Antagonistic Strains Research Articles

Exploitation of Agro-Industrial Residues for the Formulation of a New Active and Cost Effective Biofungicide to Control the Root Rot of Vegetable Crops

This study aimed to produce an economic and stable biofungicide based on a new effective antagonistic strain (Trichoderma harzianum JF419706) via the exploitation of agro-industrial lignocellulosic residues as carriers for fungal growth to control the root rot diseases of vegetable crops. Trichoderma harzianum JF419706 showed a good resistance to a chemical fungicide with two-fold of the recommended dose. It was able to propagate on corn stovers amended with 20% of date molasses, as a very cheap substrate, up to 2.90 × 1016 CFU/g after 30 days. Formulation of the bioagent on the substrate as a fine powder (FTB) increased the shelf-life up to 8 months with good viability (9.37 × 1011 CFU/g). The bioagent propagated itself in the rhizospheric soil about two-fold of the initial inoculum. Application of the FTB, as a seed treatment, suppressed the root rot disease severity percentage of cucumber, lettuce, and tomato plants to 70.0%, 61.5%, and 53.8%, respectively, from the control. The crop yield increased by 50%, 35%, and 30% in the same order of the three crops. FTB promoted the growth and physiological processes of the plants significantly compared with the control. Our study recommends the application of the FTB as a cost-effective biofungicide and biofertilizer in crop management, singly or as a part of integrated pest management, to ensure the sustainability of green farming and reduce the chemical input in cultural practices.

Green Fluorescent Protein-Tagged Bacillus axarquiensis TUBP1 Reduced Cotton Verticillium Wilt Incidence by Altering Soil Rhizosphere Microbial Communities.

Verticillium wilt is a major disease of cotton that considerably decreases yield and crop quality. Soil microbial communities play an important role in plant health. Therefore, biocontrol bacteria that regulate microbial communities in rhizosphere soil can improve plant resistance to pathogens. Previously, the antagonistic strain Bacillus axarquiensis TUBP1 was screened and found to act against Verticillium dahliae with 43% biocontrol effect in cotton fields. We studied the effect of Bacillus axarquiensis TUBP1 with a green fluorescent protein (GFP) gene marker on the microbial community structure of cotton rhizosphere soil and cotton yield and quality. Cotton Verticillium wilt incidence, soil biochemical properties, and soil bacterial and fungal communities were analyzed. Results showed that bacterial and fungal abundance in cotton rhizosphere soil was temporarily changed after applying B. axarquiensis TUBP-315GFP. However, Bacillus significantly increased, whereas V. dahliae significantly decreased. The incidence of cotton Verticillium wilt after treatment with B. axarquiensis TUBP-315GFP was significantly lower and cotton production increased by 40.6%. Our findings indicated that the application of B. axarquiensis TUBP-315GFP can change microbial community structure of cotton rhizosphere soil, leading to a reduction in the incidence of cotton Verticillium wilt and increasing cotton yield.

English

Soybean root rot is a worldwide soil-borne fungal disease threatening soybean production, causing huge losses in yield and quality of soybean. Fusarium species are well recognized as the important causal agent of Fusarium root rot. To screen the beneficial Bacillus strains with capability of suppressing soybean root rot and evaluate the impact of Bacillus combined with biochar against soybean root rot, a pot experiment was conducted with different treatments. In this study, as potential biological control measures, antagonistic Bacillus isolates and different types of biochar were added to soil separately and excellent antagonistic strains mixed with bamboo biochar were applied to the soil. The results showed that seven Bacillus strains promoted the growth of soybean seedlings and reduced root rot severity by 33 to 61%. Bacillus amylolique faciens NH2 was associated with the lowest incidence of soybean root rot, indicating its bio-control potential. The value of plant height, root length and plant dry weight of soybean in the sterilized soil mixed with biochar separately treatment were superior to those of soybean in the inoculated with pathogen treatment, especially the bamboo biochar treatment reduced soybean root rot caused by Fusarium significantly and which bio-control efficacy was 77.41%. The soybean plants shoot and root dry weights in the biochar mixed B. amylolique faciens NH2 or B. subtilis DBK treatments were increased by17.1, 10.7% and 19.51, 19.64%, respectively, which were significantly higher than those of the inoculated pathogen treatment. Compared to antagonistic strain or biochar individual treatments, the disease control efficiency on soybean root rot was up to 64.86% in NH2 strain mixed with bamboo biochar treatment, which reduced root rot severity significantly and showed a synergistic effect. These results suggest that antagonistic Bacillus strains mixed with biochar can be used as an effective alternative in managing soybean root rot. © 2021 Friends Science Publishers

Bacillus velezensis WLYS23 strain possesses antagonistic activity against hybrid snakehead bacterial pathogens.

The aims of this study were to screen an antagonistic probiotic for the prevention and control of bacterial diseases in snakehead fish and to evaluate the antimicrobial activities, biosafety and biocontrol effect of the antagonistic strain. In this study, the WLYS23 strain exhibiting the most effective antagonistic properties against several fish pathogens was selected from the intestine of healthy snakehead fish. The strain was identified as Bacillus velezensis based on morphological, physiological and biochemical characteristics, and phylogenetic analysis. This strain showed amylase, cellulase, protease and lipase activities according to extracellular enzyme activity assays. Moreover, the cell-free extract of the WLYS23 strain exhibited strong antibacterial activity, with MICs of ≤64 μg ml-1 for most fish pathogens. Additionally, the cell-free extract was heat and pH stable, and resistant to protease, whereas their antimicrobial activities were significantly influenced by metal ions at high concentration. The WLYS23 strain and its cell-free extract were safe for snakehead and zebrafish. The disease resistance of snakehead fish was significantly increased following administration of the WLYS23 strain and its cell-free extract respectively. The complete genome of the WLYS23 strain was sequenced and found to harbour seven gene clusters encoding secondary metabolites with antimicrobial activity. The WLYS23 strain possesses great potential as a biocontrol agent, which can be commercially developed to improve disease control in freshwater aquaculture. Snakehead fish are important commercially farmed fish worldwide. However, the bacterial diseases caused by Aeromonas sp. and Nocardia seriolae in farmed snakehead fish lead to huge economic losses. Safe, economical and efficient probiotics are limited to prevent and control these diseases. Here, we provide a promising biocontrol agent with antagonistic activity against bacterial diseases of snakehead.

Biocontrol of Rhizoctonia solani using volatile organic compounds of solanaceae seed-borne endophytic bacteria

Rhizoctonia solani is a broad spectrum fungal pathogen that infects crops in greenhouse and field conditions causing plants damping-off and fruit rot which provoke serious yield losses. This study prospected the use of bacterial volatile organic compounds (VOCs) to control R. solani infection on tomato seedlings and fruit in order to search for an alternative to the use of chemical pesticides. Seed-born bacterial endophytes were isolated from the cultivated Solanum lycopersicum and the wild Solanum linnaeanum species. This study showed a host- and organ-specific colonization of endophytic bacteria at early seedling stage with most of them colonizes the cotyledons in comparison to stems and roots. Overall, 51 % and 11 % of isolated endophytic bacteria produce antifungal VOCs against R. solani at 7 d and 14 d of dual culture, respectively. The majority (about 78 %) of the antagonistic bacterial endophytes showed promoting activity on tomato seedling growth. For the bioprotection tests the strains TRC7 and TRC10 of Bacillus subtilis and TRT11 of B. megateriumwere selected as the most antagonistic and PGP endophytic bacteria and a non-antagonistic strain SMLR7 of Paenibacillus sp., with this later strain reported for the first time colonizing internal seed tissues of S. linnaeanum. The VOCs of the strain TRC7 showed the best pattern of decrease of R. solani rotting on tomato fruit, and increase the hypocotyl length, the radicle length, the fresh weight, and the vigor of tomato seedlings. The identification of the VOCs produced by the antagonistic Bacillus strains showed a core set of four compounds i.e. 2-Heptanone; Pyrazine, 2,5-dimethyl-; Naphthalene; and Benzenamine, N-ethyl- which was the most abundant. All the four VOCs showed antifungal activity against R. solani in vitro growth, and to our knowledge this activity is reported for the first time for Benzenamine, N-ethyl- and 2-Heptanone. The Benzenamine, N-ethyl- showed the best antifungal activity with an IC50 about 0.09 mL L−1 headspace and proved to be effective in reducing R. solani rotting on tomato fruit at the same concentration. So, this work provides evidence about VOCs-mediated biocontrol ability of Bacillus strains to reduce R. solani seedling damping-off and fruit rot of tomato making them valuable agents for pre- and postharvest control of this disease.

Alleviation of Salt Stress in Wheat Seedlings via Multifunctional Bacillus aryabhattai PM34: An In-Vitro Study

Plant growth-promoting rhizobacteria play a substantial role in plant growth and development under biotic and abiotic stress conditions. However, understanding about the functional role of rhizobacterial strains for wheat growth under salt stress remains largely unknown. Here we investigated the antagonistic bacterial strain Bacillus aryabhattai PM34 inhabiting ACC deaminase and exopolysaccharide producing ability to ameliorate salinity stress in wheat seedlings under in vitro conditions. The strain PM34 was isolated from the potato rhizosphere and screened for different PGP traits comprising nitrogen fixation, potassium, zinc solubilization, indole acetic acid, siderophore, and ammonia production, along with various extracellular enzyme activities. The strain PM34 showed significant tolerance towards both abiotic stresses including salt stress (NaCl 2 M), heavy metal (nickel, 100 ppm, and cadmium, 300 ppm), heat stress (60 °C), and biotic stress through mycelial inhibition of Rhizoctonia solani (43%) and Fusarium solani (41%). The PCR detection of ituC, nifH, and acds genes coding for iturin, nitrogenase, and ACC deaminase enzyme indicated the potential of strain PM34 for plant growth promotion and stress tolerance. In the in vitro experiment, NaCl (2 M) decreased the wheat growth while the inoculation of strain PM34 enhanced the germination% (48%), root length (76%), shoot length (75%), fresh biomass (79%), and dry biomass (87%) over to un-inoculated control under 2M NaCl level. The results of experiments depicted the ability of antagonistic bacterial strain Bacillus aryabhattai PM34 to augment salt stress tolerance when inoculated to wheat plants under saline environment.

Isolation and efficacy of two bacterial strains antagonists of Erwinia amylovora and Pectobacterium carotovorum

BackgroundThe development of ecofriendly tools against plant diseases is an important issue in crop protection. Screening and selection process of bacterial strains antagonists of 2 pathogenic bacterial species that limit very important crops, Erwinia amylovora, the causal agent of the fire blight disease, and Pectobacterium carotovorum, the causal agent of bacterial potato soft rot, were reported. Bacterial colonies were isolated from different ecological niches, where both pathogens were found: rhizosphere of potato tubers and fruits and leaves of pear trees from the northwest region of Algeria. Direct and indirect confrontation tests against strains of E. amylovora and P. carotovorum were performed.ResultsResults showed a significant antagonistic activity against both phytopathogenic species, using direct confrontation method and supernatants of cultures (p<0.005). In vitro assays showed growth inhibitions of both phytopathogenic species. Furthermore, results revealed that the strains of S. plymuthica had a better inhibitory effect than the strains of P. fluorescens against both pathogens. In vivo results on immature pear fruits showed a significant decrease in the progression of the fire blight symptoms, with a variation in the infection index from one antagonistic strain to another between 31.3 and 50%, and slice of potato showed total inhibition of the pathogen (P. carotovorum) by the antagonistic strains of Serratia plymuthica (p<0.005).ConclusionThis study highlighted that the effective bacteria did not show any infection signs towards plant tissue, and considered as a potential strategy to limit the fire blight and soft rot diseases.

Antagonistic Activity of Indigenous Rhizobacteria through Biosynthesis of Indole-3-Acetic Acid (IAA), Hydrogen Cyanide (HCN), and Siderophores

This study aimed to isolate indigenous Antagonistic Bacteria (AB) against common soil-borne phytopathogens, including Rhizoctonia solani, Phythium sp., Fusarium oxysporum. Biosynthesis of Indole-3-Acetic Acid (IAA), generation of Hydrogen Cyanide (HCN), and siderophores production were assessed for their involvement in the antagonistic activities. Rhizospheric soil of bean roots, sunflowers, wheat, rice, and humic and semi flooded soils were used to isolate twenty-one bacterial strains for phytopathogenic antagonism. It was found that nine isolates have potential antagonistic activity against three common soilborne pathogens. Antifungal productivity for IAA, HCN, and siderophores was screened on the isolates while nine ABs were identified. To choose statistically significant isolate for the formulation, the principal component analysis was performed with five variables (IAA production, siderophores production index, antagonistic activities against three phytopathogens). Among the nine isolates, the isolate Pseudomonas alicaligenes shew a positive correlation with all variables. In particular, the strain demonstrated to be an antagonistic strain against the fungal pathogens and a strong producer of siderophores, HCN and IAA, We prepared the biocontrol agents with rice flour, glutinous rice flour, Monosodium Glutamate and Chitosan that were found to maintain the up to three months for convenience of field applications.

Killing Effect of Bacillus Velezensis FZB42 on a Xanthomonas Campestris pv. Campestris (Xcc) Strain Newly Isolated from Cabbage Brassica Oleracea Convar. Capitata (L.): A Metabolomic Study.

The potential use of Bacillus velezensis FZB42 for biological control of various phytopathogens has been documented over the past few years, but its antagonistic interactions with xanthomonads has not been studied in detail. Novel aspects in this study consist of close observation of the death of Xanthomonas campestris pv. campestris cells in a co-culture with B. velezensis FZB42, and quantification of lipopeptides and a siderophore, bacillibactin, involved in the killing process. A new robust Xcc-SU isolate tolerating high concentrations of ferric ions was used. In a co-culture with the antagonist, the population of Xcc-SU was entirely destroyed within 24–48 h, depending on the number of antagonist cells used for inoculation. No inhibitory effect of Xcc-SU on B. velezensis was observed. Bacillibactin and lipopeptides (surfactin, fengycin, and bacillomycin) were present in the co-culture and the monoculture of B. velezensis. Except for bacillibactin, the maximum contents of lipopeptides were higher in the antagonist monoculture compared with the co-culture. Scanning electron microscopy showed that the death of Xcc-SU bacteria in co-culture was caused by cell lysis, leading to an enhanced occurrence of distorted cells and cell ghosts. Analysis by mass spectrometry showed four significant compounds, bacillibactin, surfactin, fengycin, and bacillomycin D amongst a total of 24 different forms detected in the co-culture supernatant: Different forms of surfactin and fengycin with variations in their side-chain length were also detected. These results demonstrate the ability of B. velezensis FZB42 to act as a potent antagonistic strain against Xcc.

Antagonic Activity of Endophytic Bacteria Isolated from Man Trau Grass on Stem Rot Disease Of Pitaya (Hylocereus Undatus)

Endophytic bacteria reside in the intercellular spaces in different plant tissues without causing damage. This study aimed to select endophytic bacterial strains from Man Trau grass (Eleusine indica) that are able to inbibit the fungus A. alternata causing stem rot disease on pitaya. The result showed that one fungal isolate was pathogenic and caused stem rot disease on dragonfruit. The analysis results based on morphological characteristics and ITS region sequence indicated that the isolated fungal strain is 100% identical to A. alternata. In addition, a total of 16 endophytic bacterial strains were isolated from Man Trau grass samples in Binh Thuan and screened for antifungal activity. Ten bacterial strains with antagonistic activity against A. alternata causing stem rot disease on pitaya were detected. Among those, strain MT47 showed the strongest antifungal activity with an efficiency of 36.67%. Moreover, the result also presented that the antagonistic strain MT47 pocesses the ability of biofilm formation significantly higher than the control. The results suggest that these endophytic bacteria can be used in biocontrol of the stem rot disease on pitaya.

Beneficial Microorganisms to Control the Gray Mold of Grapevine: From Screening to Mechanisms.

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.

Diversity and community structure of endophytic Bacillus with antagonistic and antioxidant activity in the fruits of Xisha Wild Noni (Morinda citrifolia L.)

Noni (Morinda citrifolia L.) is a tropical crop with strong antibacterial, antioxidant and other abilities, and its fruit has a strong potential for adjuvant treatment of diseases. This study aimed to explore the dynamic change of endophytic bacteria in Noni fruit at different stages and the correlation between the antagonistic and antioxidant activity of the Bacillus which was screened and the change of the host's growth stage. In this study, though the high-throughput sequencing technology (HTS), 106 endophytic bacteria species were found in A, B, C, D, E and F stages of Noni fruit, among which the dominant group were Pantoea (0.3%–20.9%), and Candidatus_Uzinura (2.3%–35.2%) etc. The endophytic bacteria were isolated by culture-dependent method. Through their antagonistic experiments on Staphylococcus aureus and Escherichia coli, the results of 16S polyphasic taxonomic identification showed that the 34 antagonistic strains belonged to Bacillus. Five species of these Bacillus were identified by gyrA polyphase taxonomy, including Bacillus subtilis (76% of all Bacillus), Bacillus licheniformis (9%), Bacillus amyloliquefaciens (6%), Bacillus velezensis (6%) and Bacillus mojavensi (3%), and the RAPD showed these Bacillus are no signs of stable passage. In C, D, E and F stages, the average total antioxidant activity of Bacillus endophytic antagonists against Noni was 7.812 U/mL, 8.144 U/mL, 7.817 U/mL and 7.144 U/mL, which was much higher than that of Noni fruit, and antioxidant activity of Noni juice and Bacillus bacterial liquid vary with host's growth period showed the same trend, both rose slowly at first, and reached the highest in period E, then declined slightly in period F, it showed that the antagonistic Bacillus of Noni had synergistic function with Noni fruit. This study clarified the relationship of function between Noni fruit and endophytic bacteria, and laid a foundation for future study on the dynamic change of endophytic flora succession and efficacy.

Successful biocontrol of major postharvest and soil-borne plant pathogenic fungi by antagonistic yeasts

Fungal pathogens are the main biotic burden of productivity for economically important crops under field, greenhouse or postharvest conditions. The discovery and development of new environmental-friendly solutions, such as application of living organisms and their derivatives to control plant diseases and pests, are of enormous interest. This study presents the results of a mass screening designed to detect yeast strains with antagonistic activity against postharvest pathogens (Alternaria alternata, Penicillium expansum and Botrytis cinerea) and soil-borne diseases (Verticillium dahliae and Fusarium oxysporum). In fact, this is the first study that focuses on screening the antagonistic potential of a wide variety of yeast genera (13) and species (30) against vascular wilts. The results from in vivo trials demonstrated that fungal infected tomato plants, grown under hydroponic or soil conditions, showed a significant reduction in disease severity after yeast treatment. Wickerhamomyces anomalus Wa-32 was able to antagonise both pathogens and reduce the disease severity up to 40% (V. dahliae) and 50% (F. oxysporum) in soil conditions. In addition, this strain became endophytic in tomato plants. The features of Wa-32 are of enormous interest since no effective antagonistic biocontrol product is available for the simultaneous control of these two fungal pathogens. Postharvest assays with wounded tomato fruits showed that several strains displayed very high biocontrol levels against P. expansum and B. cinerea (up to 86 and 97% reduction in disease severity, respectively) but none of them showed protection against A. alternata. The best protection against B. cinerea was again achieved with W. anomalus Wa-32 and two Metschnikowia pulcherrima strains (Mp-22 and Mp-30). However, the best antagonistic strains of P. expansum were Candida lusitaniae Cl-28, Candida oleophila Co-13, Debaryomyces hansenii Dh-67 and Hypopichia pseudoburtonii Hp-54. These biocontrol effects were also demonstrated in grapes and apples.

Colonization Characteristics of Poplar Fungal Disease Biocontrol Bacteria N6-34 and the Inhibitory Effect on Pathogenic Fungi by Real-Time Fluorescence Quantitative PCR Detection.

Botryosphaeria dothidea is one of the most important diseases which can cause poplar canker. In our previous study, the endophytic Bacillus subtilis N6-34 screened from poplar tissue was found to be an antagonistic strain against B. dothidea. In order to ascertain the colonization rule of B. subtilis N6-34 in poplar plants, colonization of B. subtilis N6-34 labeled with a green fluorescent protein (GFP) was investigated in poplar plants and the rhizosphere soil. To confirm the inhibitory effect of the strain N6-34 on pathogenic fungi, real-time fluorescent quantitative PCR experiment with Fusarium oxysporum as the target strain was carried out. Firstly, a plasmid (pHT01-P43GFPmut3a) containing gfp gene was successfully transformed into wild B. subtilis N6-34, which has the similar characteristics with the strain N6-34 in cell growth and antifungal activity. The poplar pot experiments were carried out to examine the colonization rules and colonization quantity in poplar plants and rhizosphere soil. Observation with a confocal laser scanning microscope showed that GFP-labeled B. subtilis N6-34 (N6-34-GFP) could colonize in primary root, lateral root and adventitious root. With the extension of inoculation time, the colonization quantity of N6-34-GFP in the rhizosphere soil and poplar plants showed a trend of first increasing, then stabilizing for a period of time and then decreasing. The real-time fluorescent quantitative PCR result showed a gradual decrease in the number of F. oxysporum with increasing inoculation time. Therefore, N6-34-GFP exhibited colonization in the rhizosphere soil and different parts of poplar plants. In addition, the strain N6-34 could inhibit the growth of pathogenic fungi. The ability of B. subtilis N6-34 to colonize in the rhizosphere soil and poplar plants and to inhibit fungal growth in vitro suggest a potential application of this strain as a biological control agent.

English

The powdery mildew caused by air borne pathogen (Podosphaera fusca) is an important disease of cucurbits including melon (Cucumis melo L.) plants. Three antagonistic bacterial strains (M4, M10 and M11); isolated from the melon plants were tested for antagonistic activity against P. fusca and soil-borne pathogens of melon plants (Monosporascus cannonballus, Fusarium oxysporum f. spp. melonis, F. solani and Phomopsis spp.). All the three strains were identified as Bacillus velezensis based on sequence analysis of gyrase subunit A (gyrA) gene sequence. The bacterial strains showed significant antagonistic activity against soil and air borne pathogenic fungi. Among all strains, M10 showed a broad spectrum of mycelial growth inhibition against phytopathogenic fungi. The tested culture broth did not affect the pollen fertilization, flowering, fruit rot occurrence and fruit set development during blooming and cultivation season of the melon plants. The M10 culture broth stored for 3 and 6 months displayed biocontrol efficiency of 73.2 and 72.3%, respectively. Application of mixed solution of M10 culture broth + paraffin oil strongly suppressed the incidence and spread of powdery mildew. These results suggested that the combination of paraffin oil and B. velezensis M10 culture broth is an ecofriendly approach and possess strong biocontrol potential against melon powdery mildew and can also be used as antifungal agents for several plant pathogens. © 2021 Friends Science Publishers

Antagonistic Activity of Bacillus velezensis SDTB038 against Phytophthora infestans in Potato.

Potato late blight is a severe and highly epidemic disease caused by Phytophthora infestans that can affect all parts of the plant. This study mainly screened antagonistic strains for good control of potato late blight and identified strain SDTB038 as Bacillus velezensis according to its morphological and chemical properties and the 16S rRNA, gyrA, and gyrB gene sequences. This antagonistic strain achieved good control of potato late blight in greenhouses and fields and promoted potato plant growth. Two-year field trials (2018 and 2019) showed that B. velezensis SDTB038 can be used to reduce food losses caused by late blight, achieving late blight reductions of 40.79% (2018) and 37.67% (2019). In two-year field trials, the control effects of the highest concentrations of fluopimomide and B. velezensis SDTB038 were better than those of the other treatments. The control effect of 85 g ha-1 fluopimomide and B. velezensis SDTB038 and that of 170 g ha-1 fluopimomide alone showed no significant differences. These field results indicate that a low concentration of fungicide and a high concentration of SDTB038 can be effective in controlling potato late blight. Foliar detection showed that lipopeptides have an inhibitory effect on P. infestans. The amplification of lipopeptide genes revealed surfactin (srfAB and srfAC) and fengycin (fenB) genes in SDTB038, but only surfactin production by B. velezensis SDTB038 was observed by ultra-high-performance liquid chromatography-quadrupole-time-of-flight mass spectrometry analysis. Therefore, the strain B. velezensis SDTB038 can produce secondary metabolites that help potato plants resist late blight development, can effectively inhibit the infection of potato leaves by P. infestans, and has potential value for development as a biological pesticide against potato late blight.

Evaluation of the symbiotic performance of tomato plants inoculated with Bacillus velezensis NKG-2 and challenged with Fusarium wilt pathogen

There has been an increased interest in investigating how plants interact with microbes by inoculation of bacteria that promote plant growth. In this study, the effect of co-inoculation of tomato seedlings with B. velezensis NKG-2 and induction of plant defense response against F. oxysporum f. sp. lycopersici was assessed in greenhouse assay. This antagonistic strain protected tomato plants from the detrimental effect of Fusarium oxysporum f. sp. lycopersici, reducing the Fusarium wilt incidence. The plant fitness parameters (total chlorophyll and shoot nitrogen contents) from the plants inoculated with NKG-2 and fungal-pathogen-challenged plants were significantly higher than those in un-inoculated challenged plants. NKG-2-inoculated plants improved its root surface colonisation by forming biofilm-like structures and protected the plants against infectious pathogens. The results showed in this work will help to expand our understanding of the mode of action of NKG-2 as a biological control agent and consequently, its application in agriculture.

In vitro antifungal activity of endophytic bacteria isolated from date palm (Phoenix doctylifera L.) against fungal pathogens causing leaf spot of date palm

BackgroundDate palm ((Phoenix doctylifera L.) suffers from several fungal diseases. The endophytic microorganisms present in higher plants generally offer protection to their host plants against invading phytopathogenic fungi and bacteria. In the present study, endophytic bacteria associated with date palm leaves were isolated and their in vitro antagonistic potential against fungal pathogens causing leaf spots in date palm was demonstrated.ResultsEndophytic bacteria were isolated from date palm leaves of 3 different cultivars viz., Nighal, Khalas and Khinaizi and evaluated for their inhibitory activity against leaf spot pathogens of date palm viz., Fusarium solani, Alternaria sp., Nigrospora sp., Thieloviopsis sp., Curvularia subpapendrofii and Tilletiopsis minor using an in vitro dual culture assay. Of the 24 endophytic bacterial strains tested, the endophytes designated B1, B7, B8 and B9 obtained from cv. Nighal showed inhibitory activities (more than 55% mycelial growth inhibition) against F. solani and Alternaria sp. None of the bacterial endophytes inhibited the growth of other fungal pathogens tested. These antagonistic bacterial strains were identified as Pantoea septica on the basis of 16S rRNA gene sequence analysis. The hyphae of F. solani and Alternaria sp. exhibited morphological abnormalities such as shrinkage and disintegration when grown in the presence of antagonistic bacterial endophytes. The cell-free culture filtrates of the bacterial endophytes caused inhibition of mycelial growth and induced leakage of electrolytes from the mycelia of F. solani and Alternaria sp. This is the first study that describes inhibition of the date palm pathogens F. solani and Alternaria sp. by P. septica.ConclusionEndophytic Pantoea septica strains isolated from date palm leaves inhibited the mycelial growth of F. solani and Alternaria sp. and induced morphological changes in their mycelia. The culture filtrates of these bacterial strains also inhibited the mycelial growth and caused leakage of electrolytes from the mycelia of F. solani and Alternaria sp. These promising bacterial strains can be exploited as biocontrol agents to control F. solani and Alternaria sp.-induced leaf spot diseases of date palm.

In-vitro compatibility assay of indigenous Trichoderma and Pseudomonas species and their antagonistic activities against black root rot disease (Fusarium solani) of faba bean (Vicia faba L.)

BackgroundFaba bean (Vicia faba L.) cultivation is highly challenged by faba bean black root rot disease (Fusarium solani) in high lands of Ethiopia. To ensure sustainable production of faba beans, searching for eco-friendly disease management options is necessary to curb the progress of the disease timely. The indigenous biocontrol agents that suit local environments may effectively strive with in-situ microorganisms and suppress local pathogen strains. This study aimed to screen antagonistic indigenous compatible Trichoderma and Pseudomonas strains against Fusarium solani. In the pathogenicity test, soil-filled pots were arranged in complete random block design and sown with health faba bean seeds. The effect of some fungicides was evaluated against Fusarium by food poisoning methods to compare with the biocontrol agents. The antagonistic efficacy of biocontrol agents and their compatibility was investigated on Potato dextrose agar medium.ResultsFusarium solani AAUF51 strain caused an intense root rotting in faba bean plant. The effect of Mancozeb 80% WP at 300 ppm was comparable with Trichoderma and Pseudomonas strains against Fusarium. The mycelial growth of test the pathogen was significantly (P ≤ 0.05) reduced to 86.67 and 85.19% by Trichoderma harzianum AAUW1 and Trichoderma viridae AAUC22 strains in dual culture, respectively. The volatile metabolites of Pseudomonas aeruginosa AAUS31 (77.78%) found the most efficient in reducing mycelial growth of Fusarium followed by Pseudomonas fluorescens AAUPF62 (71.11%) strains. The cell-free culture filtrates of Pseudomonas fluorescens AAUPF62 and Pseudomonas aeruginosa AAUS31 were more efficient than the Trichoderma strain in reducing the growth of Fusarium isolates. There was no zone of inhibition recorded between Trichoderma harzianum AAUW1, Trichoderma viridae AAUC22, Pseudomonas aeruginosa AAUS31, and Pseudomonas fluorescens AAUPF62 strains, hence they were mutually compatible.ConclusionsThe compatible Trichoderma and Pseudomonas strains showed antagonistic potentiality that could be explored for faba bean protection against black root rot disease and might have a future dual application as biocontrol agents.

EFECTO DE ESPECIES DE Trichoderma SOBRE LA INCIDENCIA DE F. verticillioides EN CUATRO GENOTIPOS DE MAÍZ

&lt;div class="page" title="Page 1"&gt;&lt;div class="layoutArea"&gt;&lt;div class="column"&gt;&lt;p class="CuerpoA"&gt;&lt;strong&gt;Background. &lt;/strong&gt;&lt;em&gt;Fusarium verticillioides&lt;/em&gt; is a fungus most frequently isolated from corn cobs and the most widely distributed in the world; affecting a wide range of hosts and contaminated products with mycotoxins. &lt;strong&gt;Objective.&lt;/strong&gt; The present study aimed to determine the incidence of &lt;em&gt;F. verticillioides&lt;/em&gt; in four maize genotypes treated with &lt;em&gt;Trichoderma&lt;/em&gt; strains as biocontrol under field conditions. &lt;strong&gt;Methodology. &lt;/strong&gt;Three &lt;em&gt;Trichoderma&lt;/em&gt; strains were inoculated by three inoculation methods to test their effectiveness in controlling the fungus &lt;em&gt;F. verticillioide&lt;/em&gt;s. Four maize genotypes were used to determine this effect. The antagonist strains were inoculated at sowing time as seed inoculation and foliar spray applied in stage R2 and R3.&lt;strong&gt; Results. &lt;/strong&gt;&lt;em&gt;Fusarium verticillioides&lt;/em&gt; was identified morphologically and molecularly. The three strains significantly reduced the incidence of the fungus, however &lt;em&gt;T. harzianum&lt;/em&gt; T1-4 was the one that presented the best control. The evaluated methods, seed inoculation and foliar spraying evaluated simultaneously significantly reduced the incidence of the phytopathogen. The Mestizo Diamante genotype presented a better response to the invasion by &lt;em&gt;F. verticillioides&lt;/em&gt; in interaction with the antagonist strains. &lt;strong&gt;Implications. &lt;/strong&gt;Due to the limited field work for the biological control of &lt;em&gt;F. verticillioides&lt;/em&gt;, the present results contribute to this scarce information. &lt;strong&gt;Conclusion. &lt;/strong&gt;&lt;em&gt;Trichoderma&lt;/em&gt; species reduced the incidence of &lt;em&gt;F. verticillioides&lt;/em&gt; in maize genotypes from the state of Veracruz.&lt;/p&gt;&lt;/div&gt;&lt;/div&gt;&lt;/div&gt;