In vitro potencijal antagonista Bacillus spp. za suzbijanje fitopatogena Xanthomonas euvesicatoria

Bacterial pathogen Xanthomonas euvesicatoria, principal causer of bacterial spot, represents a significant problem in agricultural practice due to high yield losses in the production of pepper and tomato. The development of resistance to copper pesticides has shifted research, in the field of its suppression, towards biopesticides. In this study, several Bacillus strains were tested against Xanthomonas euvesicatoria strains, isolated from pepper leaves with symptoms of bacterial spot, to select a sufficiently effective antagonist. When it comes to the testing of cultivation broth, containing biomass of tested antagonists, the best results were achieved using isolate Bacillus sp3. On the other hand, when biomass-free supernatants, containing produced antimicrobial compounds, were tested, Bacillus sp1 and Bacillus sp2 have shown the highest antimicrobial activity. The results of this study represent a basis for further development of bioprocess solutions for the production of biopesticides based on Bacillus spp. biomass or antimicrobial compounds, showing high efficiency in suppression of pepper bacterial spot.Bakterijski patogen Xanthomonas euvesicatoria predstavlja glavnog uzročnika bakteriozne pegavosti, stoga predstavlja značajan problem u poljoprivrednoj praksi usled izazivanja velikih gubitaka prinosa u proizvodnji paprike i paradajza. Uobičajena sredstva za suzbijanje i kontrolu ovog fitopatogena predstavljaju preparati na bazi bakra. Međutim, razvoj rezistentnosti prema pesticidima na bazi bakra doveo je do zaokreta u polju suzbijanja ovih patogena ka primeni biopesticida, odnosno bioloških kontrolnih agensa. Bakterije roda Bacillus i njihovi metaboliti sa izraženom antimikrobnom aktivnošću protiv ciljanih fitopatogena predstavljaju najperspektivnije aktivne komponente biokontrolnih preparata za zaštitu bilja. U ovom istraživanju nekoliko sojeva roda Bacillus ispitano je sa ciljem odabira antagonista dovoljno efikasnih u suzbijanju sojeva Xanthomonas euvesicatoria, koji su izolovani sa listova paprike sa simptomima bakteriozne pegavosti. Prilikom testiranja antimikrobne aktivnosti uzoraka kultivacionih tečnosti, koji sadrže i biomasu testiranih antagonista, najbolji rezultati u suzbijanju testiranih fitopatogena su postignuti primenom izolata Bacillus sp3. Sa druge strane, prilikom testiranja antimikrobne aktivnosti supernatanata oslobođenih biomase antagonista, koji sadrže samo produkovana antimikrobna jedinjenja, izolati Bacillus sp1 i Bacillus sp2 su pokazali najveću antimikrobnu aktivnost protiv fitopatogena Xanthomonas euvesicatoria. Rezultati ovog istraživanja predstavljaju osnovu za dalji razvoj bioprocesnih rešenja za proizvodnju biopesticida na bazi biomase ili antimikrobnih jedinjenja koja proizvode antagonisti roda Bacillus, a koji pokazuju visoku efikasnost u suzbijanju bakteriozne pegavosti paprike

Selection of antagonists for biocontrol of xanthomonas euvesicatoria

Xanthomonas euvesicatoria is a worldwide causer of pepper bacterial spot, a bacterial plant disease responsible for massive losses of fresh pepper fruits. Considering the current problems in management of bacterial plant diseases, biological control using antagonistic microbial strains with high potential for plant pathogens suppression emerges as a possible solution. The aim of this study was to select suitable antagonists for suppression of X. euvesicatoria among the bacteria, yeast and fungi from the genera Pseudomonas, Lactobacillus, Saccharomyces and Trichoderma, based on in vitro antimicrobial activity testing using the diffusion disc method. The results of this study have revealed that cultivation broth samples of the antagonists Lactobacillus MK3 and Trichoderma reseii QM 9414, as well as supernatant samples of the antagonist Pseudomonas aeruginosa I128, have showed significant potential to be applied in biological control of X. euvesicatoria. Further research would be required to formulate suitable cultivation medium and optimize bioprocess conditions for production of the proposed pepper bacterial spot biocontrol agents

Bacillus spp. as potential biocontrol agents of bacterial spot on pepper caused by xanthomonas euvesicatoria

The objective of this research was to identify bacterial spot-causing pathogen and bacterial antagonists for management of the disease using biocontrol agents as environmentally friendly alternatives. Isolates of Bacillus spp. were obtained from the soil samples collected at different localities in Serbia. Antibacterial activity of natural antagonists toward the pathogen isolated from infected pepper leaves was examined using a modified well-diffusion assay and standard germination test. Our results confirmed the presence of Xanthomonas euvesicatoria as the causal agent of bacterial spot of pepper. Screening of 32 Bacillus spp. isolates for antibacterial activity showed that 8 isolates inhibit growth of examined X. euvesicatoria isolates. Four isolates identified as Bacillus subtilis exhibited the highest antibacterial activity by in vitro test (from 5 to 14 mm inhibition zone of bacterial growth). The isolates positively influenced germination of pepper seeds, causing up to 16% and 70% increase in germination and germination viability compared to control seeds infected with pathogen. The most effective isolates of Bacillus subtilis could be used as potential biocontrol agents of bacterial spot of pepper

Plant Growth-Promoting Activity of Pseudomonas aeruginosa FG106 and Its Ability to Act as a Biocontrol Agent against Potato, Tomato and Taro Pathogens

Simple Summary Microbial bio-stimulants are attracting increasing attention in agricultural research. In particular, plant growth-promoting rhizobacteria (PGPR) have great potential to improve crops' productivity and tolerance of biotic and abiotic stresses. It is anticipated that PGPR could eventually replace synthetic fungicides in agriculture. This research evaluated Pseudomonas aeruginosa strain FG106-which was isolated from tomato plants- as a potential biocontrol agent against several plant pathogens. This strain displayed multiple plant growth-promoting attributes and high in vitro and in vivo inhibition of growth and pathogenicity of tested phytopathogens. It is thus a multifunctional PGPR with potential applications as a biocontrol agent to control fungal and bacterial pathogens. P. aeruginosa strain FG106 was isolated from the rhizosphere of tomato plants and identified through morphological analysis, 16S rRNA gene sequencing, and whole-genome sequencing. In vitro and in vivo experiments demonstrated that this strain could control several pathogens on tomato, potato, taro, and strawberry. Volatile and non-volatile metabolites produced by the strain are known to adversely affect the tested pathogens. FG106 showed clear antagonism against Alternaria alternata, Botrytis cinerea, Clavibacter michiganensis subsp. michiganensis, Phytophthora colocasiae, P. infestans, Rhizoctonia solani, and Xanthomonas euvesicatoria pv. perforans. FG106 produced proteases and lipases while also inducing high phosphate solubilization, producing siderophores, ammonia, indole acetic acid (IAA), and hydrogen cyanide (HCN) and forming biofilms that promote plant growth and facilitate biocontrol. Genome mining approaches showed that this strain harbors genes related to biocontrol and growth promotion. These results suggest that this bacterial strain provides good protection against pathogens of several agriculturally important plants via direct and indirect modes of action and could thus be a valuable bio-control agent

Occurrence of bacterial spot disease in Illinois tomato fields, characterization of the casual agents, and management of the disease

Bacterial spot, caused by Xanthomonas spp., is one of the most important diseases of tomato in Illinois. Field surveys were conducted in 2017, 2018, and 2019, to assess occurrence of bacterial spot disease in commercial tomato fields. Severity of foliage and fruit infections were recorded, and symptomatic samples for isolation of the pathogen were collected from three-to-five cultivars in three different farms in each of northern, central, and southern regions of Illinois. In 2017 and 2019, average disease severity was the highest in southern Illinois, while it was the highest in northern Illinois in 2018. Incidence of symptomatic fruit was generally low. During the surveys, 266 isolates were collected and identified as Xanthomonas gardneri or X. perforans using Xanthomonas-specific hrp primers. Eighty-five percent of Xanthomonas isolates identified from northern region were X. gardneri, whereas 70% of isolates from southern region were X. perforans. Isolates from the central region were 55 and 45% X. perforans and X. gardneri, respectively. Multilocus sequence analysis using six housekeeping genes (fusA, gap-1, gltA, gyrB, lepA, lacF) revealed five and four distinct genetic groups for X. gardneri and X. perforans, respectively. In addition to Xanthomonas, non-Xanthomonas bacterial genera were isolated from the diseased fields, with the majority of the isolates being classified as Microbacterium, Pantoea, and Pseudomonas. Field experiments were conducted in two different locations (Fayette and Champaign Counties), using two different tomato cultivars, ‘Red Deuce’ and ‘Mt. Fresh’. The results showed that plots treated with the combination of copper hydroxide (Kocide-3000 46.1DF) and mancozeb (Manzate PRO Stick) had the lowest disease severity. Field isolates of X. gardneri and X. perforans were grown on mannitol-glutamate-yeast agar (MGYA) amended with 0.8 mM copper sulfate. Two copper resistance genes, copA and copM, were present only in the isolates that developed colonies on the copper-amended MGYA. Additionally, in vitro laboratory studies were conducted to determine the effectiveness of selected chemical compounds and biopesticides at preventing colony formation of copper resistant and copper sensitive isolates of X. gardneri and X. perforans. The results showed that the combination of copper hydroxide (Kocide-3000 46.1DF) and mancozeb (Manzate PRO-stick) produced the largest inhibition zone for the copper-sensitive isolates of both species (X. perforans and X. gardneri). In contrast, the combination of Bacillus amyloliquefaciens strain D747 (Double Nickel LC) and copper octanoate (Cueva) produced the largest inhibition zone for copper resistant isolates of both species

Endophytic Fungi of Tomato and Their Potential Applications for Crop Improvement

In this work, considerations are made to the effects and methods of introduction and detection of Endophytic Fungi on tomato plants, consolidating in a review the main findings that regard pest and pathogen control, and improvement of plant performance. Moreover, a survey was undertaken of the naturally occurring constitutive endophytes present in this horticultural crop, with the aim to evaluate the potential role in the selection of new beneficial Endophytic Fungi useful for tomato crop improvement

Bacteriophage-mediated control of phytopathogenic xanthomonads: A promising green solution for the future

Xanthomonads, members of the family Xanthomonadaceae, are economically important plant pathogenic bacteria responsible for infections of over 400 plant species. Bacteriophage-based biopesticides can provide an environmentally friendly, effective solution to control these bacteria. Bacteriophage-based biocontrol has important advantages over chemical pesticides, and treatment with these biopesticides is a minor intervention into the microflora. However, bacteriophages’ agricultural application has limitations rooted in these viruses’ biological properties as active sub-stances. These disadvantageous features, together with the complicated registration process of bacteriophage-based biopesticides, means that there are few products available on the market. This review summarizes our knowledge of the Xanthomonas-host plant and bacteriophage-host bacterium interaction’s possible influence on bacteriophage-based biocontrol strategies and provides examples of greenhouse and field trials and products readily available in the EU and the USA. It also details the most important advantages and limitations of the agricultural application of bacteriophages. This paper also investigates the legal background and industrial property right issues of bacteriophage-based biopesticides. When appropriately applied, bacteriophages can provide a promising tool against xanthomonads, a possibility that is untapped. Information presented in this review aims to explore the potential of bacteriophage-based biopesticides in the control of xanthomonads in the future

Evaluation of Biofungicides and Plant Defense Elicitors against Bacterial Pathogens of Agronomic Importance

Plant bacterial diseases are nowadays routinely managed with scheduled treatments based on heavy metal compounds or, in the worst cases, on antibiotics; to overcome the environmental consequences linked to the use of these chemical compounds, such as pollution or selection of antibiotic resistant pathogens, an integrated control management is required. The use of bacterial antagonists, biological agents, plant defence response elicitors or resistant host plant genotypes play an important role in the frame of sustainable agriculture. In this work, the activity of plasma activated water (PAW) and different bioagents aimed to the control of the two bacterial pathogens Xanthomonas vesicatoria and Pseudomonas syringae pv. actinidiae, causal agents of tomato bacterial leaf spot and kiwifruit bacterial canker, respectively, were studied. All these tools were assayed for their direct efficacy and for their ability, as elicitors, to trigger the plant immune system against these two bacterial pathogens. Moreover, a study on several Actinidia sp. accessions was carried out to evaluate their susceptibility against bacterial canker of kiwifruit. PAW resulted unable to direct inhibit X. vesicatoria growth in in vitro assays, however it showed the ability to trigger tomato plant immune system by reducing disease severity up to approx. 38% when tested in three experiments on two tomato genotypes conducted under greenhouse conditions. When tested in in vitro and in vivo experiments against X. vesicatoria and P. syringae pv. actidinidiae, the tested bioagents, based on natural extracted compounds or on different strains of Bacillus sp., showed a direct efficacy against both bacterial pathogens. Moreover, they were also able to elicit the plant defence response by significantly lowering the disease severity on tomato and kiwifruit leaves. In addition, the A. chinensis accession NPK3 resulted the less susceptible to the bacterial canker in comparison to more than 20 accessions tested