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Fungal pathogens are the main causal agents of postharvest diseases of fruits and vegetables. To prevent this problem and avoid the use of harmful chemical fungicides, safer and greener alternatives have been sought. One of these alternatives is the use of plant-growth-promoting bacteria (PGPB). In this study, we evaluated in vitro four well-known PGPB strains (Pseudomonas fluorescens UM270, Bacillus toyonensis COPE52, Bacillus sp. E25, and Bacillus thuringiensis CR71) for their biocontrol potential against nineteen postharvest fungal pathogens. In vivo assays were also performed, and bacterial cells were inoculated on harvested strawberries and grapes with the pathogens Botrytis cinerea, Alternaria alternata, and Fusarium brachygibbosum to evaluate loss of firmness and disease incidence. Our results show that the four strains antagonized fungi in direct and indirect confrontation assays. Stronger antagonism was observed by the action of diffusible metabolites (DMs) compared to volatile organic compound (VOC) activity. All PGPB significantly improved the fruit firmness and reduced disease incidence caused by the fungal pathogens tested. However, strain UM270 showed excellent biocontrol activity, reducing the disease incidence of Fusarium brachygibbosum, Botrytis cinerea, and Alternaria alternata on strawberry fruits by 60%, 55%, and 65%, respectively. Diffusible antifungals and VOCs such as 2,4-diacetyl phloroglucinol, siderophores, auxins, fengycins, and N, N-dimethyl-hexadecyl amine, among others, might be responsible for the beneficial activities observed. These results suggest excellent biocontrol activities to inhibit postharvest pathogenic fungi and improve harvested fruit quality. [ABSTRACT FROM AUTHOR]

Botrytis cinerea is the causal agent of grey mould and one of the most important plant pathogens in the world because of the damage it causes to fruits and vegetables. Although the application of botrycides is one of the most common plant protection strategies used in the world, the application of plant-beneficial bacteria might replace botrycides facilitating agroecological production practices. Based on this, we reviewed the different stages of B. cinerea infection in plants and the biocontrol mechanisms exerted by plant-beneficial bacteria, including the well-known plant growth-promoting bacteria (PGPB). Some PGPB mechanisms to control grey mould disease include antibiosis, space occupation, nutrient uptake, ethylene modulation, and the induction of plant defence mechanisms. In addition, recent studies on the action of anti-Botrytis compounds produced by PGPB and how they damage the conidial and mycelial structures of the pathogen are reviewed. Likewise, the advantages of individual inoculations of PGPB versus those that require the joint action of antagonist agents (microbial consortia) are discussed. Finally, it should be emphasised that PGPB are an excellent option to prevent grey mould in different crops and their use should be expanded for environmentally friendly agricultural practices. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Plant Pathology is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Strawberry (Fragaria x ananassa) is an exquisite food, which provides health benefits, making it the berry with the highest production and export in Mexico. However, it is highly perishable, susceptible to postharvest damage, mainly by Botrytis cinerea and Rhizopus stolonifer, among others. The use of pesticides in preharvest is the control strategy of these pathogens; however, pesticides are documented to harm human health and the ecosystem, showing the need to explore friendly alternatives. Reagent grade chitosan (QGR) is an innocuous polymer with widely reported antifungal activity, while sodium octanoate (8:0) (OS) also has this property; however, so far it is unknown whether commercial grade chitosan (QGC) (the most suitable candidate to conduct a larger commercial study, due to its cost), available in Mexico, has the same effect. Therefore, the objective of this research was to evaluate the effectiveness of QGR and the QGR-OS composite in the protection of strawberry in postharvest and compare it with that of QGC and that of the QGCOS composite. The compounds were sprayed on the fruits and incubated simulating export conditions. The results showed significant reduction in the severity and incidence of postharvest strawberry fungal diseases after the application of QGR, QGC and QGR-OS, QGC-OS, but not that of OS applied alone. QGC and the QGC-OS composite are excellent candidates for use in a larger commercial study. [ABSTRACT FROM AUTHOR]

Introduction: The plants harbor a microbiome that includes plant growth-promoting bacteria, which can act as biological agents that antagonize the growth of phytopathogens, diminishing or eliminating their harmful effects in plants. In this work, the presence and association of the phlD and hcnC antifungal genes with the production of siderophores (Fe chelating agents) in bacteria isolated from the endosphere and rhizosphere of blackberry plants (Rubus fruticosus L.) was evaluated. Method: In total, 410 bacterial isolates associated with blackberry plants (Rubus fruticosus L.), from the rhizosphere (205) and endosphere (205) were analyzed for the detection of the phlD and hcnC antimicrobial genes by polymerase chain reaction and subsequent sequencing. The search of the genes was carried out only in siderophore producing strains, using the CAS medium (Chromium Azurol) for its production. Of the strains selected, antagonism bioassays were carried out against the plant pathogens Botrytis cinerea, Fusarium oxysporum, F. solani and Rhizoctonia solani. Results: The results showed that from the 410 bacterial isolates analyzed here (50% endophytes and 50% rhizospheric), it was confirmed that 70 strains were siderophores-producing (24 from rhizosphere and 46 endophytes). It was observed that 70% (49/70) of the siderophore producing strains present either one or two of the phlD or hcnC genes. The nucleotide sequences of the phlD and hcnC genes showed high identity to homologous genes to species Pseudomonas sp., P. fluorescens, P. chlororaphis, P. protegens, P. putida and P. brassicacearum. The abundance of the hcnC gene was also higher in the endophytic and rhizospheric isolates (36/70), with respect to the phlD gene (13/70). Greater detection of phlD or hcnC genes was found in strains isolated from the endosphere (43/70), compared with those of rhizospheric origin (6/70). Finally, a high ratio was observed between the production of siderophores, the presence of genes phlD and hcnC with the antagonistic activity towards important phytopathogenic fungi, like Botrytis cinerea, Fusarium oxysporum, Fusarium solani and Rhizoctonia solani. Conclusion: These results showed the potential to identify quickly, efficiently and at low cost, mechanisms of antagonism towards phytopatogens in bacteria associated with blackberry plants (Rubus fruticosus L.), such as siderophore production. [ABSTRACT FROM AUTHOR]

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The potential use ofBacillus thuringiensisUM96 as a biocontrol agent for the grey mould phytopathogenBotrytis cinereawas evaluated. In order to dissect the mode of action of this UM96 strain, we also examined the role of lytic activities in the antagonism. First,B. thuringiensisUM96 was characterised based on 16S rRNA andgyrAgene sequencing and phenotypic traits. Petri dish biocontrol assays demonstrated that when strain UM96 was inoculated 24 h previous toB. cinerea,the mycelial growth was inhibited by up to 70%. Test for lytic enzymes activities of cellulase and glucanase was negative. Chitinase was the only positive enzyme activity in two different culture media. PCR detection of thechiBgene was also positive. Chitinolytic supernatants, obtained from rich and minimal media supplemented with colloidal chitin as the sole carbon source, fromB. thuringiensis UM96 showed a strong inhibitory effect ofB. cinereathat was not observed with heat-treated supernatant. Interestingly, when the supernatant was supplemented with 100 µM allosamidin, a chitinase specific inhibitor, the antagonistic activity was suppressed significantly. A lack of chitinase activity was also observed in allosamidin-treated supernatants. Our pathogenicB. cinereastrain also exhibited susceptibility to pureStreptomyces griseuschitinase. Finally, the chitinolytic strainB. thuringiensisUM96 was able to protectMedicago truncatulaplants in vitro fromB. cinereainfection and significantly reduced the necrotic zones and root browning of the plants. Together, these results suggest a potential use ofB. thuringiensisUM96 for the biological control ofB. cinereaand a role for chitinases during the antagonism displayed. [ABSTRACT FROM PUBLISHER]

In this work, we report an analysis of the draft genome of the blueberry (Vaccinium spp. var. Biloxi) growth-promoting endophyte Bacillus toyonensis, strain COPE52. The genome of COPE52 consists of a single 5,806,513 bp replicon, with a 35.1% G + C content. Strain COPE52 was strongly affiliated to B. toyonensis species, based on species delimitation cut-off values established for average nucleotide identity (> 95–96%), genome-to genome distance calculator (> 70%) and phylogenomic analysis. The RAST genomic annotation of the COPE52 strain revealed a total of 5979 total genes, including 5631 protein-coding genes, 11 rRNA genes, 5 ncRNAs, 81 tRNA genes, and 251 pseudogenes. To further validate the in silico analysis results, experiments were carried out to detect the production of indoleacetic acid, protease activity, and the emission of volatiles like acetoin, 2,3-butanediol and dimethyl disulphide as potential plant growth-promoting mechanisms. COPE52 also showed antifungal action against the grey mould phytopathogen, Botrytis cinerea, during in vitro bioassays. In addition, inoculation with strain COPE52 promoted growth biomass and chlorophyll content in blueberry plants (Vaccinium spp. var. Biloxi) under greenhouse conditions. To our knowledge, this is the first study showing genomic and experimental evidence of B. toyonensis as plant growth-promoting bacteria (PGPB). [ABSTRACT FROM AUTHOR]

We analyzed the antifungal and plant growth-promoting (PGP) effects of diffusible and volatile organic compounds (VOCs) produced by new rhizospheric isolates. The bacterial strains were identified as Pseudomonas fluorescens UM16, UM240, UM256, and UM270, based on their complete 16S ribosomal gene sequencing. These pseudomonads showed a high degree of antagonism against the phytopathogen Botrytis cinerea during confrontation assays. In addition, all strains significantly increased Medicago truncatula biomass and chlorophyll content. Interestingly, these activities were exerted by the emission of either diffusible organic compounds or VOCs. During biocontrol experiments, the four P. fluorescens strains were able to protect M. truncatula plants from B. cinerea infection by reducing stem disease symptoms and root browning. The potential presence of phenazines, cyanogens, and ACC (1-aminocyclopropane-1-carboxylate) deaminase, as well as the production of biofilm, siderophores, proteases, and indole-3-acetic acid were identified in most of the strains. The VOCs emitted by all four Pseudomonas strains were similar, and sulfur-containing compounds were among the most abundant, including dimethyl disulfide. Interestingly, the strain UM270 was the only one that produced dimethylhexadecylamine, a compound with antifungal and PGP activities. In conclusion, the Pseudomonas strains analyzed here exert multiple antagonistic and PGP mechanisms, and represent an excellent option to be used as either biocontrol or biopromoting agents in crops. [ABSTRACT FROM AUTHOR]