the efficiency of R. paludigenum in maintaining the quality of postharvest fruits and vegetables. Significance and Impact of the Study: The marine yeast R. paludigenum combined with CaCl₂ has greatly potential use as an alternative to chemical fungicides in inhibiting postharvest decay on cherry tomatoes.     

Effects of a biocontrol agent and methyl jasmonate on postharvest diseases of peach fruit and the possible mechanisms involved

AIMS: To investigate effects of application of 200 micromol l(-1) methyl jasmonate [MeJA (200)] and Cryptococcus laurentii alone or in combination against postharvest diseases (Monilinia fructicola and Penicillium expansum) in peach fruit stored at 25 and 0 degrees C, and to evaluate the possible mechanisms involved. METHODS AND RESULTS: The efficacy of controlling postharvest diseases by resistance induced in peach fruit treated with MeJA (200) and C. laurentii alone or in combination and the relationship between activities of defence-related enzymes in peach fruit and lesions caused by M. fructicola and P. expansum were examined. At the same time, the effects of MeJA (200) on the population of C. laurentii in the peach wounds and on the mycelial growth of M. fructicola and P. expansumin vitro were investigated. The results indicated that treatment of peach fruit with C. laurentii at 1 x 10(8) CFU ml(-1) alone, or combining C. laurentii at 5 x 10(7) CFU ml(-1) with MeJA (200) all resulted in a lower lesion diameter of brown rot and blue mould caused by M. fructicola and P. expansum compared with the controls in peach fruit. MeJA (200) enhanced the population of C. laurentii, and inhibited mycelial growth of P. expansum. However, it had a little effect on M. fructicolain vitro. MeJA and C. laurentii alone or in combination induced higher activities of Chitinase, beta-1,3-glucanase, phenylalanine ammonia-lyase and peroxidase (POD) than applying the yeast alone at both 25 and 0 degrees C. CONCLUSIONS: MeJA (200) not only directly inhibited mycelial spread of postharvest pathogens, but also increased population of C. laurentii, which induced stronger disease resistance in fruit than MeJA or yeast alone, and resulted in a lower lesion diameter of brown rot and blue mould caused by M. fructicola and P. expansum. SIGNIFICANCE AND IMPACT OF THE STUDY: MeJA (200) in combination with C. laurentii was beneficial for controlling brown rot and blue mould caused by M. fructicola and P. expansum in peach fruit. The inhibitory mechanism was mainly because of resistance induced in peach fruit by MeJA and C. laurentii. In addition, direct inhibition of MeJA on P. expansum also played a role in controlling blue mould.     

Improving water stress tolerance of the biocontrol yeast Candida sake grown in molasses-based media by physiological manipulation

The biocontrol agent Candida sake was cultured on either an unmodified molasses-based medium (water activity, a(w) 0.996) or on water stressed media produced by the addition of glycerol, glucose, NaCl, sorbitol, or proline to 0.98, and 0.96 a(w) for 24, 48, and 72 h, to study their impact on subsequent cell viability, and on concentrations of endogenous sugars (trehalose and glucose) and polyols (glycerol, erythritol, arabitol, and mannitol). The viability of cells of different ages cultured on these media was evaluated on NYDA medium with freely available water (a(w) 0.995), and on medium modified with polyethylene glycol to a(w) 0.95. Regardless of solute used, viable counts of cells grown on molasses-based medium (a(w) 0.98) were equal to or higher than those obtained from the medium with water freely available. The amino acid proline stimulated growth at 10% concentration. In contrast, water stress induced by addition of NaCl, glucose, or sorbitol at a(w) 0.96 caused a significant reduction in viable counts. Older cultures were more resistant to water stress. Glycerol and arabitol were the main solutes accumulated by C. sake cells in response to lowered a(w). Intracellular concentration of these polyols depended more on the solute used to adjust the a(w) than on the a(w) itself. Candida sake was more resistant to water stress with higher intracellular concentration of glycerol and erythritol.     

Improvement in the biocontrol of postharvest diseases of apples with the use of yeast mixtures

Mixtures of yeasts were tested for theirability to control Penicillium expansum andBotrytis cinerea on Red Delicious apple fruits. The occurrence of synergistic or antagonisticinteractions between yeast strains in differentmixtures was also evaluated. Two strains ofRhodotorula (R. glutinis SL 1 and R. glutinisSL 30) and two strains of Cryptococcus (C. albidus SL 43 and C. laurentii SL 62) were selected fordeveloping yeasts mixtures.The R. glutinis SL 1–R. glutinis SL 30 mixtureexhibited a lower effectiveness than eachstrain alone, against both moulds. Othermixtures (R. glutinis SL 1–C. albidus SL 43 and R. glutinis SL 30–C. albidus SL 43) showedsynergism against P. expansum but not against B. cinerea. The R. glutinis SL 1–C. laurentii SL62 mixture was the only mixture which showedsynergism against gray mould. There was not anymixture, which showed high effectivenessagainst both moulds at the same time. Differentresults could be explained by the dynamics ofthe population of the yeasts.By using yeast mixtures, it was possible toimprove biocontrol without increasing theamount of antagonists applied. The synergismobserved could be useful in enhancingbiological control.     

Indole-3-acetic acid enhances the biocontrol of Penicillium expansum and Botrytis cinerea on pear fruit by Cryptococcus laurentii

This study evaluated the efficacy of indole-3-acetic acid (IAA) alone or with a biocontrol yeast, Cryptococcus laurentii, in the inhibition of blue and gray mold diseases (Penicillium expansum and Botrytis cinerea) on pear fruit. The results demonstrated that a combination of C. laurentii with IAA at 100 microg mL(-1) was more effective in suppressing blue and gray mold infections on pear fruit than application of C. laurentii alone. IAA alone or with C. laurentii stimulated catalase, peroxidase and polyphenol oxidase activities of pear fruit, indicating that IAA can induce fruit-mediated resistance, although this agent alone had no direct antifungal activity.     

Influence of antagonist, host fruit and pathogen on the biological control of postharvest fungal diseases by yeasts

The yeasts Rhodotorula glutinis (LS-11), Cryptococcus laurentii (LS-28), Candida famata (21-D) and Pichia guilliermondii (29-A) and the yeast-like fungus Aureobasidium pullulans (LS-30), previously selected and characterized for mechanisms of action and antagonistic activity against postharvest pathogens in small and large-scale experiments, were used in this study in order to assess interrelationships among the main factors (antagonist, host fruit and fungal pathogen) involved in biological control of postharvest diseases. The antagonists were evaluated for their inhibitory activity (IA) against six common postharvest fungal pathogens on six different host fruits. Artificially wounded fruits were first inoculated with the antagonist and 2 h later with the pathogen; subsequently they were kept at 20°C for 4–6 days. The IA of each antagonist was evaluated and data were submitted to factorial analysis of variance. The populations of antagonists were also monitored on wounded and unwounded fruits kept at 20°C for 7 days. Each factor examined (antagonist, host fruit and fungal pathogen) as well as their interactions significantly affected the IA. However, among the antagonists, isolates LS-28 and LS-30 were only slightly affected by both host and pathogen, showing a wide range of activity, whereas isolate LS-11 had a variable IA. All the antagonists rapidly colonized the wounds, while their population remained substantially unchanged on unwounded fruits. These results suggest that in order to select yeasts with a broad spectrum of action, more suitable for commercial development, it would be advantageous to perform preliminary assays against several pathogens and in particular on different fruit species. Received 23 February 1999/ Accepted in revised form 09 July 1999