Whitefly-induced tomato volatiles enhance the virulence of Lecanicillium lecanii

Colonization effect of Beauveria bassiana (Bals.) Vuill. on tomato plant and Bemisia tabaci

Whitefly (Bemisia tabaci) is an insect threatening tomato production in Egypt. This study investigated the impacts of the entomopathogenic fungi species, Beauveria bassiana, isolate against B. tabaci on tomato plants under natural conditions in two seasons (2023-2024). Conidial powder was directly applied to the soil. Fungus was added to the fertilization treatments (BF) and was compared with fertilization (CF) and control (C0). The findings indicated notable significant variations in the population densities of B. tabaci in comparison to the other groups in two seasons. This fungus can also be used as a growth enhancer besides being a biopesticide for tomato crops. Tomato leaf samples were collected in three growth phases: vegetative, flowering, and fruiting phases in addition to ripe tomato fruits. Collected leaves were dried and used to detect defense mechanisms through estimating phenolic compounds such as tannins and flavonoids and total protein content, while tomato fruits were used to estimate ascorbic acid level as a growth promotion indicator in the tested tomato plants. B. bassiana -treated plants showed a significant increase in total tannins compared to fertilization-treated plants and non-significant increase compared to control. While Total Protein Content (TPC) was significantly higher in fertilization-treated plants than in B. bassiana -treated plants and control it was only increased significantly in the bioagent treatment than in the control. For total flavonoids, a non-significant increase was detected in total flavonoids content in B. bassiana-treated plants than in fertilization- treated plants and controls. Beauveria bassiana -treated tomato fruits recorded the highest value of ascorbic acid content, which significantly increased than fertilization treatment and non-significantly increased compared to the control. Generally, the interaction between treatments and growth phases in total tannin content, total protein content, and total flavonoid content was not statistically significant, which means there is no behavior for B. bassiana treatment on the plant resistance mechanism during the different growth stages, and the highest level for each was recorded in the flowering phase compared to the vegetative and fruiting phases. Also, the findings indicated the highest yield was represented by adding B. bassiana to the soil. The obtained results from this study refer to the beneficial role of B. bassiana in systemic resistance induction stimulated by tannin content in the tested tomato plants against whitefly attacks.

Metabolomics and Transcriptomics Reveal the Role of the Terpene Biosynthetic Pathway in the Mechanism of Insect Resistance in Solanum habrochaites

Terpenes are a large variety of natural organic compounds that can enhance the resistance of plants to phytophagous insects through induction. In this study, differential expression genes and metabolites of Alice Craig (AC) and Solanum habrochaite (SH) were screened and analyzed by transcriptomics and metabolomics. The results show that terpene biosynthesis is one of the most crucial secondary metabolic pathways in plants. SH significantly accumulates more terpenes than AC by up regulating the expression of relevant genes. It is worth noting that virus-induced SlHDR silencing not only reduces the expression of downstream genes (SlTPS3, SlFPP, and SlGGPPS) in the terpene biosynthesis pathway, but also significantly affects the synthesis of related terpenoids, there by reducing the insect resistance of tomatoes. The results will be beneficial for understanding the synthesis mechanism of terpenoids in tomatoes and supply new genetic resources for the development of insect-resistant tomatoes.

Tripartite interactions of an endophytic entomopathogenic fungus, Asian corn borer, and host maize under elevated carbon dioxide

BACKGROUND

Biological control of insect pests is encountering an unprecedented challenge in agricultural systems due to the ongoing rise in carbon dioxide (CO2) level. The use of entomopathogenic fungi (EPF) in these systems is gaining increased attention, and EPF as crop endophytes hold the potential for combining insect pest control and yield enhancement of crops, but the effects of increased CO2 concentration on this interaction are poorly understood. Here, the introduction of endophytic EPF was explored as an alternative sustainable management strategy benefiting crops under elevated CO2, using maize (Zea mays), Asian corn borer (Ostrinia furnacalis), and EPF (Beauveria bassiana) to test changes in damage to maize plants from O. furnacalis, and the nutritional status (content of carbon, nitrogen, phosphorus, potassium), biomass, and yield of maize.

RESULTS

The results showed that endophytic B. bassiana could alleviate the damage caused by O. furnacalis larvae for maize plants under ambient CO2 concentration, and this effect was enhanced under higher CO2 concentration. Inoculation with B. bassiana effectively counteracted the adverse impact of elevated CO2 on maize plants by preserving the nitrogen content at its baseline level (comparable with ambient CO2 conditions without B. bassiana). Both simultaneous effects could explain the improvement of biomass and yield of maize under B. bassiana inoculation and elevated CO2.

CONCLUSION

This finding provides key information about the multifaceted benefits of B. bassiana as a maize endophyte. Our results highlight the promising potential of incorporating EPF as endophytes into integrated pest management strategies, particularly under elevated CO2 concentrations. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Fungal infection of insects: molecular insights and prospects

Entomopathogenic fungi (EPF) distribute in different fungal phyla with variable host ranges and play essential role in regulating insect populations by infecting hosts via cuticle penetration. The representative ascomycete EPF of Metarhizium and Beauveria species have been widely used in mechanistic investigations of fungus-insect interactions and as ecofriendly mycoinsecticides. Here, we review the function of diverse genes, pathways, and secondary metabolites associated with EPF stepwise infections. In particular, emerging evidence has shown that EPF have to outcompete insect ectomicrobiotas prior to penetrating cuticles, and subvert or evade host antifungal immunity by using effector-like proteins and chemicals like plant pathogens. Future prospects are discussed for a better understanding of fungal pathobiology, which will provide novel insights into microbe-animal interactions.

Analysis of the virulence, infection process, and extracellular enzyme activities of Aspergillus nomius against the Asian corn borer, Ostrinia furnacalis guenée (Lepidoptera: Crambidae)

The control of Ostrinia furnacalis, a major pest of maize in Xinjiang, is challenging owing to the occurrence of resistant individuals. Entomopathogenic fungi (EPF) are natural insect regulators used as substitutes for synthetic chemical insecticides. The fungus Aspergillus nomius is highly pathogenic to O. furnacalis; however, its virulence characteristics have not been identified. This study aimed to analyse the lethal efficacy, mode of infection on the cuticle, and extracellular enzyme activity of A. nomius against O. furnacalis. We found that the mortality and mycosis of O. furnacalis were dose-dependent when exposed to A. nomius and varied at different life stages. The egg-hatching and adult emergence rates decreased with an increase in conidial suspension. The highest mortality (83.33%, 7 d post-infection [DPI]) and mycosis (74.33%, 7 DPI) and the lowest mortality response (8.52 × 103 conidia mL-1) and median lethal time (4.91 d) occurred in the 3rd instar larvae of O. furnacalis. Scanning electron microscopy indicated that numerous conidia germination and infection structure formation may have contributed to the high pathogenicity of A. nomius against O. furnacalis. There were significant correlations between O. furnacalis mortality and the activities of extracellular protease, lipase, and chitinase of A. nomius. This study revealed the infection process of the highly pathogenic A. nomius against O. furnacalis, providing a theoretical basis and reference for strain improvement and field application of EPF.

Chitinases as key virulence factors in microbial pathogens: Understanding their role and potential as therapeutic targets

Chitinases are crucial for the survival of bacterial and fungal pathogens both during host infection and outside the host in the environment. Chitinases facilitate adhesion onto host cells, act as virulence factors during infection, and provide protection from the host immune system, making them crucial factors in the survival of microbial pathogens. Understanding the mechanisms behind chitinase action is beneficial to design novel therapeutics to control microbial infections. This review explores the role of chitinases in the pathogenesis of bacterial, fungal, and viral infections. The mechanisms underlying the action of chitinases of bacterial, fungal, and viral pathogens in host cells are thoroughly reviewed. The evolutionary relationships between chitinases of various bacterial, fungal, and viral pathogens are discussed to determine their involvement in processes, such as adhesion and host immune system modulation. Gaining a better understanding of the distribution and activity of chitinases in these microbial pathogens can help elucidate their role in the invasion and infection of host cells.

Herbivore-induced tomato plant volatiles lead to the reduction of insecticides susceptibility in Spodoptera litura

Herbivore-induced plant volatiles (HIPVs) have been associated with plant-plant-herbivorous-natural enemies communication and an enhanced response to the subsequent attack. Spodoptera litura is a serious cosmopolitan pest that has developed a high level of resistance to many insecticides. However, the underlying molecular and biochemical mechanism by which HIPV priming reduces S. litura larval sensitivity to insecticides remains largely unknown. This study was conducted to explore the potential of volatile from undamaged, or artificially damaged, or S. litura-damaged tomato plants on the susceptibility of S. litura to the insecticides beta-cypermethrin indoxacarb and chlorpyrifos. We found that larvae exposed to volatile from S. litura-damaged or artificially damaged tomato plants were significantly less susceptible to the three insecticides than those exposed to volatile from undamaged tomato plants. Elevated activities of detoxifying enzymes [cytochrome P450 monooxygenases (P450s), glutathione S-transferases (GSTs), and esterases (ESTs)], were expressed in S. litura larvae exposed to volatile from S. litura-damaged tomato plants than those exposed to volatile from undamaged tomato plants. Similarly, seven detoxification-related genes [GSTs (SlGSTe1, SlGSTo1, and SlGSTe3) and P450s (CYP6B48, CYP9A40, CYP321A7, and CYP321B1)] in the midgut and fat body of larvae were up-regulated under exposure to volatile from S. litura-damaged tomato plants. Increased volatile organic compounds emissions were detected in the headspace of tomato plants damaged by S. litura compared to the undamaged plants. Collectively, these findings suggest that HIPVs can considerably reduce caterpillar susceptibility to insecticides, possibly through induction-enhanced detoxification mechanisms, and provide valuable information for implementing an effective integrated pest management strategy.