Antimicrobial Terpenes Suppressed the Infection Process of Phytophthora in Fennel-Pepper Intercropping System

Effects of pepper-maize intercropping on the physicochemical properties, microbial communities, and metabolites of rhizosphere and bulk soils

BACKGROUND

Intercropping increases land use efficiency and farmland ecological diversity. However, little is understood about whether and how soil biota, metabolites, and nutrients change under interspecific competition among plants. Thus, this study aimed to explore the changes in the physicochemical properties, microbial communities, and metabolites of rhizosphere and bulk soils of pepper monocropping and pepper-maize intercropping systems.

RESULTS

Intercropping significantly increased the contents of available phosphorus (AP) and available potassium (AK), and decreased the pH value, whereas it had little effect on the total nitrogen (TN) and organic matter (OM) in the rhizosphere and bulk soils, compared with those in monocropping pepper. Moreover, the OM content was higher in rhizosphere soil than in bulk soil. The microbial community structures and metabolite profiles also differed between the two systems. The diversity of bacteria and fungi increased in intercropped pepper. The relative abundances of Actinobacteria, Chloroflexi, Cyanobacteria, and Ascomycota were higher while those of Proteobacteria, Planctomycetes, Mucoromycota, and Basidiomycota were significantly lower in the rhizosphere and bulk soils from the intercropping system than in those from the monocropping system. Linear discriminant analysis revealed that the predominant bacteria and fungi in the rhizosphere soil from the intercropping system belonged to the order Sphingomonadales and genera Nitrospira, Phycicoccus and Auricularia, whereas those in the bulk soil from the intercropping system belonged to the phylum Acidobacteria and genera Calocera, Pseudogymnoascus, and Trichosporon. Intercropping promoted the secretion of flavonoids, alkaloids, and nucleotides and their derivatives in the rhizosphere soil and significantly increased the contents of organoheterocyclic compounds in the bulk soil. Furthermore, the AP and AK contents, and pH value had strong positive correlations with bacteria. In addition, co-occurrence network analysis also showed that asebogenin, trachelanthamidine, 5-methyldeoxycytidine, and soil pH were the key factors mediating root-soil-microbe interactions.

CONCLUSION

Intercropping can alter microbial community structures and soil metabolite composition in rhizosphere and bulk soils, enhancing soil nutrient contents, enriching soil beneficial microbes and secondary metabolites (flavonoids and alkaloids) of intercropped pepper, and provided a scientific basis for sustainable development in the pepper-maize intercropping system.

Comparative Transcriptomics of Soybean Genotypes with Partial Resistance Toward Phytophthora sojae, Conrad, and M92-220 to Moderately Susceptible Fast Neutron Mutant Soybeans and Sloan

The breeding of disease-resistant soybeans cultivars to manage Phytophthora root and stem rot caused by the pathogen Phytophthora sojae involves combining quantitative disease resistance (QDR) and Rps gene-mediated resistance. To identify and confirm potential mechanisms of QDR toward P. sojae, we conducted a time course study comparing changes in gene expression among Conrad and M92-220 with high QDR to susceptible genotypes, Sloan, and three mutants derived from fast neutron irradiation of M92-220. Differentially expressed genes from Conrad and M92-220 indicated several shared defense-related pathways at the transcriptomic level but also defense pathways unique to each cultivar, such as stilbenoid, diarylheptanoid, and gingerol biosynthesis and monobactam biosynthesis. Gene Ontology pathway analysis showed that the susceptible fast neutron mutants lacked enrichment of three terpenoid-related pathways and two cell wall-related pathways at either one or both time points, in contrast to M92-220. The susceptible mutants also lacked enrichment of potentially important Kyoto Encyclopedia of Genes and Genomes pathways at either one or both time points, including sesquiterpenoid and triterpenoid biosynthesis; thiamine metabolism; arachidonic acid; stilbenoid, diarylheptanoid, and gingerol biosynthesis; and monobactam biosynthesis. Additionally, 31 genes that were differentially expressed in M92-220 following P. sojae infection were not expressed in the mutants. These 31 genes have annotations related to unknown proteins; valine, leucine, and isoleucine biosynthesis; and protein and lipid metabolic processes. The results of this study confirm previously proposed mechanisms of QDR, provide evidence for potential novel QDR pathways in M92-220, and further our understanding of the complex network associated with QDR mechanisms in soybean toward P. sojae.

Repeated exposure of wheat to the fungal root pathogen Bipolaris sorokiniana modulates rhizosphere microbiome assembly and disease suppressiveness

BACKGROUND

Disease suppressiveness of soils to fungal root pathogens is typically induced in the field by repeated infections of the host plant and concomitant changes in the taxonomic composition and functional traits of the rhizosphere microbiome. Here, we studied this remarkable phenomenon for Bipolaris sorokiniana in two wheat cultivars differing in resistance to this fungal root pathogen.

RESULTS

The results showed that repeated exposure of the susceptible wheat cultivar to the pathogen led to a significant reduction in disease severity after five successive growth cycles. Surprisingly, the resistant wheat cultivar, initially included as a control, showed the opposite pattern with an increase in disease severity after repeated pathogen exposure. Amplicon analyses revealed that the bacterial families Chitinophagaceae, Anaerolineaceae and Nitrosomonadaceae were associated with disease suppressiveness in the susceptible wheat cultivar; disease suppressiveness in the resistant wheat cultivar was also associated with Chitinophagaceae and a higher abundance of Comamonadaceae. Metagenome analysis led to the selection of 604 Biosynthetic Gene Clusters (BGCs), out of a total of 2,571 identified by AntiSMASH analysis, that were overrepresented when the soil entered the disease suppressive state. These BGCs are involved in the biosynthesis of terpenes, non-ribosomal peptides, polyketides, aryl polyenes and post-translationally modified peptides.

CONCLUSION

Combining taxonomic and functional profiling we identified key changes in the rhizosphere microbiome during disease suppression. This illustrates how the host plant relies on the rhizosphere microbiome as the first line of defense to fight soil-borne pathogens. Microbial taxa and functions identified here can be used in novel strategies to control soil-borne fungal pathogens.

The performance of plant essential oils against lactic acid bacteria and adverse microorganisms in silage production

Plant essential oils have played an important role in the field of antibiotic alternatives because of their efficient bacteriostatic and fungistatic activity. As plant essential oils are widely used, their activity to improve the quality of plant silage has also been explored. This review expounds on the active ingredients of essential oils, their bacteriostatic and fungistatic activity, and mechanisms, as well as discusses the application of plant essential oils in plant silage fermentation, to provide a reference for the development and application of plant essential oils as silage additives in plant silage fermentation feed.

Soil and Phytomicrobiome for Plant Disease Suppression and Management under Climate Change: A Review

The phytomicrobiome plays a crucial role in soil and ecosystem health, encompassing both beneficial members providing critical ecosystem goods and services and pathogens threatening food safety and security. The potential benefits of harnessing the power of the phytomicrobiome for plant disease suppression and management are indisputable and of interest in agriculture but also in forestry and landscaping. Indeed, plant diseases can be mitigated by in situ manipulations of resident microorganisms through agronomic practices (such as minimum tillage, crop rotation, cover cropping, organic mulching, etc.) as well as by applying microbial inoculants. However, numerous challenges, such as the lack of standardized methods for microbiome analysis and the difficulty in translating research findings into practical applications are at stake. Moreover, climate change is affecting the distribution, abundance, and virulence of many plant pathogens, while also altering the phytomicrobiome functioning, further compounding disease management strategies. Here, we will first review literature demonstrating how agricultural practices have been found effective in promoting soil health and enhancing disease suppressiveness and mitigation through a shift of the phytomicrobiome. Challenges and barriers to the identification and use of the phytomicrobiome for plant disease management will then be discussed before focusing on the potential impacts of climate change on the phytomicrobiome functioning and disease outcome.

Nitrogen application enhances yield, yield-attributes, and physiological characteristics of dryland wheat/maize under strip intercropping

Intercropping has been acknowledged as a sustainable practice for enhancing crop productivity and water use efficiency under rainfed conditions. However, the contribution of different planting rows towards crop physiology and yield is elusive. In addition, the influence of nitrogen (N) fertilization on the physiology, yield, and soil water storage of rainfed intercropping systems is poorly understood; therefore, the objective of this experiment was to study the contribution of different crop rows on the physiological, yield, and related traits of wheat/maize relay-strip intercropping (RSI) with and without N application. The treatments comprised of two factors viz. intercropping with three levels (sole wheat, sole maize, and RSI) and two N application rates, with and without N application. Results showed that RSI significantly improved the land use efficiency and grain yield of both crops under rainfed conditions. Intercropping with N application (+N treatment) resulted in the highest wheat grain yield with 70.37 and 52.78% increase as compared with monoculture and without N application in 2019 and 2020, respectively, where border rows contributed the maximum followed by second rows. The increase in grain yield was attributed to higher values of the number of ears per square meter (10-25.33% more in comparison to sole crop without N application) during both study years. The sole wheat crop without any N application recorded the least values for all yield-related parameters. Despite the absence of significant differences, the relative decrease in intercropped maize under both N treatments was over 9% compared to the sole maize crop, which was mainly ascribed to the border rows (24.65% decrease compared to the sole crop) that recorded 12 and 13% decrease in kernel number and thousand-grain weight, respectively than the sole crop. This might be attributed to the reduced photosynthesis and chlorophyll pigmentation in RSI maize crop during the blended growth period. In a nutshell, it can be concluded that wheat/maize RSI significantly improved the land use efficiency and the total yield compared to the sole crops' yield in arid areas in which yield advantages were mainly ascribed to the improvement in wheat yield.

Fatal attraction: How Phytophthora zoospores find their host

Oomycete plant pathogens, such as Phytophthora and Pythium species produce motile dispersal agents called zoospores that actively target host plants. Zoospores are exceptional in their ability to display taxis to chemical, electrical and physical cues to navigate the phyllosphere and reach stomata, wound sites and roots. Many components of root exudates have been shown attractive or repulsive to zoospores. Although some components possess very strong attractiveness, it seems that especially the mix of components exuded by the primary host is most attractive to zoospores. Zoospores actively approach attractants with swimming behaviour reminiscent of other microswimmers. To achieve a unified description of zoospore behaviour when sensing an attractant, we propose the following terms for the successive stages of the homing response: reorientation, approaching, retention and settling. How zoospores sense and process attractants is poorly understood but likely involves signal perception via cell surface receptors. Since zoospores are important for infection, undermining their activity by luring attractants or blocking receptors seem promising strategies for disease control.