Bacillus sp. BS061 Suppresses Powdery Mildew and Gray Mold

Microbial Biofungicides as a Substitute for Chemical Fungicides in the Control of Phytopathogens: Current Perspectives and Research Directions

These days, two important issues are causing concern in the global community: the alarmingly growing trend of the human population and the issue of food security. To this end, people around the world have been searching for solutions that could feed the needy in a sustainable way. In response to this urgent call, scientists from around the world started working on increasing crop production and productivity by controlling crop pathogens that could harm the productivity of crops. Synthetic fungicides have been in use for controlling crop diseases for several decades, but later, due to the evidenced side effects of the fungicides, there have been attempts to shift towards a less cost-effective and eco-friendly method of controlling crop diseases, and so far, many remarkable results have been achieved. However, due to the less effective and shorter shelf life of microbial biofungicides, as well as the less accessibility of these microbial biofungicides to growers around the world, it became difficult to remove the fungicides totally from the market. To minimize this problem, researchers suggested an integrated approach: the combination of microbial biofungicides with a reduced dose of synthetic fungicides. Hence, this review explored the status as well as the merits and demerits of microbial biofungicides as compared to synthetic fungicides.

Long-Chain Molecules with Agro-Bioactivities and Their Applications

Long-chain molecules play a vital role in agricultural production and find extensive use as fungicides, insecticides, acaricides, herbicides, and plant growth regulators. This review article specifically addresses the agricultural biological activities and applications of long-chain molecules. The utilization of long-chain molecules in the development of pesticides is an appealing avenue for designing novel pesticide compounds. By offering valuable insights, this article serves as a useful reference for the design of new long-chain molecules for pesticide applications.

Waterlogging stress alters the structure of sugar beet rhizosphere microbial community structure and recruiting potentially beneficial bacterial

Waterlogging has been shown to have a significant inhibitory effect on plant growth. However, the response mechanisms of the soil environment of sugar beet seedlings under waterlogging conditions still need to be fully understood. This study aimed to investigate the effects of waterlogging treatments on the content of effective nutrients and the microbial communities in the rhizosphere and non-rhizosphere using high-throughput sequencing. We set up waterlogging and non-waterlogging treatments, sampled sugar beet seedlings after 10 days of waterlogging, determined the effective soil nutrients in the rhizosphere and non-rhizosphere of the plants, and analyzed the differences in microbial diversity at ten days of waterlogging. The results showed that waterlogging significantly affected available potassium (AK) content. The Ak content of waterlogged soil was significantly higher than that of non-waterlogged soil. Waterlogging caused no significant difference in available nitrogen (AN) content and pH. Moreover, the plant growth-promoting bacteria Pseudomonas was significantly enriched in sugar beet waterlogged rhizospheres compared with the non-waterlogged ones. Similarly, the harmful fungi Gibellulopsis and Alternaria were enriched in sugar beet non-waterlogged rhizosphere. The network analysis revealed that waterlogging built a less complex root-microbial network than non-waterlogging. These findings implied that sugar beets subjected to waterlogging stress were enriched with beneficial microorganisms in the rhizosphere, potentially alleviating the stress.

Unlocking antagonistic potential of Bacillus amyloliquefaciens KRS005 to control gray mold

To establish a safe, efficient, and simple biocontrol measure for gray mold disease caused by Botrytis cinerea, the basic characteristics and antifungal activity of KRS005 were studied from multiple aspects including morphological observation, multilocus sequence analysis and typing (MLSA-MLST), physical-biochemical assays, broad-spectrum inhibitory activities, control efficiency of gray mold, and determination of plant immunity. The strain KRS005, identified as Bacillus amyloliquefaciens, demonstrated broad-spectrum inhibitory activities against various pathogenic fungi by dual confrontation culture assays, of which the inhibition rate of B. cinerea was up to 90.3%. Notably, through the evaluation of control efficiency, it was found that KRS005 fermentation broth could effectively control the occurrence of tobacco leaves gray mold by determining the lesion diameter and biomass of B. cinerea on tobacco leaves still had a high control effect after dilution of 100 folds. Meanwhile, KRS005 fermentation broth had no impact on the mesophyll tissue of tobacco leaves. Further studies showed that plant defense-related genes involved in reactive oxygen species (ROS), salicylic acid (SA), and jasmonic acid (JA)-related signal pathways were significantly upregulated when tobacco leaves were sprayed with KRS005 cell-free supernatant. In addition, KRS005 could inhibit cell membrane damage and increase the permeability of B. cinerea. Overall, KRS005, as a promising biocontrol agent, would likely serve as an alternative to chemical fungicides to control gray mold.

Plant growth-promoting microorganisms as biocontrol agents of plant diseases: Mechanisms, challenges and future perspectives

Plant diseases and pests are risk factors that threaten global food security. Excessive chemical pesticide applications are commonly used to reduce the effects of plant diseases caused by bacterial and fungal pathogens. A major concern, as we strive toward more sustainable agriculture, is to increase crop yields for the increasing population. Microbial biological control agents (MBCAs) have proved their efficacy to be a green strategy to manage plant diseases, stimulate plant growth and performance, and increase yield. Besides their role in growth enhancement, plant growth-promoting rhizobacteria/fungi (PGPR/PGPF) could suppress plant diseases by producing inhibitory chemicals and inducing immune responses in plants against phytopathogens. As biofertilizers and biopesticides, PGPR and PGPF are considered as feasible, attractive economic approach for sustainable agriculture; thus, resulting in a "win-win" situation. Several PGPR and PGPF strains have been identified as effective BCAs under environmentally controlled conditions. In general, any MBCA must overcome certain challenges before it can be registered or widely utilized to control diseases/pests. Successful MBCAs offer a practical solution to improve greenhouse crop performance with reduced fertilizer inputs and chemical pesticide applications. This current review aims to fill the gap in the current knowledge of plant growth-promoting microorganisms (PGPM), provide attention about the scientific basis for policy development, and recommend further research related to the applications of PGPM used for commercial purposes.

Endophytic bacteria from strawberry plants control gray mold in fruits via production of antifungal compounds against Botrytis cinerea L

Botrytis cinerea causes the gray mold disease in a wide range of plant hosts, especially in post-harvest periods. The control of this phytopathogen has been accomplished through the application of fungicides. However, this practice can cause environmental problems and increase fruit production costs. In addition, this fungus species has developed resistance to conventional synthetic fungicides. In this context, plant growth-promoting bacteria have shown potential for application in agricultural production because they are able to stimulate plant growth through different mechanisms, including the biological control of phytopathogens (indirect growth promotion mechanism). The aim of this work was to evaluate in vitro and in fruits the potential for indirect plant growth-promotion of bacteria isolated from strawberry leaves and roots. Dual plate method and inverted plate method were used to verify the ability of controlling in vitro the growth of Botrytis cinerea via the production of diffusible and volatile antifungal compounds, respectively. The effect of six bacterial isolates that showed greater potential for biological control in vitro was evaluated by scanning electron microscopy. Antifungal compounds produced by these bacterial isolates were identified by liquid chromatography coupled with mass spectrometry. Six bacterial strains were tested on strawberry pseudofruits. Five selected strains belong to the genus Bacillus and one to the genus Pantoea sp. Selected strains were able to inhibit more than 80 % of the mycelial growth of B. cinerea by the production of diffusible compounds and 90 % by volatile antifungal compounds production. Scanning electron microscopy showed the intense degradation of fungal hyphae caused by the presence of all bacterial strains. Bioactive compounds (salycilamide, maculosin, herniarin, lauroyl diethanolamide, baptifoline, undecanedioic acid, botrydial, 8 3-butylidene-7-hydroxyphthalide and N-(3-oxo-henoyl)-homoserine lactone) were obtained from liquid culture of these strains and extraction with ethyl acetate. All six isolates tested in vivo reduced the incidence of gray mold in strawberry pseudofruits in postharvest. It is concluded that isolates 26, 29, 65, 69, 132 (Bacillus sp.) and MQT16M1 (Pantoea sp.) have potential application for the biological control of Botrytis cinerea in strawberry via the production of diffusible and volatile antifungal compounds.

Bacillus strain selection with plant growth-promoting mechanisms as potential elicitors of systemic resistance to gray mold in pepper plants

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Bacillus licheniformis induced resistance against gray mold in pepper plants.

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Bacillus licheniformis and Bacillus pumilus inhibited the growth of Botrytis cinerea and Fusarium solani.

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Plant growth promoting mechanisms were confirmed by isolated Bacillus strains.

Certain soil bacteria produce beneficial effects on the growth and health of plants; hence, their use is steadily increasing. Five strains of Bacillus with plant growth-promoting potential were selected in this study, which produced indole-3-acetic acid levels below 50 µg.mL⁻¹. On the other hand, while only strains M8 and M15 dissolved phosphorus, the latter was the only strain that did not produce siderophores. Only strains M8 and M16 significantly inhibited the in vitro growth of Botrytis cinerea and Fusarium solani phytopathogens, whose inhibition ranges fluctuated between 60% and 63% for strains M8 and M16 against B. cinerea and between 40% and 53% for strains M8 and M16 against F. solani. Based on these results, the need to implement resistance induction against gray mold on pepper plants was determined using strains M8 and M16. In this case, strain M16 inhibited the propagation of the necrotic spot by approximately 70%, whereas strain M8 significantly reduced the superoxide dismutase activity in systemic leaves, which substantially increased in plants inoculated with strain M8 and infected with the pathogen. Accordingly, the use of native rhizobacteria may entail biotechnological progress for the integrated management of crops in agriculture industry.

Acute toxicity of triflumizole to freshwater green algae Chlorella vulgaris

Triflumizole is one of imidazole fungicides that works by inhibiting ergosterol biosynthesis, and is widely used for the control of powdery mildew and scabs on various fruits and crops. Triflumizole residue has been frequently detected in soil and aquatic ecosystems. While many studies have focused on its toxic effect on terrestrial and aquatic animals, little attention has been paid to aquatic algae, the primary producers of aquatic environments. Therefore, we evaluated the acute (96 h) toxicity effects of triflumizole on the freshwater algae Chlorella vulgaris, by examining growth, cell morphology, photosynthesis, and oxidative stress. The results showed that the 96 h median inhibition concentration (96 h-EC₅₀) was 0.82 mg/L (95% confidential interval 0.70-0.98 mg/L).The growth of algal cells was conspicuously inhibited by triflumizole exposure, and the cell surfaces appeared to be shrunkThe chlorophyll content (including Chl-a, Chl-b and T-Chl) dramatically decreased at triflumizole concentrations of 0.2 and 1.0 mg/L. In addition, the transcript abundance of photosynthesis-related genes (psaB, psbC and rbcL) showed obvious decreases in above treatments after 96 h of exposure to triflumizole. Moreover, the algal growth inhibition was accompanied by an increase in intracellular reactive oxygen species and malondialdehyde content, as well as increased activity of antioxidant enzymes such as superoxide dismutase and peroxidase, indicating oxidative stress and lipid peroxidation. Our findings reveal that triflumizole has potential toxicity to the primary producers (freshwater algae) in aquatic ecosystems.

Development of triflumizole ionic liquids containing anions of natural origin for improving the utilization and minimizing the adverse impacts on aquatic ecosystems

Triflumizole, a broad-spectrum systemic fungicide, has been widely used for the management of fungal diseases in plants. However, rapid photolysis and high risk to the aquatic environment limit its application. Ionic liquid (IL) forms of active pharmaceutical ingredients are innovative and promising agents that can optimize the application of the starting chemicals through the selection, or functionalization of the counterions (cation or anion). In this study, triflumizole was paired with various natural organic acids to develop novel ILs for improving the physicochemical properties and reducing the toxicity to fish. The results showed that the obtained ILs had low surface tension and lipophilicity and could protect triflumizole against degradation under UV irradiation as well as exhibit more excellent biological activity against Botrytis cinerea than triflumizole. The IL forms of triflumizole reduced the dosage and frequency of this fungicide, accordingly minimized the negative effect on environment. The IL contained salicylic acid as anion decreased > 4-fold toxicity to adult zebrafish over TFM. The results reported here create new application possibilities for imidazole fungicides and offer some heuristic rules for the design of active pharmaceutical ingredients-ionic liquids.

Influence of agro-environmental pollutants on a biocontrol strain of Bacillus velezensis

Metal- and pesticide-tolerant biocontrol agents are preferred in integrated pest management, as such strains can be applied in combination with different pesticides. The Bacillus velezensis strain SZMC 6161J proved to be sensitive to copper, nickel, zinc, and cadmium, while manganese elevated its growth. At concentrations higher than 1 mmol L^-1 , zinc and iron inhibited the chymotrypsin-like activity of this strain. In addition, trypsin-like protease and palmitoyl esterase activities were insensitive to all tested heavy metals in the applied concentration range. We studied the effects of some widely used herbicides and fungicides on the growth of this strain. The presence of sulfonylurea herbicides, like bensulfuron-methyl, cinosulfuron, chlorsulfuron, ethoxysulfuron, triasulfuron, and primisulfuron-methyl strongly inhibited the biomass production of the strain even at the concentration of 6.25 mg L^-1 . Glyphosate also inhibited the growth above 30 mg L^-1 . Similarly, contact fungicides like captan, maneb, mancozeb, and thiram resulted in total inhibition at the concentration as low as 6.25 mg L^-1 . Interestingly, the sterol-biosynthesis-inhibiting fungicides imazalil, fenarimol, penconazole, and tebuconazole also proved to be potent inhibitors. Heavy metal- and fungicide-tolerant strains were isolated from the parental strain and their antagonistic abilities were evaluated. There was no substantial difference between the antagonism capability of wild-type strain and the resistant mutants.

Importance of prumycin produced by Bacillus amyloliquefaciens SD-32 in biocontrol against cucumber powdery mildew disease

BACKGROUND

Powdery mildew disease of cucurbits is caused mainly by Podosphaera fusca, which is one of the most important limiting factors in cucurbit production worldwide. Previously we reported that Bacillus amyloliquefaciens biocontrol strain SD-32 produces C₁₇ bacillomycin D and [Ile 2002]surfactin, and that these metabolites play important roles in SD-32's biocontrol over cucumber gray mold disease. Our further investigation demonstrated that the culture broth and its supernatant suppressed cucumber powdery mildew disease in greenhouse experiments. However, the active principle(s) remained unknown.

RESULTS

The active compound was isolated from the culture supernatant after anti-powdery mildew disease activity-guided purification and identified as prumycin. Prumycin significantly suppressed the disease, whereas bacillomycin D and [Ile 2002]surfactin did not. Prumycin did not induce the expression of plant defense genes (PR1a and VSP1), suggesting that it does not act via plant defense response. Light microscopic observations of prumycin-treated cucumber cotyledon suggested that prumycin inhibits the conidial germination of P. fusca.

CONCLUSION

This study demonstrates that prumycin is a major factor in SD-32's suppression of cucumber powdery mildew disease. Our findings shed light for the first time on prumycin's role in biocontrol by Bacillus against this disease. © 2017 Society of Chemical Industry.

Entomopathogenic Fungi as Dual Control Agents against Both the Pest Myzus persicae and Phytopathogen Botrytis cinerea

The green peach aphid (Myzus persicae), a plant pest, and gray mold disease, caused by Botrytis cinerea, affect vegetables and fruit crops all over the world. To control this aphid and mold, farmers typically rely on the use of chemical insecticides or fungicides. However, intensive use of these chemicals over many years has led to the development of resistance. To overcome this problem, there is a need to develop alternative control methods to suppress populations of this plant pest and pathogen. Recently, potential roles have been demonstrated for entomopathogenic fungi in endophytism, phytopathogen antagonism, plant growth promotion, and rhizosphere colonization. Here, the antifungal activities of selected fungi with high virulence against green peach aphids were tested to explore their potential for the dual control of B. cinerea and M. persicae. Antifungal activities against B. cinerea were evaluated by dual culture assays using both aerial conidia and cultural filtrates of entomopathogenic fungi. Two fungal isolates, Beauveria bassiana SD15 and Metarhizium anisopliae SD3, were identified as having both virulence against aphids and antifungal activity. The virulence of these isolates against aphids was further tested using cultural filtrates, blastospores, and aerial conidia. The most virulence was observed in the simultaneous treatment with blastospores and cultural filtrate. These results suggest that the two fungal isolates selected in this study could be used effectively for the dual control of green peach aphids and gray mold for crop protection.

Development of a Biofungicide Using a Mycoparasitic Fungus Simplicillium lamellicola BCP and Its Control Efficacy against Gray Mold Diseases of Tomato and Ginseng

To develop a commercial product using the mycoparasitic fungus Simplicillium lamellicola BCP, the scaleup of conidia production from a 5-l jar to a 5,000-l pilot bioreactor, optimization of the freeze-drying of the fermentation broth, and preparation of a wettable powder-type formulation were performed. Then, its disease control efficacy was evaluated against gray mold diseases of tomato and ginseng plants in field conditions. The final conidial yields of S. lamellicola BCP were 3.3 × 10⁹ conidia/ml for a 5-l jar, 3.5 × 10⁹ conidia/ml for a 500-l pilot vessel, and 3.1 × 10⁹ conidia/ml for a 5,000-l pilot bioreactor. The conidial yield in the 5,000-l pilot bioreactor was comparable to that in the 5-l jar and 500-l pilot vessel. On the other hand, the highest conidial viability of 86% was obtained by the freeze-drying method using an additive combination of lactose, trehalose, soybean meal, and glycerin. Using the freeze-dried sample, a wettable powder-type formulation (active ingredient 10%; BCP-WP10) was prepared. A conidial viability of more than 50% was maintained in BCP-WP10 until 22 weeks for storage at 40°C. BCP-WP10 effectively suppressed the development of gray mold disease on tomato with control efficacies of 64.7% and 82.6% at 500- and 250-fold dilutions, respectively. It also reduced the incidence of gray mold on ginseng by 65.6% and 81.3% at 500- and 250-fold dilutions, respectively. The results indicated that the new microbial fungicide BCP-WP10 can be used widely to control gray mold diseases of various crops including tomato and ginseng.

Bacillus sp. BS061 Suppresses Gray Mold and Powdery Mildew through the Secretion of Different Bioactive Substances

A Bacillus sp. BS061 significantly reduced disease incidence of gray mold and powdery mildew. To identify the active principle, the culture filtrate was partitioned between butanol and water. The antifungal activity against B. cinerea was evident in the butanol-soluble portion, and active substances were identified as cyclic lipopeptides, iturin A series, by nuclear magnetic resonance spectrometry (NMR) and mass analysis. Interestingly, antifungal activity against powdery mildew was observed in the water-soluble portion, suggesting that cyclic lipopeptides have no responsibility to suppress powdery mildew. This finding reveals that biocontrol agents of Bacillus origin suppress gray mold and powdery mildew through the secretion of different bioactive substances.