Changes in the Density and Composition of Rhizosphere Pathogenic Fusarium and Beneficial Trichoderma Contributing to Reduced Root Rot of Intercropped Soybean

Exploring Endophytic Fungi as Natural Antagonists against Fungal Pathogens of Food Crops

The yield and quality of cultivated food crops are frequently compromised by the prevalent threat from fungal pathogens that can cause widespread damage in both the pre-harvest and post-harvest stages. This paper investigates the challenges posed by fungal pathogens to the sustainability and yield of essential food crops, leading to significant economic and food security repercussions. The paper critiques the long-standing reliance on synthetic fungicides, emphasizing the environmental and health concerns arising from their widespread and occasionally inappropriate use. In response, the paper explores the potential of biological control agents, specifically endophytic fungi in advancing sustainable agricultural practices. Through their diverse symbiotic relationships with host plants, these fungi exhibit strong antagonistic capabilities against phytopathogenic fungi by producing various bioactive compounds and promoting plant growth. The review elaborates on the direct and indirect mechanisms of endophytic antagonism, such as antibiosis, mycoparasitism, induction of host resistance, and competition for resources, which collectively contribute to inhibiting pathogenic fungal growth. This paper consolidates the crucial role of endophytic fungi, i.e., Acremonium, Alternaria, Arthrinium, Aspergillus, Botryosphaeria, Chaetomium, Cladosporium, Cevidencealdinia, Epicoccum, Fusarium, Gliocladium, Muscodor, Nigrospora, Paecilomyces, Penicillium, Phomopsis, Pichia, Pochonia, Pythium, Ramichloridium, Rosellinia, Talaromyces, Trichoderma, Verticillium, Wickerhamomyces, and Xylaria, in biological control, supported by the evidence drawn from more than 200 research publications. The paper pays particular attention to Muscodor, Penicillium, and Trichoderma as prominent antagonists. It also emphasizes the need for future genetic-level research to enhance the application of endophytes in biocontrol strategies aiming to highlight the importance of endophytic fungi in facilitating the transition towards more sustainable and environmentally friendly agricultural systems.

Biocontrol Potential of Trichoderma Ghanense and Trichoderma Citrinoviride toward Pythium aphanidermatum

Pythium-induced damping-off of cucumber is a major constraint to cucumber production in different parts of the world. Although chemical fungicides are used for managing this disease, they have many drawbacks to the environment. The ability of the antagonistic fungi isolated from the rhizosphere and endosphere of Dactyloctenium robecchii and Moraea sisyrinchium in the control of soilborne pathogen Pythium aphanidermatum was inspected. Native Trichoderma isolates, Trichoderma ghanense and Trichoderma citrinoviride, were isolated from plant stem and soil samples collected from Al-Seeb, Oman. Using a dual culture technique, the antagonistic activity of the fungal isolates against P. aphanidermatum was examined in vitro. Among Trichoderma isolates, T. ghanense was more efficient in restraining the mycelial growth of P. aphanidermatum, causing an inhibition percentage of 44.6%. Further, T. citrinoviride induced significantly lower cessation of P. aphanidermatum mycelial growth (31.3%). Microscopic and electrolyte leakage inspection of the pathogen mycelia depicted extreme morphological malformations in their mycelium, which can be attributed to the antifungal metabolites of antagonists. Greenhouse studies demonstrated the effectivity of T. ghanense in controlling Pythium damping-off of cucumber plants, where the number of surviving plants was over 90% when the biocontrol agents were used compared to 0 in the control plants. Furthermore, treatment of the plants with the antagonists promoted growth characteristics of plants compared to uninoculated plants. This included improvements in shoot and root lengths, leaf length and width, and dry weight. These findings suggest that T. ghanense and T. citrinoviride can be developed as alternatives to synthetic chemical fungicides to manage soilborne pathogens of cucumber. This research is also the first to clarify the biocontrol ability of T. citrinoviride and T. ghanense against cucumber damping-off caused by P. aphanidermatum.

Pseudomonas chlororaphis IRHB3 assemblies beneficial microbes and activates JA-mediated resistance to promote nutrient utilization and inhibit pathogen attack

Introduction

The rhizosphere microbiome is critical to plant health and resistance. PGPR are well known as plant-beneficial bacteria and generally regulate nutrient utilization as well as plant responses to environmental stimuli. In our previous work, one typical PGPR strain, Pseudomonas chlororaphis IRHB3, isolated from the soybean rhizosphere, had positive impacts on soil-borne disease suppression and growth promotion in the greenhouse, but its biocontrol mechanism and application in the field are not unclear.

Methods

In the current study, IRHB3 was introduced into field soil, and its effects on the local rhizosphere microbiome, disease resistance, and soybean growth were comprehensively analyzed through high-throughput sequencing and physiological and molecular methods.

Results and discussion

We found that IRHB3 significantly increased the richness of the bacterial community but not the structure of the soybean rhizosphere. Functional bacteria related to phosphorus solubilization and nitrogen fixation, such as Geobacter, Geomonas, Candidatus Solibacter, Occallatibacter, and Candidatus Koribacter, were recruited in rich abundance by IRHB3 to the soybean rhizosphere as compared to those without IRHB3. In addition, the IRHB3 supplement obviously maintained the homeostasis of the rhizosphere microbiome that was disturbed by F. oxysporum, resulting in a lower disease index of root rot when compared with F. oxysporum. Furthermore, JA-mediated induced resistance was rapidly activated by IRHB3 following PDF1.2 and LOX2 expression, and meanwhile, a set of nodulation genes, GmENOD40b, GmNIN-2b, and GmRIC1, were also considerably induced by IRHB3 to improve nitrogen fixation ability and promote soybean yield, even when plants were infected by F. oxysporum. Thus, IRHB3 tends to synergistically interact with local rhizosphere microbes to promote host growth and induce host resistance in the field.

Identification and pathogenicity of Fusarium spp. associated with tea wilt in Zhejiang Province, China

BACKGROUND

Tea is one of the most widely consumed beverages in the world, with significant economic and cultural value. However, tea production faces many challenges due to various biotic and abiotic stresses, among which fungal diseases are particularly devastating.

RESULTS

To understand the identity and pathogenicity of isolates recovered from tea plants with symptoms of wilt, phylogenetic analyses and pathogenicity assays were conducted. Isolates were characterized to the species level by sequencing the ITS, tef-1α, tub2 and rpb2 sequences and morphology. Four Fusarium species were identified: Fusarium fujikuroi, Fusarium solani, Fusarium oxysporum, and Fusarium concentricum. The pathogenicity of the Fusarium isolates was evaluated on 1-year-old tea plants, whereby F. fujikuroi OS3 and OS4 strains were found to be the most virulent on tea.

CONCLUSIONS

To the best of our knowledge, this is the first report of tea rot caused by F. fujikuroi in the world. This provides the foundation for the identification and control of wilt disease in tea plants.

Locally Isolated Trichoderma harzianum Species Have Broad Spectrum Biocontrol Activities against the Wood Rot Fungal Species through Both Volatile Inhibition and Mycoparasitism

Pathogenic root/wood rot fungal species infect multiple urban tree species in Singapore. There is a need for sustainable and environmentally friendly mitigation. We report the local Trichoderma strains as potential biocontrol agents (BCAs) for pathogenic wood rot fungal species such as Phellinus noxius, Rigidoporus microporus, and Fulvifomes siamensis. Isolated Trichoderma strains were DNA-barcoded for their molecular identities and assessed for their potential as a BCA by their rate of growth in culture and effectiveness in inhibiting the pathogenic fungi in in vitro dual culture assays. Trichoderma harzianum strain CE92 was the most effective in inhibiting the growth of the pathogenic fungi tested. Preliminary results suggested both volatile organic compound (VOC) production and direct hyphal contact contributed to inhibition. SPME GC-MS identified known fungal inhibitory volatiles. Trichoderma harzianum strain CE92 hyphae were found to coil around Phellinus noxius and Lasiodiplodia theobromae upon contact in vitro and were possibly a part of the mycoparasitism. In summary, the work provides insight into Trichoderma inhibition of pathogenic fungi and identifies local strains with good potential for broad-spectrum BCAs against root/wood rot fungi in Singapore.

Identification of a New Pathogenic fungi Causing Sorghum Leaf Spot Disease and Its Management Using Natural Product and Microorganisms

Sorghum bicolor is cultivated worldwide. Leaf spot of sorghum, which leads to leaf lesions and yield reduction, is a prevalent and serious disease in Guizhou Province, southwest China. In August 2021, new leaf spot symptoms were observed on sorghum leaves. In this study, traditional methods and modern molecular biology techniques were used to isolate and identify the pathogen. Sorghum inoculated with the isolate GY1021 resulted in reddish brown lesion that similar to symptoms observed in the field: the original isolate inoculated was reisolated and Koch's postulates were fulfilled. Based on morphological features and phylogenetic analysis of the internal transcribed spacer (ITS) combined sequence with β-tubulin (TUB2) and translation elongation factor 1-α (TEF-1α) genes, the isolate was identified as Fusarium thapsinum (Strain accession: GY 1021; GenBank Accession: ITS (ON882046), TEF-1α (OP096445), and β-TUB (OP096446)). Then, we studied the bioactivity of various natural products and microorganisms against F. thapsinum using the dual culture experiment. Carvacrol, 2-allylphenol, honokiol, and cinnamaldehyde showed excellent antifungal activity, with EC₅₀ values of 24.19, 7.18, 46.18, and 52.81 µg/mL, respectively. The bioactivity of six antagonistic bacteria was measured using a dual culture experiment and the mycelial growth rate method. Paenibacillus polymyxa, Bacillus amyloliquefaciens and Bacillus velezensis displayed significant antifungal effects against F. thapsinum. This study provides a theoretical basis for the green control of leaf spot of sorghum.

Editorial for the Special Issue: “Fungal Pathogenicity Factors”

Pathogenicity factors are important aspects of the arsenal of fungal agents, allowing them to infect a broad range of hosts or to specifically target a crop by being capable of evading host defenses or having enzymatic activities that target plant tissues [...]

First Report on Colletotrichum fructicola Causing Anthracnose in Chinese Sorghum and Its Management Using Phytochemicals

Sorghum bicolor is cultivated worldwide. Leaf spots on sorghum, which lead to leaf lesions and impaired growth, are prevalent and severe in Guizhou Province, Southwest China. In August 2021, new leaf spot symptoms were observed on sorghum plants growing in agricultural fields. We used conventional tissue isolation methods and pathogenicity determination tests. Inoculations of sorghum with isolate 022ZW resulted in brown lesions similar to those observed under field conditions. The original inoculated isolates were reisolated and fulfilled Koch's postulates. Based on the morphological character and phylogenetic analyses of the combined sequences of the internal transcribed spacer (ITS) region and the β-tubulin (TUB2) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) genes, we identified the isolated fungus as C. fructicola. This paper is the first to report this fungus-causing disease in sorghum leaves. We studied the sensitivity of the pathogen to various phytochemicals. The sensitivity of C. fructicola to seven phytochemicals was measured using the mycelial growth rate method. Honokiol, magnolol, thymol, and carvacrol displayed good antifungal effects, with EC₅₀ (concentration for 50% of the maximal effect) values of 21.70 ± 0.81, 24.19 ± 0.49, 31.97 ± 0.51, and 31.04 ± 0.891 µg/mL, respectively. We tested the control effect of the seven phytochemicals on the anthracnose caused by C. fructicola: honokiol and magnolol displayed good field efficacy. In this study, we expand the host range of C. fructicola, providing a basis for controlling sorghum leaf diseases caused by C. fructicola.

Trichoderma and its role in biological control of plant fungal and nematode disease

Trichoderma is mainly used to control soil-borne diseases as well as some leaf and panicle diseases of various plants. Trichoderma can not only prevent diseases but also promotes plant growth, improves nutrient utilization efficiency, enhances plant resistance, and improves agrochemical pollution environment. Trichoderma spp. also behaves as a safe, low-cost, effective, eco-friendly biocontrol agent for different crop species. In this study, we introduced the biological control mechanism of Trichoderma in plant fungal and nematode disease, including competition, antibiosis, antagonism, and mycoparasitism, as well as the mechanism of promoting plant growth and inducing plant systemic resistance between Trichoderma and plants, and expounded on the application and control effects of Trichoderma in the control of various plant fungal and nematode diseases. From an applicative point of view, establishing a diversified application technology for Trichoderma is an important development direction for its role in the sustainable development of agriculture.

Rhizosphere inoculation of Nicotiana benthamiana with Trichoderma harzianum TRA1-16 in controlled environment agriculture: Effects of varying light intensities on the mutualism-parasitism interaction

Trichoderma spp., a genus of fast-growing and highly adaptable fungi that form symbiotic relationships with plant roots, rendering them ideal for practical use in controlled environment agriculture. Herein, this paper aims to understand how the Nicotiana benthamiana with inoculation of Trichoderma harzianum strain TRA1-16 responds to light intensity variation. Pot experiments were conducted under low and high light intensities (50 and 150 μmol·m^-2·s^-1, respectively) and microbial treatments. Plant growth, physio-biochemical attributes, activities of antioxidant enzymes, and phytohormones regulation were investigated. The results showed that for non-inoculated plants, the reduction in light intensity inhibited plant growth, nitrogen (N) and phosphorus (P) uptake, chlorophyll a/b, and carotenoid content. Trichoderma inoculation resulted in 1.17 to 1.51 times higher concentrations of available N and P in the soil than the non-inoculated group, with higher concentrations at high light intensity. Plant height, dry weight, nutrient uptake, and antioxidant activity were significantly increased after inoculation (p<0.05). However, the growth-promoting effect was less effective under low light conditions, with lower plant height and P content in plants. We suggested that when the light was attenuated, the mutualism of the Trichoderma turned into parasitism, slowing the growth of the host plant. The application of fungal inoculation techniques for plant growth promotion required coordination with appropriate light complementation. The mechanisms of coordination and interaction were proposed to be incorporated into the biological market theory.