Enhanced resistance in barley (Hordeum vulgare) against pathogens, such as the powdery mildew-causing fungus Blumeria graminis f. sp. hordei, is of high importance. The beneficial effects of bacterial quorum sensing molecules on resistance and plant growth have been shown in different plant species. Here, we present the effects of the N-3-oxotetradecanoyl-l-homoserine lactone (oxo-C14-HSL) on the resistance of different barley genotypes. Genetically diverse accessions of barley were identified and exposed to the beneficial, oxo-C14-HSL-producing bacterium Ensifer meliloti or the pure N-acyl homoserine lactone (AHL) molecule. Metabolic profiling along with expression analysis of selected genes and physiological assays revealed that the capacity to react varies among different barley genotypes. We demonstrate that upon pretreatment with AHL molecule, AHL-primable barley genotype expresses enhanced resistance against B. graminis f. sp. hordei. We further show that pretreatment with AHL correlates with stronger activation of barley MAP kinases and regulation of defense-related PR1 and PR17b genes after a subsequent treatment with chitin. Noticeable was the stronger accumulation of lignin. Our results suggest that appropriate genetic background is required for AHL-induced priming. At the same time, they bear potential to use these genetic features for new breeding and plant protection approaches.

Plant-parasitic nematodes are a major constraint on agricultural production. They significantly impede crop yield. To complete their parasitism, they need to locate, disguise, and interact with plant signals exuded in the rhizosphere of the host plant. A specific subset of the soil microbiome can attach to the surface of nematodes in a specific manner. We hypothesized that host plants recruit species of microbes as helpers against attacking nematode species, and that these helpers differ among plant species. We investigated to what extend the attached microbial species are determined by plant species, their root exudates, and how these microbes affect nematodes. We conditioned the soil microbiome in the rhizosphere of different plant species, then employed culture-independent and culture-dependent methods to study microbial attachment to the cuticle of the phytonematode Pratylenchus penetrans. Community fingerprints of nematode-attached fungi and bacteria showed that the plant species govern the microbiome associated with the nematode cuticle. Bacteria isolated from the cuticle belonged to Actinobacteria, Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Sphingobacteria, and Firmicutes. The isolates Microbacterium sp. i.14, Lysobacter capsici i.17, and Alcaligenes sp. i.37 showed the highest attachment rates to the cuticle. The isolates Bacillus cereus i.24 and L. capsici i.17 significantly antagonized P. penetrans after attachment. Significantly more bacteria attached to P. penetrans in microbiome suspensions from bulk soil or oat rhizosphere compared to Ethiopian mustard rhizosphere. However, the latter caused a better suppression of the nematode. Conditioning the cuticle of P. penetrans with root exudates significantly decreased the number of Microbacterium sp. i.14 attaching to the cuticle, suggesting induced changes of the cuticle structure. These findings will lead to a more knowledge-driven exploitation of microbial antagonists of plant-parasitic nematodes for plant protection.

Root lesion nematodes, Pratylenchus penetrans, are major pests of legumes with little options for their control. We aimed to prime soybean cv. Primus seedlings to improve basic defense against these nematodes by root application of N-3-oxo-tetradecanoyl-L-homoserine lactone (oxo-C14-HSL). The invasion of soybean roots by P. penetrans was significantly reduced in plants that were pre-treated with the oxo-C14-HSL producing rhizobacterium Ensifer meliloti strain ExpR+, compared to non-inoculated plants or plants inoculated with the nearly isogenic strain E. meliloti AttM with plasmid-mediated oxo-C14-HSL degradation. The nematodes were more clustered in the root tissues of plants treated with the AttM strain or the control compared to roots treated with the ExpR+ strain. In split-root systems primed on one side with strain ExpR+, root invasion was reduced on the opposite side compared to non-primed plants indicating a systemic plant response to oxo-C14-HSL. No additional local effect was detected, when inoculating nematodes on the ExpR+ primed side. Removal of oxo-C14-HSL after root exposure resulted in reduced root invasion compared to non-primed plants when the nematodes were added 3, 7, or 15 days later. Thus, probably the plant memorized the priming stimulus. Similarly, the plants were primed by compounds released from the surface of the nematodes. HPLC analysis of the root extracts of oxo-C14-HSL treated and untreated plants revealed that priming resulted in enhanced phytoalexin synthesis upon P. penetrans challenge. Without root invading nematodes, the phytoalexin concentrations of primed and non-primed plants did not significantly differ, indicating that priming did not lead to a persistently increased stress level of the plants. Upon nematode invasion, the phytoalexins coumestrol, genistein, and glyceollin increased in concentration in the roots compared to control plants without nematodes. Glyceollin synthesis was significantly more triggered by nematodes in primed plants compared to non-primed plants. The results indicated that the priming of soybean plants led to a more rapid and strong defense induction upon root invasion of nematodes.

Plant-parasitic nematode research in the Middle East and North Africa (MENA) region faces significant challenges rooted in a need for proper assembly, diversity, and a unified and purpose-driven framework. This led to exacerbating their detrimental effects on crop production. This systematic review addresses the current situation and challenges that require targeted interventions to sustainably manage plant-parasitic nematodes and reduce their detrimental impact on agriculture production in the MENA region. We analyzed the nematode-related research conducted within the region over the past three decades to assess available resources and promote diverse research approaches beyond basic morphology-focused surveys. We show that crops are attacked by a diverse spectrum of plant-parasitic nematodes that exceed the global economic threshold limits. In particular, Meloidogyne species exceed the threshold limit by 8 - 14-fold, with a 100% frequency of occurrence in the collected soil samples, posing a catastrophic threat to crop production and the economy. We highlight detrimental agriculture practices in the MENA region, such as transferring soil from established fields to barren land, which enhances the dissemination of plant-parasitic nematodes, disrupting soil ecology and causing significant agricultural challenges in newly cultivated areas. Looking into the behavior of farmers, raising awareness must be accompanied by available solutions, as more practical alternatives are needed to gain the confidence of the farmers. We propose integrating microbial-based products and soil development practices in hygienic farming as resilient and sustainable solutions for nematode management. Increased emphasis is required to diversify the nematode-related research areas to bridge the gaps and facilitate the transition from fundamental knowledge to practical solutions. A cohesive network of nematologists and collaboration with national and international entities is crucial for exchanging knowledge related to legislation against invasive species.

Deserts cover one-third of Earth’s land and support life forms uniquely adapted to extreme climatic and environmental conditions. Restoring these ecosystems remains difficult and costly, yet knowledge of native plants, soils, and their associated microbiomes offers promising solutions. This review outlines the drivers and consequences of desertification feedback loops and explains how microbial adaptations sustain soil functions under stress. We highlight the role of plant–microbe–soil interactions in shaping functional networks that support restoration and the development of synergistic plant communities. We also highlight how the integration of ecological frameworks such as niche differentiation, network theory, and stoichiometric balance reveals new directions for restoration efforts. In this framework, emerging microbiome-based strategies can offer a path to transform barren or degraded landscapes into diverse, resilient vegetative islands.