Indirect Plant Defense Research Articles

Overexpressing a cotton terpene synthase for (E)-β-ocimene biosynthesis in Nicotiana tabacum to recruit the parasitoid wasps

(E)-β-ocimene is a predominant component of volatile terpenes emitted from many plant species in response to herbivore attack, which plays an impotant role in direct and indirect defense of plants. In the current study, (E)-β-ocimene was induced and released in upland cotton Gossypium hirsutum plants infested by chewing caterpillars or sucking bugs. Using genome data mining, a key terpene synthase for (E)-β-ocimene biosynthesis in cotton, GhTPS16, was initially identified. In vitro, recombinant GhTPS16 catalyzed the formation of (E)-β-ocimene using geranyl diphosphate as a substrate. Besides, the GhTPS16 was transferred into Nicotiana tabacum to generate (E)-β-ocimene synthase overexpression lines. Consequently, compared with wild type plants both GhTPS16 expression and (E)-β-ocimene emission of transgenic plants were up-regulated. In behavioral trials, two parasitoid wasps, Peristenus spretus parasitizing green bug Apolygus lucorum and Microplitis mediator parasitizing cotton bollworm Helicoverpa armigera, showed tendency preference for synthetic (E)-β-ocimene and transgenic tobacco plants, respectively. These findings provide new insights into understanding the roles of (E)-β-ocimene in plant-insect interaction. Oversynthesis of (E)-β-ocimene in plants could enhance indirect defense by recruiting parasitoids to facilitate control of the two target pests, green bug and cotton bollworm.

Multitrophic and Multilevel Interactions Mediated by Volatile Organic Compounds.

Plants communicate with insects and other organisms through the release of volatile organic compounds (VOCs). Using Boolean operators, we retrieved 1093 articles from the Web of Science and Scopus databases, selecting 406 for detailed analysis, with approximately 50% focusing on herbivore-induced plant volatiles (HIPVs). This review examines the roles of VOCs in direct and indirect plant defense mechanisms and their influence on complex communication networks within ecosystems. Our research reveals significant functions of VOCs in four principal areas: activating insect antennae, attracting adult insects, attracting female insects, and attracting natural enemies. Terpenoids like α-pinene and β-myrcene significantly alter pest behavior by attracting natural enemies. β-ocimene and β-caryophyllene are crucial in regulating aboveground and belowground interactions. We emphasize the potential applications of VOCs in agriculture for developing novel pest control strategies and enhancing crop resilience. Additionally, we identify research gaps and propose new directions, stressing the importance of comparative studies across ecosystems and long-term observational research to better understand VOCs dynamics. In conclusion, we provide insights into the multifunctionality of VOCs in natural ecosystems, their potential for future research and applications, and their role in advancing sustainable agricultural and ecological practices, contributing to a deeper understanding of their mechanisms and ecological functions.

Root inoculation with beneficial soil microbes enhances indirect plant defences induced by insect feeding and egg deposition

Abstract Plants can respond to insect egg deposition by emitting oviposition‐induced plant volatiles (OIPVs) recruiting parasitoids. The recruitment of carnivore insects in response to egg deposition is considered an indirect defence strategy that is widespread in the plant kingdom. In recent years, there has been increasing evidence showing that microbial colonization can influence the strength of plant responses to insect herbivory, yet no information is available on how beneficial microbes modulate indirect defences induced by insect egg deposition. In this work, we evaluated the effects of inoculation with the beneficial soil fungus Trichoderma harzianum strain T22 on a tritrophic system consisting of tomato, the southern green stink bug Nezara viridula and its associated egg parasitoid Trissolcus basalis. We used Y‐tube olfactometer assays to evaluate the behavioural responses of the parasitoids to OIPVs emitted by plants colonized with beneficial soil microbes. We also used gas chromatography coupled with mass spectrometry (GC–MS) to investigate whether and how root inoculation with T. harzianum T22 affects the chemical composition of induced plant volatiles. In olfactometer assays, we found that root inoculation with T. harzianum T22 enhanced the attraction of the egg parasitoid towards tomato plants induced by N. viridula feeding and oviposition activities. In particular, the egg parasitoid preferred OIPVs emitted by tomato plants previously inoculated with T. harzianum T22 over OIPVs emitted by non‐inoculated plants. Furthermore, chemical analysis showed that root inoculation with T. harzianum T22 resulted in changes in the composition of OIPVs, which was consistent with the behavioural observations. Among the compounds that strongly contribute to the chemical differences between OIPVs from non‐inoculated and inoculated plants, chemical analysis identified green leaf volatiles ((Z)‐3‐hepten‐1‐ol, (E,E)‐2,4‐hexadienal), along with terpenoids (terpinen 4‐ol, α‐tujene and δ‐elemene). Taken together our results indicate that beneficial soil microbes enhance indirect plant defences induced by feeding and oviposition, broadening our understanding of plant responses to insect eggs. Our results underscore the importance of taking into account the role of microorganisms to fully comprehend the intricate interactions among plants, herbivore eggs and their associated egg parasitoids. Read the free Plain Language Summary for this article on the Journal blog.

The evolution of glandularity as a defense against herbivores in the tarweed clade.

Glandular trichomes are implicated in direct and indirect defense of plants. However, the degree to which glandular and non-glandular trichomes have evolved as a consequence of herbivory remains unclear, because their heritability, their association with herbivore resistance, their trade-offs with one another, and their association with other functions are rarely quantified. We conducted a phylogenetic comparison of trichomes and herbivore resistance against the generalist caterpillar, Heliothis virescens, among tarweed species (Asteraceae: Madiinae) and a genetic correlation study comparing those same traits among maternal half-sibs of three tarweed species. Within a tarweed species, we found no evidence that herbivore growth rate decreased on tarweed individuals or maternal sib groups with more glandularity or denser trichomes. However, tarweed species with more glandularity and fewer non-glandular trichomes resulted in slower-growing herbivores. Likewise, a trade-off between glandular and non-glandular trichomes was apparent among tarweed species, but not among individuals or sib groups within a species. Our results suggest that this key herbivore does not select for trichomes as a direct defense in tarweed species. However, trichomes differed substantially among species and likely affect herbivore pressure on those species. Our results demonstrate that trade-offs among plant traits, as well as inference on the function of those traits, can depend on scale.

Two jasmonic acid carboxyl methyltransferases in Gossypium hirsutum involved in MeJA biosynthesis may contribute to plant defense.

Jasmonic acid (JA) and methyl jasmonate (MeJA), the crucial plant hormones, can induce the emission of plant volatiles and regulate the behavioral responses of insect pests or their natural enemies. In this study, two jasmonic acid carboxyl methyltransferases (JMTs), GhJMT1 and GhJMT2, involved in MeJA biosynthesis in Gossypium. hirsutum were identified and further functionally confirmed. In vitro, recombinant GhJMT1 and GhJMT2 were both responsible for the conversion of JA to MeJA. Quantitative real-time PCR (qPCR) measurement indicated that GhJMT1 and GhJMT2 were obviously up-regulated in leaves and stems of G. hirsutum after being treated with MeJA. In gas chromatography-mass spectrometry (GC-MS) analysis, MeJA treatment significantly induced plant volatiles emission such as (E)-β-ocimene, (Z)-3-hexenyl acetate, linalool and (3E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), which play vital roles in direct and indirect plant defenses. Moreover, antennae of parasitoid wasps Microplitis mediator showed electrophysiological responses to MeJA, β-ocimene, (Z)-3-hexenyl acetate and linalool at a dose dependent manner, while our previous research revealed that DMNT excites electrophysiological responses and behavioral tendencies. These findings provide a better understanding of MeJA biosynthesis and defense regulation in upland cotton, which lay a foundation to JA and MeJA employment in agricultural pest control.

Climate and ant diversity explain the global distribution of ant‐plant mutualisms

Biotic interactions play an important role in shaping species geographic distributions and diversity patterns. However, the role of mutualistic interactions in shaping global plant diversity patterns remains poorly understood, particularly with respect to interactions with invertebrates. It is unclear how the nature of different mutualisms interacts with abiotic drivers and affects the distribution of mutualistic organisms. Here, we present a global‐scale biogeographic analysis of three distinct ant‐plant mutualisms, differentiating between plants bearing domatia, extrafloral nectaries (EFNs), and elaiosomes, based on comprehensive geographic distributions of ~ 19 000 flowering plants and ~ 13 000 ant species. Domatia and extrafloral nectaries involve indirect plant defences provided by ants, while elaiosomes attract ants to disperse seeds. Our results reveal distinct biogeographic patterns of different ant‐plant mutualisms, with domatium‐ and EFN‐bearing plant diversity decreasing sharply from the equator towards the poles, while elaiosome‐bearing plants prevail at mid‐latitudes. Present climate, especially mean annual temperature and precipitation, emerge as the strongest predictors of ant‐associated plant diversity. In hot and moist regions, typically the tropics, the representation of EFN‐bearing plants increases with the proportion of potential ant partners while domatium‐bearing plants show no correlation with ants. In dry regions, plants with elaiosomes are strongly linked to interacting ant seed dispersers. Our results suggest that ants in combination with climate drive the spatial variation of plants bearing domatia, extrafloral nectaries, and elaiosomes, highlighting the importance of mutualistic interactions for understanding plant biogeography.

Flavonoid production in tomato mediates both direct and indirect plant defences against whiteflies in tritrophic interactions.

The role of plant flavonoids in direct defences against chewing and sap-sucking herbivorous insects has been extensively characterized. However, little is known about flavonoid-mediated tritrophic interactions between plants, herbivorous insects and natural enemies. In this study, we investigated how flavonoids modulate plant-insect interactions in a tritrophic system involving near-isogenic lines (NILs) of cultivated tomato (Solanum lycopersicum) with high (line NIL-purple hypocotyl [PH]) and low (line NIL-green hypocotyl [GH]) flavonoid levels, with a generalist herbivore whitefly (Bemisia tabaci) and its predatory bug (Orius sauteri). By contrasting levels of tomato flavonoids (direct defence) while manipulating the presence of predators (indirect defence), we found that high production of flavonoids in tomato was associated with a higher inducibility of direct defences and a stronger plant resistance to whitefly infestation and stimulated the emissions of induced volatile organic compounds, thereby increasing the attractiveness of B. tabaci-infested plants to the predator O. sauteri. Furthermore, suppression of B. tabaci population growth and enhancement of plant growth were mediated directly by the high production of flavonoids and indirectly by the attraction of O. sauteri, and the combined effects were larger than each effect individually. Our results conclude that high flavonoid production in tomato enhances herbivore-induced direct and indirect defences to better defend against herbivores in tritrophic interactions. Thus, the development of transgenic plants may present an opportunity to utilize the beneficial role of flavonoids in integrated pest management, while simultaneously maintaining or improving resistance against other pests and pathogens. This article is protected by copyright. All rights reserved.

Experimental Growth Conditions affect Direct and Indirect Defences in two Cotton Species

Cotton has been used as a model plant to study direct and indirect plant defence against herbivorous insects. However, the plant growing conditions could have an important effect on the outcome of such plant defence studies. We examined how common experimental growth conditions influence constitutive and inducible defences in two species of cotton, Gossypium hirsutum and G. herbaceum. We induced plants by applying caterpillar regurgitant to mechanical wounds to compare the induction levels between plants of both species grown in greenhouse or phytotron conditions. For this we measured defence metabolites (gossypol and heliocides) and performance of Spodoptera frugiperda caterpillars on different leaves, the emission of plant volatiles, and their attractiveness to parasitic wasps. Induction increased the levels of defence metabolites, which in turn decreased the performance of S. frugiperda larvae. Constitutive and induced defence levels were the highest in plants grown in the phytotron (compared to greenhouse plants), G. hirsutum and young leaves. Defence induction was more pronounced in plants grown in the phytotron and in young leaves. Also, the differences between growing conditions were more evident for metabolites in the youngest leaves, indicating an interaction with plant ontogeny. The composition of emitted volatiles was different between plants from the two growth conditions, with greenhouse-grown plants showing more variation than phytotron-grown plants. Also, G. hirsutum released higher amounts of volatiles and attracted more parasitic wasps than G. herbaceum. Overall, these results highlight the importance of experimental abiotic factors in plant defence induction and ontogeny of defences. We therefore suggest careful consideration in selecting the appropriate experimental growing conditions for studies on plant defences.

Role of herbivore‐induced maize volatiles in the chemotactic behaviour of Telenomus podisi and Diceraeus melacanthus

AbstractPlants respond indirectly to herbivore injury in a species‐specific way and emit a specific blend of volatiles that are attractive to the enemies of herbivores. We evaluated whether maize plants, Zea mays L. (Poaceae), can recognize herbivory damage from a generalist stink bug, Diceraeus melacanthus Dallas (Hemiptera: Pentatomidae). This species is not a common pest in maize, but is currently found on maize crops in Brazil. We aimed to answer the following questions: (1) does D. melacanthus use maize plant volatiles for host location? (2) Do maize plant chemical volatile profiles change due to feeding by D. melacanthus? And (3) do herbivore‐induced plant volatiles (HIPVs) emitted by maize plants play a role in the foraging behaviour of the generalist stink bug egg parasitoid Telenomus podisi Ashmead (Hymenoptera: Scelionidae)? The results show that females of D. melacanthus do not use constitutive volatiles or HIPVs as host location cues. However, feeding by D. melacanthus activates maize indirect defence, inducing emission of HIPVs and attracting the herbivore's enemy. Thus, strengthening indirect defence of plants can be a strategy to protect crops in the field by recruiting natural enemies through chemical information, as an additional approach to control D. melacanthus within an integrated pest management program.

Plants strike back: Plant volatiles and their role in indirect defence against aphids

As sessile organisms, plants have evolved different strategies to defend themselves against various biotic stressors. An important aspect of the complex response of plants to biotic stress is the emission of volatile compounds (VOCs), which are involved in direct and indirect plant defence mechanisms. Indirect plant defences include a range of plant traits that mediate defence against herbivores and play an important ecological role by not only utilising plants' own capabilities, but also signalling and attracting natural enemies of herbivores. Often the combination of volatiles emitted is specific to herbivores; they are consequently recognised by parasites and other predators, providing a clear link between the volatile signature and the prey. In this review, we focus on indirect plant defence and summarise current knowledge and perspectives on relationships between plants, aphids and parasitic wasps.

Exogenous Application of a Plant Elicitor Induces Volatile Emission in Wheat and Enhances the Attraction of an Aphid Parasitoid Aphidius gifuensis.

It is well known that plant elicitors can induce plant defense against pests. The herbivore-induced plant volatile (HIPV) methyl salicylate (MeSA), as a signaling hormone involved in plant pathogen defense, is used to recruit natural enemies to protect wheat and other crops. However, the defense mechanism remains largely unknown. Here, the headspace volatiles of wheat plants were collected and analyzed by gas chromatography-mass spectrometry (GC-MS), gas chromatography with electroantennographic detection (GC-EAD) and principal component analysis (PCA). The results showed that exogenous application of MeSA induced qualitative and quantitative changes in the volatiles emitted from wheat plants, and these changes were mainly related to Carveol, Linalool, m-Diethyl-benzene, p-Cymene, Nonanal, D-limonene and 6-methyl-5-Hepten-2-one. Then, the electroantennogram (EAG) and Y-tube bioassay were performed to test the physiological and behavioral responses of Aphidius gifuensis Ashmesd to the active volatile compounds (p-Cymene, m-Diethyl-benzene, Carveol) that identified by using GC-EAD. The female A. gifuensis showed strong physiological responses to 1 μg/μL p-Cymene and 1 μg/μL m-Diethyl-benzene. Moreover, a mixture blend was more attractive to female A. gifuensis than a single compound. These findings suggested that MeSA could induce wheat plant indirect defense against wheat aphids through attracting parasitoid in the wheat agro-ecosystem.

Effects of nitrogen fertilization on crops and their associated insect communities: a global food security perspective

Nitrogen (N) fertilization reduces worldwide food insecurity by boosting crop yield and stability. N is one of the most essential macromolecules required for the growth and reproduction of plants. It occurs in diverse chemical forms and circulates in natural and agricultural ecosystems. It is a constituent of chlorophyll, hence is required for the photosynthesis of plants. Plants receive N through their roots in the form of ammonia or nitrate. Nutritional quality and defense of plants that have a direct impact on herbivorous insects are altered by N fertilization and herbivorous insects can differentiate between plants that receive different applications of N fertilizer. Increasing N fertilization has a variable impact on plant species composition, plant growth, plant biomass, and yields. Plant tissue N and protein contents are also affected by nitrogen fertilization. Moreover, nitrogen fertilization affects many aspects of insects such as population dynamics, larval count, larval weight, feeding choice, and oviposition preference. Furthermore, predatory insect abundance, parasitization performance, and development of parasitoids on host insects are negatively affected by N fertilization. Other important effects of N fertilization are the hemolymph protein profile of herbivores, emission of VOCs, phytohormone biosynthesis, and direct and indirect defense of plants. The aim of this literature research is to demonstrate the effects of variable doses of N fertilization on the crop-herbivore-natural enemy tri-trophic systems. The information gathered in this review might help researchers understand the impact of optimal and excessive N fertilization on crop production and food security. Asian Australas. J. Food Saf. Secur. 2022, 6 (2), 48-56

Role of trichomes in plant defence – A crop specific review

Trichomes have long been investigated as an initial line of defence against insect herbivores. The structure, categorization and diversity of trichomes in flowering plants, as well as their mechanisms of action against abiotic and biotic stresses, are discussed. Plant-herbivore interactions are complicated interactions involving intricate networks of chemicals, signals and tactics to overcome each other's defences. To gain nutrients from host plants, herbivores employ a variety of feeding techniques. Plants respond by activating several defence mechanisms. Context of this review is based over the research on herbivore-trichome interactions and how trichomes are involved in both direct and indirect plant defences. Importance of trichome exudates like terpenes, acyl sugars, phenyl propanoid derivatives, methyl ketones, flavonoids and defensive proteins have been discussed. In our study, we emphasized on the relevance of trichomes as a reliable indicator of plant defence and how it is involved in defence responses of some economically important crops. Finally, we suggest several promising new study avenues for future work on trichomes and trichome-mediated responses.

Effects of Below-Ground Microbial Biostimulant Trichoderma harzianum on Diseases, Insect Community, and Plant Performance in Cucurbita pepo L. under Open Field Conditions.

Agrochemicals are generally used in agriculture to maximize yields and product quality, but their overuse can cause environmental pollution and human health problems. To reduce the off-farm input of chemicals, numerous biostimulant products based on beneficial symbiont plant fungi are receiving a great deal of attention. The evolution of plant diseases and the performance of insects are influenced by plant chemical defences, both of which are, in turn, influenced by below-ground symbionts. Direct and indirect plant defences mediated by belowground symbionts against plant diseases and insect herbivores were demonstrated in greenhouses experiments. However, little attention has been paid to the use of Trichoderma under open field conditions, and no data are available for zucchini (Cucurbita pepo L.) plants in the field. To determine the effects of a commercial Trichoderma harzianum strain T22 on plant viruses, powdery mildew, the arthropod community, and on the agronomic performance associated with zucchini plants, an experiment was conducted in 2022 under open field conditions in South Italy. Our results indicate that T. harzianum T22 makes zucchini plants more attractive to aphids and to Hymenoptera parasitoid but failed to control zucchini pathogens. The complex plant-disease-arthropod-microorganism interactions that occurred in the field during the entire plant cycle are discussed to enrich our current information on the possibilities of using these microorganisms as a green alternative in agriculture.

Volatile Organic Compounds as Mediators of Plant Communication and Adaptation to Climate Change.

Plant volatile organic compounds are the most abundant and structurally diverse plant secondary metabolites. They play a key role in plant lifespan via direct and indirect plant defenses, attracting pollinators, and mediating various interactions between plants and their environment. The ecological diversity and context-dependence of plant-plant communication driven by volatiles are crucial elements that influence plant performance in different habitats. Plant volatiles are also valued for their multiple applications in the food, flavor, pharmaceutical, and cosmetics industries. In the current review, we summarize recent advances that have elucidated the functions of plant volatile organic compounds as mediators of plant interaction at community and individual levels, highlighting the complexities of plant receiver feedback to various signals and cues. This review emphasizes volatile terpenoids, the most abundant class of plant volatile organic compounds, highlighting their role in plant adaptability to global climate change and stress-response pathways that are integral to plant growth and survival. Lastly, we identify research gaps and suggest future research directions. This article is protected by copyright. All rights reserved.

Oviposition preferences of the oriental fruit moth Grapholita molesta (Lepidoptera: Tortricidae) to pear HIPVs

Herbivore-induced plant volatiles (HIPVs) are regarded as an indirect plant defense against herbivores, since they attract natural enemies to infested plants. On the other hand, HIPVs also affect behavioral responses of herbivores. In a previous study, Lytopylus rufipes, a parasitoid of the oriental fruit moth (Grapholita molesta), showed positive responses to pear HIPVs, but the influence of pear HIPVs on G. molesta is still unclear. To better understand these responses, we first tested oviposition preferences of G. molesta to uninfested and infested pear shoots (US and IS, respectively) and uninfested mature leaves (ML) in dual-choice bioassays using a cylindrical tube. Then, preferences to volatile components were also assessed. G. molesta females preferred US-, IS-, and ML-treated areas compared to the control area (no leaves), respectively. Subsequently, G. molesta females preferred IS over US, and US more than ML in bioassays. Furthermore, G. molesta females did not show any significant preference for individual volatile components, but more eggs were laid in an area treated with a synthetic pear HIPV blend, compared to the hexane-treated area (control). These results indicate that G. molesta females do not avoid infested pear shoots nor HIPVs. Moreover, HIPVs may recruit not only natural enemies, but also G. molesta females to the release point of HIPVs. Thus, it is important to examine responses of G. molesta females to HIPVs in the field before employing them for pest management.

Wearable Plant Sensor for In Situ Monitoring of Volatile Organic Compound Emissions from Crops.

Methanol is a major volatile organic compound (VOC) emitted from plants. Methanol emission reflects indirect plant defense against insects, promotes cell-to-cell communication, and adapts plants to various environmental stresses. This paper reports a wearable plant sensor that can monitor methanol emission directly on the leaf of a plant under field conditions with low cost, high portability, and easy installation and use. The sensor technology eliminates the need for complex sampling, expensive instruments, and skilled operators for conventional gas chromatography-mass spectrometry. The sensor uses a composite of conducting polymer microcrystallites and platinum nanoparticles (PtNPs). The conducting poly(2-amino-1,3,4-thiadiazole) or poly(ATD) provides a high electrocatalytic activity with redox behavior. The modification of poly(ATD) with catalytic PtNPs enables efficient electrochemical oxidation of methanol at a specific potential. The advantages of poly(ATD) and PtNPs are synergized for high sensitivity and selectivity of the sensor for detecting methanol emissions with a sub-ppm limit of detection. Further, the infusion of a polymer electrolyte into the porous electrode of the sensor enables an all-solid-state VOC sensor. The sensor is integrated into a miniature gas collection chamber and capped with a hydrophobic gas diffusion membrane to minimize the influence of environmental humidity on the sensor performance. The sensor is installed on the leaf surface. In situ detection shows a difference in methanol emission between the lower and upper leaves of greenhouse maize plants. Further, under field conditions, the sensor reveals a noticeable difference in methanol emission concentration between two genotypes (Mo17 and B73 inbred lines) of maize plants. Therefore, the sensor will provide a promising new means of directly monitoring volatile emission of plants, which is a physiological phenotype as a function of genes and environment.

Effects of Trichoderma harzianum Strain T22 on the Arthropod Community Associated with Tomato Plants and on the Crop Performance in an Experimental Field.

Simple SummaryThere is currently a global research interest in reducing off-farm input of chemical pesticides and fertilizers by using green alternative practices. Fungi belonging to the genus Trichoderma colonize plant roots and activate systemic plant defenses against the attack of pests and pathogens. Trichoderma spp. have positive impacts on the environment and guarantee food security, which, in turn, offer important economic benefits in agriculture. The purpose of the present study was to investigate the effects of the inoculation of a commercial Trichoderma strain on the arthropod community, downy mildew, and the agronomic performance of tomato plants in an experimental field. Our results showed that inoculation with Trichoderma positively influenced tomato fruit yields and could reduce the abundance of specific pests under field conditions.Fungi belonging to the genus Trichoderma have received much attention in recent years due to their beneficial effects on crop health and their use as pest control agents. Trichoderma activates direct plant defenses against phytophagous arthropods and reinforces indirect plant defense through the attraction of predators. Although the plant defenses against insect herbivores were demonstrated in laboratory experiments, little attention has been paid to the use of Trichoderma spp. in open field conditions. In the present study, we investigated the effects of the inoculation of the commercial Trichoderma harzianum strain T22 on the arthropod community associated with tomato plants and on the crop performance in an experimental field located in South Italy. Our results showed that inoculation with T. harzianum could alter the arthropod community and reduce the abundance of specific pests under field conditions with respect to the sampling period. The present study also confirmed the beneficial effect of T. harzianum against plant pathogens and on tomato fruit. The complex tomato–arthropod–microorganism interactions that occurred in the field are discussed to enrich our current information on the possibilities of using Trichoderma as a green alternative agent in agriculture.

Characterization of scents from Juniperus chinensis by headspace in-needle microextraction using graphene oxide-polyaniline nanocomposite coated wire followed by gas chromatography-mass spectrometry

Scents released by trees are the secondary metabolites that play various roles, including indirect plant defense against insects, attraction to pollinators, communication, adaptation to heat resistance, environmental stress, and protection from predators. In this study, the scents of three individual trees designated as Korean natural monuments (pair of Chinese junipers, Chinese juniper, and horizontal Chinese juniper tree) were analyzed using headspace in-needle microextraction (HS-INME) method with graphene oxide-polyaniline (GO-PANI) adsorbent followed by gas chromatography-mass spectrometry (GC/MS). GO-PANI layer was coated on a stainless steel wire using cyclic voltammetry (CV). It was characterized through thermogravimetric analysis (TGA), Fourier transform-infrared spectroscopy (FT-IR), and field emission-scanning electron microscope (FE-SEM). As a result, it was confirmed that the GO-PANI coating was successfully prepared. α-Longipinene, α-cedrene, and cedrol, which are representative scent components of common juniper trees, were selected as target compounds through a preliminary test and used in the optimization processes. Response surface methodology (RSM) with Box Behnken Design (BBD) was applied to optimize the experimental conditions. The developed analytical method was validated by checking the limit of detection (LOD), the limit of quantitation (LOQ), recovery rate, sensitivity, and reproducibility. Significant scientific findings from three Korean natural monuments of Juniperus chinensis were characterized by their major scent components such as α-cedrene, γ-cadinene, thujopsene, and cedrol of pungent-woody base note.

Pine defense against eggs of an herbivorous sawfly is elicited by an annexin-like protein present in egg-associated secretion.

Known elicitors of plant defenses against eggs of herbivorous insects are low-molecular-weight organic compounds associated with the eggs. However, previous studies provided evidence that also proteinaceous compounds present in secretion associated with eggs of the herbivorous sawfly Diprion pini can elicit defensive responses in Pinus sylvestris. Pine responses induced by the proteinaceous secretion are known to result in enhanced emission of (E)-β-farnesene, which attracts egg parasitoids killing the eggs. Here, we aimed to identify the defense-eliciting protein and elucidate its function. After isolating the defense-eliciting protein from D. pini egg-associated secretion by ultrafiltration and gel electrophoresis, we identified it by MALDI-TOF mass spectrometry as an annexin-like protein, which we named 'diprionin'. Further GC-MS analyses showed that pine needles treated with heterologously expressed diprionin released enhanced quantities of (E)-β-farnesene. Our bioassays confirmed attractiveness of diprionin-treated pine to egg parasitoids. Expression of several pine candidate genes involved in terpene biosynthesis and regulation of ROS homeostasis was similarly affected by diprionin and natural sawfly egg deposition. However, the two treatments had different effects on expression of pathogenesis-related genes (PR1, PR5). Diprionin is the first egg-associated proteinaceous elicitor of indirect plant defense against insect eggs described so far.