Survival of the biological control agent Candida sake CPA-1 on grapes under the influence of abiotic factors

Enhancing the Storage Longevity of Apples: The Potential of Bacillus subtilis and Streptomyces endus as Preventative Bioagents against Post-Harvest Gray Mold Disease, Caused by Botrytis cinerea

Gray mold, caused by Botrytis cinerea Pers. Fr., is one of the most vital plant diseases, causing extensive pre- and post-harvest losses in apple fruits. In the current study, we isolated and identified two potential endophytic bioagents, Bacillus subtilis and Streptomyces endus. Both bioagents exhibited a potent fungistatic effect against B. cinerea under both in vitro and in planta conditions. Moreover, two experiments were carried out; (i) the first experiment was conducted at room temperature after artificial inoculation with B. cinerea to monitor the progression of the infection and the corresponding biochemical responses of the apples. Our in vivo findings showed that the treated B. cinerea-infected apple fruits with the cell-free bacterial filtrate of B. subtilis and S. endus (dipping or wrapping) significantly reduced the rotten area of the treated apple at room temperature. Additionally, B. subtilis and S. endus enhanced the enzymatic (POX and PPO) and non-enzymatic (phenolics and flavonoids) antioxidant defense machinery in treated apples. (ii) The second experiment focused on the preventive effects of both bioagents over a 90-day storage period at 1 °C of healthy apples (no artificial inoculation). The application of both bacterial filtrates prolonged the storage period, reduced the relative weight loss, and maintained high-quality parameters including titratable acidity, firmness, and total soluble solids of apple fruits under cold storage at 1 °C. The Kaplan-Meier analysis of rotten apples over 90 days during cold storage showed that the treated apples lasted longer than the non-treated apples. Moreover, the lifespan of apple fruits dipped in the culture filtrate of B. subtilis, or a fungicide, was increased, with no significant differences, compared with the non-treated apples. The current results showed the possibility of using both bioagents as a safe and eco-friendly alternative to chemical fungicides to control gray mold disease in apples.

Colonization and population dynamics of total, viable, and culturable cells of two biological control strains applied to apricot, peach, and grapevine crops

The ecological fitness of the biological control strains Bacillus velezensis A17 and Lactiplantibacillus plantarum PM411 was evaluated in different crops, geographical zones, and growing seasons. Both strains (2 g L-1 of dried formulation) were spray-inoculated on apricot trees, peach trees, and grapevines. Depending on the crop, flowers, fruits, and leaves were picked at several sampling time points. The population dynamics of viable, viable but non-culturable, and dead cells were studied by comparing viability qPCR (v-qPCR), qPCR, and plate counting estimations. A17 showed high survival rates in apricot, peach, and grapevine organs. The A17 viability was confirmed since qPCR and v-qPCR estimations did not significantly differ and were rather constant after field applications. However, higher population levels were estimated by plate counting due to the non-selective characteristics of the medium used. The viability of PM411 was constrained by plant organ, crop, and climate conditions, being higher in apricot than in grapevine. PM411 survival declined after field application, indicating difficulties in its establishment. The PM411 population level was made up of dead, culturable, and viable but non-culturable cells since significant differences between the three methods were observed. In conclusion, A17 and PM411 differ strongly in their survival in grapevine, peach, and apricot.

Assessment of microbial biocontrol agent (BCA) viability to mechanical and thermal stress by simulating spray application conditions

BACKGROUND

In order to improve the biological control agent (BCA) efficacy, stress factors threatening the viability of microorganisms during spray application need to be determined. The effect of spray mixture temperature and exposure time on Trichoderma harzianum T 22 and Bacillus amyloliquefaciens QST713 viability were tested. Concurrently the combined effect of mechanical and thermal stress effect on BCA viability were tested at two initial spray mixture temperatures (14 and 25 °C) by simulating a spray application using airblast sprayers featured by different tank capacity and a spray liquid circuit (without and with hydraulic agitation system). To assess the BCA microorganism viability, spray mixture samples were collected at time intervals along trials and plated to count the colony forming units (CFU).

RESULTS

The critical temperature threshold that inhibited BCA viability was 35 °C with 30 min of exposure. The sprayer type, the initial temperature of the spray mixture and the temperature increment during the trials significantly decreased the number of CFU recovered. When simulating a spray application, the spray mixture temperature increase rate was determined mainly by the residual amount of spray mixture in the tank. Even if the tank capacity does not substantially affect the final temperature reached by the spray mixture, the higher residual spray mixture in bigger tanks can expose the BCAs for a longer time to critical temperatures.

CONCLUSIONS

Experimental trials allowed us to identify the effect of factors affecting the viability of tested BCAs, providing information about the actual chance to guarantee the biological efficacy of BCA treatments. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Biocontrol of Botrytis cinerea as Influenced by Grapevine Growth Stages and Environmental Conditions

The growth of four commercial biocontrol agents (BCAs: Bacillus amyloliquefaciens (BAD), Aureobasidium pullulans (APD), Metschnikowia fructicola (MFN), and Trichoderma atroviride (TAS)) was evaluated using turbidimetric assays on artificial substrates mimicking the chemical berry composition at four stages: pea-sized berries, veraison, softening, and ripe berries. The response of BCA growth differed among BCAs. Subsequently, the BCAs' population size was assessed after 1 to 13 days of incubation on the substrate mimicking ripe berries at 15 to 35 °C. The population size of BAD increased with temperatures, while that of MFN decreased; the population sizes of APD and TAS showed bell-shaped patterns with lower growth at 15 or 35 °C. Finally, the BCAs were applied to ripe berries and then incubated at 15 to 30 °C. After 1 to 13 days, the berries were inoculated with B. cinerea and incubated for 7 days, after which the BCA control efficacy was assessed. The highest control was observed at 25 °C for BAD and APD, at 15 to 20 °C for MFN, and at 25 to 30 °C for TAS. The results confirm that the plant substrates and temperature affect the population size of the BCA following application; temperature also affects the preventative efficacy of BCA against B. cinerea.

Efficacy of preharvest application of biocontrol agents against gray mold in grapevine

The use of biocontrol agents (BCAs) represents a promising alternative to conventional methods for the management of gray mold in vineyards during the berry ripening stage. The main advantages of BCAs are the short preharvest interval and lack of chemical fungicide residues in wine. In this study, eight commercial BCAs (based on different Bacillus or Trichoderma species and strains, Aureobasidium pullulans, Metschnikowia fructicola, and Pythium oligandrum) and a reference fungicide (boscalid) were applied to a vineyard during berry ripening over three seasons to evaluate the dynamics over time in terms of their relative efficacies in gray mold control. At 1-13 days after application of BCAs to the berry surfaces in field conditions, the berries were collected and artificially inoculated with conidia of Botrytis cinerea under controlled laboratory conditions, and gray mold severity was observed after 7 days of incubation. Significant differences were observed in gray mold severity among years, according to the number of days the BCAs grew on the berry surface before B. cinerea inoculation, and the season by day interaction (altogether accounting for >80% of the experimental variance). The variability in BCA efficacy was closely related to the environmental conditions at the time of application and in the following days. Overall, the BCA efficacy increased with the degree days accumulated between BCA application in the vineyard and B. cinerea inoculation in the dry (no rain) periods (r = 0.914, P = 0.001). Rainfall and the associated drop in temperature caused a relevant reduction of BCA efficacy. These results demonstrate that BCAs are an effective alternative to conventional chemicals for the preharvest control of gray mold in vineyards. However, environmental conditions can considerably affect the BCA efficacy.

Culturable Yeasts as Biofertilizers and Biopesticides for a Sustainable Agriculture: A Comprehensive Review

The extensive use of synthetic fertilizers and pesticides has negative consequences in terms of soil microbial biodiversity and environmental contamination. Faced with this growing concern, a proposed alternative agricultural method is the use of microorganisms as biofertilizers. Many works have been focused on bacteria, but the limited literature on yeasts and their potential ability to safely promote plant growth is gaining particular attention in recent years. Thus, the objective of this review is to highlight the application of yeasts as biological agents in different sectors of sustainable agricultural practices through direct or indirect mechanisms of action. Direct mechanisms include the ability of yeasts to provide soluble nutrients to plants, produce organic acids and phytohormones (indole-3-acetic acid). Indirect mechanisms involve the ability for yeasts to act as biocontrol agents through their high antifungal activity and lower insecticidal and herbicidal activity, and as soil bioremediating agents. They also act as protective agents against extreme environmental factors by activating defense mechanisms. It is evident that all the aspects that yeasts offer could be useful in the creation of quality biofertilizers and biopesticides. Hence, extensive research on yeasts could be promising and potentially provide an environmentally friendly solution to the increased crop production that will be required with a growing population.

Dispersion, persistence, and stability of the biocontrol agent Penicillium frequentans strain 909 after stone fruit tree applications

The capacity of dispersion, persistence, and stability from biocontrol agents is essential before these organisms can be developed into a commercial product. Interactions that microorganisms establish with stone fruit trees may be beneficial in the exploitation of trees in agriculture as crop production. The natural background levels of Penicillium frequentans strain 909 dispersion, persistence, and stability were assessed after tree applications and postharvest conditions. A fingerprinting-based approach to trace genetic stability of P. frequentans along stored time and its release in the field was developed. P. frequentans was successfully traced and discriminated. This strain was dispersed well in treated trees, persisting in the ecosystem up to 2 weeks and staying genetically stable after 36 months of storage. However, the dispersal of P. frequentans was very limited on around untreated trees and soil. P. frequentans dispersed randomly into the air, and its presence reduced from the first day to disappear completely at 15-21 days after application. Great losses of P. frequentans and its increased dispersal in open field conditions probably resulted from rainfall. Biological control strategies with Pf909 were discussed.

Verifying the biocontrol activity of novel film-forming formulations of Candida sake CPA-1: resilience in relation to environmental factors, rainfall episodes, and control of Botrytis cinerea on different hosts

BACKGROUND

The efficacy of Candida sake CPA-1 as a biocontrol agent against several diseases has been studied since it was isolated 20 years ago. However, it was only recently that two suitable and effective film-forming formulations based on potato starch and maltodextrins were developed using the fluidized-bed spray-drying system. The present work aimed to confirm the capability of both novel formulations by testing their resilience on grapes at different temperatures (0, 22, and 30 °C), relative humidities (40% and 85%), and simulated rainfall levels. Another objective was to examine the control of Botrytis cinerea in different hosts.

RESULTS

The CPA-1 cells from both dried formulations survived better than the liquid formulation on grapes stored at 0 and 22 °C regardless of the relative humidity. After simulated rainfall, potato starch formulation achieved significantly higher populations than maltodextrin formulation, although the highest reduction was -1.6 log N N₀ ^-1 . A positive effect of cell establishment prior to the simulated rainfall was shown, and recovered cells from the potato starch formulation were significantly higher after 72 h of cell establishment. Finally, both formulations reduced the incidence and severity of B. cinerea on pears, apples, and tomatoes.

CONCLUSION

The potential of these novel film-forming formulations of C. sake CPA-1 was verified. The resilience of formulated C. sake was better than the commercialized liquid formulation, the adherence of the formulations to the grapes improved after an establishment period prior to rain exposure, and the control of B. cinerea was verified in a wider range of hosts. © 2019 Society of Chemical Industry.

Microbial Antagonism Toward Botrytis Bunch Rot of Grapes in Multiple Field Tests Using One Bacillus ginsengihumi Strain and Formulated Biological Control Products

Botrytis bunch rot (BBR), caused by the necrotrophic fungus Botrytis cinerea, is a major disease of wine and table grapes worldwide. Due to negative effects of pesticides on the environment and human health, alternative control strategies against BBR, such as biological control agents (BCAs), are required to produce high-quality grapes and wines with high standards of food safety. However, few biological control products against BBR are available, and their efficacy is sometimes variable. This study aimed to evaluate and compare (1) the efficacy of new bacterial BCA strains developed at INRA Bordeaux and (2) the BBR reductions achieved by commercial biocontrol products that are already registered or close to being registered. During three consecutive seasons, 10 field experiments were established in six different experimental vineyards in southwestern France. Spray applications were performed at key phenological stages (five or six during the season), or at high BBR-risk periods late in the season according to a Disease Risk Index model. At harvest, BBR incidence and severity (% of symptomatic berries per bunch) were visually determined. The experiments included four bacterial strains at an early experimental stage, particularly Bacillus ginsengihumi (S38). Nine commercial BCA products were also tested, including Bacillus subtilis, Bacillus amyloliquefaciens, Aureobasidium pullulans, Ulocladium oudemansii, and Candida sake. Among the four experimental bacterial strains, only B. ginsengihumi S38 significantly controlled the BBR, presenting reductions in the average severity ranging from 35 to 60%, compared to untreated control, throughout the three seasons. Several commercial BCAs achieved significant reductions in BBR severity ranging from 21 to 58%, although not in every trial. The treatments that achieved higher reductions in severity rates were based on C. sake (45%), B. subtilis (54%), and B. amyloliquefaciens (58%). The efficacy of those BCAs was consistent throughout the studied seasons. The results confirmed the suitability of several biological control products under the conditions in vineyards in southwestern France, while also highlighting the good performance of the novel experimental BCA B. ginsengihumi S38 strain, which achieved similar control rates to the products registered for commercial use. The major factors involved in the variability in the results are also discussed.

Environmental fate and behaviour of the biocontrol agent Bacillus amyloliquefaciens CPA-8 after preharvest application to stone fruit

BACKGROUND

Bacillus amyloliquefaciens strain CPA-8 has been described as an effective biocontrol agent to control brown rot in stone fruit for both preharvest and postharvest applications. However, no information about the environmental fate and behaviour of this strain under field conditions is available.

RESULTS

The dispersion of the CPA-8 application was evaluated using water-sensitive papers, and complete coverage was observed on the leaves of treated trees, while <1% of non-treated tree leaves had CPA-8. CPA-8 persisted on the fruit of treated trees during preharvest and postharvest conditions, while a significant decrease on leaves and weeds was observed 21 days after treatment. On non-treated trees, CPA-8 was detected on leaves until 180 days after treatment, and on weeds, the CPA-8 population was dependent on the distance from the treated trees. A high persistence of CPA-8 was detected on inert materials, such as clothes and gloves worn by handlers and plastic harvesting boxes. More than 99% of the samples with a CPA-8 phenotype were confirmed as CPA-8 using polymerase chain reaction (PCR).

CONCLUSION

This work demonstrated a good distribution, persistence and adaptation of the CPA-8 strain to field and postharvest conditions. Monitoring of dispersion and persistence is an excellent tool to determine the time of application and provides valuable information for registering issues. © 2017 Society of Chemical Industry.

Dispersal of Bacillus subtilis and its effect on strawberry phyllosphere microbiota under open field and protection conditions

Using biological control agents (BCAs) is an essential component of integrated pest and diseases management. Despite much research on biocontrol of plant diseases, success in field crops has been limited with most successes being achieved in greenhouse cultivation. This lack of success is often attributed to the complex ecological processes involved in biocontrol. We used next generation sequencing (NGS) technology to study environmental fate of Bacillus subtilis, a widely used BCA, focusing on its dispersal aspect in open field and under protection. The dispersal of B. subtilis was very limited, particularly under protection. The reduction in the BCA population size was relatively small within 8 days; indeed, no overall reduction in the relative abundance was observed under the protected condition. These results suggested that limited dispersal is probably the main reason for its variable (and often low) control efficacy under field conditions. Thus to increase biocontrol efficacy, it is necessary to frequently apply this BCA with the application interval depending on the growth rate of target host tissues. Phyllosphere microbiota differed significantly between plants grown in open field and under protection but were not greatly affected by the introduced BCA.