From laboratory to the field: biological control of Fusarium graminearum on infected maize crop residues

Wheat rhizosphere dynamics of Trichoderma gamsii A5MH and suppression of a Pythium root rot-Fusarium crown rot disease complex over two consecutive cropping seasons

AIMS

Determine the wheat rhizosphere competence of Trichoderma gamsii strain A5MH and in planta suppression of the Pythium root and Fusarium crown rot pathogens Globisporangium irregulare and Fusarium pseudograminearum.

METHODS AND RESULTS

Wheat was continuously cropped (eight years) at a minimum tillage, low growing season rainfall (GSR ≤ 170 mm) site shown as highly conducive to Pythium root and Fusarium crown rots. Root isolation frequency (RIF) and qPCR were used to determine the rhizosphere dynamics of strain A5MH and the target pathogens at tillering, grain harvest, and in postharvest stubble over the final 2 years. Strain A5MH actively colonized the wheat rhizosphere throughout both growing seasons, had high root abundance at harvest [log 4.5 genome copies (GC) g-1] and persisted in standing stubble for at least 293-d postinoculation. Globisporangium irregulare was most abundant in roots at tillering, whereas F. pseudograminearum was only abundant at harvest and up to 9-fold greater in the drier, second year (GSR 105 mm). Strain A5MH decreased RIF of both pathogens by up to 40%, root abundance of G. irregulare by 100-fold, and F. pseudogaminearum by 700-fold, but was ineffective against crown rot in the second year when pathogen abundance was >log 6.0 GC g-1 root. Strain A5MH increased crop emergence and tillering biomass by up to 40%.

CONCLUSIONS

Further trials are required to determine if the A5MH-induced pathogen suppression translates to yield improvements in higher rainfall regions where non-cereal rotations reduce crown rot inoculum.

Biocontrol Agents of Fusarium Head Blight in Wheat: A Meta-Analytic Approach to Elucidate Their Strengths and Weaknesses

The use of biocontrol agents (BCAs) coping with fungal pathogens causing Fusarium head blight (FHB) is a compelling strategy for disease management, but a better elucidation of their effectiveness is crucial. Meta-analysis is the analysis of the results of multiple studies, which is typically performed to synthesize evidence from many possible sources in a formal probabilistic manner. This meta-analytic study, including 30 pathometric, biometric, physiochemical, genetic, and mycotoxin response variables reported in 56 studies, evidences the BCA effects on FHB in wheat. The effectiveness of BCAs of FHB in wheat in terms of pathogen abundance and disease reductions, biomass and yield conservation, and mycotoxin prevention/control was confirmed. BCAs showed higher efficacy (i) in studies published more recently; (ii) under controlled conditions; (iii) in high susceptible wheat cultivars; (iv) when Fusarium inoculation and BCA treatment did not occur directly on the plant (i.e., at the seed and kernel levels) in terms of disease development and mycotoxin control, and vice versa in terms of biomass conservation; (v) if Fusarium inoculation and BCA treatment occurred by spraying spikes in terms of yield; (vi) at 15 to 21 days post Fusarium inoculation or BCA treatment; and (vii) if they were filamentous fungi. However, BCAs overall were less efficacious than conventional agrochemicals, especially in terms of pathogen abundance and FHB reductions, as well as of mycotoxin prevention/control, although inconsistencies were reported among the investigated moderator variables. This study also highlights the complexity of reaching a good balance among BCA effects, and the need for further research.

Biocontrol Effect of Clonostachys rosea on Fusarium graminearum Infection and Mycotoxin Detoxification in Oat (Avena sativa)

Oat (Avena sativa) is susceptible to Fusarium head blight (FHB). The quality of oat grain is threatened by the accumulation of mycotoxins, particularly the trichothecene deoxynivalenol (DON), which also acts as a virulence factor for the main pathogen Fusarium graminearum. The plant can defend itself, e.g., by DON detoxification by UGT-glycosyltransferases (UTGs) and accumulation of PR-proteins, even though these mechanisms do not deliver effective levels of resistance. We studied the ability of the fungal biocontrol agent (BCA) Clonostachys rosea to reduce FHB and mycotoxin accumulation. Greenhouse trials showed that C. rosea-inoculation of oat spikelets at anthesis 3 days prior to F. graminearum inoculation reduced both the amount of Fusarium DNA (79%) and DON level (80%) in mature oat kernels substantially. DON applied to C. rosea-treated spikelets resulted in higher conversion of DON to DON-3-Glc than in mock treated plants. Moreover, there was a significant enhancement of expression of two oat UGT-glycosyltransferase genes in C. rosea-treated oat. In addition, C. rosea treatment activated expression of genes encoding four PR-proteins and a WRKY23-like transcription factor, suggesting that C. rosea may induce resistance in oat. Thus, C. rosea IK726 has strong potential to be used as a BCA against FHB in oat as it inhibits F. graminearum infection effectively, whilst detoxifying DON mycotoxin rapidly.

Equilibrium kinetics and thermodynamic studies on biosorption of heavy metals by metal-resistant strains of Trichoderma isolated from tannery solid waste

This study was aimed at finding the metal sorption potential of six indigenous Trichoderma strains by using batch experiments for Cd (II), Cr (VI), Cu (II), and Pb (II). Trichoderma atrobrunneum showed maximum metal biosorption potential at 800 mg L^-1 of initial concentration. Two adsorption isotherm models, (1) Langmuir (2) Freundlich models, were employed on the biosorption data obtained at various initial metal concentrations (10 mg L^-1-200 mg L^-1) and pseudo-first (PSI) and pseudo-second (PSII) order equilibrium kinetic models were subjected to data of agitation time (3-7 days). A maximum correlation coefficient value (R²) of ≤ 1 was observed for the Langmuir and PSII model. Results revealed that pH 6-7 was the best for metal sorption, while metal removal efficiency was increased by increasing temperature (298 K, 303 K, 308 K, 313 K). The results of thermodynamic study parameters (∆G°, ∆H°, ∆S°) indicated that heavy metal biosorption by Trichoderma strains was an endothermic, spontaneous, and feasible process. Moreover, surface characterization analysis through SEM, BET, FTIR, and XRD showed that T. atrobrunneum and Trichoderma sp. could adsorb more metal ions when grown in high metal concentrations. The results indicate that living biomass of T. atrobrunneum and Trichoderma sp. is an effective multi-metal biosorbent that can be used for efficacious bioremediation of bio-treatment of heavy metal polluted wastewater.

The Fungal Endophyte Penicillium olsonii ML37 Reduces Fusarium Head Blight by Local Induced Resistance in Wheat Spikes

The fungal endophyte Penicillium olsonii ML37 is a biocontrol agent of Fusarium head blight in wheat (caused by Fusarium graminearum), which has shown a limited direct inhibition of fungal growth in vitro. We used RNA-seq and LC-MS/MS analyses to elucidate metabolic interactions of the three-way system Penicillium–wheat–Fusarium in greenhouse experiments. We demonstrated that P. olsonii ML37 colonises wheat spikes and transiently activates plant defence mechanisms, as pretreated spikes show a faster and stronger expression of the defence metabolism during the first 24 h after pathogen inoculation. This effect was transient and the expression of the same genes was lower in the pathogen-infected spikes than in those infected by P. olsonii alone. This response to the endophyte includes the transcriptional activation of several WRKY transcription factors. This early activation is associated with a reduction in FHB symptoms and significantly lower levels of the F. graminearum metabolites 15-acetyl-DON and culmorin. An increase in the Penicillium-associated metabolite asperphanamate confirms colonisation by the endophyte. Our results suggest that the mode of action used by P. olsonii ML37 is via a local defence activation in wheat spikes, and that this fungus has potential as a novel biological alternative in wheat disease control.

The sexual spore pigment asperthecin is required for normal ascospore production and protection from UV light in Aspergillus nidulans

Many fungi develop both asexual and sexual spores that serve as propagules for dissemination and/or recombination of genetic traits. Asexual spores are often heavily pigmented and this pigmentation provides protection from UV light. However, little is known about any purpose pigmentation may serve for sexual spores. The model Ascomycete Aspergillus nidulans produces both green pigmented asexual spores (conidia) and red pigmented sexual spores (ascospores). Here we find that the previously characterized red pigment, asperthecin, is the A. nidulans ascospore pigment. The asperthecin biosynthetic gene cluster is composed of three genes, aptA, aptB, and aptC where deletion of either aptA (encoding a polyketide synthase) or aptB (encoding a thioesterase) yields small, mishappen hyaline ascospores while deletion of aptC (encoding a monooxygenase) yields morphologically normal but purple ascospores. ∆aptA and ∆aptB but not ∆aptC or WT ascospores are extremely sensitive to UV light. We find that two historical ascospore color mutants, clA6 and clB1, possess mutations in aptA and aptB sequences respectively.

A versatile microfluidic platform measures hyphal interactions between Fusarium graminearum and Clonostachys rosea in real-time

Routinely, fungal-fungal interactions (FFI) are studied on agar surfaces. However, this format restricts high-resolution dynamic imaging. To gain experimental access to FFI at the hyphal level in real-time, we developed a microfluidic platform, a FFI device. This device utilises microchannel geometry to enhance the visibility of hyphal growth and provides control channels to allow comparisons between localised and systemic effects. We demonstrate its function by investigating the FFI between the biological control agent (BCA) Clonostachys rosea and the plant pathogen Fusarium graminearum. Microscope image analyses confirm the inhibitory effect of the necrotrophic BCA and we show that a loss of fluorescence in parasitised hyphae of GFP-tagged F. graminearum coincides with the detection of GFP in mycelium of C. rosea. The versatility of our device to operate under both water-saturated and nutrient-rich as well as dry and nutrient-deficient conditions, coupled with its spatio-temporal output, opens new opportunities to study relationships between fungi.