Antagonism of Trichoderma isolates against Leucoagaricus gongylophorus (Singer) Möller

Biocontrol of strawberry Botrytis gray mold and prolong the fruit shelf-life by fumigant Trichoderma spp

Objectives To screen high active volatile organic compounds (VOCs)-producing Trichoderma isolates against strawberry gray mold caused by Botrytis cinerea, and to explore their antagonistic mode of action against the pathogen. VOCs produced by nine Trichoderma isolates (Trichoderma atroviride T1 and T3; Trichoderma harzianum T2, T4 and T5; T6, T7, T8 and T9 identified as Trichoderma asperellum in this work) significantly inhibited the mycelial growth (13.9-63.0% reduction) and conidial germination (17.6-96.3% reduction) of B. cinerea, the highest inhibition percentage belonged to VOCs of T7; in a closed space, VOCs of T7 shared 76.9% and 100% biocontrol efficacy against gray mold on strawberry fruits and detached leaves, respectively, prolonged the fruit shelf-life by 3 days in presence of B. cinerea, completely protected the leaves from B. cinerea infecting; volatile metabolites of T7 damaged the cell membrane permeability and integrity of B. cinerea, thereby inhibiting the mycelial growth and conidial germination. Gas chromatography-mass spectrometry (GC-MS) analysis revealed the VOCs contain 23 potential compounds, and the majority of these compounds were categorised as alkenes, alcohols, and esters, including PEA and 6PP, which have been reported as substances produced by Trichoderma spp. T. asperellum T7 showed high biofumigant activity against mycelial growth especially conidial germination of B. cinerea and thus protected strawberry fruits and leaves from gray mold, which acted by damaging the pathogen's plasma membrane and resulting in cytoplasm leakage, was a potential biofumigant for controlling pre- and post-harvest strawberry gray mold.

Control of pest ants by pathogenic fungi: state of the art

Pest ants are known for their damage to biodiversity, harm to agriculture, and negative impact on human welfare. Ants thrive when environmental opportunities arise, becoming pests and/or invading non-native areas. As social insects, they are extremely difficult to control using sustainable methods like biological control. The latter, although safer to the environment, acts slowly allowing the ants to use their individual and social defenses. Among biocontrol agents, fungal pathogens were proposed as promising, however, it is difficult to ascertain their success when the bibliography has not been reviewed and condensed. Therefore, this paper is the first in performing such task by analyzing publications mainly from 2000 to 2022 about the control of pest ants by fungi. From 85 publications selected, 77% corresponded to laboratory studies. Beauveria and Metarhizium were the genera most used in laboratory and field studies. Most of them included Acromyrmex and Atta leaf-cutter ants (LCA), and Solenopsis fire ants. From laboratory experiments, we evaluated how ant net mortality was affected by ant and fungal species, and also by origin, concentration, and inoculation technique of the fungal strains tested. Beauveria bassiana and Metarhizium anisopliae produced the greatest mortality, along with the inoculation spray technique and fungal strains collected from ants. There was a positive relationship between ant mortality and fungal concentration only for those studies which evaluated more than one concentration. Twenty field experimental studies were found, covering 13 pest species, mainly LCA and Solenopsis invicta. Only B. bassiana was tested on Solenopsis, M. anisopliae was mostly used for Acromyrmex, and M. anisopliae or Trichoderma were mainly used with Atta species. The median control field efficiency varied from 20% to 85% for different fungi and ant genera. When grouping all fungal species together, the median control efficiency seemed to be better for Acromyrmex (67%) than for Atta and Solenopsis (both 43%). Our review shows that, at this stage of knowledge, it is very difficult to extrapolate any result. We offer suggestions to improve and standardize laboratory and field experimental studies in order to advance more efficiently in the fungal control of pest ants.

Fungal Community Associated with the Leaf-Cutting Ant Acromyrmex crassispinus (Hymenoptera: Formicidae) Colonies: a Search for Potential Biocontrol Agents

The leaf-cutting ant Acromyrmex crassispinus is considered an important pest in forest plantations in southern Brazil. This work aimed to study the fungal community associated with A. crassispinus colonies, subjected to treatments with subdoses of granulated baits (sulfluramid), which might reduce the ability of the ants to care for their symbiotic fungus and other fungi (maybe biocontrol fungi) would take over, to prospect for potential biological control agents. Samplings of fungus gardens and dead ants allowed the identification of 195 fungal isolates, distributed in 29 families, 36 genera, and 53 species. The most frequent genera were Trichoderma (49.2%), Penicillium (13.8%), Chaetomium (6.2%), and Fusarium (3.6%). This is the first study that conducted a survey of antagonistic and entomopathogenic fungi to A. crassispinus and its symbiotic fungus, reporting for the first time the occurrence of potential biological control agents. Escovopsis weberi, Fusarium oxysporum, Rhizomucor variabilis, Trichoderma atroviride, Trichoderma harzianum, Trichoderma koningiopsis, and Trichoderma spirale are considered some of the potential biocontrol organisms.

Effects of Trichoderma strigosellum in Eucalyptus urophylla Development and Leaf-Cutting Ant Behavior

Fungal endophytes can protect plants against herbivory and be used to control leaf-cutting ants. In this study, we aimed to evaluate the potential of endophytic colonization of Eucalyptus urophylla by three filamentous fungal species and their influence on the plant development and foraging behavior of Atta sexdens. The study design was completely randomized and comprised a factorial scheme of 4 × 3, three antagonistic fungal species (Escovopsis sp., Metarhizium anisopliae, and Trichoderma strigosellum) of the leaf-cutting ant, and one control and three inoculation methods (conidial suspension via foliar spray [FS] and soil drench [SD] inoculation, and seedlings inoculated with mycelium [SWM]). The SWM method allowed T. strigosellum to colonize all plant organs, and these plants exhibited higher height, leaf number, shoot dry mass, and total dry mass than the ones subjected to the other inoculation methods. The SWM method increased the plant height than the control plants and those inoculated with Escovopsis sp. and M. anisopliae. Trichoderma strigosellum, previously isolated from soil, colonized E. urophylla plants and positively influenced their development, as demonstrated by the SWM method. Trichoderma strigosellum promoted the increase in E. urophylla height compared with when the FS and SD methods were used (by 19.62% and 18.52%, respectively). Our results reveal that A. sexdens workers preferentially began cutting the leaves from plants not previously colonized by T. strigosellum. This behavior can be explained by modifications in the phenotypic traits of the eucalyptus leaves.

Soil actinobacteria inhibit antagonistic fungi of leafcutter ant colonies

Founder females of the leaf-cutting ant species Atta sexdens experience high mortality during the founding and establishment of their colonies. The foundation site is crucial for the success of a new colony. In this study, we isolated and identified actinobacteria from fungus garden chambers of A. sexdens colony growth in soils from (1) forested areas without leafcutter ant nests and (2) open ground areas close to leafcutter ant nests. The inhibitory effect of these isolates on pathogenic fungi and the mutualistic fungus cultivated by leafcutter ants was evaluated. The 16S rRNA gene sequences were employed to identify nine selected actinobacteria species found in the soil: Streptomyces (6), Nocardia (2), and Kitasatospora (1). One Streptomyces and one Kitasatospora isolate inhibited all the tested fungi. Since there is no evidence of actinobacteria cultivation in the workers' cuticle of the Atta genus, our results corroborate the hypothesis that these workers may establish temporary adaptive symbiosis with soil microorganisms that produce antibiotic substances, living in some parts of their nest, or even inside their bodies. Pathogenic fungi are a risk factor that can be controlled by actinobacteria metabolites from soils, with minimal energy cost to the colony.

Host Susceptibility Modulates Escovopsis Pathogenic Potential in the Fungiculture of Higher Attine Ants

Health and disease emerge from intricate interactions between genotypes, phenotypes, and environmental features. The outcomes of such interactions are context-dependent, existing as a dynamic continuum ranging from benefits to damage. In host-microbial interactions, both the host and environmental conditions modulate the pathogenic potential of a microorganism. Microbial interactions are the core of the agricultural systems of ants in the subtribe Attina, which cultivate basidiomycete fungi for food. The fungiculture environment harbors a diverse microbial community, including fungi in the genus Escovopsis that has been studied as damage-causing agent. Here, we consider the ant colony as a host and investigate to what extent its health impacts the dynamics and outcomes of host-Escovopsis interactions. We found that different ant fungal cultivars vary in susceptibility to the same Escovopsis strains in plate-assays interactions. In subcolony-Escovopsis interactions, while healthy subcolonies gradually recover from infection with different concentrations of Escovopsis conidia, insecticide-treated subcolonies evidenced traits of infection and died within 7 days. The opportunistic nature of Escovopsis infections indicates that diseases in attine fungiculture are a consequence of host susceptibility, rather than the effect of a single microbial agent. By addressing the host susceptibility as a major modulator of Escovopsis pathogenesis, our findings expand the understanding of disease dynamics within attine colonies.

Emerging nanobiotechnology in agriculture for the management of pesticide residues

Utilization of pesticides is often necessary for meeting commercial requirements for crop quality and yield. However, incessant global pesticide use poses potential risks to human and ecosystem health. This situation increases the urgency of developing nano-biotechnology-assisted pesticide formulations that have high efficacy and low risk of side effects. The risks associated with both conventional and nanopesticides are summarized in this review. Moreover, the management of residual pesticides is still a global challenge. The contamination of soil and water resources with pesticides has adverse impact over agricultural productivity and food security; ultimately posing threats to living organisms. Pesticide residues in the eco-system may be treated via several biological and physicochemical processes, such as microbe-based degradation and advanced oxidation processes. With these issues in mind, we present a review that explores both existing and emerging techniques for management of pesticide residues and environmental risks. These techniques can offer a sustainable solution to revitalize the tarnished water/soil resources. Further, state-of-the-art research approaches to investigate biotechnological alternatives to conventional pesticides are discussed along with future prospects and mitigation techniques are recommended.

Deleterious action of azadirachtin against the mutualistic fungus of leaf-cutting ants

Leaf-cutting ants have a beneficial and obligatory relationship with the fungus that they grow. This mutualism allowed the evolutionary success of these ants. The great defoliation capacity of these insects, which often exceeds the level of tolerable economic damage, includes them as severe pests in many cultures. However, given the close relationship between these two agents of mutualism, it is expected that an impact on the fungus will reflect on the performance of the colony as a whole. Therefore, the effect of azadirachtin on the development, and the macronutrient composition of Leucoagaricus gongylophorus was evaluated. Azadirachtin reduced the final fungal mass at the end of treatment at all concentrations tested, but did not reduce the final growth area. A reduction in the amount of hyphae produced with increasing azadirachtin concentration was also observed. Regarding macronutrients, the compound did not affect their total amount in the fungus. Thus, it is observed that azadirachtin did not alter the composition of L. gongylophorus macronutrients, but inhibited its growth by reducing the number of hyphae produced. This reduction reflects directly on the amount of nutrients offered to the workers and the queen and may improve the management of these insects.

The interactions of Trichoderma at multiple trophic levels: inter-kingdom communication

Trichoderma spp. are universal saprotrophic fungi in terrestrial ecosystems, and as rhizosphere inhabitants, they mediate interactions with other soil microorganisms, plants, and arthropods at multiple trophic levels. In the rhizosphere, Trichoderma can reduce the abundance of phytopathogenic microorganisms, which involves the action of potent inhibitory molecules, such as gliovirin and siderophores, whereas endophytic associations between Trichoderma and the seeds and roots of host plants can result in enhanced plant growth and crop productivity, as well as the alleviation of abiotic stress. Such beneficial effects are mediated via the activation of endogenous mechanisms controlled by phytohormones such as auxins and abscisic acid, as well as by alterations in host plant metabolism. During either root colonization or in the absence of physical contact, Trichoderma can trigger early defense responses mediated by Ca²⁺ and reactive oxygen species, and subsequently stimulate plant immunity by enhancing resistance mechanisms regulated by the phytohormones salicylic acid, jasmonic acid, and ethylene. In addition, Trichoderma release volatile organic compounds and nitrogen or oxygen heterocyclic compounds that serve as signaling molecules, which have effects on plant growth, phytopathogen levels, herbivorous insects, and at the third trophic level, play roles in attracting the natural enemies (predators and parasitoids) of herbivores. In this paper, we review some of the most recent advances in our understanding of the environmental influences of Trichoderma spp., with particular emphasis on their multiple interactions at different trophic levels.

Spores of Beauveria bassiana and Trichoderma lignorum as a bioinsecticide for the control of Atta cephalotes

Background

The leafcutter ant (Atta cephalotes) is associated with losses in the agricultural sector, due to its defoliating activity; for its control, biological, mechanical and chemical methods have been developed, the latter associated with adverse effects on human and environmental health. This research validated in the field for the control of the leafcutter ant (A. cephalotes) using a mixture of Beauveria bassiana and Trichoderma lignorum spores.

Methods

The effectiveness from the combination of spores of B. bassiana and T. lignorum with an initial concentration of 2 × 10⁹ spores/ml, in the following proportions of B. bassiana and T. lignorum, A (1:1), of each fungus. It was evaluated within the university campus, comparing it with two commercial formulations, Mycotrol (B. bassiana) and Mycobac (T. lignorum). Additionally, this formulation was evaluated in 49 nests distributed 16 in 14 locations in Colombia. The formulation application was carried out by direct application, using a pump at a speed of 10 ml/m². The effectiveness was estimated from the reduction of the flow of ants, evaluating the statistically significant differences using the ANOVA and Tukey-test.

Results

Effective control of 90% of the nests was observed in the field phase in 60 days, except in nests with areas > 50 m² that were located in regions with high rainfall (annual average precipitation above 7000 mm), such as Buenaventura.

Conclusions

In this work, it was demonstrated that the combination of B. bassiana and T. lignorum spores represent a viable alternative for the control of the leafcutter ant, in which the effectiveness is related to several factors, including the size of the nest and the rainfall in the area.

Soluble Compounds of Filamentous Fungi Harm the Symbiotic Fungus of Leafcutter Ants

Chemical compounds are key to understand symbiotic interactions. In the leafcutter ant-microbe symbiosis a plethora of filamentous fungi continuously gain access the ant colonies through plant substrate collected by workers. Many filamentous fungi are considered transient in attine ant colonies, however, their real ecological role in this environment still remains unclear. A possible role of these microorganisms is the antagonism towards Leucoagaricus gongylophorus, the mutualistic fungus that serve as food for several leafcutter ant species. Here, we showed the antagonism of filamentous fungi isolated from different sources, and the negative impacts of their metabolites on the growth of the ant-fungal cultivar. Our results demonstrate that the chemical compounds produced by filamentous fungi can harm the mutualistic fungus of leafcutter ants.