Control of citrus blue mold by the antagonist yeast Pichia guilliermondii Z1: Compatibility with commercial fruit waxes and putative mechanisms of action

Enhancing biological control of postharvest green mold in lemons: Synergistic efficacy of native yeasts with diverse mechanisms of action

Argentina is among the most important lemon fruit producers in the world. Penicillium digitatum is the primary lemon fungal phytopathogen, causing green mold during the postharvest. Several alternatives to the use of synthetic fungicides have been developed, being the use of biocontrol yeasts one of the most promising. Although many of the reports are based on the use of a single yeast species, it has been shown that the combination of agents with different mechanisms of action can increase control efficiency through synergistic effects. The combined use of native yeasts with different mechanisms of action had not been studied as a biological control strategy in lemons. In this work, the mechanisms of action of native yeasts (Clavispora lusitaniae AgL21, Clavispora lusitaniae AgL2 and Clavispora lusitaniae AcL2) with biocontrol activity against P. digitatum were evaluated. Isolate AgL21 was selected for its ability to form biofilm, colonize lemon wounds, and inhibit fungal spore germination. The compatibility of C. lusitaniae AgL21 with two killer yeasts of the species Kazachstania exigua (AcL4 and AcL8) was evaluated. In vivo assays were then carried out with the yeasts applied individually or mixed in equal cell concentrations. AgL21 alone was able to control green mold with 87.5% efficiency, while individual killer yeasts were significantly less efficient (43.3% and 38.3%, respectively). Inhibitory effects were increased when C. lusitaniae AgL21 and K. exigua strains were jointly applied. The most efficient treatment was the combination of AgL21 and AcL4, reaching 100% efficiency in wound protection. The combination of AgL21 with AcL8 was as well promising, with an efficiency of 97.5%. The combined application of native yeasts showed a synergistic effect considering that the multiple mechanisms of action involved could hinder the development of green mold in lemon more efficiently than using single yeasts. Therefore, this work demonstrates that the integration of native yeasts with diverse modes of action can provide new insights to formulate effective microbial consortia. This could lead to the development of tailor-made biofungicides, allowing control of postharvest fungal diseases in lemons while remaining competitive with traditionally used synthetic chemicals.

Biocontrol Potential of Antagonistic Yeasts on In Vitro and In Vivo Aspergillus Growth and Its AFB1 Production

Aspergillus flavus is a major aflatoxin B₁, posing significant health concerns to humans, crops, and producer fungi. Due to the undesirable consequences of the usage of synthetic fungicides, biological control using yeasts has gained more attention. In this study, eight isolates of epiphytic yeasts belonging to Moesziomyces sp., Meyerozyma sp. and Metschnikowia sp., which have been identified as antagonists, were isolated from different plants, including grapes, blueberries, hawthorns, hoşkıran, beans and grape leaf. While volatile organic compounds (VOCs) produced by Moesziomyces bullatus DN-FY, Metschnikowia aff. pulcherrima DN-MP and Metschnikowia aff. pulcherrima 32-AMM reduced in vitro A. flavus mycelial growth and sporulation, only VOCs produced by Metschnikowia aff. fructicola 1-UDM were found to be effective at reducing in vitro AFB₁ production. All yeasts reduced the mycelial growth of A. flavus by 76-91%, while AFB₁ production reduced to 1.26-10.15 ng/g and the control plates' growth was 1773 ng/g. The most effective yeast, Metschnikowia aff. Pulcherrima DN-HS, reduced Aspergillus flavus growth and aflatoxin B₁ production on hazelnuts. The AFB₁ content on hazelnuts reduced to 333.01 ng/g from 536.74 ng/g. To our knowledge, this is the first report of yeasts isolated from plants being tested as potential biological control agents to reduce AFB₁ production on hazelnuts.

Formulation of the biological control yeast Meyerozyma caribbica by electrospraying process: effect on postharvest control of anthracnose in mango (Mangifera indica L.) and papaya (Carica papaya L.)

BACKGROUND

Microorganism for biological control of fruit diseases is an eco-friendly alternative to the use of chemical fungicides.

RESULTS

This is the first study evaluating the electrospraying process to encapsulate the biocontrol yeast Meyerozyma caribbica. The effect of encapsulating material [Wey protein concentrate (WPC), Fibersol® and Trehalose], its concentration and storage temperature on the cell viability of M. caribbica, and in vitro and in vivo control of Colletotrichum gloeosporioides was evaluated. The processing with commercial resistant maltodextrin (Fibersol®) 30% (w/v) as encapsulating material showed the highest initial cell viability (95.97 ± 1.01%). The storage at 4 ± 1 °C showed lower losses of viability compared to 25 ± 1 °C. Finally, the encapsulated yeast with Fibersol 30% w/v showed inhibitory activity against anthracnose in the in vitro and in vivo tests, similar to yeast fresh cells.

CONCLUSION

Electrospraying was a highly efficient process due to the high cell viability, and consequently, a low quantity of capsules is required for the postharvest treatment of fruits. Additionally, the yeast retained its antagonistic power during storage. © 2021 Society of Chemical Industry.

Alternative Management Approaches of Citrus Diseases Caused by Penicillium digitatum (Green Mold) and Penicillium italicum (Blue Mold)

Green mold (Penicillium digitatum) and blue mold (Penicillium italicum) are among the most economically impactful post-harvest diseases of citrus fruit worldwide. Post-harvest citrus diseases are largely controlled with synthetic fungicides such as pyrimethanil, imazalil, fludioxonil, and thiabendazole. Due to their toxic effects, prolonged and excessive application of these fungicides is gradually restricted in favor of safe and more eco-friendly alternatives. This review comprehensively describes alternative methods for the control of P. digitatum and P. italicum: (a) antagonistic micro-organisms, (b) plant extracts and essential oils, (c) biofungicides, (d) chitosan and chitosan-based citrus coatings, (e) heat treatments, (f) ionizing and non-ionizing irradiations, (g) food additives, and (h) synthetic elicitors. Integrating multiple approaches such as the application of biocontrol agents with food additives or heat treatments have overcome some drawbacks to single treatments. In addition, integrating treatment approaches could produce an additive or synergistic effect on controlling both molds for a satisfactory level of disease reduction in post-harvest citrus. Further research is warranted on plant resistance and fruit-pathogen interactions to develop safer strategies for the sustainable control of P. digitatum and P. italicum in citrus.

Biocontrol activity and putative mechanism of Bacillus amyloliquefaciens (SF14 and SP10), Alcaligenes faecalis ACBC1, and Pantoea agglomerans ACBP1 against brown rot disease of fruit

This study aimed at evaluating the antagonistic activity of 16 bacterial strains for the control of brown rot disease caused by Monilinia fructigena, and M. laxa under in vitro and a semi-commercial large-scale trial. These bacterial antagonists' belonging to the genera Alcaligenes, Bacillus, Brevibacterium, Pantoea, Pseudomonas, and Serratia were previously proven effective for control of fire blight of apple. The in vitro dual culture bioassay showed the highest inhibition rates of mycelial growth ranging from 55 to 95% and from 43 to 94% for M. fructigena and M. laxa, respectively. The in vivo bioassay showed moderate and strong inhibition for M. fructigena and M. laxa, respectively. The inhibition rates were dependent on incubation time as well as pathogen virulence. The free-cell bacterial filtrate revealed substantial mycelial growth inhibition ranging from 66 to 86%. The inhibition of conidial germination was from 32 to 78%, suggesting the involvement of metabolites in their biocontrol activity. The antifungal effect of the volatile compounds (VCOs) was observed for all bacteria with mycelial inhibition varying from 12 to 70%. Overall, their efficacy was substantially affected by the nature of the bacterial strains and the modes of action. Taken together, these results underscore that ACBC1 and SF14 for M. fructigena and SP10 and ACBP1 for M. laxa were the most effective bacterial strains. These strains were confirmed effective in a semi-commercial large-scale trial. Interestingly, their efficacies were found to be comparable to those of both commercial BCAs (B. subtilis Y1336 and P. agglomerans P10c), but slightly lower than thiophanate-methyl fungicide. The ability of most bacterial strains to produce lytic enzymes (Amylase, Protease or Cellulase) and lipopeptides (bacillomycin, fengycin, iturin and surfactin) was demonstrated by biochemical and molecular analyzes. Therefore, our findings suggest that the bacterial antagonists ACBC1, SF14, SP10 and ACBP1, have the potential to prevent brown rot disease.

Attachment Capability of Antagonistic Yeast Rhodotorula glutinis to Botrytis cinerea Contributes to Biocontrol Efficacy

Rhodotorula glutinis as an antagonism show good biocontrol performance against various post-harvest diseases in fruits. In the present study, strong attachment capability of R. glutinis to spores and hyphae of Botrytis cinerea was observed. Further analysis showed that certain protein components on the yeast cell surface played critical role during the interaction between R. glutinis and B. cinerea. The components mainly distributed at the poles of yeast cells and might contain glycosylation modification, as tunicamycin treated yeast cells lost attachment capability to B. cinerea. To investigate contributions of attachment capability of R. glutinis to its biocontrol efficacy, yeast cells were mutagenized with 3% methane-sulfonic acid ethyl ester (EMS), and a mutant CE4 with stable non-attaching phenotype was obtained. No significant difference was found on colony, cell morphology, reproductive ability, and capsule formation between the mutant and wild-type. However, there was a distinct difference in India ink positive staining patterns between the two strains. Moreover, wild-type strain of R. glutinis showed better performance on inhibiting spore germination and mycelial growth of B. cinerea than CE4 strain when yeast cells and B. cinerea were co-cultured in vitro. In biocontrol assay, both wild-type and CE4 strains showed significant biocontrol efficacy against gray mold caused by B. cinerea in apple fruit, whereas, control effect of CE4 strain was lower than that of wild-type. Our findings provided new evidences that attachment capability of R. glutinis to B. cinerea contributed to its biocontrol efficacy.

Combining UV-C treatment with biocontrol yeast to control postharvest decay of melon

Significant losses in harvested melon can be directly attributable to decay fungi. In the present study, the use of UV-C treatment combined with biocontrol yeast, Pichia cecembensis, was evaluated for their ability to control postharvest decay of melon fruits after they were artificially inoculated with Fusarium oxysporum and Alternaria alternata. Natural infection of fruit was also assessed. As a stand-alone treatment, UV-C or P. cecembensis significantly reduced Fusarium rot and Alternaria rot, and also the level of natural infection on melon fruit, relative to the untreated control. The combination of UV-C or P. cecembensis, however, provided a superior level of decay control on artificially inoculated and naturally infected fruit, compared to either treatment alone. None of the treatments impaired fruit quality. Integrating the use of UV-C treatment with biocontrol yeast has potential as an effective method to control postharvest decay of melon.