Biological Control Of Diseases Research Articles

Crop rotation and fungicides impact microbial biomass, diversity and enzyme activities in the wheat rhizosphere

Sustainable crop production systems should promote large and diverse soil microbial communities to enhance biological soil processes rather than depend solely on chemical interventions that include pesticide applications. Crop rotation increases above-ground temporal diversity which, relative to monoculture, usually increases soil microbial diversity. But comparisons between short and long crop rotations that also include pesticide effects are rare. A 5-yr (2013-2017) field study was conducted to investigate crop rotation and fungicide effects on the soil microbiome and activity. There were nine rotations, with or without fungicide applications, that included four 2-yr rotations (wheat preceded by canola, barley, pea, or flax), four 3-yr rotations where barley or canola were added to the 2-yr rotations, and one rotation where canola and wheat were stacked (canola-canola-wheat-wheat). In 2017, soil microbial biomass, composition, diversity and enzyme activities were measured in the rhizosphere of the final wheat crop in each rotation. Fungicides reduced fungal richness (the number of different fungal taxa) in the wheat rhizosphere (e.g., Chao1 indices of 64.0 vs. 79.9) especially in 2-yr rotations, but rotation length/type and the crops that preceded wheat had different effects on different taxa. Two of the three most predominant prokaryotic phyla, Proteobacteriota and Actinobacteriota, responded differently to rotation length: 3-yr rotations enriched the former (27.4% vs. 20.1% relative abundances), but 2-yr rotations enriched the latter (19.9% vs. 28.3% relative abundances). Relative to oilseed crops preceding the sampled wheat, a field pea preceding crop enriched Actinobacteriota (31.7% vs. 24.8% relative abundances) and the most abundant fungal class, Sordariomycetes (39.1% vs. 22.1% relative abundances), in addition to increasing microbial biomass carbon (MBC) and arylsulphatase activity by 33% and 57%, respectively. Correlations of the relative abundances of fungal or prokaryotic genera with β-glucosidase and arylsulphatase activities were similar (both positive or negative), but they were the opposite of correlations with acid phosphomonoesterase, suggesting a close link between C and S cycling. Besides the nutrient cycling implications of these soil microbial characteristics, there is need to study their biological disease control significance.

Effectiveness of Bacillus and Pseudomonas Strains in Biological Control of Common Bacterial Blight Disease in Common Bean (Phaseolus vulgaris L.)

Effectiveness of Bacillus and Pseudomonas Strains in Biological Control of Common Bacterial Blight Disease in Common Bean (Phaseolus vulgaris L.)

Using metabolomics to explore the effects of epigenetic-modification strategies on the metabolites of Acanthus ilicifolius L. endophytic fungi against ovarian cancer

Ovarian cancer is a serious threat to women's health and safety. So far, people have discovered more than 130 small molecule compounds of natural origin for anti-tumor, of which approximately 50% are of microbial origin. The Acanthus ilicifolius L. species is primarily distributed in the Guangdong, Hainan, and Guangxi regions of China and grows in tidally accessible coastal areas. Recent studies have revealed that Acanthus ilicifolius L. extracts are endowed with a range of pharmacological properties, including anti-inflammatory, hepatoprotective, antioxidant, and antitumor activities. Endophytic fungi are commonly found in the healthy tissue and organs of medicinal plants. These fungi and the plants they inhabit form mutually beneficial symbiotic relationships. Endophytic fungi produce a series of secondary metabolites, with active substances having shown great economic value and applications prospects in drug research and development as well as for the biological control of plant diseases. Secondary metabolites production by endophytic fungi is regulated by specific gene clusters, and several techniques have been used to stimulate the secondary metabolic processes of fungi, including epigenetic-modification and OSMAC (one strain many compounds) strategies, co-culturing, and gene modification. Among these, epigenetic modification has been shown to be effective; this strategy involves the addition of small-molecule epigenetic modifiers to the culture medium, thereby activating silenced biosynthetic gene clusters without altering the DNA sequences of the fungi. This approach facilitates the expression of silenced genes in endophytic fungi, thereby increasing the number and diversity of secondary metabolites. Furthermore, it assists in overcoming the inhibition of microbial secondary-metabolite synthesis under laboratory conditions, and enhances silenced-gene expressions. The advent of novel analytical techniques and bioinformatics has provided a comprehensive, multifaceted, and holistic understanding of fungal metabolism through the development of metabolomics as a research platform. However, few studies have combined anti-ovarian cancer-activity screening with metabolomic approaches in the search for activity-differentiating metabolites from endophytic fungi under the intervention of epigenetic modifiers. Herein, we investigated the impact of epigenetic modifiers on the secondary metabolites of the endophytic Diaporthe goulteri fungus from Acanthus ilicifolius L. to determine their potential anti-ovarian cancer activities. Crude extracts were obtained by controlling three variables: the number of fermentation days, the type of epigenetic modifier, and its concentration, with activities screened using the CCK-8 (cell counting kit-8) method. Ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was subsequently employed for non-targeted metabolomic analysis. A multivariate statistical analysis model was constructed using principal component analysis and orthogonal partial least squares-discriminant analysis, which combines model and variable importance projection, with qualitative screening performed and significant changes (variable importance in the projection (VIP)≥1; P<0. 05) determined. Fifteen differential metabolites were identified in the fungal and epigenetic modification group, primarily comprising polyketides, amino acids, derivatives, alkaloids, and organic acids, including prenderol, glycine, valine, 2-ethylcaproic acid, rubratoxin B, finasteride, 6-silaspiro[5.5]undecane, 1-(2-nitrophenoxy)octane, heptadecene, 1-pentadecene, 11-ketoetiocholanolone, 3-(1-ethyl-1,3,3-trimethyl-2,3-dihydro-1H-inden-5-yl)butanal, N2-benzoylarginine, tabutrex, (3aR,6S,6aS)-6-(4-hydroxy-2-methoxy-2-butanyl)-4,4-dimethylhexahydro-1(2H)-pentalenone, and 8-aminoquinoline. The expressions of prenderol, 1-(2-nitrophenoxy)octane, 3-(1-ethyl-1,3,3-trimethyl-2,3-dihydro-1H-inden-5-yl)butanal, N2-benzoylarginine, and 8-aminoquinoline were downregulated, whereas the expressions of the remaining 10 substances were upregulated. Polyketides were the main components that exhibited higher expressions. This study showed that latent active differential metabolites can be searched by combining anti-ovarian cancer-activity screening with metabolomics analysis, thereby providing a reference for the further development of Acanthus ilicifolius L. resources and the subsequent targeted isolation of active compounds.

Application of microorganisms in Panax ginseng: cultivation of plants, and biotransformation and bioactivity of key component ginsenosides.

Panax ginseng is a precious Chinese medicinal plant with a long growth cycle and high medicinal value. Therefore, it is of great significance to explore effective ways to increase its yield and main active substance content to reduce the cost of ginseng, which is widely used in food and clinical applications. Here, we review the key roles of microorganisms in the biological control of ginseng diseases, enhancement of ginseng yield, biotransformation of ginsenosides, and augmentation of ginsenoside bioactivity. The application of microorganisms in P. ginseng faces multiple challenges, including the need for further exploration of efficient microbial strain resources used in the cultivation of ginseng and biotransformation of ginsenosides, lack of microbial application in large-scale field cultivation of ginseng, and unclear mechanism of microbial transformation of ginsenosides. This review provides a deeper understanding of the applications of microorganisms in P. ginseng.

Genome analysis of Streptomyces recifensis SN1E1 to investigate mechanisms for inhibiting fire blight disease.

Fire blight, attributed to the bacterium Erwinia amylovora, significantly damages economically important crops, such as apples and pears. Conventional methods for managing fire blight involve the application of chemical pesticides, such as streptomycin and oxytetracycline. Nevertheless, apprehensions are increasing regarding developing antibiotic and pesticide-resistant strains, compounded by documented instances of plant toxicity. Here, we present that Streptomyces recifensis SN1E1 has exhibited remarkable efficacy in suppressing apple fire blight disease. This study aims to unravel the molecular-level antimicrobial mechanisms employed by the SN1E1 strain. We identified four antimicrobial-associated biosynthetic gene clusters within the genomics of S. recifensis SN1E1. To validate antimicrobial activity against E. amylovora, knock-out mutants of biosynthetic genes linked to antimicrobial activity were generated using the CRISPR/Cas9 mutagenesis system. Notably, the whiE4 and phzB deficient mutants displayed statistically reduced antibacterial activity against E. amylovora. This research establishes a foundation for environmental and biological control studies. The potential utilization of environmentally friendly microbial agents derived from the SN1E1 strain holds promise for the biological control of fire blight disease.

Isolation of a novel Bacillus subtilis HF1 strain that is rich in lipopeptide homologs and has strong effects on the resistance of plant fungi and growth improvement of broilers.

Bacillus subtilis is an important probiotic microorganism that secretes a variety of antimicrobial compounds, including lipopeptides, which are a class of small molecule peptides with important application value in the fields of feed additives, food, biopesticides, biofertilizers, medicine and the biological control of plant diseases. In this study, we isolated a novel B. subtilis HF1 strain that is rich in lipopeptide components and homologs, has a strong antagonistic effect on a variety of plant fungi, and is highly efficient in promoting the growth of broilers. The live B. subtilis HF1 and its fermentation broth without cells showed significant inhibitory effects on 20 species of plant fungi. The crude extracts of lipopeptides in the fermentation supernatant of B. subtilis HF1 were obtained by combining acid precipitation and methanol extraction, and the lipopeptide compositions were analyzed by ultrahigh-performance liquid chromatography with quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS). The results showed that HF1 could produce 11 homologs of surfactin and 13 homologs of fengycin. Among the fengycin homologs, C13-C19 fengycin A and C15-C17 fengycin B were identified; among the surfactin homologs, C11-C17 surfactin A and C13-C16 surfactin B were characterized. C13 fengycin A, C11 surfactin A and C17 surfactin A were reported for the first time, and their functions are worthy of further study. In addition, we found that HF1 fermentation broth with and without live cells could be used as a feed additive to promote the growth of broilers by significantly increasing body weight up to 15.84%. HF1 could be a prospective strain for developing a biocontrol agent for plant fungal diseases and an efficient feed additive for green agriculture.

Determination of the prevalence of fungi associated with amaranth cultivation in the locality of Kombé, Republic of Congo

Amaranth is a nutrient-rich leafy vegetable. Phytopathogenic fungi are causing major losses in amaranth crop production in the Kombé area. The detection of these phytopathogenic fungi can play an important role. The aim of this study is to assess the abundance of endophytic and saprophytic fungi associated with amaranth cultivation in Brazzaville, with a view to recommending biological control of fungal diseases. The prevalence of fungi associated with amaranth began with a survey, then continued in the laboratory. During the survey, 15 amaranth and soil samples were then collected separately in different stomacher bags, labelled and shipped to the laboratory where they were stored in a refrigerator at 4°C for four (4) weeks for analysis. In the laboratory, endophytic and saprophytic fungi were isolated using the fresh-state inoculation method for endophytic fungi and the suspension-dilution method for saprophytic fungi. The isolated strains were identified by determining their macroscopic and microscopic characteristics. The phytosanitary survey revealed that the most dominant symptom on amaranth plants in Kombé was wilting (42.86%). The results obtained from the distribution of endophyte isolates by colour indicate the presence of 5 isolates of unidentified endophytic fungi obtained from the leaf organ. Through isolation and microscopic analysis of soil saprophytes, six genera of fungi were identified: Botrytis cineara, Rhizoporus sp, Penicillium sp, Mucor sp, Scedospirium sp and Curvularia sp.

Regulatory mechanism of C4-dicarboxylates in cyclo (Phe-Pro) production

Cyclo (Phe-Pro) (cFP), a cyclic dipeptide with notable antifungal, antibacterial, and antiviral properties, shows great promise for biological control of plant diseases. Produced as a byproduct by non-ribosomal peptide synthetases (NRPS), the regulatory mechanism of cFP biosynthesis remains unclear. In a screening test of 997 Tn5 mutants of Burkholderia seminalis strain R456, we identified eight mutants with enhanced antagonistic effects against Fusarium graminearum (Fg). Among these, mutant 88’s culture filtrate contained cFP, confirmed through HPLC and LC-MS, which actively inhibited Fg. The gene disrupted in mutant 88 is part of the Dct transport system (Dct-A, -B, -D), responsible for C4-dicarboxylate transport. Knockout mutants of Dct genes exhibited higher cFP levels than the wild type, whereas complementary strains showed no significant difference. Additionally, the presence of exogenous C4-dicarboxylates reduced cFP production in wild type R456, indicating that these substrates negatively regulate cFP synthesis. Given that cFP synthesis is related to NRPS, we previously identified an NRPS cluster in R456, horizontally transferred from algae. Specifically, knocking out gene 2061 within this NRPS cluster significantly reduced cFP production. A Fur box binding site was predicted upstream of gene 2061, and yeast one-hybrid assays confirmed Fur protein binding, which increased with additional C4-dicarboxylates. Knockout of the Fur gene led to up-regulation of gene 2061 and increased cFP production, suggesting that C4-dicarboxylates suppress cFP synthesis by enhancing Fur-mediated repression of gene 2061.

Biocontrol of Fusarium oxysporum-infested Gastrodia elata Bl. by Lactobacillus curvatus 2768-VOCs and mechanism of inhibition

Gastrodia elata Bl. Is susceptible to infestation by the fungus Fusarium oxysporum, which can cause severe post-harvest diseases. This paper presents the findings of an investigation into the control and bacteriostatic mechanisms of Lactobacillus curvatus 2768-VOCs on F. oxysporum-infected G. elata. The results of both in vitro and in vivo tests demonstrated that L. curvatus 2768-VOCs exhibited inhibitory effects against F. oxysporum, with inhibition rates of 63.37% and 44.4%, respectively. The results of the in vivo test also demonstrated that the pre-fumigation approach exhibited superior efficacy compared to direct fumigation, with the former showing a preventive effect. Furthermore, it was discovered that VOCs disrupted the integrity of F. oxysporum cell membranes and altered their permeability, resulting in the leakage of cell contents. The fumigation caused damage to the mycelial structure, accompanied by a notable decline in the total lipid and ergosterol content, and an appreciable increase in MDA content. Moreover, the fumigation of VOCs markedly diminished the activities of ATPase and mitochondrial dehydrogenase, thereby disrupting the respiration of F. oxysporum and its energy metabolism. The VOCs were subjected to GC-MS analysis, which revealed that the relative content of acids was the highest, particularly formic acid and glyoxalic acid. The study offers a theoretical basis for the biological control of postharvest diseases in G. elata.

The feeding behavior of Diaphorina citri monitored by using an electrical penetration graph (DC-EPG) on citrus plants treated with Bacillus cereus and Bacillus velezensis

Diaphorina citri, an important pest and insect vector that can transmit the pathogenic bacteria Candidatus Liberibacter asiaticus, causing Huanglongbing disease, is one of many challenges in citrus agriculture. Integrated pest management by utilizing microorganisms is a wise and efficient alternative without damaging the environment. Utilization of Plant Growth Promoting Rhizobacteria (PGPR), such as Bacillus cereus and B. velezensis, is a potential strategy for the biological control of plant diseases or insect vectors. By inducing systemic resistance in plants, PGPR can enhance plant defense against diseases and insect pests while activating molecular and physiological changes in plants. This research aimed to determine the effect of B. cereus and B. velezensis on the plant growth and feeding behavior of D. citri. The height and volume of the plant canopy were observed periodically for 6 months, while the feeding behavior of D. citri was monitored using the Electrical Penetration Graph (DC-EPG). The results showed increased height and volume of the citrus plant canopy treated with B. cereus, indicating that B. cereus could act as a PGPR. The application of B. cereus and B. velezensis to citrus seedlings affected the feeding behavior of D. citri. D citri showed difficulty in penetrating the phloem tissue of citrus plants.

Neg1 overexpression in Trichoderma harzianum T4 enhanced its ability to produce spores and antagonistic activity against phytopathogenic fungi.

Trichoderma harzianum T4 is a soil fungus that plays an important role in the biological control of plant diseases. The aim of this study was to functionally characterize the β-1,6-glucanase gene Neg1 in T. harzianum T4 and to investigate the effect of its overexpression on biocontrol traits, especially antagonism against pathogenic fungi. We found that overexpression of Neg1 did not affect growth of T. harzianum but enhanced sporulation of T. harzianum T4 cultures. Generally, spores are closely related to the defense ability of defense fungi and can assist their proliferation and improve their colonization ability. Secondly, overexpression of Neg1 also increased the secretion level of various hydrolytic enzymes and enhanced the antagonistic ability against phytopathogenic fungi of Fusarium spp. The results suggest that Neg1 is a key gene for improving the biocontrol effect of T. harzianum T4, which contributes to a better understanding of the mechanism of action of T. harzianum T4 as a fungal biocontrol agent.

A Review on Biocontrol Agents as Sustainable Approach for Crop Disease Management: Applications, Production, and Future Perspectives

Horticultural crops are vulnerable to diverse microbial infections, which have a detrimental impact on their growth, fruit quality, and productivity. Currently, chemical pesticides are widely employed to manage diseases in horticultural crops, but they have negative effects on the environment, human health, soil physiochemical properties, and biodiversity. Additionally, the use of pesticides has facilitated the development and spread of resistant pathovars, which have emerged as a serious concern in contemporary agriculture. Nonetheless, the adverse consequences of chemical pesticides on the environment and public health have worried scientists greatly in recent years, which has led to a switch to the use of biocontrol agents such as bacteria, fungi, and insects to control plant pathogens. Biocontrol agents (BCAs) form an integral part of organic farming, which is regarded as the future of sustainable agriculture. Hence, harnessing the potential of BCAs is an important viable strategy to control microbial disease in horticultural crops in a way that is also ecofriendly and can improve the soil health. Here, we discuss the role of the biological control of microbial diseases in crops. We also discuss different microbial-based BCAs such as fungal, bacterial, and viral and their role in disease management. Next, we discuss the factors that affect the performance of the BCAs under field conditions. This review also highlights the genetic engineering of BCAs to enhance their biocontrol efficiency and other growth traits. Finally, we highlight the challenges and opportunities of biocontrol-based disease management in horticulture crops and future research directions to boost their efficacy and applications.

Identification and biological control of bacterial leaf spot disease of cucurbits

Objective: The present study was conducted for isolation and detection of the phyto-pathogen responsible for bacterial leaf spot disease of cucurbits as well as evaluation of its biological control techniques. Methods: The pathogen of the disease was isolated from infected leaf of bitter gourd and cultured on Luria-Bertani (LB) growth medium. The morphological tests and biochemical tests revealed the isolated bacteria as gram negative. Furthermore, advanced molecular technique was applied to facilitate proper detection of the isolated bacteria. The PCR of the bacterial genomic DNA using specific primers generated clear band of approximately 1450 bp in gel electrophoresis. Results: In gram staining test, the bacterial strain was found to be rod shaped and pinkish in color and Gram-negative. All the biochemical test showed positive without mannitol salt agar. The nucleotide sequencing of 16S rDNA gene of the bacterial isolate showed 86.02% similarities with the original sequence of Xanthomonas cucurbitae. In antibiotic sensitivity assay, the antibiotic cefixime showed highest 28.0±0.7 mm diameter of inhibition zone against the tested bacteria. The highest antibacterial activity was 8.0±0.5 mm zone of inhibition by of Allium sativum. Conclusion: The present findings may be benevolent for the detection, characterization and development of biological control techniques to prevent the leaf spot disease of cucurbits crops in Bangladesh. It may help to find out the specific signaling pathway techniques for plant microbes relationship for disease formation in future.

Uptake and transport of antibiotic kasugamycin from leaves to roots in rice (Oryza sativa L.) seedlings

AbstractKasugamycin (KSM), an aminoglycoside antibiotic, has been widely used as a natural fungicide to control plant diseases, particularly for managing rice blast. However, its uptake mechanism and transport in rice remain to be explored. In this article, rice seedlings were treated by the foliar spraying method, and the content of KSM in rice leaves, stems and roots under different treatments was detected by high‐performance liquid chromatography tandem mass spectrometry (HPLC‐MS/MS), respectively. Results showed that leaf‐applied KSM could be transported to the phloem and migrate to roots and stems after uptake by leaves. Concentration, temperature and pH had significant effects on the uptake of KSM. Compared with the control, the competitive inhibitors d‐glucose and phlorizin both inhibited the uptake of KSM, demonstrating that sugar transporter proteins were involved in the uptake process. The energy inhibitors dinitrophenol (DNP) and carbonyl cyanide chlorophenylhydrazone (CCCP) also significantly inhibited the uptake of KSM, indicating that the uptake of KSM required energy consumption. Thus, the uptake of KSM by rice was an active process involving sugar transporter proteins, and it could migrate downward through the phloem. This study contributes to the promotion of the scientific application of antibiotics and the biological control of crop diseases. It will also provide a theoretical basis for the development of root‐targeted pesticides and transport pesticides with phloem mobility.

Biological control of the shot-hole disease in flowering cherry tree using antimicrobial compounds produced by Bacillus velezensis 8–2

BackgroundEffective control of shot-hole disease in flowering cherries is challenging because of multiple causative pathogens (bacteria and fungi). Bacillus species are well-known for their ability to control plant pathogens; therefore, biological control potential of a Bacillus isolate, B. velezensis 8–2, against SH disease on flowering cherry trees was investigated.ResultsThis study revealed strong antimicrobial activity of Bacillus velezensis 8–2 against various plant pathogenic bacteria and fungi, particularly focusing on Xanthomonas arboricola pv. pruni (Xap) and Mycosphaerella cerasella (Mc), which cause shot-hole (SH) disease in flowering cherry trees. In vitro assays showed that the fermentation filtrate of B. velezensis 8–2 inhibited bacterial and fungal growth with minimum inhibitory concentrations of 1.25–10% and 2.5–10%, respectively. UPLC-Q–Orbitrap–MS analysis revealed that B. velezensis 8–2 produced antagonistic compounds, including polyketides (difficidin and oxydifficidin) and cyclic lipopeptides (iturin A, fengycin, and surfatin). To enhance antimicrobial activity, fermentation parameters for optimal production of two antibacterial and three antifungal compounds were investigated in a 5 L jar fermenter. By regulating the agitation speed to sustain the state of vegetative cells, the production period was extended by 20 h at 400 rpm, resulting in maximum yields of 86.6 μg/mL for difficidin and 150.0 μg/mL for oxydifficidin within a 72 h fermentation period. In a field trial, a 500-fold diluted 10% suspension concentrate formulation of B. velezensis 8–2 effectively inhibited the development of SH disease, demonstrating 66.6% disease control and a 90.2% disease symptoms reduction.ConclusionsThis is the first report to assess the disease control efficacy of B. velezensis for the biocontrol of SH disease in the field. These results suggest that the application of B. velezensis 8–2 could serve as a practical alternative for managing various bacterial and fungal diseases, including the management of SH disease in flowering cherry trees.Graphical

Antifungal activity of Neowestiellopsis persica against Rhizoctonia solani in root and crown of Faba bean cultivated under modified BG-110 medium composition

Rhizoctonia solani, a fungal pathogen, affects the quality and yield of Faba bean crops and hinders plant export. Chemical fungicides effectively control fungal pathogens, but their long-term use harms the environment, soil properties, and human health. Cyanobacteria, a promising source of natural bioactive compounds, have shown efficacy against the fungal colony growth of various plant pathogens, highlighting the need for sustainable practices. As a result, this study examined the biological control of the Rhizoctonia solani disease that affects the Faba bean's root and crown. Disease assessments were then done in five groups: (1) healthy control; (2) control infected with Rhizoctonia solani and not treated with cyanobacterial extract; (3) plant infected with Rhizoctonia solani and treated with cyanobacterial extract suspension of 0.02, (4) 0.04, and (5) 0.08 g/L phosphate during 20 and 34 days. The results of the antioxidant activity by the 2,2-Diphenyl-1-picrylhydrazyl (DPPH) assay showed that with increasing phosphate concentration, the activity increased significantly. The results of enzymatic activity indicated that time did not significantly impact the enzymatic activity of glutathione peroxidase (GPx), catalase (CAT), and guaiacol peroxidase (GPX), with the highest and lowest activity being related to codes 2 and control, respectively. However, time had a significant effect on superoxidase dismutase (SOD) activity, with the highest activity reported on day 35. Moreover, the results showed that increasing the concentration of the extract significantly decreased cell viability in hepatoblastoma (HepG-2) cell lines. The cyanobacterial extract treatment caused over 66 % damage to plants infected with Rhizoctonia solani. The overall results indicated that Neowestiellopsis persica, grown under higher phosphate concentrations, can be used as an effective antifungal biocontrol against Rhizoctonia solani in Faba bean roots and crowns.

Antifungal effects of volatile organic compounds produced by Trichoderma hamatum against Neocosmospora solani.

Neocosmospora solani causes Fusarium wilt disease and root rot, which are serious problems worldwide. To determine the growth inhibition of Neocosmospora solani by Trichoderma hamatum volatile organic compounds (VOCs), the major chemical components of Trichoderma hamatum VOCs and the differences in their contents at different times were analysed, and the activity of these components was evaluated. The antifungal activity of Trichoderma hamatum was measured by a screening test, as Trichoderma hamatum exhibited strong antagonism against Neocosmospora solani in vitro. The double plate technique was used to verify the activity of Trichoderma hamatum VOCs, and the inhibition rate was 63.77%. Neocosmospora solani mycelia were uneven and expanded, the contents of the cells leaked, and the mycelia shrank and presented a diaphragm in the hyphae upon Trichoderma hamatum VOCs treatment. Trichoderma hamatum VOCs and their contents at different times were analysed by using gas chromatography-mass spectrometry. 6-Pentyl-2H-pyran-2-one clearly presented in greater amounts than the other components on day 3, 4, 5, and 6. VOCs from Trichoderma hamatum exhibited evident effects on the percentage of healthy fruit after day 3. Moreover, Trichoderma hamatum can improve the biological control of diseases caused by soilborne pathogens, and can be applied in biocontrol fields.

Determination of fermentation conditions of Streptomyces sp. VNUA116 to improve the antifungal activities against Fusarium oxysporum f.sp. cubense causing Panama wilt disease on banana plants

This study aims to identify medium components (carbon source, carbon concentration, nitrogen source) and fermentation conditions (temperature, pH) to enhance the resistance against Fusarium oxysporum f. sp. cubenseTropical Race 4 (Foc Tr4), causing Panama wilt disease of Streptomyces sp. VNUA116 (VNUA116). By using the agar well diffusion method, it was determined that strain VNUA116 has strong anti-fungal pathogen activities FocTr4 under fermentation nutrients: YIM 301 medium, carbon source CB1 (soluble starch 40 g/l: D-glucose 1 g/l, and nitrogen source N1 beef extract 3 g/l: yeast extract 5 g/l: peptone 3 g/l). Additionally, optimal fermentation conditions were established, including pH 7, and temperature 30oC. Strain VNUA116 exhibited the highest antifungal activity, reaching a diameter of 30.67±0.58 mm after 10 days of cultivation. Furthermore, under these optimised fermentation conditions, Streptomycessp. VNUA116 demonstrated an impressive inhibitory capability against Foc-Tr4, reaching up to 93.20%, equivalent to the concentration of the fungicide Ridomil gold 68WG at 3 g/l in laboratory conditions. This affirms the considerable potential of the VNUA116 strain for applications in the production of biofertilizers for the biological control of Panama wilt disease in banana plants.

Stress mitigation mechanism of rice leaf microbiota amid atmospheric deposition of heavy metals

Leaf microbiota have been extensively applied in the biological control of plant diseases, but their crucial roles in mitigating atmospheric heavy metal (HM) deposition and promoting plant growth remain poorly understood. This study demonstrates that elevated atmospheric HM deposition on rice leaves significantly shapes distinct epiphytic and endophytic microbiota across all growth stages. HM stress consistently leads to the dominance of epiphytic Pantoea and endophytic Microbacterium in rice leaves, particularly during the booting and filling stages. Leaf-bound HMs stimulate the differentiation of specialized microbial communities in both endophytic and epiphytic compartments, thereby regulating leaf microbial interactions. Metagenomic binning retrieved high-quality genomes of keystone leaf microorganisms, indicating their potential for essential metabolic functions. Notably, Pantoea and Microbacterium show significant HM resistance, plant growth-promoting capabilities, and diverse element cycling functions. They possess genes associated with metal(loid) resistance, such as ars and czc, suggesting their ability to detoxify arsenic(As) and cadmium(Cd). They also support carbon, nitrogen, and sulfur cycling, with genes linked to carbon fixation, nitrogen fixation, and sulfur reduction. Additionally, these bacteria may enhance plant stress resistance and growth by producing antioxidants, phytohormones, and other beneficial compounds, potentially improving HM stress tolerance and nutrient availability in rice plants. This study shows that atmospheric HMs affect rice leaf microbial communities, prompting plants to seek microbial help to combat stress. The unique composition and metabolic potential of rice leaf microbiota offer a novel perspective for mitigating adverse stress induced by atmospheric HM deposition. This contributes to the utilization of leaf microbiota to alleviate the negative impact of heavy metal deposition on rice development and food security.

Compatibility of Trichoderma harzianum with commercial herbicides

Biological disease control has become popular in recent years and has established itself as a viable alternative to chemical control. However, the efficiency of biological control can be limited by the application technology. Thus, the objective of this work was to evaluate the compatibility of Trichoderma harzianum with three commercial herbicides. The fungus was incubated in culture medium supplemented with doses of three commercial herbicides and incubated for 4 days. The CI50 (concentration capable of inhibiting 50% of the mycelial growth of the fungus) was determined for each herbicide and compared with the recommended doses for field application. All herbicides tested reduced mycelial growth, with CI50 lower than the recommended doses. The data suggest low compatibility between T. harzianum and the tested herbicides.