Isolate-Specific Effect of Entomopathogenic Endophytic Fungi on Population Growth of Two-Spotted Spider Mite (Tetranychus urticae Koch) and Levels of Steroidal Glycoalkaloids in Tomato

The Inevitable Fate of Tetranychus urticae on Tomato Plants Treated with Entomopathogenic Fungi and Spinosad

Tetranychus urticae (Acari: Tetranychidae) is a pervasive and damaging mite pest of tomato crops, leading to important economic losses globally. This study evaluated the acaricidal efficacy of spinosad, alone and in combination with Beauveria bassiana (Bb) WG-21 and Metarhizium robertsii (Mr) WG-04, in the laboratory (application to tomato leaf discs) and greenhouse (application to tomato plants), considering mortality and establishment, respectively. The combination treatments of Bb WG-21 or Mr WG-04 with spinosad achieved 100% mortality of T. urticae nymphs within 2 days on leaf discs, while individual applications of each control agent resulted in lower mortalities, ranging between 62.91 and 86.25% after 3 days. The paired treatment of Mr WG-04 + spinosad killed all exposed adults within 5 d, while that of Bb WG-21 + spinosad achieved the same results after 7 d. However, spinosad, Mr WG-04, and Bb WG-21 alone killed ≥77.08% of adults after 7 d. In the greenhouse, the combination treatment of WG-04 + spinosad deterred the presence of T. urticae (adults, immatures, and eggs) on either surface of the tomato leaves, while Bb WG-21 + spinosad suppressed the populations only on the adaxial surface. These findings indicate that combined treatments of the tested EPF + spinosad, especially Mr WG-04, on tomato plants under greenhouse conditions can provide substantially enhanced control of T. urticae life stages compared to each treatment applied alone.

A New Isolate Beauveria bassiana GxABT-1: Efficacy against Myzus persicae and Promising Impact on the Beet Mild Yellow Virus-Aphid Association

Within the context of ecofriendly alternatives to neonicotinoids, we explored the direct and endophytic potential of two Beauveria bassiana isolates, GHA from BotaniGard and the new endemic isolate GxABT-1, against the Sugar Beet Mild Yellow Virus (BMYV)-Myzus persicae pathosystem. A mortality rate of 96 and 91% was registered after 8 days of treatment with GHA and Gx-ABT-1, respectively. To assess the endophytic impact, sugar beet seeds were treated, and the ability of the fungi to colonize the plant was assessed and correlated with the aphids' (1) life cycle, (2) attraction towards the plants, and (3) ability to transmit BMYV. Both fungi colonized the plants, and the GxABT-1 isolate impaired the aphids' life cycle. Myzus persicae were more attracted to leaf discs from non-treated plants than to the fungal-treated ones. Interestingly, when the choice test dealt only with the fungal treatments, aphids were more attracted to leaves from plants harboring Gx-ABT-1 than those with GHA. Moreover, no significant impact was observed for BMYV transmission despite the slight decrease in the viral load in GxABT-1 isolate-treated plants. Our findings constitute a baseline to delve more into the performance of the new endemic isolate B. bassiana in other pathosystems using different treatment methods.

Enzyme regulation patterns in fungal inoculated wheat may reflect resistance and tolerance towards an insect herbivore

Seed inoculation with entomopathogenic fungi (EPF) causes plant-mediated effects against arthropod herbivores, but the responses vary among EPF isolates. We used a wheat model system with three isolates representing Beauveria bassiana and Metarhizium spp. causing either negative or positive effects against the aphid Rhopalosiphum padi. Activities of six carbohydrate enzymes increased in plants showing biomass build-up after EPF inoculations. However, only aldolase activity showed positive correlation with R. padi numbers. Plants inoculated with M. robertsii hosted fewest aphids and showed increased activity of superoxide dismutase, implying a defense strategy of resistance towards herbivores. In M. brunneum-inoculated plants, hosting most R. padi, activities of catalase and glutathione reductase were increased suggesting enhanced detoxification responses towards aphids. However, M. brunneum simultaneously increased plant growth indicating that this isolate may cause the plant to tolerate herbivory. EPF seed inoculants may therefore mediate either tolerance or resistance towards biotic stress in plants in an isolate-dependent manner.

Adaptation of an arthropod predator to a challenging environment is associated with a loss of a genome-wide plastic transcriptional response

BACKGROUND

Structural and chemical plant defence traits may reduce the efficacy of biological control agents in integrated pest management. Breeding programmes have shown arthropod predators' potential to acclimate to challenging host plants. However, whether and how these predators adapt to novel plant environments remain unclear. Using the predatory mite Phytoseiulus persimilis - herbivorous mite Tetranychus urticae system in an experimental evolution setup, we studied the adaptation mechanisms to tomato and cucumber, plants that possess a distinct repertoire of defensive traits.

RESULTS

Experimental evolution experiments on whole plants revealed that allowing P. persimilis to adapt to tomatoes led to an ~100% larger population size. Independent feeding assays showed that tomato- and cucumber-adapted prey reduced predator fecundity. The deleterious effect of ingesting low-quality prey persisted after adaptation of the predator to both cucumber and tomato. We demonstrated that jasmonic acid (JA)-dependent defences reduce prey quality by evaluating predator performance on prey fed on JA defence-deficient tomato plants. Transcriptomic profiling of the replicated P. persimilis lines showed that long-term propagation on tomato and cucumber plants produces distinctive gene-expression levels. Predator adaptation to tomatoes results in the loss of a large transcriptional response, in which predicted cuticle-building rather than detoxification pathways are affected.

CONCLUSION

We showed that the adaptation of predatory arthropods to a novel, challenging plant does not necessarily occur via the prey, but rather through the physical environment of the plant. We provided first insights into the underlying molecular mechanisms. © 2023 Society of Chemical Industry.

Development of a Green, Quick, and Efficient Method Based on Ultrasound-Assisted Extraction Followed by HPLC-DAD for the Analysis of Bioactive Glycoalkaloids in Potato Peel Waste

α-Solanine and α-chaconine are the two most predominant glycoalkaloids (GAs) present in potato. Potato peel contains a high concentration of GAs, which are especially interesting for application in the pharmaceutical industry due to their different beneficial properties (such as anticarcinogenic, anti-inflammatory, antiallergic, antipyretic, antiviral, fungicide, and antibiotic activities, among others); so, potato peel waste can be valorized by extracting these biologically active compounds. For this, a green, quick, and efficient miniaturized analytical approach based on ultrasound-assisted extraction (UAE) combined with HPLC-DAD was developed to quantify α-solanine and α-chaconine in potato peel. Some parameters of the extraction were optimized, including the extraction method, the type of solvent, and the sample/solvent ratio, by a three-factor, three-level (33) full factorial experimental design. The optimal extraction conditions were obtained with UAE using methanol as a solvent and a sample/solvent ratio of 1:10 (w/v, g/mL). The analytical greenness metric for sample preparation (AGREEprep) tool was used to assess the greenness of the methods used. The tool revealed an acceptable green analysis, with 0.61 points. The method was validated and applied to the evaluation of GAs in the peel of 15 commercial varieties of potato. The amount of glycoalkaloids found in the samples evaluated ranged from 143 to 1273 mg/kg and from 117 to 1742 mg/kg dry weight for α-solanine and α-chaconine, respectively. These results reveal the important variability that exists between potato varieties; so, their analysis is of great importance to select the most suitable ones for biovalorization (e.g., the Amandine and Rudolph varieties, with around 3000 mg/kg, in total, of both GAs). To provide higher stability to the peel during storage, freeze-drying or a medium-temperature drying process resulted preferable to avoid GA degradation. Overall, this study will contribute to the expansion of the future biovalorization of potato peel waste as well as provide a powerful analytical tool for GA analysis.

Positive effects of Cordyceps cateniannulata colonization in tobacco: Growth promotion and resistance to abiotic stress

Background

Entomopathogenic fungi can live in insects to cause disease and death and are the largest group of entomopathogenic microorganisms. Therefore, these fungi are best known for their microbial control potential. Importantly, they also have other beneficial effects, including promoting plant growth and development by colonizing plant. Here, the study sought to identify specific strains of the entomopathogenic fungus, Cordyceps cateniannulata that would form endophytic associations with tobacco, thus benefiting plant growth and resistance to abiotic stresses, thereby highlighting the application of entomopathogenic fungi in tobacco.

Methods

The C. cateniannulata-tobacco symbiont was constructed by root irrigation. The effects of C. cateniannulata on tobacco growth were evaluated by measuring the maximum leaf length, maximum leaf width, number of leaves, plant height, stem thickness, stem circumference, dry and fresh shoot weight 7, 14, 21, and 28 days after colonization. The peroxidase, catalase, superoxide dismutase, and malondialdehyde were measured to observe the impact of C. cateniannulata on tobacco defense enzyme activity. Finally, high-throughput sequencing was used to access microbial communities in the rhizosphere, with data subsequently linked to growth indicators.

Results

After tobacco was inoculated with C. cateniannulata X8, which significantly promoted growth and related enzyme activity, malondialdehyde was decreased. The most significant impact was on peroxidase, with its activity being upregulated by 98.20, 154.42, 180.65, and 170.38% in the four time periods, respectively. The high throughput sequencing results indicated that C. cateniannulata had changed the rhizosphere microbial relative abundances, such as increasing Acidobacteria and Ascomycetes, and decreasing Actinomycetes and Basidiomycetes. The redundancy analysis showed that C. cateniannulata significantly boosted tobacco growth by reducing the abundance of specific dominant genera such as Stachybotrys, Cephalotrichum, Streptomyces, Isoptericola, and Microbacterium.

Conclusion

Specific strains of C. cateniannulata can be introduced into host plants as endophytes, resulting in promotion of host plant growth and increased resistance to abiotic stress and microbial pathogens. The study provides a foundation for future studies of C. cateniannulata as an ecological agent.

Promotion of Arabidopsis immune responses by a rhizosphere fungus via supply of pipecolic acid to plants and selective augment of phytoalexins

The ascomycete insect pathogenic fungi such as Metarhizium species have been demonstrated with the abilities to form the rhizosphere or endophytic relationships with different plants for nutrient exchanges. In this study, after the evident infeasibility of bacterial disease development in the boxed sterile soils, we established a hydroponic system for the gnotobiotic growth of Arabidopsis thaliana with the wild-type and transgenic strain of Metarhizium robertsii. The transgenic fungus could produce a high amount of pipecolic acid (PIP), a pivotal plant-immune-stimulating metabolite. Fungal inoculation experiments showed that M. robertsii could form a non-selective rhizosphere relationship with Arabidopsis. Similar to the PIP uptake by plants after exogenous application, PIP level increased in Col-0 and could be detected in the PIP-non-producing Arabidopsis mutant (ald1) after fungal inoculations, indicating that plants can absorb the PIP produced by fungi. The transgenic fungal strain had a better efficacy than the wild type to defend plants against the bacterial pathogen and aphid attacks. Contrary to ald1, fmo1 plants could not be boosted to resist bacterial infection after treatments. After fungal inoculations, the phytoalexins camalexin and aliphatic glucosinolate were selectively increased in Arabidopsis via both PIP-dependent and -independent ways. This study unveils the potential mechanism of the fungus-mediated beneficial promotion of plant immunity against biological stresses. The data also highlight the added values of M. robertsii to plants beyond the direct suppression of insect pest populations.

The Entomopathogenic Fungi Metarhizium brunneum and Beauveria bassiana Promote Systemic Immunity and Confer Resistance to a Broad Range of Pests and Pathogens in Tomato

Biocontrol agents can control pathogens by reenforcing systemic plant resistance through systemic acquired resistance (SAR) or induced systemic resistance (ISR). Trichoderma spp. can activate the plant immune system through ISR, priming molecular mechanisms of defense against pathogens. Entomopathogenic fungi (EPF) can infect a wide range of arthropod pests and play an important role in reducing pests' population. Here, we investigated the mechanisms by which EPF control plant diseases. We tested two well studied EPF, Metarhizium brunneum isolate Mb7 and Beauveria bassiana as the commercial product Velifer, for their ability to induce systemic immunity and disease resistance against several fungal and bacterial phytopathogens, and their ability to promote plant growth. We compared the activity of these EPF to an established biocontrol agent, Trichoderma harzianum T39, a known inducer of systemic plant immunity and broad disease resistance. The three fungal agents were effective against several fungal and bacterial plant pathogens and arthropod pests. Our results indicate that EPF induce systemic plant immunity and disease resistance by activating the plant host defense machinery, as evidenced by increases in reactive oxygen species production and defense gene expression, and that EPF promote plant growth. EPF should be considered as control means for Tuta absoluta. We demonstrate that, with some exceptions, biocontrol in tomato can be equally potent by the tested EPF and T. harzianum T39, against both insect pests and plant pathogens. Taken together, our findings suggest that EPF may find use in broad-spectrum pest and disease management and as plant growth promoting agents.

Regulation of Tomato Specialised Metabolism after Establishment of Symbiosis with the Endophytic Fungus Serendipita indica

Specialised metabolites produced during plant-fungal associations often define how symbiosis between the plant and the fungus proceeds. They also play a role in the establishment of additional interactions between the symbionts and other organisms present in the niche. However, specialised metabolism and its products are sometimes overlooked when studying plant-microbe interactions. This limits our understanding of the specific symbiotic associations and potentially future perspectives of their application in agriculture. In this study, we used the interaction between the root endophyte Serendipita indica and tomato (Solanum lycopersicum) plants to explore how specialised metabolism of the host plant is regulated upon a mutualistic symbiotic association. To do so, tomato seedlings were inoculated with S. indica chlamydospores and subjected to RNAseq analysis. Gene expression of the main tomato specialised metabolism pathways was compared between roots and leaves of endophyte-colonised plants and tissues of endophyte-free plants. S. indica colonisation resulted in a strong transcriptional response in the leaves of colonised plants. Furthermore, the presence of the fungus in plant roots appears to induce expression of genes involved in the biosynthesis of lignin-derived compounds, polyacetylenes, and specific terpenes in both roots and leaves, whereas pathways producing glycoalkaloids and flavonoids were expressed in lower or basal levels.

Root-Associated Entomopathogenic Fungi Modulate Their Host Plant's Photosystem II Photochemistry and Response to Herbivorous Insects

The escalating food demand and loss to herbivores has led to increasing interest in using resistance-inducing microbes for pest control. Here, we evaluated whether root-inoculation with fungi that are otherwise known as entomopathogens improves tomato (Solanum lycopersicum) leaflets' reaction to herbivory by Spodoptera exigua (beet armyworm) larvae using chlorophyll fluorescence imaging. Plants were inoculated with Metarhizium brunneum or Beauveria bassiana, and photosystem II reactions were evaluated before and after larval feeding. Before herbivory, the fraction of absorbed light energy used for photochemistry (Φ_PSII) was lower in M. brunneum-inoculated than in control plants, but not in B. bassiana-inoculated plants. After herbivory, however, Φ_PSII increased in the fungal-inoculated plants compared with that before herbivory, similar to the reaction of control plants. At the same time, the fraction of energy dissipated as heat (Φ_NPQ) decreased in the inoculated plants, resulting in an increased fraction of nonregulated energy loss (Φ_NO) in M. brunneum. This indicates an increased singlet oxygen (¹O₂) formation not detected in B. bassiana-inoculated plants, showing that the two entomopathogenic fungi differentially modulate the leaflets' response to herbivory. Overall, our results show that M. brunneum inoculation had a negative effect on the photosynthetic efficiency before herbivory, while B. bassiana inoculation had no significant effect. However, S. exigua leaf biting activated the same compensatory PSII response mechanism in tomato plants of both fungal-inoculated treatments as in control plants.