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Controlling crown gall in grapevine (Vitis vinifera L.) caused by the pathogenic bacterium Allorhizobium vitis is a major challenge for global viticulture, as this pathogen is highly persistent in vineyards once infected. The bacteria can enter the plant through open wounds during pruning and then systemically colonize the plant. This study aimed at evaluating the potential of Paraburkholderia phytofirmans PsJN, a beneficial endophytic bacterium able to colonize the xylem of grapevine, the same ecological niche as A. vitis, to control grapevine crown gall disease. P. phytofirmans PsJN was root-inoculated on grapevine plantlets before infection by A. vitis S4 on shoots. A. vitis S4 level in planta, vitopine production, accumulation of lignin in tumors, and symptoms of crown gall were investigated on grapevine prebacterized or not with PsJN. The expression of 28 grapevine genes involved in defense mechanisms was also simultaneously determined by quantitative real-time PCR. Despite a direct antibacterial effect against AvS4, PsJN has no significant impact on the incidence of crown gall or disease severity. However, PsJN leads to a stronger accumulation of vitopine in tumors and significantly reduced the population level of the pathogen in planta. [Figure: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Background: Phytopathogens, encompassing fungi, bacteria, viruses, and nematodes, pose a significant threat to the agricultural industry by causing substantial economic losses through severe plant diseases. The excessive use of synthetic fungicides to combat phytopathogens has raised environmental and human health concerns. Results: Consequently, there is an increasing demand for safe and environmentally friendly biopesticides to align with consumer preferences for uncontaminated food. One particularly promising alternative to synthetic fungicides involves harnessing biocontrol bacteria that produce extracellular hydrolytic enzymes. These enzymes serve to effectively manage phytopathogens while concurrently fostering sustainable plant protection. Among the pivotal hydrolytic enzymes generated by biocontrol bacteria are chitinase, cellulase, protease, lipase, glucanase, and amylase. These enzymes exert their influence by breaking down the cell wall, proteins, and DNA of phytopathogens, thereby establishing a dependable method of biocontrol. Conclusions: Recognizing the critical role of these hydrolytic enzymes in sustainable biocontrol, this review seeks to delve into their primary functions, contribution to sustainable plant protection, and mechanisms of action. Through an exploration of the potential presented by biocontrol bacteria and their enzymatic mechanisms, we can discern effective and environmentally conscious strategies for managing phytopathogens in agriculture.

Citrus fruits stand as pivotal and extensively cultivated fruit crops on a global scale, boasting substantial economic and nutritional significance. Despite their paramount importance, citrus growers and the industry face a formidable obstacle in the form of post-harvest losses caused by plant pathogens. Effectively addressing this challenge has become imperative. The predominant approach to tackle these pathogens has traditionally involved the use of chemical fungicides. However, the escalating environmental concerns associated with chemical interventions, coupled with a growing consumer preference for pesticide-free produce, have catalyzed an earnest quest for alternative methods of disease control in the citrus industry. The antagonistic yeasts hold great promise as biocontrol agents for mitigating post-harvest fungal diseases in citrus. In this regard, this review summarizes the current state of knowledge regarding the study of yeast strains with biocontrol potential. Thus, the various modes of action employed by these yeasts and their effectiveness against prominent citrus pathogens such as Penicillium digitatum, Penicillium italicum and Geotrichum citri were discussed. Additionally, the review delved into the challenges associated with the practical implementation of yeast-based biocontrol strategies in citrus post-harvest management and investigated the potential of yeast-based approaches to enhance the safety and quality of citrus produce, while reducing the reliance on chemical fungicides and contributing to the sustainable and environmentally responsible future of the citrus industry.

Tomato is one of the world’s most commonly grown and consumed vegetables. However, it can be attacked by the Gram-positive bacterium Clavibacter michiganensis subsp. michiganensis (Cmm), which causes bacterial canker on tomato plants, resulting in significant financial losses in field production and greenhouses worldwide. The current management strategies rely principally on the application of various chemical pesticides and antibiotics, which represent a real danger to the environment and human safety. Plant growth-promoting rhizobacteria (PGPR) have emerged as an attractive alternative to agrochemical crop protection methods. PGPR act through several mechanisms to support plant growth and performance, while also preventing pathogen infection. This review highlights the importance of bacterial canker disease and the pathogenicity of Cmm. We emphasize the application of PGPR as an ecological and cost-effective approach to the biocontrol of Cmm, specifying the complex modes of biocontrol agents (BCAs), and presenting their direct/indirect mechanisms of action that enable them to effectively protect tomato crops. Pseudomonas and Bacillus are considered to be the most interesting PGPR species for the biological control of Cmm worldwide. Improving plants’ innate defense mechanisms is one of the main biocontrol mechanisms of PGPR to manage bacterial canker and to limit its occurrence and gravity. Herein, we further discuss elicitors as a new management strategy to control Cmm, which are found to be highly effective in stimulating the plant immune system, decreasing disease severity, and minimizing pesticide use.

Several diseases affect the productivity of olive trees, including root rot disease caused by Pythium genera. Chemical fungicides, which are often used to manage this disease, have harmful side effects on humans as well as environmental components. Biological management is a promising control approach that has shown its great potential as an efficient eco-friendly alternative to treating root rot diseases. In the present study, the antagonistic activity of ten bacterial isolates was tested both in vitro and in planta against Pythium schmitthenneri, the causal agent of olive root rot disease. These bacterial isolates belonging to the genera Alcaligenes, Pantoea, Bacillus, Sphingobacterium, and Stenotrophomonas were chosen for their potential antimicrobial effects against many pathogens. Results of the in vitro confrontation bioassay revealed a high reduction of mycelial growth exceeding 80%. The antifungal effect of the volatile organic compounds (VOCs) was observed for all the isolates, with mycelial inhibition rates ranging from 28.37 to 70.32%. Likewise, the bacterial cell-free filtrates showed important inhibition of the mycelial growth of the pathogen. Overall, their efficacy was substantially affected by the nature of the bacterial strains and their modes of action. A greenhouse test was then carried out to validate the in vitro results. Interestingly, two bacterial isolates, Alcaligenes faecalis ACBC1 and Bacillus amyloliquefaciens SF14, were the most successful in managing the disease. Our findings suggested that these two antagonistic bacterial isolates have promising potential as biocontrol agents of olive root rot disease.

In many vineyards around the world, Botrytis cinerea (B. cinerea) causes one of the most serious diseases of aerial grapevine (Vitis vinifera L.) organs. The control of the disease relies mainly on the use of chemical products whose use is increasingly challenged. To develop new sustainable methods to better resist B. cinerea, beneficial bacteria were isolated from vineyard soil. Once screened based on their antimicrobial effect through an in vivo test, two bacterial strains, S3 and S6, were able to restrict the development of the pathogen and significantly reduced the Botrytis-related necrosis. The photosynthesis analysis showed that the antagonistic strains also prevent grapevines from considerable irreversible PSII photo-inhibition four days after infection with B. cinerea. The 16S rRNA gene sequences of S3 exhibited 100% similarity to Bacillus velezensis, whereas S6 had 98.5% similarity to Enterobacter cloacae. On the other hand, the in silico analysis of the whole genome of isolated strains has revealed the presence of “biocontrol-related” genes supporting their plant growth and biocontrol activities. The study concludes that those bacteria could be potentially useful as a suitable biocontrol agent in harvested grapevine.

Damping-off caused by Pythium aphanidermatum, as one of the most infamous plant diseases, is considered as a significant disease that causes severe damages in greenhouse and field crops in a vast range of hosts especially vegetables. The application of chemical fungicides as a common method to control this disease poses negative side effects on humans and the environmental components. Actinobacteria, especially members of the genus Streptomyces, are fascinating biocontrol agents and plant growth-promoting rhizobacteria, which exhibit safer alternative managements to control this disease. The present study aims to explore for bioactives soil Streptomyces isolates that are able to control P. aphanidermatum, which is the causal agent of damping-off in tomato. Out of a total of 116 actinobacteria isolates collected from the soil, 53 have showed an antagonistic activity against P. aphanidermatum, as deduced through in vitro dual cultures. Based on in vitro Petri plate seedling-bioassays (IPSB), from the 53 tested isolates in dual cultures, two isolates coded as H2 and H3, considered as the most bioactive agents, were selected to assess their biocontrol performances against P. aphanidermatum in the Sandwich bed-mix technique in greenhouse experiments. In vivo greenhouse statistical studies were performed to compare seven treatments using completely randomized design experiments. Metalaxyl fungicide was applied as the chemical-control treatment. To evaluate biocontrol efficiencies of the two Streptomyces symbionts, disease incidence recorded throughout the course of experiment and criteria of number of leaves, length of the plants, plant fresh and dry weights, were measured at the end of experiment and analyzed statistically. The resulted disease incidences for all treatments indicated that the two Streptomyces strains had PGPR activity, and they were effective in decreasing disease incidence and improving plant performances regarding number of leaves, height, and plant fresh and dry weights. Based on the phylogenetic analysis of the partial sequences of the 16S rRNA gene, the strain H2 revealed a close relation to six Streptomyces species, namely S. badius, S. caviscabies, S. globisporus, S. parvus, S. sindenensis, and S. griseoplanus, with 99.9% similarity. The strain H3 also indicated a close relation of the same similarity to two species, namely S. flavogriseus and S. pratensis. In overall, collected data dictated that the two bioactive root symbiont Streptomyces strains effectively controlled the damping-off disease caused by P. aphanidermatum.

The effectiveness of biological control agent, Ulocladium atrum (isolates U13 and U16) in protecting Vitis vinifera L. cv. Chardonnay against gray mold disease caused by Botrytis cinerea, and simulation of the foliar defense responses was investigated. A degraded mycelium structure during cultural assay on potato dextrose agar revealed that U. atrum isolates U13 and U16 were both antagonistic to B. cinerea, mainly when isolates were inoculated two days before Botrytis. Under in vitro conditions, foliar application of U. atrum protected grapevine leaves against gray mold disease. An increase in chitinase activity was induced by the presence of U. atrum isolates indicating that the biological control agents triggered plant defense mechanisms. Moreover, U13 has the potential to colonize the grapevine plantlets and to improve their growth. The ability of U. atrum isolates to exhibit an antagonistic effect against B. cinerea in addition to their aptitude to induce plant resistance and to promote grapevine growth may explain a part of their biological activity. Hence, this study suggests that U. atrum provides a suitable biocontrol agent against gray mold in grapevines.