Enhanced Plant Defense Research Articles

The Roles of Phytohormones in Plant Defense Mechanisms Against the Brown Planthopper

The brown planthopper (BPH; Nilaparvata lugens Stål) is the most significant insect pest compromising rice production globally. Phytohormones, which are small organic compounds produced by plants, play a crucial role in regulating plant growth and development. Nevertheless, extensive research has established that phytohormones are essential in modulating plant defense against BPH. Plants can achieve equilibrium between growth and defense by utilizing the intricate network of phytohormone signaling pathways to initiate optimal and efficient defensive responses to insects. In this review, we primarily address the roles of phytohormones in conferring resistance against BPH, with a focus on hormone cross-talk. We also discuss the potential value of integrating hormones with other agricultural practices to enhance plant defense and agricultural yield, which highlights the significance of novel approaches for environment-friendly insect pest management.

Effect of elevated ammonium on biotic and abiotic stress defense responses and expression of related genes in cucumber (Cucumis sativus L.) plants

Ammonium (NH4+) enhances plant defense mechanisms but can be phytotoxic as the sole nitrogen source. To investigate the impact of a balanced NH4+ and NO3− ratio on plant defense parameters without adverse effects, cucumber plants (Cucumis sativus L.) were grown under control (14 mM NO3− + 2 mM NH4+) and elevated level of NH4+ (eNH4+, 8 mM NO3−+ 8 mM NH4+). Plants subjected to eNH4+ showed significantly increased shoot and root biomass by about 41% and 47%, respectively. Among the antioxidant enzymes studied, ascorbate peroxidase (EC 1.11.1.11) activity was increased up to 3.3 fold in eNH4+ compared with control plants, which was associated with enhanced resistance to paraquat. Upregulation of PATHOGENESIS RELATED PROTEIN 4 (PR4) and LIPOXYGENASE 1 (LOX1), accompanied by increased concentrations of salicylic acid and nitric oxide, conferred more excellent resistance of eNH4+ plants to powdery mildew infection. However, the expression levels of ACC OXIDASE 1 (ACO1) and RESPIRATORY BURST OXIDASE HOMOLOGS B (RBOHB) were lower in eNH4+ plants, which was consistent with decreased NADPH oxidase activity and lower leaf H2O2 levels. The biosynthesis of phenolics was enhanced, whereas the activities of polymerizing enzymes and lignin deposition were reduced by half in eNH4+ plants. Besides, a significant effect on plant biomass under salt or drought stress has not been observed between control and eNH4+ plants. These results showed that different defense pathways are distinctively affected by eNH4+ treatment, and the NH4+ to NO3− ratio may play a role in fine-tuning the plant defense response.

Respons Fisiologis Bibit Kopi Robusta dalam Kondisi Cekaman Kekeringan terhadap Aplikasi Trichoderma spp. Cair

Abiotic stresses caused by climate change can affect on the growth of coffee trees. The application of liquid Trichoderma spp. might stimulate growth and enhance plant defense mechanisms in suboptimal conditions. The purpose of this study was to Evaluating the physiological responses of Robusta coffee seedlings BP 939 and BP 308 and obtaining Robusta coffee seedlings that produce the best physiological responses under drought stress conditions against Trichoderma spp. applications in liquid medium. The experiment was carried out using a Randomized Group Design (RAG) with 8 treatments repeated 4 times, namely : coffea clone BP 939 control; coffea clone BP 308 control.; coffea clone BP 939 Trichoderma spp.; coffea clone BP 308 Trichoderma spp.; coffea clone BP 939 with drought; coffea clone BP 308 with drought; coffea clone BP 939 with drought + Trichoderma spp.; coffea clone BP 308 with drought + Trichoderma spp. The experiment results show that the application of Trichoderma spp. in liquid medium does not exhibit significant physiological responses, and the Robusta coffee seedlings of clones BP 939 and BP 308 show the same effect under drought stress conditions. However, the Robusta coffee clone BP 308 treated with Trichoderma spp. showed significant physiological responses at 12 hours after treatment.

Navigational Signals for Insect and Slug Parasitic Nematodes: The Role of Ascorbate-Glutathione System and Volatiles Released by Insect-Damaged Sweet Pepper Roots.

This study of underground multitrophic communication, involving plant roots, insects, and parasitic nematodes, is an emerging field with significant implications for understanding plant-insect-nematode interactions. Our research investigated the impact of wireworm (Agriotes lineatus L. [Coleoptera: Elateridae]) infestations on the ascorbate-glutathione system in sweet pepper (Capsicum annuum L.) plants in order to study the potential role in root-exudate-mediated nematode chemotaxis. We observed that an A. lineatus infestation led to a decrease in leaf ascorbate levels and an increase in root ascorbate, with corresponding increases in the glutathione content in both roots and leaves. Additionally, a pigment analysis revealed increased carotenoid and chlorophyll levels and a shift towards a de-epoxidized state in the xanthophyll cycle. These changes suggest an individual and integrated regulatory function of photosynthetic pigments accompanied with redox modifications of the ascorbate-glutathione system that enhance plant defense. We also noted changes in the root volatile organic compound (VOC). Limonene, methyl salicylate, and benzyl salicylate decreased, whereas hexanal, neoisopulegol, nonanal, phenylethyl alcohol, m-di-tert-butylbenzene, and trans-β-ionone increased in the roots of attacked plants compared to the control group. Most notably, the VOC hexanal and amino acid exudate cysteine were tested for the chemotaxis assay. Nematode responses to chemoattractants were found to be species-specific, influenced by environmental conditions such as temperature. This study highlights the complexity of nematode chemotaxis and suggests that VOC-based biological control strategies must consider nematode foraging strategies and environmental factors. Future research should further explore these dynamics to optimize nematode management in agricultural systems.

An asymptomatic geminivirus activates autophagy and enhances plant defenses against diverse pathogens

Plant viral diseases cause great losses in agricultural production. Virus cross-protection is a strategy in which a mild virus is employed to shield plants against subsequent infections by severe viral strains. However, this approach is restricted to protection against the same viruses. In this study, we observed that pre-inoculation with apple geminivirus (AGV) reduced the accumulation of secondarily infected heterologous viruses, such as cucumber mosaic virus, potato virus X, and tobacco mosaic virus in Nicotiana benthamiana, tomato, and pepper plants. Transcriptional expression analysis showed that autophagy-related genes were transcriptionally up-regulated upon AGV inoculation at an early stage of infection. Accordingly, autophagic activity was observed to be elevated following AGV infection. Interestingly, AGV accumulation was reduced in autophagy-deficient plants, suggesting that autophagy activation promotes AGV infection in the plant. Moreover, pre-inoculation with AGV provided cross-protection against infection with a phytopathogenic bacterium (Pseudomonas syringae) and fungus (Botrytis cinerea) in Nicotiana species. In summary, our study showed that AGV, an asymptomatic virus, could protect plants against severe viral, fungal, and bacterial diseases to some extent through the activation of autophagy pathways, highlighting its potential as a biocontrol agent for managing a wide range of plant crop diseases in the field.

The feeding behavior of Diaphorina citri monitored by using an electrical penetration graph (DC-EPG) on citrus plants treated with Bacillus cereus and Bacillus velezensis

Diaphorina citri, an important pest and insect vector that can transmit the pathogenic bacteria Candidatus Liberibacter asiaticus, causing Huanglongbing disease, is one of many challenges in citrus agriculture. Integrated pest management by utilizing microorganisms is a wise and efficient alternative without damaging the environment. Utilization of Plant Growth Promoting Rhizobacteria (PGPR), such as Bacillus cereus and B. velezensis, is a potential strategy for the biological control of plant diseases or insect vectors. By inducing systemic resistance in plants, PGPR can enhance plant defense against diseases and insect pests while activating molecular and physiological changes in plants. This research aimed to determine the effect of B. cereus and B. velezensis on the plant growth and feeding behavior of D. citri. The height and volume of the plant canopy were observed periodically for 6 months, while the feeding behavior of D. citri was monitored using the Electrical Penetration Graph (DC-EPG). The results showed increased height and volume of the citrus plant canopy treated with B. cereus, indicating that B. cereus could act as a PGPR. The application of B. cereus and B. velezensis to citrus seedlings affected the feeding behavior of D. citri. D citri showed difficulty in penetrating the phloem tissue of citrus plants.

Identifying the key motif essential for enhancing plant defense against Botrytis cinerea by β-glucanase from Bacillus velezensis LJ02

The glycosyl hydrolase β-glucanase elicits plant immune responses against pathogens and enhances plant immunity by activating signaling pathways. The specific functional domains responsible for disease prevention remain unclear. In this study, transient expression of β-glucanase significantly increased leaves resistance to Botrytis cinerea in Nicotiana benthamiana systemic leaves. Through sequence alignment and similarity analysis, five conserved motifs in the amino acid sequence of β-glucanase were identified, and five deletion mutants were generated to investigate its essential regions further. Notably, the N-terminal amino acid sites 5-54 deletion mutation of β-glucanase decreased resistance to B. cinerea infection. These results indicate that N-terminal amino acids 5-54 (N54) are crucial for β-glucanase induced N. benthamiana defense response and for enhancing resistance to B. cinerea. Further analysis using real-time quantitative fluorescent PCR (qRT-PCR) revealed a significant reduction in gene expression within the N54 region compared to that of unmutated β-glucanase. Additionally, there was a notable reduction in the relative expression levels of FRK, CYP71D20, WRKY7, WRKY8, ACRE31 and PTI genes. Therefore, the first 50 amino acids at positions 5-54 within the N-terminal domain were essential for triggering plant defense responses and enhancing resistance against B. cinerea infection. This study provides an important theoretical foundation for systematic investigation into key functional domains within β-glucanase that trigger defensive responses in plants against B. cinerea.

Optimizing oilseed rape growth: Exploring the effect of foliar biostimulants on the interplay among metabolism, phenology, and yield.

The current agricultural system is in search of new strategies to achieve a more sustainable production while keeping or even increasing crop yield and quality. In this scenario, the application of biostimulants constitutes a potent solution. In the current study, the impact of a blue-green microalgal extract (MB) and a pig tissue hydrolysate (PTH) on rapeseed plants' development was characterized. Obtained results revealed a positive effect on yield parameters of plants treated with MB and, especially, PTH; this was associated to an improvement on the photosynthetic performance. Moreover, this study remarked the effects of biostimulants on plant phenology through their pivotal role in modulating developmental processes. More specifically, proteomic, metabolomic, and hormone content analyses revealed distinct alterations associated with the acceleration of phenology induced by biostimulant application. Additionally, some antioxidant enzymes and stress-related compounds were up-regulated upon MB and PTH treatments, indicating enhanced plant defense mechanisms in response to accelerated phenological transitions. Such findings highlight the intricate interplay between biostimulants and plant physiology, wherein biostimulants orchestrate rapid developmental changes, ultimately influencing growth dynamics. Altogether, the current study reveals that the application of both MB and PTH biostimulants promoted rapeseed plant phenology and productivity associated with an improvement in the photosynthetic machinery while boosting other physiological and molecular mechanisms.

Duality of H2O2 detoxification and immune activation of Ralstonia solanacearum alkyl hydroperoxide reductase C (AhpC) in tobacco

Although microbial pathogens utilize various strategies to evade plant immunity, host plants have evolved powerful defense mechanisms that can be activated in preparation for threat by infective organisms. Here, we identified one 24 kDa alkyl hydroperoxide reductase C (AhpC) from the culture supernatant of Ralstonia solanacearum strain FQY-4 (denoted RsAhpC) in the presence of host roots. RsAhpC contributes to H2O2 detoxification and the pathogenicity of R. solanacearum. However, the introduction of RsAhpC into the apoplast could activate immune defense, leading to suppression of pathogen colonization in both Nicotiana benthamiana and the Honghua Dajinyuan (HD) cultivar of N. tabacum. Consequently, overexpression of RsAhpC in the HD cultivar enhanced the resistance of tobacco to bacterial wilt disease caused by FQY-4. Overall, this study provides insight into the arms race between pathogens and their plant hosts. Specifically, it is firstly reported that plants can sense pathogen-derived AhpC to activate defenses, in addition to the role of AhpC in pathogen ROS detoxification. Therefore, the macromolecule AhpC produced by Ralstonia solanacearum has the ability to enhance plant defense as an elicitor, which provides a practical strategy for disease resistance breeding.

Engineering the Rhizosphere Microbiome with Plant Growth Promoting Bacteria for Modulation of the Plant Metabolome.

Plant-growth-promoting bacteria (PGPB) have beneficial effects on plants. They can promote growth and enhance plant defense against abiotic stress and disease, and these effects are associated with changes in the plant metabolite profile. The research problem addressed in this study was the impact of inoculation with PGPB on the metabolite profile of Salicornia europaea L. across controlled and field conditions. Salicornia europaea seeds, inoculated with Brevibacterium casei EB3 and Pseudomonas oryzihabitans RL18, were grown in controlled laboratory experiments and in a natural field setting. The metabolite composition of the aboveground tissues was analyzed using GC-MS and UHPLC-MS. PGPB inoculation promoted a reconfiguration in plant metabolism in both environments. Under controlled laboratory conditions, inoculation contributed to increased biomass production and the reinforcement of immune responses by significantly increasing the levels of unsaturated fatty acids, sugars, citric acid, acetic acid, chlorogenic acids, and quercetin. In field conditions, the inoculated plants exhibited a distinct phytochemical profile, with increased glucose, fructose, and phenolic compounds, especially hydroxybenzoic acid, quercetin, and apigenin, alongside decreased unsaturated fatty acids, suggesting higher stress levels. The metabolic response shifted from growth enhancement to stress resistance in the latter context. As a common pattern to both laboratory and field conditions, biopriming induced metabolic reprogramming towards the expression of apigenin, quercetin, formononetin, caffeic acid, and caffeoylquinic acid, metabolites that enhance the plant's tolerance to abiotic and biotic stress. This study unveils the intricate metabolic adaptations of Salicornia europaea under controlled and field conditions, highlighting PGPB's potential to redesign the metabolite profile of the plant. Elevated-stress-related metabolites may fortify plant defense mechanisms, laying the groundwork for stress-resistant crop development through PGPB-based inoculants, especially in saline agriculture.

Unveiling the biocontrol potential of Pseudomonas syringae through seed biopriming against charcoal rot disease in maize

In Punjab, Pakistan, maize production faces a significant threat from charcoal rot disease, caused by the soil-borne fungus Macrophomina phaseolina. To mitigate this issue and ensure food safety, researchers explored the potential of Pseudomonas syringae, a harmless gram-negative bacterium against charcoal rot disease in maize. Maize seeds treated with P. syringae (PS) were planted in soil containing the charcoal rot fungus in pot experiments. The outcome was then compared with the impact of NPK fertilizers and mancozeb fungicide. The positive control, with M. phaseolina alone, exhibited high disease severity resulting in a greater reduction of 30–70 % in the plant's biophysical and biochemical traits. Mancozeb, NPK, or PS, managed 66, 41, and 55 % of diseases and improved the biophysical and biochemical traits of the plants by up to 200 %. Applying P. syringae in combination with the recommended dose of NPK was found as the most promising treatment which significantly improved plant resistance by managing 90 % of disease through improving growth and biochemical traits (up to 300 %). This research suggests effective control of M. phaseolina by combining P. syringae with NPK, enhancing plant defense mechanisms and potentially improving pathogen-induced resistance in the maize plants.

Green Routes: Exploring Protein-Based Virus-like Nanoparticle Transport and Immune Activation in Nicotiana benthamiana for Biotechnological Applications.

Viral, bacterial, fungal, and nematode infections cause significant agricultural losses, with limited treatment options, necessitating novel approaches to enhance plant defense systems and protection against pathogens. Virus-like nanoparticles (VLPs), extensively used in animal and human therapies (e.g., vaccines and immune enhancers), hold potential for novel agricultural solutions and advancing plant nanotechnology. This study employed various methodologies, including VLP production, confocal microscopy, and real-time qPCR. Our findings demonstrated the presence of 30 nm Qβ-VLPs, fluorescently labeled, within the intercellular space of Nicotiana benthamiana leaves one hour post-infiltration. Furthermore, infiltration with Qβ-VLPs led to an upregulation of key defense genes (NbPR1a, NbPR5, NbNPR, NbERF1, NbMYC2, and NbLRR2) in treated plants. Using RT-qPCR, a significant increase in the relative expression levels of defense genes was observed, with sustained high levels of NbERF1 and NbLRR2 even after 24 h. These findings suggest that Qβ-VLPs effectively upregulate genes crucial for pathogen defense in N. benthamiana, initiating PAMP-triggered immunity and launching signaling cascades that enhance defense mechanisms. This innovative application of VLPs to activate plant defense programs advances plant nanobiotechnology, offering new agricultural solutions.

Optimization and characterization of essential oil-loaded nanoemulsions for enhanced antiviral activity against tobacco mosaic virus (TMV) in tobacco plants

Tobacco mosaic virus (TMV) is a significant viral pathogen that infects various economically important crops, including tobacco, tomatoes, and cucumbers. The current study aimed to develop and optimize essential oil-loaded nanoemulsions using Response Surface Methodology (RSM) to enhance antiviral activity against TMV in Nicotiana tabacum plants. Essential oils from tea tree (Melaleuca alternifolia) and lime peel (Citrus latifolia) were chemically analyzed using gas chromatography-mass spectrometry (GC-MS). Terpinene-4-ol (70.92 %) and trans-isolimonene (33.82 %) were identified as the major components in tea tree and lime peel oils, respectively. RSM was used to optimize the nanoemulsion formulations based on oil concentration, hydrophilic-lipophilic balance (HLB), and stirring speed. Optimal tea tree oil (TTEO) and lime peel oil (LPEO) nanoemulsions were developed and characterized using Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and particle size analysis. The antiviral efficacy of the optimized formulations was tested against TMV using RT-qPCR analysis and physiological measurements. TTEO nanoemulsions significantly inhibited TMV expression by 89.78 %, while LPEO nanoemulsions achieved a 42.22 % reduction after six days. Additionally, these essential oils (EOs) enhanced plant defense mechanisms by modulating the activities of phenylalanine ammonia-lyase (PAL) and peroxidase (POD), along with maintaining chlorophyll levels. This study demonstrates that TTEO and LPEO nanoemulsions offer promising eco-friendly antiviral agents for TMV management in tobacco plants. The research underscores the potential of essential oil-based formulations in mitigating viral infections in crops, providing a sustainable alternative to synthetic chemicals.

Effector MoSDT1 enhances Magnaporthe oryzae virulence and plays a dual role in regulating rice defense.

C2H2 zinc effectors are a class of pathogen proteins that play a dual role in plant-pathogen interactions, promoting pathogenicity and enhancing plant defense. In our previous research, we identified Magnaporthe oryzae Systemic Defense Trigger 1 (MoSDT1) as a C2H2 zinc effector that activates rice (Oryza sativa) defense when overexpressed in rice. However, its regulatory roles in pathogenicity and defense require further investigation. In this study, we generated an MoSDT1 overexpressing strain and 2 knockout strains of M. oryzae to assess the impact of MoSDT1 on pathogenicity, rice defense, and phenotypic characteristics. Our analyses revealed that MoSDT1 substantially influenced vegetative growth, conidia size, and conidiation, and was crucial for the virulence of M. oryzae while suppressing rice defense. MoSDT1 localized to the nucleus and cytoplasm of rice, either dependent or independent of M. oryzae delivery. Through RNA-seq, scRNA-seq, and ChIP-seq, we identified that MoSDT1 modulates rice defense by regulating the phosphorylation and ubiquitination of various rice signaling proteins, including transcription factors, transcription repressors, kinases, phosphatases, and the ubiquitin system. These findings provide valuable insights into the regulatory mechanisms of C2H2 zinc finger effector proteins and offer important foundational information for utilizing their target genes in disease resistance breeding and the design of targets for disease management.

Salicylic acid-mediated alleviation of salt stress: Insights from physiological and transcriptomic analysis in Asarum sieboldii Miq

As global agriculture faces the pressing threat of salt stress, innovative solutions are imperative for sustainable agriculture. The remarkable potential of salicylic acid (SA) in enhancing plant resilience against environmental stressors has recently gained attention. However, the specific molecular mechanisms by which SA mitigates salt stress in Asarum sieboldii Miq., a valuable medicinal plant, remain poorly understood. Here, we evaluated the physiological and transcriptomic regulatory responses of A. sieboldii under salt stress (100 mM NaCl), both in the presence (1 mM SA) and absence of exogenous SA. The results highlighted that SA significantly alleviates salt stress, primarily through enhancing antioxidant activities as evidenced by increased superoxide dismutase, and peroxidase activities. Additionally, we observed an increment in chlorophyll (a and b), proline, total soluble sugar, and plant fresh weight, along with a decrease in malondialdehyde contents. Transcriptome analysis suggested consistency in the regulation of many differentially expressed genes and transcription factors (TFs); however, genes targets (GSTs, TIR1, and NPR1), and TFs (MYB, WRKY, TCP, and bHLH) possessed expressional uniqueness, and majority had significantly up-regulated trends in SA-coupled salt stress treatments. Further, bioinformatics and KEGG enrichment analysis indicated several SA-induced significantly enriched biological pathways. Specifically, plant hormone signal transduction was identified as being populated with key genes distinctive to auxin, cytokinin, ethylene, and salicylic acid signaling, suggesting their important role in salt stress alleviation. Inclusively, this report presents a comprehensive analysis encompassing gene targets, TFs, and biological pathways, and these insights may offer a valuable contribution to our knowledge of SA-mediated regulation and its crucial role in enhancing plant defense against diverse abiotic stressors.

Root Exudates Metabolic Profiling Confirms Distinct Defense Mechanisms Between Cultivars and Treatments with Beneficial Microorganisms and Phosphonate Salts Against Verticillium Wilt in Olive Trees.

Root exudates play a key role in the life cycle of Verticillium dahliae, the causal agent of Verticillium wilt diseases, because they induce microsclerotia germination to initiate plant infection through the roots. In olive plants, the genotype and the application of biological control agents (BCAs) or phosphonate salts influence the ability of root exudates to decrease V. dahliae viability. Understanding the chemical composition of root exudates could provide new insights into the mechanisms of olive plant defense against V. dahliae. Therefore, the main goal of this study was to analyze the metabolomic profiles of root exudates collected from the olive cultivars Arbequina, Frantoio, and Picual subjected to treatment with BCAs (Aureobasidium pullulans AP08, Bacillus amyloliquefaciens PAB-024) or phosphonate salts (copper phosphite, potassium phosphite). These treatments were selected due to their effectiveness as inducers of resistance against Verticillium wilt in olive plants. Our metabolomic analysis revealed that the olive cultivars exhibited differences in root exudates, which could be related to the different degrees of susceptibility to V. dahliae. The composition of root exudates also changed with the application of BCAs or phosphonate fertilizer, highlighting the complex and dynamic nature of the interactions between olive cultivars and treatments preventing V. dahliae infections. Thus, the identification of genotype-specific metabolic changes and specific metabolites induced by these treatments emphasizes the potential of resistance inducers for enhancing plant defense and promoting the growth of beneficial microorganisms.

Biological Control of Tomato Bacterial Leaf Spots and Its Impact on Some Antioxidant Enzymes, Phenolic Compounds, and Pigment Content.

Tomato bacterial spots, caused by Xanthomonas campestris pv. vesicatoria (Xcv1) and X. euvesicatoria (Xe2), as well as bacterial specks, caused by two strains of Pseudomonas syringae pv. tomato (Pst1 and Pst2), represent significant threats to tomato production in the El-Sharkia governorate, often resulting in substantial yield losses. The objective of this study was to evaluate the efficacy of various biocontrol culture filtrates, including bacteria and fungi agents, in managing the occurrence and severity of these diseases, while also monitoring physiological changes in tomato leaves, including antioxidant enzymes, phenolics, and pigment content. The culture filtrates from examined Trichoderma species (T. viride, T. harzianum, and T. album), as well as the tested bacteria (Bacillus subtilis, Pseudomonas fluorescens, and Serratia marcescens) at concentrations of 25%, 50%, and 100%, significantly inhibited the proliferation of pathogenic bacteria In vitro. For the In vivo experiments, we used specific doses of 5 mL of spore suspension per plant for the fungal bioagents at a concentration of 2.5 × 107 spores/mL. The bacterial bioagents were applied as a 10 mL suspension per plant at a concentration of 1 × 108 CFU/mL. Spraying the culture filtrates of the tested bioagents two days before infection In vivo significantly reduced disease incidence and severity. Trichoderma viride exhibited the highest efficacy among the fungal bioagents, followed by T. harzianum and T. album. Meanwhile, the culture filtrate of B. subtilis emerged as the most potent among the bacterial bioagents, followed by P. fluorescens. Furthermore, applying these culture filtrates resulted in elevated levels of chitinase, peroxidase, and polyphenol oxidase activity. This effect extended to increased phenol contents, as well as chlorophyll a, chlorophyll b, and carotenoids in sprayed tomato plants compared to the control treatment. Overall, these findings underscore the potential of these biocontrol strategies to effectively mitigate disease incidence and severity while enhancing plant defense mechanisms and physiological parameters, thus offering promising avenues for sustainable disease management in tomato production.

Plants attacked above-ground by leaf-mining flies change below-ground microbiota to enhance plant defense.

Root-associated microbiomes play a crucial role in plant responses to biotic and abiotic stresses. Plants can enrich beneficial microbes to increase their stress-relieving ability. Above-ground insect herbivory is among the most detrimental stresses for plants, especially to crop production. However, few studies have explored how root-associated microbiomes respond to herbivores and influence plant-defense functions under herbivory stress. We investigate the changes and functional role of root-associated microbial communities under herbivory stress using leafminer (Liriomyza trifolii) and cowpea (Vigna unguiculata) as a focal system. We did this by using a combination of 16S ribosomal RNA gene profiling and metagenomic sequencing to test for differences in co-occurrence networks and functions between cowpea plants infested and noninfested with leafminers. The results demonstrated that leafminer infestation caused a shift in the rhizosphere microbiome, which was characterized by a significant variation in microbiome community structure and composition, the selection of hub microbes involved in nitrogen (N) metabolism, and functional enrichment related to N metabolism. Notably, nitrogen-fixing bacteria Bradyrhizobium species were actively enriched and selected to be hubs in the rhizosphere. Inoculation with Bradyrhizobium enhanced cowpea performance under leafminer stress and increased protease inhibitor levels to decrease leafminer fitness. Overall, our study characterized the changes of root-associated microbiota between leafminer-infested and noninfested cowpea plants and revealed the mechanisms underlying the rhizosphere microbiome shift that enhance plant performance and defense against herbivory. Our findings provide further support for the notion that plants enrich rhizosphere microbes to counteract aboveground insect herbivores.

The proteomic landscape of fall armyworm oral secretion reveals its role in plant adaptation.

The fall armyworm (FAW, Spodoptera frugiperda (J.E. Smith)) is a polyphagous agricultural pest with rapidly evolving adaptations to host plants. We found the oral secretion (OS) of FAW from different plants influences plant defense response differentially, suggesting its role in adapting to host plants. However, the protein expression profile of FAW OS respond to different plants is largely unknown. Here, from the mass spectrometry assay, we identified a total of 256 proteins in the OS of FAW fed on cotton (Gossypium hirsutum L.), tobacco (Nicotiana benthamiana Domin), maize (Zea mays L.) and artificial diet. The FAW OS primarily comprise of 60 proteases, 32 esterases and 92 non-enzymatic proteins. It displays high plasticity across different diets. We found that more than half of the esterases are lipases which have been reported as insect elicitors to enhance plant defense response. The lipase accumulation in cotton-fed larvae was the highest, followed by maize-fed larvae. In the presence of lipase inhibitors, the enhanced induction on defense genes in wounded leaves by OS was attenuated. However, the putative effectors were most highly accumulated in the OS from FAW larvae fed on maize compared to those fed on other diets. We identified that one of them (VRLP4) reduces the OS-mediated induction on defense genes in wounded leaves. Together, our investigation presents the proteomic landscape of the OS of FAW influenced by different diets and reveals diet-mediated plasticity of OS is involved in FAW adaptation to host plants. © 2024 Society of Chemical Industry.

Evaluation of PSP1 biostimulant on Fusarium graminearum-wheat pathosystem: impact on disease parameters, grain yield, and grain quality.

Plant defense elicitors are valuable tools in sustainable agriculture, providing an environmentally friendly and effective means of enhancing plant defense and promoting plant health. Fusarium head blight (FHB) is one of the most important fungal diseases of cereal crops worldwide. The PSP1 is a novel biopesticide formulated based on an elicitor, the extracellular protein AsES, from the fungus Sarocladium strictum. The present work aimed to evaluate the effectiveness of PSP1 in controlling FHB under field conditions. Experiments were conducted during three consecutive growing seasons (2019, 2020, and 2021). Three biostimulant treatments were tested in different physiological stages (from late tillering to heading stage), and FHB inoculations were performed at anthesis. Disease parameters, seed parameters, grain yield, and grain quality parameters were evaluated. Depending on the year and the genotype, reductions in disease incidence (up to 11%) and disease severity (up to 5%) were reported, although these differences could not be attributed to the use of the PSP1 biostimulant. Occasional improvements in seed parameters and grain quality were observed, suggesting that early treatments could work better than late treatments, probably due to early activation/priming of defense response mechanisms. However, more studies are deemed necessary. The use of PSP1 biostimulant in commercial wheat crops could be a biological alternative or complement to traditional chemical fungicides to manage FHB. The reduced environmental impact and the potential benefits in grain yield and quality are other reasons that can generate new adherents of this technology in worldwide agriculture systems in the coming years. © 2024 Society of Chemical Industry.