The Herbivore-Induced Plant Volatiles Methyl Salicylate and Menthol Positively affect Growth and Pathogenicity of Entomopathogenic Fungi

Endophytic Entomopathogenic Fungi: Their Role in Enhancing Plant Resistance, Managing Insect Pests, and Synergy with Management Routines

The interaction between plants and microorganisms plays a major role in plant growth promotion and disease management. While most microorganisms directly influence plant health, some indirectly support growth through pest and disease suppression. Endophytic entomopathogenic fungi are diverse, easily localized, and have long-lasting effects on insect pests. When inhabiting plants, these fungi alter secondary metabolites, volatile organic compounds, and microbiomes, enhancing plant resistance to pests and diseases and sometimes improving growth. However, their persistence in plant systems may be challenged by the plant's defense mechanisms or by human interventions such as insecticides, fungicides, herbicides, and phyto-insecticides, which are common in agriculture. As effective biocontrol agents, endophytic entomopathogenic fungi can also be integrated with other pest management strategies like predators, parasitoids, and chemicals. This review will explore the impact of endophytic entomopathogens on plant systems and their compatibility with other management practices.

Effect of Chitosan/Gum Arabic Blends Enriched by Sodium Nitroprusside or Methyl Salicylate on the Storability and Antioxidant Activity of Tomato Fruit

The impact of methyl salicylate (MeSA) or sodium nitroprusside (SNP) in chitosan (CS)/Gum Arabic (GA) mixture on physio-chemical characteristics and antioxidant status during the postharvest ripening of green tomato fruits was studied. CS/GA-MeSA at a 1 mM formulation was the best treatment to retard firmness and titratable acidity (TA) losses. Moreover, this formulation retarded pigmentation progress where it had the lowest significant values of total carotenes (TCs) and lycopene (LYP) contents until the 15th day of the storage period, as well as efficiently faced the rise in malondialdehyde (MDA) levels. Moreover, peroxidase (POD), polyphenol oxidase (PPO), catalase (CAT), and phenylalanine ammonia-lyase (PAL) activities of tomatoes treated with CS/GA-SNP at 2 mM were significantly better than that of control in the primary stages of storage. CS/GA-SNP at a 2 mM formulation showed an extremely high significant content of total polyphenol (TP) in the early stage of storage, while CS/GA and CS/GA-MeSA at 1 and 2 mM accumulated higher significant TP contents than uncoated fruits at the late stage of storage. All formulations were characterized by FTIR spectroscopy. Furthermore, the polymer formulations exhibited strong antifungal activity against Alternaria alternata and Botrytis cinerea as major pathogens of postharvest tomatoes. Transmission electron microscope (TEM) observations for the mycelia of both fungi treated by CS/GA-MeSA at 2 mM revealed serious ultrastructural damage, including distortion of the cell wall and cell membrane and degradation of cytoplasmic organelles.

Plant-Entomopathogenic Fungi Interaction: Recent Progress and Future Prospects on Endophytism-Mediated Growth Promotion and Biocontrol

Entomopathogenic fungi, often acknowledged primarily for their insecticidal properties, fulfill diverse roles within ecosystems. These roles encompass endophytism, antagonism against plant diseases, promotion of the growth of plants, and inhabitation of the rhizosphere, occurring both naturally and upon artificial inoculation, as substantiated by a growing body of contemporary research. Numerous studies have highlighted the beneficial aspects of endophytic colonization. This review aims to systematically organize information concerning the direct (nutrient acquisition and production of phytohormones) and indirect (resistance induction, antibiotic and secondary metabolite production, siderophore production, and mitigation of abiotic and biotic stresses) implications of endophytic colonization. Furthermore, a thorough discussion of these mechanisms is provided. Several challenges, including isolation complexities, classification of novel strains, and the impact of terrestrial location, vegetation type, and anthropogenic reluctance to use fungal entomopathogens, have been recognized as hurdles. However, recent advancements in biotechnology within microbial research hold promising solutions to many of these challenges. Ultimately, the current constraints delineate potential future avenues for leveraging endophytic fungal entomopathogens as dual microbial control agents.

Small volatile lipophilic molecules induced belowground by aphid attack elicit a defensive response in neighbouring un-infested plants

In pioneering studies on plant-aphid interactions, we have observed that Vicia faba plants infested by aphids can transmit signals via the rhizosphere that induce aboveground defence in intact, neighbouring plants. The aphid parasitoid Aphidius ervi is significantly attracted towards intact broad bean plants grown in a hydroponic solution previously harbouring Acyrtosiphon pisum-infested plants. To identify the rhizosphere signal(s) possibly mediating this belowground plant-plant communication, root exudates were collected using Solid-Phase Extraction (SPE) from 10-day old A. pisum-infested and un-infested Vicia faba plants hydroponically grown. To verify the ability of these root exudates to trigger defence mechanisms against the aphids we added them to V. fabae plants grown in hydroponic solution, and tested these plants in the wind-tunnel bioassay to assess their attractiveness towards the aphids' parasitoids A. ervi. We identified three small volatile lipophilic molecules as plant defence elicitors: 1-octen-3-ol, sulcatone and sulcatol, in SPE extracts of A. pisum-infested broad bean plants. In wind tunnel assays, we recorded a significant increase in the attractiveness towards A. ervi of V. faba plants grown in hydroponic solution treated with these compounds, compared to plants grown in hydroponic treated with ethanol (control). Both 1-octen-3-ol and sulcatol have asymmetrically substituted carbon atoms at positions 3 and 2, respectively. Hence, we tested both their enantiomers alone or in mixture. We highlighted a synergistic effect on the level of attractiveness towards the parasitoid when testing the three compounds together in respect to the response recorded against them singly tested. These behavioural responses were supported by the characterization of headspace volatiles released by tested plants. These results shed new light on the mechanisms underlying plant-plant communication belowground and prompt the use of bio-derived semiochemicals for a sustainable protection of agricultural crops.

Regulation of the regulators: Transcription factors controlling biosynthesis of plant secondary metabolites during biotic stresses and their regulation by miRNAs

Biotic stresses threaten to destabilize global food security and cause major losses to crop yield worldwide. In response to pest and pathogen attacks, plants trigger many adaptive cellular, morphological, physiological, and metabolic changes. One of the crucial stress-induced adaptive responses is the synthesis and accumulation of plant secondary metabolites (PSMs). PSMs mitigate the adverse effects of stress by maintaining the normal physiological and metabolic functioning of the plants, thereby providing stress tolerance. This differential production of PSMs is tightly orchestrated by master regulatory elements, Transcription factors (TFs) express differentially or undergo transcriptional and translational modifications during stress conditions and influence the production of PSMs. Amongst others, microRNAs, a class of small, non-coding RNA molecules that regulate gene expression post-transcriptionally, also play a vital role in controlling the expression of many such TFs. The present review summarizes the role of stress-inducible TFs in synthesizing and accumulating secondary metabolites and also highlights how miRNAs fine-tune the differential expression of various stress-responsive transcription factors during biotic stress.

Associational resistance through intercropping reduces yield losses to soil-borne pests and diseases

Associational resistance to herbivore and pathogen attack is a well documented ecological phenomenon and, if applied to agriculture, may reduce impact of pests and diseases on crop yields without recourse to pesticides. The value of associational resistance through intercropping, planting multiple crops alongside each other, as a sustainable control method remains unclear, due to variable outcomes reported in the published literature. We performed a meta-analysis to provide a quantitative assessment of benefits of intercropping for target plant resistance to plant-parasitic nematodes and soil-borne diseases. We found that intercropping reduced damage to focal crops from nematodes by 40% and disease incidence by 55%. Intercropping efficacy varied with biological variables, such as field fertilisation status and intercrop family, and methodology, including whether study samples were potted or in fields. Nematode control using intercropping was sufficient to offset reductions in focal crop yield from intercrop presence, making intercropping a viable agricultural tool. We identify key drivers for underpinning the success of intercropping and indicate areas for future research to improve efficacy. This study also highlights the potential benefits of harnessing ecological knowledge on plant-enemy interactions for improving agricultural and landscape sustainability.

The Endophyte Trichoderma asperellum M2RT4 Induces the Systemic Release of Methyl Salicylate and (Z)-jasmone in Tomato Plant Affecting Host Location and Herbivory of Tuta absoluta

The use of endophytic fungi has dramatically increased plant performance through the enhancement of plant protection against abiotic and biotic stressors. We previously demonstrated that the endophytic fungus Trichoderma asperellum M2RT4 improves tomato defenses against the tomato leafminer Tuta absoluta through the reduction of oviposition, leafmining, pupation, and adult emergence. However, the underlying mechanism by which the presence of this endophytic fungus within tomato host plant affects T. absoluta host selection and life-history traits is unknown. We tested the behavioral responses of T. absoluta in Y-tube olfactometer bioassays and found that females preferred non-inoculated tomato plants against those inoculated by endophytes. Additionally, T. absoluta females were not attracted to non-inoculated infested nor to inoculated-infested tomato plants. Chemical analysis revealed the emission of methyl salicylate in inoculated tomato plant and an increase in the amounts of monoterpenes emitted from non-inoculated infested plants. Additionally, we found that upon herbivory, T. asperellum M2RT4 modulates tomato plant chemistry through the production of (Z)-jasmone thus activating both salicylic and jasmonic acid defense pathways. Further, T. absoluta females were attracted to monoterpernes including α-pinene, 2-carene, and β-phellandrene but repelled by methyl salicylate. Methyl salicylate could therefore be considered as a good semiochemical-based candidate for sustainable T. absoluta management using a "push-pull" approach. However, in dose-response bioassays, females of T. absoluta did not show any preference to the four component-blend (α-pinene, 2-carene, β-phellandrene, and methyl salicylate). (Z)-jasmone-treated tomato leaflets significantly reduced the leafmining activity of the pest at the concentration of 10 ng/μL and causing the highest larval mortality rate (83%) with the shortest LT₅₀ (1.73 days) 7 days post-treatment. T. asperellum M2RT4 effect on herbivore performance was then (Z)-jasmone-mediated. These findings expand our understanding of how the endophytic fungus T. asperellum M2RT4 could mediate chemical interactions between T. absoluta and its host plant which are potentially important for development of environmentally friendly T. absoluta management programs.

Volatiles Emission by Crotalaria nitens after Insect Attack

Plants are known to increase the emission of volatile organic compounds upon the damage of phytophagous insects. However, very little is known about the composition and temporal dynamics of volatiles released by wild plants of the genus Crotalaria (Fabaceae) attacked with the specialist lepidopteran caterpillar Utetheisa ornatrix (Linnaeus) (Erebidae). In this work, the herbivore-induced plant volatiles (HIPV) emitted by Crotalaria nitens Kunth plants were isolated with solid phase micro-extraction and the conventional purge and trap technique, and their identification was carried out by GC/MS. The poly-dimethylsiloxane/divinylbenzene fiber showed higher affinity for the extraction of apolar compounds (e.g., trans-β-caryophyllene) compared to the Porapak™-Q adsorbent from the purge & trap method that extracted more polar compounds (e.g., trans-nerolidol and indole). The compounds emitted by C. nitens were mainly green leaf volatile substances, terpenoids, aromatics, and aldoximes (isobutyraldoxime and 2-methylbutyraldoxime), whose maximum emission was six hours after the attack. The attack by caterpillars significantly increased the volatile compounds emission in the C. nitens leaves compared to those subjected to mechanical damage. This result indicated that the U. ornatrix caterpillar is responsible for generating a specific response in C. nitens plants. It was demonstrated that HIPVs repelled conspecific moths from attacked plants and favored oviposition in those without damage. The results showed the importance of volatiles in plant-insect interactions, as well as the choice of appropriate extraction and analytical methods for their study.

In Vitro Effects of Leaf Extracts from Brassica rapa on the Growth of Two Entomopathogenic Fungi

This study aimed to determine the inhibitive or stimulatory effects of leaf extracts from two Brassica rapa subspecies on the hyphal growth of two well-known entomopathogenic fungi, Cordyceps fumosorosea and Beauveria bassiana. Extract concentrations of 50, 25, and 10% w/v based on leaf fresh weight were prepared from turnip (B. rapa subspecies rapa) and bok choy (B. rapa subspecies chinensis) leaves. Each concentration was individually incorporated into potato dextrose agar plates for in vitro bioassays. The center of each plate was inoculated with 20 µL of a fungal suspension that was allowed 24 h to soak into the agar before sealing the plates and incubating them at 25 °C under a 14-h photophase. The fungal colony perimeter was marked 5 days after inoculation on two perpendicular lines drawn on the bottom of each plate. Radial colony growth was measured from 4 marks per plate 5, 10, and 15 days later. Radial growth rates for both fungi were 1.3-2.0 and 0.9-1.4 times faster with bok choy and turnip extracts, respectively, at the 25% and 50% concentrations compared to the no-extract control treatment. Therefore, bok choy and turnip leaf extracts can stimulate entomopathogenic fungus growth within 15 days. Biochemical compounds in the extracts include sesquiterpenes, α-copaene, β-selinene, γ-gurjunene, calamenene, cubenene, and α-calacorene.

Endophytic Colonization by the Entomopathogenic Fungus Beauveria Bassiana Affects Plant Volatile Emissions in the Presence or Absence of Chewing and Sap-Sucking Insects

Entomopathogenic fungi are gaining acceptance in Integrated Pest Management (IPM) systems as effective and environmental safety biological control agents to protect a great variety of crops against pest insects. Many of these insect-pathogenic fungi can establish themselves as endophytes and thereby may induce the plant immune system. The activation of plant defenses by the fungal endophytic colonization can have a direct impact on herbivores and plant pathogens. An integral component of many plant defense responses is also the release of volatile organic compounds, which may serve as an indirect defense by attracting the natural enemies of herbivores. Here we investigated the effect of endophytic colonization by the entomopathogenic fungus Beauveria bassiana on the volatile emission by melon and cotton plants, either unharmed or after being damaged by sap-sucking aphids or leaf chewing caterpillars. We found that when the plants are colonized by B. bassiana they emit a different blend of volatile compounds compared to uncolonized control plants. Some of the emitted compounds have been reported previously to be released in response to herbivory and have been implicated in natural enemy attraction. Several of the compounds are also known to have antimicrobial properties. Therefore, endophytic colonization by B. bassiana might help to not only direct control insect pests but also increase the resistance of plants against agronomically important pests and phytopathogens.

Whitefly-induced tomato volatiles enhance the virulence of Lecanicillium lecanii

Entomopathogenic fungi (EPF) are a group of microorganisms that have potential for replacing synthetic chemical pesticides. However, EPF virulence is often insufficient, and therefore adoption of EPF biopesticides has been relatively limited. Previous studies have shown that herbivore-induced plant volatiles (HIPVs) promoted the virulence of Lecanicillium lecanii, and that extracellular proteases and chitinases are important virulence factors of entomopathogenic fungi. We therefore put forward the hypothesis that HIPVs promote L. lecanii virulence by inducing extracellular protease or/and chitinase activity. Lecanicillium lecanii was treated with tomato HIPVs induced by various numbers/densities of Bemisia tabaci, the effect of HIPVs on L. lecanii virulence and activities of virulence-related enzymes (extracellular proteases and chitinases) was analyzed. Changes in enzyme activities were confirmed by measuring the variations in Pr1 and Chit II genes expression of virulence-related enzymes under the influence of HIPVs. Finally, the correlation between virulence and virulence-related enzymes or genes was analyzed to explore the mechanism of promoting HIPVs in L. lecanii virulence enhancement. The results showed that volatiles produced by the tomato plants induced by 50 B. tabaci adults (50-HIPVs) significantly enhanced the virulence of L. lecanii. When exposed to both 50-HIPVs and L. lecanii, the mortality rate of B. tabaci reached 79.0% within 7 days compared to 28.87% in the control group. Additionally, 50-HIPVs significantly promoted the activity of chitinase and the relative expression of Chit II genes, which consequently increased by 62.74% and 48.55%, respectively. However, each group of HIPVs had no promoting effect on extracellular protease and Pr1 gene expression. Correlation analysis results showed that the virulence of L. lecanii is significantly correlated with the activity of chitinase and relative expression of Chit II genes. Thus, HIPVs induced virulence of L. lecanii by increasing chitinase activity. This study demonstrates important methods to enhance the virulence of L. lecanii. Moreover, from the perspective of chemical ecology, the findings provide theoretical support for field application of EPF, and also reveal the impact of HIPVs on EPF from a biochemical perspective.

Insects-plants-pathogens: Toxicity, dependence and defense dynamics

In a natural ecosystem, the pathogen-plant-insect relationship has diverse implications for each other. The pathogens as well as insect-pests consume plant tissues as their feed that mostly results in damage. In turn, plant species have evolved specialized defense system to not only protect themselves but reduce the damage also. Such tripartite interactions involve toxicity, metabolic modulations, resistance etc. among all participants of interaction. These attributes result in selection pressure among participants. Coevolution of such traits reveals need to focus and unravel multiple hidden aspects of insect-plant-pathogen interactions. The definite modulations during plant responses to biotic stress and the operating defense network against herbivores are vital to research areas. Different types of plant pathogens and herbivores are tackled with various changes in plants, e.g. changes in genes expression, glucosinolate metabolism detoxification, signal transduction, cell wall modifications, Ca²⁺dependent signaling. It is essential to clarify which chemical in plants can work as a defense signal or weapon in plant-pathogen-herbivore interactions. In spite of increased knowledge regarding signal transduction pathways regulating growth-defense balance, much more is needed to unveil the coordination of growth rate with metabolic modulations in bi-trophic interactions. Here, we addressed plant-pathogen-insect interaction for toxicity as well as dependnce along with plant defense dynamics against pathogens and insects with broad range effects at the physio-biochemical and molecular level. We have reviewed interfaces in plant-pathogen-insect research to show pulsating regulation of plant immunity for attuning survival and ecological equilibrium. An improved understanding of the systematic foundation of growth-defense stability has vital repercussions for enhancing crop yield, including insights into uncoupling of host-parasite tradeoffs for ecological and environmental sustainability.

Natural Occurrence of Entomopathogenic Fungi as Endophytes of Sugarcane (Saccharum officinarum) and in Soil of Sugarcane Fields

Simple Summary

Sugarcane, an important cash crop in Malawi, is susceptible to numerous insect pests, and many farmers rely heavily on chemical insecticides for their control. Biopesticides containing insect pathogens are used in several countries outside Malawi; however, the occurrence and use of insect pathogens is limited in Malawi. In this study, we evaluated the natural occurrence of insect pathogenic fungi in sugarcane (Saccharum officinarum) and in soil samples from sugarcane fields in Chikwawa District, southern Malawi. Insect pathogenic fungi from soil were isolated by baiting using larvae of the greater wax moth (Galleria mellonella). Insect pathogenic fungi were also isolated from surface-sterilized sugarcane leaves, stems, and roots. We found three types of insect pathogenic fungi: Beauveria bassiana, Metarhizium spp., and Isaria spp. Beauveria bassiana and Isaria spp. were found mostly from sugarcane leaves and stems, while Metarhizium spp. was mainly found in soils. To the best of our knowledge, this is the first report of B. bassiana and Isaria spp. occurring naturally as endophytes in sugarcane. Further, it is the first report of B. bassiana, Isaria spp. and Metarhizium spp. in the soil of sugarcane fields in Africa.

Abstract

The natural occurrence of entomopathogenic fungal endophytes in sugarcane (Saccharum officinarum) and in soil samples from sugarcane fields was evaluated in Chikwawa District, southern Malawi. Fungi from soil were isolated by baiting using Galleria mellonella larva. Fungal endophytes were isolated from surface-sterilized plant tissue sections. Forty-seven isolates resembled the genus Beauveria, 9 isolates were Metarhizium, and 20 isolates were Isaria. There was no significant difference in the number and type of fungal isolates collected from soil and from plant tissue. There was, however, a significant difference in the part of the plant where fungal species were isolated, which fungal species were isolated, and the number of fungal species isolated at each location. Phylogenetic analysis of 47 Beauveria isolates based on DNA sequencing of the Bloc intergenic region indicated that these isolates all belonged to B. bassiana and aligned with sequences of B. bassiana isolates of African and Neotropical origin. The Malawian B. bassiana isolates formed a distinct clade. No larvae died from infestation by multiple fungi. To the best of our knowledge, this is the first report of B. bassiana and Isaria spp. occurring naturally as endophytes in sugarcane. Further, it is the first report of B. bassiana, Isaria spp., and Metarhizium spp. in the soil of sugarcane fields in Africa.

Internal state configures olfactory behavior and early sensory processing in Drosophila larvae

Animals exhibit different behavioral responses to the same sensory cue depending on their internal state at a given moment. How and where in the brain are sensory inputs combined with state information to select an appropriate behavior? Here, we investigate how food deprivation affects olfactory behavior in Drosophila larvae. We find that certain odors repel well-fed animals but attract food-deprived animals and that feeding state flexibly alters neural processing in the first olfactory center, the antennal lobe. Hunger differentially modulates two output pathways required for opposing behavioral responses. Upon food deprivation, attraction-mediating uniglomerular projection neurons show elevated odor-evoked activity, whereas an aversion-mediating multiglomerular projection neuron receives odor-evoked inhibition. The switch between these two pathways is regulated by the lone serotonergic neuron in the antennal lobe, CSD. Our findings demonstrate how flexible behaviors can arise from state-dependent circuit dynamics in an early sensory processing center.

Double Gamers-Can Modified Natural Regulators of Higher Plants Act as Antagonists against Phytopathogens? The Case of Jasmonic Acid Derivatives

As key players in biotic stress response of plants, jasmonic acid (JA) and its derivatives cover a specific and prominent role in pathogens-mediated signaling and hence are promising candidates for a sustainable management of phytopathogenic fungi. Recently, JA directed antimicrobial effects on plant pathogens has been suggested, supporting the theory of oxylipins as double gamers in plant-pathogen interaction. Based on these premises, six derivatives (dihydrojasmone and cis-jasmone, two thiosemicarbazonic derivatives and their corresponding complexes with copper) have been evaluated against 13 fungal species affecting various economically important herbaceous and woody crops, such as cereals, grapes and horticultural crops: Phaeoacremonium minimum, Neofusicoccum parvum, Phaeomoniella chlamydospora, Fomitiporia mediterranea, Fusarium poae, F. culmorum, F. graminearum, F. oxysporum f. sp. lactucae,F. sporotrichioides, Aspergillus flavus, Rhizoctonia solani,Sclerotinia spp. and Verticillium dahliae. The biological activity of these compounds was assessed in terms of growth inhibition and, for the two mycotoxigenic species A. flavus and F. sporotrichioides, also in terms of toxin containment. As expected, the inhibitory effect of molecules greatly varied amongst both genera and species; cis-jasmone thiosemicarbazone in particular has shown the wider range of effectiveness. However, our results show that thiosemicarbazones derivatives are more effective than the parent ketones in limiting fungal growth and mycotoxins production, supporting possible applications for the control of pathogenic fungi.

The effects of a myrmecochore-produced chemical on entomopathogenic fungal growth and seed-dispersing ant survival rates and foraging patterns

Myrmecochory, a type of ant-mediated seed dispersal, is a diffuse, widespread mutualism in which both partners are purported to benefit from the services or rewards of the other. However, ant benefits in this interaction are conflicted and understudied, especially in the context of microbial third parties. Here, we investigate the effect of a myrmecochore plant-produced antimicrobial chemical (sanguinarine) on the growth of a common entomopathogenic fungus (Beauveria bassiana). We then explore whether sanguinarine, through its effect on entomopathogen growth, might influence ant survival and foraging behavior. At high concentrations, sanguinarine increased the growth of B. bassiana, but fungal growth was not affected at concentrations of sanguinarine near natural levels produced in seeds. When ant colonies were exposed to B. bassiana, survival was not affected by a sanguinarine-supplemented diet. Furthermore, ant foraging patterns (preference for or avoidance of food items with sanguinarine) did not change when ants were exposed to the entomopathogen. Though sanguinarine promotes the growth of an entomopathogen at higher concentrations, which might pose an additional risk for ants in myrmecochory, we assert that social immune behavioral defenses (such as grooming or redispersal of seeds after elaiosome consumption) help ants mitigate this risk. By incorporating a microbial third party into this ant-plant interaction, we seek to more fully understand the risks and benefits provided to both partners in this mutualism. We encourage the investigation of third-party influences in reciprocal pairwise interactions to assist in the understanding of the evolution and persistence of mutualisms.

Genome-wide identification and expression analysis of SABATH methyltransferases in tea plant (Camellia sinensis): insights into their roles in plant defense responses

SABATH methyltransferases convent plant small-molecule metabolites into volatile methyl esters, which play important roles in many biological processes and defense reactions in plants. In this study, a total of 32 SABATH genes were identified in the Camellia sinensis var. sinensis (CSS) genome, which were renamed CsSABATH1 to CsSABATH32. Genome location annotation suggested that tandem duplication was responsible for the expansion of SABATH genes in tea plant. Multiple sequence alignment and phylogenetic analysis showed that the CsSABATHs could be classified into three groups (I, II and III), which were also supported by gene structures and conserved motifs analysis. Group II contained only two CsSABATH proteins, which were closely related to PtIAMT, AtIAMT and OsIAMT. The group III SABATH genes of tea plant exhibited expansion on the CSS genome compared with Camellia sinensis var. assamica (CSA) genome. Based on RNA-seq data, the CsSABATHs exhibited tissue-specific expression patterns, and the members with high expression in buds and young leaves were also obviously upregulated after MeJA treatment. The expression of many transcription factors was significantly correlated with that of different members of the CsSABATH gene family, suggesting a potential regulatory relationship between them. Quantitative real-time PCR (qPCR) expression analysis showed that CsSABATHs could respond to exogenous JA, SA and MeSA treatments in tea plants. RNA-seq data analysis and qPCR validation suggested that CsSABATH8, 11, 16, 25, 29 and 32 might play a special role in plant defense against insect herbivory. These results provide references for evolutionary studies of the plant SABATH family and the exploration of the potential roles of CsSABATHs in tea plant defense responses.

Inhibition of plant pathogenic fungi by endophytic Trichoderma spp. through mycoparasitism and volatile organic compounds

Antagonism of plant pathogenic fungi by endophytic fungi is a well-known phenomenon. In plate assays, the antagonism could be due to mycoparasitism, competition for space or antibiosis, involving a chemical diffusate, or a volatile organic compound (VOC). In this study, we demonstrate that besides mycoparasitism, VOCs play a major role in antagonism of pathogenic fungi by four endophytic fungi belonging to the genus Trichoderma. Using a double-plate assay, we show that all the four endophytic Trichoderma species significantly inhibited mycelial growth of three of the four pathogens, (Sclerotinia sclerotiorum-TSS, Sclerotium rolfsii-CSR and Fusarium oxysporum-CFO), while that of Macrophomina phaseolina-CMP was not affected. GC-MS analysis of the pure cultures of one of the endophytic fungi studied, namely, Trichoderma longibrachiatum strain 2 (Acc. No. MK751758) and the pathogens, F. oxysporum-CFO and M. phaseolina-CMP revealed the presence of several VOCs including hydrocarbons, alcohols, ketones, aldehydes, esters, acids, ethers and different classes of terpenes. In mixed double plates, where the endophyte was grown along with either of the two plant pathogens, F. oxysporum-CFO or M. phaseolina-CMP, there was an induction of a number of new VOCs that were not detected in the pure cultures of either the endophyte or the pathogens. Several of these new VOCs are reported to possess antifungal and cytotoxic activity. We discuss these results and highlight the importance of such interactions in endophyte-pathogen interactions.

Tomato Metabolic Changes in Response to Tomato-Potato Psyllid (Bactericera cockerelli) and Its Vectored Pathogen Candidatus Liberibacter solanacearum

The bacterial pathogen ‘Candidatus Liberibacter solanacearum’ (Lso) is transmitted by the tomato potato psyllid (TPP), Bactericera cockerelli, to solanaceous crops. In the present study, the changes in metabolic profiles of insect-susceptible (cv CastleMart) and resistant (RIL LA3952) tomato plants in response to TPP vectoring Lso or not, were examined after 48 h post infestation. Non-volatile and volatile metabolites were identified and quantified using headspace solid-phase microextraction equipped with a gas chromatograph-mass spectrometry (HS-SPME/GC-MS) and ultra-high pressure liquid chromatography coupled to electrospray quadrupole time-of-flight mass spectrometry (UPLC/ESI-HR-QTOFMS), respectively. Partial least squares-discriminant analysis (PLS-DA) was used to define the major uncorrelated metabolite components assuming the treatments as the correlated predictors. Metabolic changes in various classes of metabolites, including volatiles, hormones, and phenolics, were observed in resistant and susceptible plants in response to the insects carrying the pathogen or not. The results suggest the involvement of differentially regulated and, in some cases, implicates antagonistic metabolites in plant defensive signaling. Upon validation, the identified metabolites could be used as markers to screen and select breeding lines with enhanced resistance to reduce economic losses due to the TPP-Lso vector-pathogen complex in Solanaceous crops.

Monitoring Plant Health with Near-Infrared Fluorescent H2O2 Nanosensors

Near-infrared (nIR) fluorescent single-walled carbon nanotubes (SWCNTs) were designed and interfaced with leaves of Arabidopsis thaliana plants to report hydrogen peroxide (H₂O₂), a key signaling molecule associated with the onset of plant stress. The sensor nIR fluorescence response (>900 nm) is quenched by H₂O₂ with selectivity against other stress-associated signaling molecules and within the plant physiological range (10-100 H₂O₂ μM). In vivo remote nIR imaging of H₂O₂ sensors enabled optical monitoring of plant health in response to stresses including UV-B light (-11%), high light (-6%), and a pathogen-related peptide (flg22) (-10%), but not mechanical leaf wounding (<3%). The sensor's high biocompatibility was reflected on similar leaf cell death (<5%) and photosynthetic rates to controls without SWCNT. These optical nanosensors report early signs of stress and will improve our understanding of plant stress communication, provide novel tools for precision agriculture, and optimize the use of agrochemicals in the environment.

Tracking Short-Range Attraction and Oviposition of European Grapevine Moths Affected by Volatile Organic Compounds in a Four-Chamber Olfactometer

The identification of volatile organic compounds (VOCs) leading to short-range attraction and oviposition of the European grapevine moth Lobesia botrana and European grape berry moth Eupoecilia ambiguella (Lepidoptera: Tortricidae) is crucial in order to establish bait-based decision support systems for control of these pests. Therefore, we developed a method to measure the real-time behavioral response of female moths to VOCs using a four-chamber olfactometer coupled with a video tracking system. Ten synthetic VOCs were selected for this study: (S)-(−)-perillaldehyde, (E)/(Z)-linalool oxide, (±)-limonene, linalool, (E)-β-caryophyllene, α/β-farnesene, (−)-α-cedrene, methyl salicylate and cumene. The effect of VOCs on egg deposition was determined using a dual-choice oviposition test, whereas perception by female antennae was verified using electroantennography (EAG). During video tracking, females responded to volatile compounds emitted by grapevine with higher antennae and ovipositor activity than to air control. (E)/(Z)-linalool oxide, cumene and (S)-(−)-perillaldehyde released ovipositor activity of L. botrana, while the latter provoked oviposition. (R)/(S)-limonene affected ovipositor activity of E. ambiguella, whereas none of the VOCs tested attracted for oviposition. The results suggest that females have the ability to perceive specific VOCs by the antennae but also by the ovipositor, which could attract or repel for egg deposition.

Use of plant hormones to activate silent polyketide biosynthetic pathways in Arthrinium sacchari, a fungus isolated from a spider

Plant hormones were evaluated for their ability to activate fungal secondary metabolite production. Three synthetic cytokinins, kinetin, 6-benzylaminopurine, and forchlorfenuron, showed remarkable enhancement of the production of aromatic polyketides derived from emodin in a fungus, Arthrinium sacchari, and allowed us to isolate a new polyketide. Furthermore, we firstly demonstrated the potential of plant hormones to activate a wide range of fungal secondary metabolite production processes.

Genomic Analysis of the Insect-Killing Fungus Beauveria bassiana JEF-007 as a Biopesticide

Insect-killing fungi have high potential in pest management. A deeper insight into the fungal genes at the whole genome level is necessary to understand the inter-species or intra-species genetic diversity of fungal genes, and to select excellent isolates. In this work, we conducted a whole genome sequencing of Beauveria bassiana (Bb) JEF-007 and characterized pathogenesis-related features and compared with other isolates including Bb ARSEF2860. A large number of Bb JEF-007 genes showed high identity with Bb ARSEF2860, but some genes showed moderate or low identity. The two Bb isolates showed a significant difference in vegetative growth, antibiotic-susceptibility, and virulence against Tenebrio molitor larvae. When highly identical genes between the two Bb isolates were subjected to real-time PCR, their transcription levels were different, particularly in heat shock protein 30 (hsp30) gene which is related to conidial thermotolerance. In several B. bassiana isolates, chitinases and trypsin-like protease genes involved in pathogenesis were highly conserved, but other genes showed noticeable sequence variation within the same species. Given the transcriptional and genetic diversity in B. bassiana, a selection of virulent isolates with industrial advantages is a pre-requisite, and this genetic approach could support the development of excellent biopesticides with intellectual property protection.

Bemisia tabaci-mediated facilitation in diversity of begomoviruses: Evidence from recent molecular studies

Begomoviruses are considered as one of the most notorious plant viruses worldwide, which cause substantial economic losses to various field crops. Management of begomoviruses has become a challenge due to the continuous evolution and the emergence of new strains. Bemisia tabaci is globally known to be the key vector of begomoviruses, having relatively high reproductivity, fast dispersal ability, high survival rate due to its polyphagous nature and high resistance to various groups of insecticides. Continuous transmission of begomoviruses by the vector has led to the development and spread of epidemics of various diseases worldwide. In this review, we have critically analyzed the various dynamics which facilitate the diversity of begomoviruses through their vector. The interaction of begomovirus-whitefly leads to continuous research activities regarding management of both virus and its vector, thus opening exciting new horizons to formulate potential control strategies to ensure a disease-free cropping environment.