Bottlenecks in commercialisation and future prospects of PGPR

The use of novel isolates of Trichoderma with efficient antagonistic capacity against Fusarium oxysporum f. sp. lycopersici (FOL) is a promising alternative strategy to pesticides for tomato wilt management. We evaluated the antagonistic activity of 30 isolates of T. asperellum against 4 different isolates of FOL. The production of extracellular cell wall degrading enzymes of the antagonistic isolates was also measured. The random amplified polymorphic DNA (RAPD) method was applied to assess the genetic variability among the T. asperellum isolates. All of the T. asperellum isolates significantly reduced the mycelial growth of FOL isolates but the amount of growth reduction varied significantly as well. There was a correlation between the antagonistic capacity of T. asperellum isolates towards FOL and their lytic enzyme production. Isolates showing high levels of chitinase and β-1,3-glucanase activities strongly inhibited the growth of FOL isolates. RAPD analysis showed a high level of genetic variation among T. asperellum isolates. The UPGMA dendrogram revealed that T. asperellum isolates could not be grouped by their anta- gonistic behavior or lytic enzymes production. Six isolates of T. asperellum were highly antagonistic towards FOL and potentially could be used in commercial agriculture to control tomato wilt. Our results are consistent with the conclusion that understanding the genetic variation within Trichoderma isolates and their biochemical capabilities are required for the selection of effective indigenous fungal strains for the use as biocontrol agents.

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Characterization of Novel Trichoderma asperellum Isolates to Select Effective Biocontrol Agents Against Tomato Fusarium Wilt.

Trichoderma spp. are well-known biological agents that have significant antagonistic activity against several plant pathogenic fungi. In the present study, Trichoderma spp. were tested in vitro for...

Antagonistic assessment of Trichoderma spp. by producing volatile and non-volatile compounds against different fungal pathogens

Summary

Mitogen-activated protein (MAP) kinases play crucial roles in regulating fungal development, growth and pathogenicity, and in responses to the environment. In this study, we characterized a MAP kinase kinase FgMkk1 in Fusarium graminearum, the causal agent of wheat head blight. Phenotypic analyses of the FgMKK1 mutant (ΔFgMKK1) showed that FgMkk1 is involved in the regulation of hyphal growth, pigmentation, conidiation, deoxynivalenol biosynthesis and virulence of F. graminearum. ΔFgMKK1 also showed increased sensitivity to cell wall-damaging agents, and to osmotic and oxidative stresses, but exhibited decreased sensitivity to the fungicides iprodione and fludioxonil. In addition, the mutant revealed increased sensitivity to a biocontrol agent, Trichoderma atroviride. Western blot assays revealed that FgMkk1 positively regulates phosphorylation of the MAP kinases Mgv1 and FgOs-2, the key component in the cell wall integrity (CWI) and high-osmolarity glycerol (HOG) signalling pathway respectively. Yeast two-hybrid assay indicated that Mgv1 interacts with a transcription factor FgRlm1. The FgRLM1 mutant (ΔFgRLM1) showed increased sensitivity to cell wall-damaging agents and exhibited decreased virulence. Taken together, our data indicated that FgMkk1 is an upstream component of Mgv1, and regulates vegetative differentiation, multiple stress response and virulence via the CWI and HOG signalling pathways. FgRlm1 may be a downstream component of Mgv1 in the CWI pathway in F. graminearum.

The MAPKK FgMkk1 of Fusarium graminearum regulates vegetative differentiation, multiple stress response, and virulence via the cell wall integrity and high‐osmolarity glycerol signaling pathways

The genus Trichoderma is ubiquitous in the environment, particularly in soils. Trichoderma species could be readily isolated from soil by all available conventional methods, largely because they grow rapidly and also because of their abundant conidiation. Based on the phylogenetic study, several researchers reported that Trichoderma and Hypocrea form a single holomorph genus, within which two major clades can be distinguished. The species of Trichoderma possess diverse biotechnological applications such as they act as biofungicide for controlling various plant diseases, as biofertilizers for plant growth promotion. Trichoderma secrete diverse volatile compounds including alcohols, aldehydes and ketones, ethylene, hydrogen cyanide, and monoterpenes, as well as nonvolatile compounds including peptaibols and diketopiperazine-like gliotoxin and gliovirin which are known to exhibit antibiotic activity. The interaction of Trichoderma with the host plant results in parasitism/predation; production of antibiotic is combined with mycoparasitism (penetration and infection), production of cell wall-degrading enzymes or lytic enzymes, competition for nutrients or for space, and establishment of induced resistance in the plant.

Trichoderma: Biodiversity, Ecological Significances, and Industrial Applications

Several Trichoderma isolates were screened for their biocontrol activity against Fusarium oxysporum f.sp. pisi. Eighteen of these isolates (T1 to T18) showed considerable biocontrol potential and were taken further in the study. Initial counter inhibition was observed in all the eighteen dual culture sets where Trichoderma and Fusarium both posed varying degree of inhibition on each other. In three of the sets, Fusarium was found extending narrow outgrowths towards Trichoderma. Trichoderma was later found extending its mycelia along these narrow outgrowths of Fusarium representing a chemo-attractive mechanism of interaction. Finally, parasitic interaction was noticed in all the sets except two. In these two sets, Trichoderma was unable to overcome inhibition posed by Fusarium and, therefore, could not parasitize Fusarium. In the interaction between Trichoderma and Fusarium, the sequence of events noticed was categorized as pre-contact antagonistic interaction, chemo-attractive intermediate phase and, finally, parasitic interaction. Most of the Trichoderma isolates showed considerably good antibiosis and parasitism. Therefore, the primary criterion for selection of the best potential biocontrol agent was poised on the time taken by Trichoderma to complete the sequence of events until parasitism of target pathogen. Among the eighteen isolates of Trichoderma, T. atroviride (Isolate T1) was found to show best activity followed by two isolates of Trichoderma harzianum (Isolate T8 and T11) in terms of time taken to parasitize Fusarium. The present study stresses on quick control on plant disease as a desired quality for popularization of biocontrol agents.

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Poornima Sharma

Papers

Complexity of Trichoderma-Fusarium interaction and manifestation of biological control