A phytochemical perspective on plant defense against nematodes

Given the large yield losses attributed to plant-parasitic nematodes and the limited availability of sustainable control strategies, new plant-parasitic nematode control strategies are urgently needed. To defend themselves against nematode attack, plants possess sophisticated multi-layered immune systems. One element of plant immunity against nematodes is the production of small molecules with anti-nematode activity, either constitutively or after nematode infection. This review provides an overview of such metabolites that have been identified to date and groups them by chemical class (e.g., terpenoids, flavonoids, glucosinolates, etc.). Furthermore, this review discusses strategies that have been used to identify such metabolites and highlights the ways in which studying anti-nematode metabolites might be of use to agriculture and crop protection. Particular attention is given to emerging, high-throughput approaches for the identification of anti-nematode metabolites, in particular the use of untargeted metabolomics techniques based on nuclear magnetic resonance (NMR) and mass spectrometry (MS)

Female sweet-likers have enhanced cross-modal interoceptive abilities

There are well known phenotypic differences in sweet-liking across individuals, but it remains unknown whether these are related to broader underlying differences in interoceptive abilities (abilities to sense the internal state of the body). Here, healthy women (N = 64) classified as sweet likers (SLs) or sweet dislikers (SDs) completed a bimodal interoception protocol. A heartbeat tracking and a heartbeat discrimination task determined cardiac interoception; both were accompanied by confidence ratings. A water load task, where participants consumed water to satiation and then to maximum fullness was used to assess gastric interoceptive abilities. Motivational state, psychometric characteristics and eating behaviour were also assessed. SLs performed significantly better than SDs on both heartbeat tasks, independently of impulsivity, anxiety, depression, and alexithymia. No differences in metacognitive awareness and subjective interoceptive measures were found. With gastric interoception, SLs were more sensitive to stomach distention, and they ingested less water than SDs to reach satiety when accounting for stomach capacity. SLs also scored higher on mindful and intuitive eating scales and on emotional eating particularly in response to negative stimuli; emotional overeating was fully mediated via interoceptive performance. Overall, our data suggest the SL phenotype may reflect enhanced responsiveness to internal cues more broadly

Plant defense priming in the field : a review

Plant defense priming is a form of plant immunological “memory” in which an external stimulus is perceived by the plant as a warning signal that leads to a minor activation of induced defense mechanisms. This challenge is memorized and leads to a faster and/or stronger defense response upon subsequent attack by a pest or pathogen. The external stimulus in question can be chemical, biotic (a pest, pathogen, or beneficial microbe), or abiotic (an environmental stressor). This review focuses on chemical priming agents, that is, small compounds and macromolecules with priming activity. Although priming has been extensively studied in the lab, comparatively few priming agents have made the transition to commercial use in agriculture and horticulture. The principal objective of this review is to summarize the available literature on the efficacy of priming agents in field conditions. In addition, the effect of priming on interactions with beneficial organisms and the integration of priming agents into broader integrated pest management programs will be discussed

Distinct chemical resistance-inducing stimuli induce common transcriptional, metabolic and nematode community signatures in rice root and rhizosphere

Induced resistance (IR), a phenotypic state induced by an exogenous stimulus and characterized by enhanced resistance to future (a)biotic challenge, is an important component of plant immunity. Numerous IR-inducing stimuli have been described in various plant species, but relatively little is known about ‘core’ systemic responses shared by these distinct IR stimuli and the effects of IR on plant-associated microbiota. In this study, we foliarly applied four distinct IR stimuli (β-aminobutyric acid, acibenzolar-S-methyl, dehydroascorbic acid and piperonylic acid) capable of inducing systemic IR in rice (Oryza sativa) against the root-knot nematode Meloidogyne graminicola and evaluated their effect on the root transcriptome, exudome and root-associated nematode communities. Our results reveal shared transcriptional responses –notably induction of jasmonic acid and phenylpropanoid metabolism – and shared alterations to the exudome that include increased amino acid, benzoate and fatty acid exudation. In rice plants grown in soil from a rice field, IR stimuli significantly affected the composition of rhizosphere nematode communities three days after treatment, but by 14 days after treatment these changes had largely reverted . Notably, IR stimuli did not reduce nematode diversity, which suggests that IR might offer a sustainable option for managing plant-parasitic nematodes

Dehydroascorbate induces plant resistance in rice against root‐knot nematode Meloidogyne graminicola

Ascorbic acid (AsA) is an important antioxidant in plants and regulates various physiological processes. In this study, we show that exogenous treatments with the oxidized form of AsA, that is, dehydroascorbate (DHA), activates induced systemic resistance in rice against the root-knot nematode Meloidogyne graminicola, and investigate the molecular and biochemical mechanisms underlying this phenotype. Detailed transcriptome analysis on roots of rice plants showed an early and robust transcriptional response on foliar DHA treatment, with induction of several genes related to plant stress responses, immunity, antioxidant activity, and secondary metabolism already at 1 day after treatment. Quantitative and qualitative evaluation of H2O2 levels confirmed the appearance of a reactive oxygen species (ROS) burst on DHA treatment, both at the site of treatment and systemically. Experiments using chemical ROS inhibitors or scavengers confirmed that H2O2 accumulation contributes to DHA-based induced resistance. Furthermore, hormone measurements in DHA-treated plants showed a significant systemic accumulation of the defence hormone salicylic acid (SA). The role of the SA pathway in DHA-based induced resistance was confirmed by nematode infection experiments using an SA-signalling deficient WRKY45-RNAi line and reverse transcription-quantitative PCR on SA marker genes. Our results collectively reveal that DHA activates induced systemic resistance in rice against the root-knot nematode M. graminicola, mediated through the production of ROS and activation of the SA pathway

Comparing pesticide regulations : what can Belgium (EU) and Washington State (US) learn from one another?

On a global scale, pesticide use has almost doubled since 1990, with the world market expected to reach $130 billion by the end of 2023. With a rapidly growing world population, the use of pesticides, also called plant protection products (PPP), has played an important role in increasing crop yields to ensure adequate food availability. In the early 1960s, growing concern and awareness about the potential for PPP to non-specifically affect the surrounding ecosystem led to a growing field of resistance. Governmental and intergovernmental bodies have since placed sustainable agricultural practices at the top of their agendas, leading to the use of PPP becoming an increasingly controversial topic of discussion. This policy analysis broadly describes PPP regulation systems in the US and the EU by providing historic accounts of key policy developments of PPP use and their regulations. A direct comparison between regulatory systems for PPP in the US and in the EU is then explored. Washington State and Belgium were chosen as case studies in order to provide a more detailed look into the complexities of such systems and allow for a comparative approach to examine the opportunities and challenges for policy changes. Additionally, suggestions as to what the EU and the US entities can learn from one another to improve the respective PPP regulation systems are investigated. Finally, the analysis explores the potential of strengthening transatlantic cooperation through the establishment of an intergovernmental framework that deals with collection of scientific evidence on PPP and their use. As a result, this analysis acts as a tool for policymakers to better comprehend the different approaches to PPP regulation in the US and the EU as the need to feed the growing world population becomes more urgent, all while safeguarding human and ecosystem health through well-informed policies on PPP use

Rice diterpenoid phytoalexins are involved in defence against parasitic nematodes and shape rhizosphere nematode communities

Summary • Research and rationale: Rice diterpenoid phytoalexins (DPs) are secondary metabolites with a well-known role in resistance to foliar pathogens. Since DPs are also known to be produced and exuded by rice roots, we hypothesized that they might play an important role in plant-nematode interactions, and particularly in defense against phytoparasitic nematodes. • Methods: We used transcriptome analysis on rice roots to analyze the effect of infection by the root-knot nematode Meloidogyne graminicola or treatment with resistance-inducing chemical stimuli on DP biosynthesis genes, and assessed the susceptibility of mutant rice lines impaired in DP biosynthesis to M. graminicola. Moreover, we grew these mutants and their wild type in field soil and used metabarcoding to assess the effect of impairment in DP biosynthesis on rhizosphere and root nematode communities. • Key results: We show that M. graminicola suppresses DP biosynthesis genes early in its invasion process, and conversely that resistance-inducing stimuli transiently induce the biosynthesis of DPs. Moreover, we show that loss of DPs increases susceptibility to M. graminicola. Metabarcoding on wild-type and DP-deficient plants grown in field soil reveals that DPs significantly alter the composition of rhizosphere and root nematode communities • Main conclusions: DPs are important players in basal and inducible defense against nematode pathogens of rice and help shape rice-associated nematode communities.This is the peer reviewed version of the following article: Desmedt, Willem, Enoch Narh Kudjordjie, Satish Namdeo Chavan, Juan Zhang, Riqing Li, Bing Yang, Mogens Nicolaisen et al. "Rice diterpenoid phytoalexins are involved in defence against parasitic nematodes and shape rhizosphere nematode communities." New Phytologist (2022), which has been published in final form at doi:10.1111/nph.18152. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited