Uncovering the multifaceted properties of 6-pentyl-alpha-pyrone for control of plant pathogens.

Some volatile organic compounds (VOCs) produced by microorganisms have the ability to inhibit the growth and development of plant pathogens, induce the activation of plant defenses, and promote plant growth. Among them, 6-pentyl-alpha-pyrone (6-PP), a ketone produced by Trichoderma fungi, has emerged as a focal point of interest. 6-PP has been isolated and characterized from thirteen Trichoderma species and is the main VOC produced, often accounting for >50% of the total VOCs emitted. This review examines abiotic and biotic interactions regulating the production of 6-PP by Trichoderma, and the known effects of 6-PP on plant pathogens through direct and indirect mechanisms including induced systemic resistance. While there are many reports of 6-PP activity against plant pathogens, the vast majority have been from laboratory studies involving only 6-PP and the pathogen, rather than glasshouse or field studies including a host plant in the system. Biopesticides based on 6-PP may well provide an eco-friendly, sustainable management tool for future agricultural production. However, before this can happen, challenges including demonstrating disease control efficacy in the field, developing efficient delivery systems, and determining cost-effective application rates must be overcome before 6-PP's potential for pathogen control can be turned into reality.

Fungistatic Activity Mediated by Volatile Organic Compounds Is Isolate-Dependent in Trichoderma sp. "atroviride B".

Trichoderma spp. produce multiple bioactive volatile organic compounds (VOCs). While the bioactivity of VOCs from different Trichoderma species is well documented, information on intraspecific variation is limited. The fungistatic activity of VOCs emitted by 59 Trichoderma sp. "atroviride B" isolates against the pathogen Rhizoctonia solani was investigated. Eight isolates representing the two extremes of bioactivity against R. solani were also assessed against Alternaria radicina, Fusarium oxysporum f. sp. lycopersici and Sclerotinia sclerotiorum. VOCs profiles of these eight isolates were analyzed using gas chromatography-mass spectrometry (GC-MS) to identify a correlation between specific VOCs and bioactivity, and 11 VOCs were evaluated for bioactivity against the pathogens. Bioactivity against R. solani varied among the fifty-nine isolates, with five being strongly antagonistic. All eight selected isolates inhibited the growth of all four pathogens, with bioactivity being lowest against F. oxysporum f. sp. lycopersici. In total, 32 VOCs were detected, with individual isolates producing between 19 and 28 VOCs. There was a significant direct correlation between VOC number/quantity and bioactivity against R. solani. 6-pentyl-α-pyrone was the most abundant VOC produced, but 15 other VOCs were also correlated with bioactivity. All 11 VOCs tested inhibited R. solani growth, some by >50%. Some of the VOCs also inhibited the growth of the other pathogens by >50%. This study demonstrates significant intraspecific differences in VOC profiles and fungistatic activity supporting the existence of biological diversity within Trichoderma isolates from the same species, a factor in many cases ignored during the development of biological control agents.

The NADPH Oxidases Nox1 and Nox2 Differentially Regulate Volatile Organic Compounds, Fungistatic Activity, Plant Growth Promotion and Nutrient Assimilation in Trichoderma atroviride.

In eukaryotic systems, membrane-bound NADPH oxidases (Nox) generate reactive oxygen species (ROS) as a part of normal physiological functions. In the soil-borne mycoparasitic and plant facultative symbiont Trichoderma atroviride, Nox1 and the regulator NoxR are involved in differentiation induced by mechanical damage, while the role of Nox2 has not been determined. The knock-out strains Δnox1, ΔnoxR and Δnox2 were compared to the parental strain (WT) in their ability to grow and conidiate under a series of stress conditions (osmotic, oxidative, membrane, and cell-wall stresses). All three genes were differentially involved in the stress-response phenotypes. In addition, several interactive experiments with biotic factors (plant seedlings and other fungi) were performed comparing the mutant phenotypes with the WT, which was used as the reference strain. Δnox1 and ΔnoxR significantly reduced the antagonistic activity of T. atroviride against Rhizoctonia solani and Sclerotinia sclerotiorum in direct confrontation assays, but Δnox2 showed similar activity to the WT. The Δnox1, ΔnoxR, and Δnox2 mutants showed quantitative differences in the emission of several volatile organic compounds (VOCs). The effects of a blend of these volatiles on plant-growth promotion of Arabidopsis thaliana seedlings were determined in closed-chamber experiments. The increase in root and shoot biomass induced by T. atroviride VOCs was significantly lowered by ΔnoxR and Δnox1, but not by Δnox2. In terms of fungistatic activity at a distance, Δnox2 had a significant reduction in this trait against R. solani and S. sclerotiorum, while fungistasis was highly increased by ΔnoxR and Δnox1. Identification and quantification of individual VOCs in the blends emitted by the strains was performed by GC-MS and the patterns of variation observed for individual volatiles, such as 6-Pentyl-2H-pyran-2-one (6PP-1) and (E)-6-Pent-1-enylpyran-2-one (6PP-2) were consistent with their negative effects in plant-growth promotion and positive effects in fungistasis at a distance. Nox1 and NoxR appear to have a ubiquitous regulatory role of in a variety of developmental and interactive processes in T. atroviride either as positive or negative modulators. Nox2 may also have a role in regulating production of VOCs with fungistatic activity.

Methods for the Evaluation of the Bioactivity and Biocontrol Potential of Species of Trichoderma.

Members of the genus Trichoderma comprise the majority of commercial fungal biocontrol agents of plant diseases. As such, there is a wealth of information available on the analysis of their biocontrol potential and the mechanisms behind their superior abilities. This chapter aims to summarize the most common methods utilized within a Trichoderma biocontrol program for assessing the biological properties of individual strains.

Potential of the beneficial fungus Trichoderma to enhance ecosystem-service provision in the biofuel grass Miscanthus x giganteus in agriculture.

The sterile hybrid grass Miscanthus x giganteus (Mxg) can produce more than 30 t dry matter/ha/year. This biomass has a range of uses, including animal bedding and a source of heating fuel. The grass provides a wide range of other ecosystem services (ES), including shelter for crops and livestock, a refuge for beneficial arthropods, reptiles and earthworms and is an ideal cellulosic feedstock for liquid biofuels such as renewable (drop-in) diesel. In this study, the effects of different strains of the beneficial fungus Trichoderma on above- and below-ground biomass of Mxg were evaluated in glasshouse and field experiments, the latter on a commercial dairy farm over two years. Other ES benefits of Trichoderma measured in this study included enhanced leaf chlorophyll content as well as increased digestibility of the dried material for livestock. This study shows, for the first time for a biofuel feedstock plant, how Trichoderma can enhance productivity of such plants and complements other recent work on the wide-ranging provision of ES by this plant species.