A biological agent modulates the physiology of barley infected with Drechslera teres

Rhizobacteria Revolution: Amplifying Crop Resilience and Yield in a Changing Climate Through Plant Growth Promotion

The rapid progression of climate change poses significant challenges to global agriculture, necessitating innovative solutions to ensure food security for an expanding population. Plant growth-promoting rhizobacteria (PGPR) offer a promising avenue for sustainable agriculture by enhancing crop resilience and productivity under environmental constraints. These beneficial microbes regulate key physiological processes in plants, such as phytohormone synthesis and nutrient solubilization. This enhances root architecture, improves soil fertility, and enables crops to adapt to resource-limited conditions. Moreover, PGPR strengthen plant defenses against abiotic stressors such as salinity, drought, and nutrient deficiencies, as well as biotic threats like pathogens. Empirical evidence demonstrates that PGPR inoculation can significantly enhance crop yields across diverse agroecosystems by increasing nutrient use efficiency and stress tolerance. Despite their proven potential, the effective deployment of PGPR in farming systems requires addressing critical issues related to scalability, formulation, and integration with existing practices. This review underscores the role of PGPR in mitigating climate-induced agricultural challenges, highlighting the need for interdisciplinary collaborations and robust knowledge-sharing networks to drive the adoption of PGPR-based interventions. By leveraging these microbial allies, we can pave the way for climate-resilient farming systems and safeguard global food security amidst an uncertain future.

Halophilic Bacillus improve barley growth on calcareous soil via enhanced photosynthetic performance and metabolomic re-programing

Plant Growth Promoting Rhizobacteria are a sustainable biological alternative to agrochemicals to improve plant growth and stress tolerance. In this work we used two Bacillus strains native to the saline rhizosphere of halophytic plants in order to improve the growth of barley on a calcareous soil (CS). This soil negatively affected plant development; however, the inoculation of barley with the halophytic Bacillus strains enhanced barley growth and photosynthesis performance. In fact, a significant increase of the maximum photochemical yield of PSII and PSI was observed following inoculation, leading to improved protection of these photosystems against photoinhibition. Moreover, a pairwise metabolomic pathway analysis in barley leaves and roots was performed. Compared to barley grown on non-calcareous soil (NCS), CS led to a downregulation of sugar-related metabolic pathways, which can be correlated with lower photosynthesis performance. Furthermore, the abundance of metabolites related to amino acids in leaves and phenylpropanoids and lipids in roots was also reduced by CS. This negative effect was reverted by the inoculation of the bacteria strains. In conclusion, halophilic Bacillus native to the saline rhizosphere of halophyte plants induced metabolic changes leading to an enhanced photosynthesis activity, and hence, alleviating the deleterious effect of CS on barley development.

The potential of Paraburkholderia species to enhance crop growth

Agrochemicals are the primary alternative for maintaining the high yields necessary to produce sufficient plant-based foods to supply the world population. In recent decades, one of the most extensively explored alternatives to replace agrochemicals and reduce their environmental impact has been the use of microorganism-based products to boost crop yields with less environmental impact. This review focuses on the results of studies that have demonstrated the potential of the genus Paraburkholderia to increase crop yields and be utilized in biofertilizers and biocontrol products. A literature search was performed electronically considering articles and books published until August 19, 2024. We identified 24 species of Paraburkholderia with the ability to improve crop yields after their inoculation by different methods on seeds, seedlings, plantlets, adult crops, or fruits. The effects of these bacteria have been tested under laboratory, greenhouse, or field conditions. These Paraburkholderia species mediate their positive impact on crop growth by direct and indirect plant growth-promoting mechanisms, which include improving nutrient uptake, stimulating growth by phytohormone production, regulation and stimulation of metabolic pathways, induction of abiotic stress tolerance, and disease control by direct pathogen inhibition or induction of systemic resistance in plants. The literature reviewed here supports the use of Paraburkholderia in bio-inputs under the actual panorama of climate change and the necessity to increase sustainable agriculture worldwide.

Deep Learning-Based Barley Disease Quantification for Sustainable Crop Production

Net blotch disease caused by Drechslera teres is a major fungal disease that affects barley (Hordeum vulgare) plants and can result in significant crop losses. In this study, we developed a deep learning model to quantify net blotch disease symptoms on different days postinfection on seedling leaves using Cascade R-CNN (region-based convolutional neural network) and U-Net (a convolutional neural network) architectures. We used a dataset of barley leaf images with annotations of net blotch disease to train and evaluate the model. The model achieved an accuracy of 95% for Cascade R-CNN in net blotch disease detection and a Jaccard index score of 0.99, indicating high accuracy in disease quantification and location. The combination of Cascade R-CNN and U-Net architectures improved the detection of small and irregularly shaped lesions in the images at 4 days postinfection, leading to better disease quantification. To validate the model developed, we compared the results obtained by automated measurement with a classical method (necrosis diameter measurement) and a pathogen detection by real-time PCR. The proposed deep learning model could be used in automated systems for disease quantification and to screen the efficacy of potential biocontrol agents to protect against disease.

A plant's perception of growth-promoting bacteria and their metabolites

Many recent studies have highlighted the importance of plant growth-promoting (rhizo)bacteria (PGPR) in supporting plant's development, particularly under biotic and abiotic stress. Most focus on the plant growth-promoting traits of selected strains and the latter's effect on plant biomass, root architecture, leaf area, and specific metabolite accumulation. Regarding energy balance, plant growth is the outcome of an input (photosynthesis) and several outputs (i.e., respiration, exudation, shedding, and herbivory), frequently neglected in classical studies on PGPR-plant interaction. Here, we discuss the primary evidence underlying the modifications triggered by PGPR and their metabolites on the plant ecophysiology. We propose to detect PGPR-induced variations in the photosynthetic activity using leaf gas exchange and recommend setting up the correct timing for monitoring plant responses according to the specific objectives of the experiment. This research identifies the challenges and tries to provide future directions to scientists working on PGPR-plant interactions to exploit the potential of microorganisms' application in improving plant value.

Hordeum vulgare differentiates its response to beneficial bacteria

BACKGROUND

In nature, beneficial bacteria triggering induced systemic resistance (ISR) may protect plants from potential diseases, reducing yield losses caused by diverse pathogens. However, little is known about how the host plant initially responds to different beneficial bacteria. To reveal the impact of different bacteria on barley (Hordeum vulgare), bacterial colonization patterns, gene expression, and composition of seed endophytes were explored.

RESULTS

This study used the soil-borne Ensifer meliloti, as well as Pantoea sp. and Pseudomonas sp. isolated from barley seeds, individually. The results demonstrated that those bacteria persisted in the rhizosphere but with different colonization patterns. Although root-leaf translocation was not observed, all three bacteria induced systemic resistance (ISR) against foliar fungal pathogens. Transcriptome analysis revealed that ion- and stress-related genes were regulated in plants that first encountered bacteria. Iron homeostasis and heat stress responses were involved in the response to E. meliloti and Pantoea sp., even if the iron content was not altered. Heat shock protein-encoding genes responded to inoculation with Pantoea sp. and Pseudomonas sp. Furthermore, bacterial inoculation affected the composition of seed endophytes. Investigation of the following generation indicated that the enhanced resistance was not heritable.

CONCLUSIONS

Here, using barley as a model, we highlighted different responses to three different beneficial bacteria as well as the influence of soil-borne Ensifer meliloti on the seed microbiome. In total, these results can help to understand the interaction between ISR-triggering bacteria and a crop plant, which is essential for the application of biological agents in sustainable agriculture.

Plant Beneficial Bacteria as Bioprotectants against Wheat and Barley Diseases

Wheat and barley are the main cereal crops cultivated worldwide and serve as staple food for a third of the world's population. However, due to enormous biotic stresses, the annual production has significantly reduced by 30-70%. Recently, the accelerated use of beneficial bacteria in the control of wheat and barley pathogens has gained prominence. In this review, we synthesized information about beneficial bacteria with demonstrated protection capacity against major barley and wheat pathogens including Fusarium graminearum, Zymoseptoria tritici and Pyrenophora teres. By summarizing the general insights into molecular factors involved in plant-pathogen interactions, we show to an extent, the means by which beneficial bacteria are implicated in plant defense against wheat and barley diseases. On wheat, many Bacillus strains predominantly reduced the disease incidence of F. graminearum and Z. tritici. In contrast, on barley, the efficacy of a few Pseudomonas, Bacillus and Paraburkholderia spp. has been established against P. teres. Although several modes of action were described for these strains, we have highlighted the role of Bacillus and Pseudomonas secondary metabolites in mediating direct antagonism and induced resistance against these pathogens. Furthermore, we advance a need to ascertain the mode of action of beneficial bacteria/molecules to enhance a solution-based crop protection strategy. Moreover, an apparent disjoint exists between numerous experiments that have demonstrated disease-suppressive effects and the translation of these successes to commercial products and applications. Clearly, the field of cereal disease protection leaves a lot to be explored and uncovered.

Handheld Multifunctional Fluorescence Imager for Non-invasive Plant Phenotyping

Fluorescence imaging has shown great potential in non-invasive plant monitoring and analysis. However, current systems have several limitations, such as bulky size, high cost, contact measurement, and lack of multifunctionality, which may hinder its applications in a wide range of settings including indoor vertical farming. Herein, we developed a compact handheld fluorescence imager enabling multipurpose plant phenotyping, such as continuous photosynthetic activity monitoring and non-destructive anthocyanin quantification. The compact imager comprises of pulse-amplitude-modulated multi-color light emitting diodes (LEDs), optimized light illumination and collection, dedicated driver circuit board, miniaturized charge-coupled device camera, and associated image analytics. Experiments conducted in drought stressed lettuce proved that the novel imager could quantitatively evaluate the plant stress by the non-invasive measurement of photosynthetic activity efficiency. Moreover, a non-invasive and fast quantification of anthocyanins in green and red Batavia lettuce leaves had excellent correlation (>84%) with conventional destructive biochemical analysis. Preliminary experimental results emphasize the high throughput monitoring capability and multifunctionality of our novel handheld fluorescence imager, indicating its tremendous potential in modern agriculture.

Genotypic Variation of Nitrogen Use Efficiency and Amino Acid Metabolism in Barley

Owing to the large genetic diversity of barley and its resilience under harsh environments, this crop is of great value for agroecological transition and the need for reduction of nitrogen (N) fertilizers inputs. In the present work, we investigated the diversity of a North African barley genotype collection in terms of growth under limiting N (LN) or ample N (HN) supply and in terms of physiological traits including amino acid content in young seedlings. We identified a Moroccan variety, Laanaceur, accumulating five times more lysine in its leaves than the others under both N nutritional regimes. Physiological characterization of the barley collection showed the genetic diversity of barley adaptation strategies to LN and highlighted a genotype x environment interaction. In all genotypes, N limitation resulted in global biomass reduction, an increase in C concentration, and a higher resource allocation to the roots, indicating that this organ undergoes important adaptive metabolic activity. The most important diversity concerned leaf nitrogen use efficiency (LNUE), root nitrogen use efficiency (RNUE), root nitrogen uptake efficiency (RNUpE), and leaf nitrogen uptake efficiency (LNUpE). Using LNUE as a target trait reflecting barley capacity to deal with N limitation, this trait was positively correlated with plant nitrogen uptake efficiency (PNUpE) and RNUpE. Based on the LNUE trait, we determined three classes showing high, moderate, or low tolerance to N limitation. The transcriptomic approach showed that signaling, ionic transport, immunity, and stress response were the major functions affected by N supply. A candidate gene encoding the HvNRT2.10 transporter was commonly up-regulated under LN in the three barley genotypes investigated. Genes encoding key enzymes required for lysine biosynthesis in plants, dihydrodipicolinate synthase (DHPS) and the catabolic enzyme, the bifunctional Lys-ketoglutarate reductase/saccharopine dehydrogenase are up-regulated in Laanaceur and likely account for a hyperaccumulation of lysine in this genotype. Our work provides key physiological markers of North African barley response to low N availability in the early developmental stages.

Gene expression and metabolite analysis in barley inoculated with net blotch fungus and plant growth-promoting rhizobacteria

Net blotch, caused by the ascomycete Drechslera teres, can compromise barley production. Beneficial bacteria strains are of substantial interest as biological agents for plant protection in agriculture. Belonging to the genus Paraburkholderia, a bacterium, referred to as strain B25, has been identified as protective for barley against net blotch. The strain Paraburkholderia phytofirmans (strain PsJN), which has no effect on the pathogen's growth, has been used as control. In this study, the expression of target genes involved in cell wall-related processes, defense responses, carbohydrate and phenylpropanoid pathways was studied under various conditions (with or without pathogen and/or with or without bacterial strains) at different time-points (0-6-12-48 h). The results show that specific genes were subjected to a circadian regulation and that the expression of most of them increased in barley infected with D. teres and/or bacterized with the strain PsJN. On the contrary, a decreased gene expression was observed in the presence of strain B25. To complement and enrich the gene expression analysis, untargeted metabolomics was carried out on the same samples. The data obtained show an increase in the production of lipid compounds in barley in the presence of the pathogen. In addition, the presence of strain B25 leads to a decrease in the production of defense compounds in this crop. The results contribute to advance the knowledge on the mechanisms occurring at the onset of D. teres infection and in the presence of a biocontrol agent limiting the severity of net blotch in barley.