Plant-plant-microbe mechanisms involved in soil-borne disease suppression on a maize and pepper intercropping system

Effects of wheat intercropping on growth and occurrence of Fusarium wilt in watermelon

Watermelon is commonly affected by Fusarium wilt in a monoculture cropping system. Wheat intercropping alleviates the affection of Fusarium wilt of watermelon. The objective of this study was to determine the effects of wheat and watermelon intercropping on watermelon growth and Fusarium wilt. Our results showed that wheat and watermelon intercropping promoted growth, increased chlorophyll content, and photosynthesis of watermelon. Meanwhile, wheat and watermelon intercropping inhibited watermelon Fusarium wilt occurrence, decreased spore numbers, increased root vigor, increased antioxidant enzyme activities, and decreased malondialdehyde (MDA) content in watermelon roots. Additionally, wheat and watermelon intercropping enhanced the bacterial colonies and total microbes growth in soil, decreased fungi and Fusarium oxysporum f. sp. niveum (FON) colonies, and increased soil enzyme activities in watermelon rhizosphere soil. Our results indicated that wheat and watermelon intercropping enhanced watermelon growth and decreased the incidence of Fusarium wilt in watermelon. These effects could be due to intercropping inducing physiological changes, regulating soil enzyme activities, and/or modulating soil microbial communities.

Mechanism of benzoxazinoids affecting the growth and development of Fusarium oxysporum f. sp. fabae

Continuous cropping of faba bean (Vicia faba L.) has led to a high incidence of wilt disease. The implementation of an intercropping system involving wheat and faba bean can effectively control the propagation of faba bean wilt disease. To investigate the mechanisms of wheat in mitigating faba bean wilt disease in a wheat-faba bean intercropping system. A comprehensive investigation was conducted to assess the temporal variations in Fusarium oxysporum f. sp. fabae (FOF) on the chemotaxis of benzoxazinoids (BXs) and wheat root through indoor culture tests. The effects of BXs on FOF mycelial growth, spore germination, spore production, and electrical conductivity were examined. The influence of BXs on the ultrastructure of FOF was investigated through transmission electron microscopy. Eukaryotic mRNA sequencing was utilized to analyze the differentially expressed genes in FOF upon treatment with BXs. FOF exhibited a significant positive chemotactic effect on BXs in wheat roots and root secretions. BXs possessed the potential to exert significant allelopathic effects on the mycelial growth, spore germination, and sporulation of FOF. In addition, BXs demonstrated a remarkable ability to disrupt the structural integrity and stability of the membrane and cell wall of the FOF mycelia. BXs possessed the capability of posing threats to the integrity and stability of the cell membrane and cell wall. This ultimately resulted in physiological dysfunction, effectively inhibiting the regular growth and developmental processes of the FOF.

Benzoxazinoids secreted by wheat root weaken the pathogenicity of Fusarium oxysporum f. sp. fabae by inhibiting linoleic acid and nucleotide metabolisms

KEY MESSAGE

The regulatory action of BXs secreted by wheat on the pathogenicity of FOF causing Fusarium wilt in faba bean were analyzed. DIMBOA and MBOA weakened the pathogenicity of FOF. A large number of pathogenic bacteria in continuous cropping soil infect faba bean plants, leading to the occurrence of wilt disease, which restricts their production. Faba bean-wheat intercropping is often used to alleviate this disease. This study investigates the effect of benzoxazinoids (BXs) secreted by wheat root on the pathogenicity of Fusarium oxysporum f. sp. Fabae (FOF) and underlying molecular mechanisms. The effects of DIMBOA(2,4-dihydroxy-7-methoxy-1,4-benzoxazine-4-one) and MBOA(6-methoxybenzoxazolin-2-one) on the activity of cell-wall-degrading enzymes in FOF(cellulase, pectinase, amylase, and protease), FOF Toxin (fusaric acid, FA) content were investigated through indoor culture experiments. The effect of BXs on the metabolic level of FOF was analyzed by metabonomics to explore the ecological function of benzoxazines intercropping control of Fusarium wilt in faba bean. The results show that the Exogenous addition of DIMBOA and MBOA decreased the activity of plant-cell-wall-degrading enzymes and fusaric acid content and significantly weakened the pathogenicity of FOF. DIMBOA and MBOA significantly inhibited the pathogenicity of FOF, and metabolome analysis showed that DIMBOA and MBOA reduced the pathogenicity of FOF by down-regulating related pathways such as nucleotide metabolism and linoleic acid metabolism, thus effectively controlling the occurrence of Fusarium wilt in faba bean.

Microplastic fibres affect soil fungal communities depending on drought conditions with consequences for ecosystem functions

Microplastics affect soil functions depending on drought conditions. However, how their combined effect influences soil fungi and their linkages with ecosystem functions is still unknown. To address this, we used rhizosphere soil from a previous experiment in which we employed microplastic fibres addition and drought in a factorial design, and evaluated their effects on soil fungal communities. Microplastics decreased soil fungal richness under well-watered conditions, likely linked to microplastics leaching toxic substances into the soil, and microplastic effects on root fineness. Under drought, by contrast, microplastics increased pathogen and total fungal richness, likely related to microplastic positive effects on soil properties, such as water holding capacity, porosity or aggregation. Soil fungal richness was the attribute most affected by microplastics and drought. Microplastics altered the relationships between soil fungi and ecosystem functions to the point that many of them flipped from positive to negative or disappeared. The combined effect of microplastics and drought on fungal richness mitigated their individual negative effect (antagonism), suggesting that changes in soil water conditions may alter the action mode of microplastics in soil. Microplastic leaching of harmful substances can be mitigated under drought, while the improvement of soil properties by microplastics may alleviate such drought conditions.

A biological product of Bacillus amyloliquefaciens QST713 strain for promoting banana plant growth and modifying rhizosphere soil microbial diversity and community composition

Introduction

Bananas are not only an important food crop for developing countries but also a major trading fruit for tropical and semitropical regions, maintaining a huge trade volume. Fusarium wilt of banana (FWB) caused by Fusarium oxysporum f. sp. cubense is becoming a serious challenge to the banana industry globally. Biological control has the potential to offer both effective and sustainable measures for this soil-borne disease.

Methods

In order to explore the biocontrol effects of the biological agent Bacillus amyloliquefaciens QST713 strain on banana plants, two cultivars, Brazilian and Yunjiao No. 1, with varied resistance to FWB, were used in greenhouse pot experiments.

Results

Results showed that the plant height and pseudostem diameter of banana-susceptible cultivar Brazilian increased by 11.68% and 11.94%, respectively, after QST713 application, while the plant height and pseudostem diameter of resistant cultivar Yunjiao No. 1 increased by 14.87% and 12.51%, respectively. The fresh weight of the two cultivars increased by 20.66% and 36.68%, respectively, indicating that this biological agent has potential effects on plant growth. Analysis of the rhizosphere soil microbial communities of two different cultivars of banana plants showed that TR4 infection and B. amyloliquefaciens QST713 strain application significantly affected the bacterial and fungal diversity of Yunjiao No. 1, but not in the cultivar Brazilian. In addition, TR4 infection and QST713 application changed the bacterial community composition of both banana cultivars, and the fungal community composition of Yunjiao No. 1 also changed significantly. Relevance analysis indicated that the relative richness of Bacillus and Pseudomonas in the rhizosphere of both cultivars increased significantly after QST713 application, which had a good positive correlation with plant height, pseudostem girth, aboveground fresh weight, leaf length, and leaf width.

Discussion

Therefore, the outcome of this study suggests that the biological agent QST713 strain has potential application in banana production for promoting plant growth and modification of soil microbial communities, particularly in the TR4-infected field.

Integrated analysis of transcriptome, metabolome, and histochemistry reveals the response mechanisms of different ages Panax notoginseng to root-knot nematode infection

Panax notoginseng (P. notoginseng) is an invaluable perennial medicinal herb. However, the roots of P. notoginseng are frequently subjected to severe damage caused by root-knot nematode (RKN) infestation. Although we have observed that P. notoginseng possessed adult-plant resistance (APR) against RKN disease, the defense response mechanisms against RKN disease in different age groups of P. notoginseng remain unexplored. We aimed to elucidate the response mechanisms of P. notoginseng at different stages of development to RKN infection by employing transcriptome, metabolome, and histochemistry analyses. Our findings indicated that distinct age groups of P. notoginseng may activate the phenylpropanoid and flavonoid biosynthesis pathways in varying ways, leading to the synthesis of phenolics, flavonoids, lignin, and anthocyanin pigments as both the response and defense mechanism against RKN attacks. Specifically, one-year-old P. notoginseng exhibited resistance to RKN through the upregulation of 5-O-p-coumaroylquinic acid and key genes involved in monolignol biosynthesis, such as PAL, CCR, CYP73A, CYP98A, POD, and CAD. Moreover, two-year-old P. notoginseng enhanced the resistance by depleting chlorogenic acid and downregulating most genes associated with monolignol biosynthesis, while concurrently increasing cyanidin and ANR in flavonoid biosynthesis. Three-year-old P. notoginseng reinforced its resistance by significantly increasing five phenolic acids related to monolignol biosynthesis, namely p-coumaric acid, chlorogenic acid, 1-O-sinapoyl-D-glucose, coniferyl alcohol, and ferulic acid. Notably, P. notoginseng can establish a lignin barrier that restricted RKN to the infection site. In summary, P. notoginseng exhibited a potential ability to impede the further propagation of RKN through the accumulation or depletion of the compounds relevant to resistance within the phenylpropanoid and flavonoid pathways, as well as the induction of lignification in tissue cells.

Phosphorus availability and planting patterns regulate soil microbial effects on plant performance in a semiarid steppe

BACKGROUND AND AIMS

Growing evidence has suggested that plant responses to model soil microorganisms are context dependent; however, few studies have investigated the effects of whole soil microbial communities on plant performance in different abiotic and biotic conditions. To address this, we examined how soil phosphorus (P) availability and different planting patterns regulate soil microbial effects on the growth of two native plant species in a semiarid steppe.

METHODS

We carried out a glasshouse experiment to explore the effects of the whole indigenous soil microbiota on the growth and performance of Leymus chinensis and Cleistogenes squarrosa using soil sterilization with different soil P availabilities and planting patterns (monoculture and mixture). Transcriptome sequencing (RNA-seq) was used to explain the potential molecular mechanisms of the soil microbial effects on C. squarrosa.

KEY RESULTS

The soil sterilization treatment significantly increased the biomass of L. chinensis and C. squarrosa in both monoculture and mixture conditions, which indicated that the soil microbiota had negative growth effects on both plants. The addition of P neutralized the negative microbial effects for both L. chinensis and C. squarrosa, whereas the mixture treatment amplified the negative microbial effects on L. chinensis but alleviated them on C. squarrosa. Transcriptomic analysis from C. squarrosa roots underscored that the negative soil microbial effects were induced by the upregulation of defence genes. The P addition treatment resulted in significant decreases in the number of differentially expressed genes attributable to the soil microbiota, and some defence genes were downregulated.

CONCLUSIONS

Our results underline that indigenous soil microbiota have negative effects on the growth of two dominant plant species from a semiarid steppe, but their effects are highly dependent on the soil P availability and planting patterns. They also indicate that defence genes might play a key role in controlling plant growth responses to the soil microbiota.

The effects and interrelationships of intercropping on Cotton Verticillium wilt and soil microbial communities

BACKGROUND

Cotton Verticillium wilt, causing by Verticillium dahliae, has seriously affected the yield and quality of cotton. The incidence of Verticillium wilt in cotton fields has been on the rise for many years, especially after straw has been returned to the fields. Intercropping can reduce the incidence of soil borne diseases and is often used to control crop diseases, but the relationship between the effects of intercropping on microbial communities and the occurrence of plant diseases is unclear. This research explored the relationship between soil microbial community structure and Cotton Verticillium wilt in interplanting of cotton-onion, cotton-garlic, cotton-wheat and cotton monocultures. Amplicon sequencing applied to the profile of bacterial and fungal communities.

RESULTS

The results showed that the disease index of Cotton Verticillium wilt was significantly reduced after intercropping with cotton-garlic and cotton-onion. Chao1 and Sobs indices were not significantly different in the rhizosphere soil and pre-plant soils of the four planting patterns, but the pre-plant fungal shannon index was significantly lower in the cotton-onion intercropping plot than in the other three plots. PCoA analysis showed that the soil microbial communities changed to a certain extent after intercropping, with large differences in the microbial communities under different cropping patterns. The abundance of Chaetomium was highest in the cotton-garlic intercropping before planting; the abundance of Penicillium was significantly higher in the cotton-wheat intercropping than in the other three systems.

CONCLUSION

Cotton-garlic and cotton-onion interplanting can control Cotton Verticillium wilt by affecting the soil microbial community. Fungi of the genera Chaetomium and Penicillium may be associated with plant disease resistance.

2,3-Butanediol from the leachates of pine needles induces the resistance of Panax notoginseng to the leaf pathogen Alternaria panax

Compared with the use of monocultures in the field, cultivation of medicinal herbs in forests is an effective strategy to alleviate disease. Chemical interactions between herbs and trees play an important role in disease suppression in forests. We evaluated the ability of leachates from needles of Pinus armandii to induce resistance in Panax notoginseng leaves, identified the components via gas chromatography-mass spectrometry (GC-MS), and then deciphered the mechanism of 2,3-Butanediol as the main component in the leachates responsible for resistance induction via RNA sequencing (RNA-seq). Prespraying leachates and 2,3-Butanediol onto leaves could induce the resistance of P. notoginseng to Alternaria panax. The RNA-seq results showed that prespraying 2,3-Butanediol onto leaves with or without A. panax infection upregulated the expression of large number of genes, many of which are involved in transcription factor activity and the mitogen-activated protein kinase (MAPK) signaling pathway. Specifically, 2,3-Butanediol spraying resulted in jasmonic acid (JA) -mediated induced systemic resistance (ISR) by activating MYC2 and ERF1. Moreover, 2,3-Butanediol induced systemic acquired resistance (SAR) by upregulating pattern-triggered immunity (PTI)- and effector-triggered immunity (ETI)-related genes and activated camalexin biosynthesis through activation of WRKY33. Overall, 2,3-Butanediol from the leachates of pine needles could activate the resistance of P. notoginseng to leaf disease infection through ISR, SAR and camalexin biosynthesis. Thus, 2,3-Butanediol is worth developing as a chemical inducer for agricultural production.

Maize-soybean relay strip intercropping reshapes the rhizosphere bacterial community and recruits beneficial bacteria to suppress Fusarium root rot of soybean

Rhizosphere microbes play a vital role in plant health and defense against soil-borne diseases. Previous studies showed that maize-soybean relay strip intercropping altered the diversity and composition of pathogenic Fusarium species and biocontrol fungal communities in the soybean rhizosphere, and significantly suppressed soybean root rot. However, whether the rhizosphere bacterial community participates in the regulation of this intercropping on soybean root rot is not clear. In this study, the rhizosphere soil of soybean healthy plants was collected in the continuous cropping of maize-soybean relay strip intercropping and soybean monoculture in the fields, and the integrated methods of microbial profiling, dual culture assays in vitro, and pot experiments were employed to systematically investigate the diversity, composition, and function of rhizosphere bacteria related to soybean root rot in two cropping patterns. We found that intercropping reshaped the rhizosphere bacterial community and increased microbial community diversity, and meanwhile, it also recruited much richer and more diverse species of Pseudomonas sp., Bacillus sp., Streptomyces sp., and Microbacterium sp. in soybean rhizosphere when compared with monoculture. From the intercropping, nine species of rhizosphere bacteria displayed good antagonism against the pathogen Fusarium oxysporum B3S1 of soybean root rot, and among them, IRHB3 (Pseudomonas chlororaphis), IRHB6 (Streptomyces), and IRHB9 (Bacillus) were the dominant bacteria and extraordinarily rich. In contrast, MRHB108 (Streptomyces virginiae) and MRHB205 (Bacillus subtilis) were the only antagonistic bacteria from monoculture, which were relatively poor in abundance. Interestingly, introducing IRHB3 into the cultured substrates not only significantly promoted the growth and development of soybean roots but also improved the survival rate of seedlings that suffered from F. oxysporum infection. Thus, this study proves that maize-soybean relay strip intercropping could help the host resist soil-borne Fusarium root rot by reshaping the rhizosphere bacterial community and driving more beneficial microorganisms to accumulate in the soybean rhizosphere.

Intercropping of Euonymus japonicus with Photinia × fraseri Improves Phytoremediation Efficiency in Cd/Cu/Zn Contaminated Field

Intercropping plants for phytoremediation is a promising strategy in heavy metal-polluted soils. In this study, two typical greening plant species, Euonymus japonicus (E. japonicus) and Photinia × fraseri (P. × fraseri), were intercropped in a Cd/Cu/Zn-contaminated field. The phytoremediation efficiency was investigated by measuring the plant biomass, metal concentration, and mycorrhizal colonisation, as well as the effects on soil properties, including soil pH; soil total N; and available N, P, K, Cd, Cu, and Zn. The results showed that, compared with the monoculture system, intercropping significantly lowered the available Cd, Cu, and Zn contents, significantly improved the total and available N contents in rhizosphere soils of both plant species, and increased the hyphae colonisation rate of P. × fraseri. In both plants, intercropping significantly improved the total plant biomass. Furthermore, the concentrations Zn and Cd in the root of E. japonicus and Cu concentration in the root of P. × fraseri were enhanced by 58.16%, 107.74%, and 20.57%, respectively. Intercropping resulted in plants accumulating higher amounts of Cd, Cu, and Zn. This was particularly evident in the total amount of Cd in E. japonicus, which was 2.2 times greater than that in the monoculture system. Therefore, this study provides a feasible technique for improving phytoremediation efficiency using greening plants.

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

The interactions between non-host roots and pathogens may be key to the inhibition of soilborne pathogens in intercropping systems. Fennel (Foeniculum vulgare) can be intercropped with a wide range of other plants to inhibit soilborne pathogens in biodiversity cultivation. However, the key compounds of fennel root exudates involved in the interactions between fennel roots and pathogens are still unknown. Here, a greenhouse experiment confirmed that intercropping with fennel suppressed pepper (Capsicum annuum) blight disease caused by Phytophthora capsici. Experimentally, the roots and root exudates of fennel can effectively interfere with the infection process of P. capsici at rhizosphere soil concentrations by attracting zoospores and inhibiting the motility of the zoospores and germination of the cystospores. Five terpene compounds (D-limonene, estragole, anethole, gamma-terpenes, and beta-myrcene) that were identified in the fennel rhizosphere soil and root exudates were found to interfere with P. capsica infection. D-limonene was associated with positive chemotaxis with zoospores, and a mixture of the five terpene compounds showed a strong synergistic effect on the infection process of P. capsici, especially for zoospore rupture. Furthermore, the five terpene compounds can induce the accumulation of reactive oxygen species (ROS), especially anethole, in hyphae. ROS accumulation may be one of the antimicrobial mechanisms of terpene compounds. Above all, we proposed that terpene compounds secreted from fennel root play a key role in Phytophthora disease suppression in this intercropping system.

Intercropping Pinto Peanut in Litchi Orchard Effectively Improved Soil Available Potassium Content, Optimized Soil Bacterial Community Structure, and Advanced Bacterial Community Diversity

Intercropping is widely used in agricultural production due to its capability of raising land productivity and providing an opportunity to achieve sustainable intensification of agriculture. In this study, soil samples from 10 to 20 cm depth of intercropping Pinto peanut in litchi orchard and litchi monoculture mode were established to determine soil attributes, enzyme activities, as well as the effect on soil bacterial diversity. On this basis, 16S rRNA V4-V5 region of soil bacterial communities in litchi/Pinto peanut intercropping (LP) mode and litchi monoculture mode (CK) was detected by the Illumina MiSeq sequencing platform. The results showed that the content of available potassium (AK) in LP was significantly higher than that in CK by 138.9%, and the content of available nitrogen (AN) in LP was significantly lower than that in CK by 19.6%. The soil enzyme activities were higher in LP as a whole, especially sucrase (SC) and acid protease (PT) were significantly higher by 154.4 and 76.5%, respectively. The absolute abundance and alpha diversity of soil microbiota were significantly higher in the intercropping group. Most importantly, endemic species with a significant difference in LP was higher by ~60 times compared to CK treatment. In the aspect of soil bacterial community structure, the dominant phyla of the two groups were Acidobacteria, Proteobacteria, Chloroflexi, and Actinobacteria. At the genus level, the absolute abundance of Flavobacterium and Nitrososphaera was significantly higher by 79.20 and 72.93%, respectively, while that of Candidatus_Koribacter was significantly lower with an amplitude of 62.24% in LP than in CK. Furthermore, the redundancy analysis (RDA) suggested that AK, which was highly associated with the dominant genera and phyla, is the vitally dominating environmental factors in LP groups, while in CK groups, it is AN and pH. In addition, PICRUSt2 analysis indicated that intercropping improved the metabolic activity of bacteria which can be correlated to the resistance of litchi root systems to soil-borne diseases. Overall, this study is expected to provide a theoretical basis and technical support for the healthy intercropping cultivation of litchi.

Root-associated microbiota drive phytoremediation strategies to lead of Sonchus Asper (L.) Hill as revealed by intercropping-induced modifications of the rhizosphere microbiome

Intercropping or assistant endophytes promote phytoremediation capacities of hyperaccumulators and enhance their tolerance to heavy metal (HM) stress. Findings from a previous study showed that intercropping the hyperaccumulator Sonchus asper (L.) Hill grown in HM-contaminated soils with maize improved the remediating properties and indicated an excluder-to-hyperaccumulator switched mode of action towards lead. In the current study, RNA-Seq analysis was conducted on Sonchus roots grown under intercropping or monoculture systems to explore the molecular events underlying this shift in lead sequestering strategy. The findings showed that intercropping only slightly affects S. asper transcriptome but significantly affects expression of root-associated microbial genomes. Further, intercropping triggers significant reshaping of endophytic communities associated with a 'root-to-shoot' transition of lead sequestration and improved phytoremediation capacities of S. asper. These findings indicate that accumulator activities of a weed are partially attributed to the root-associated microbiota, and a complex network of plant-microbe-plant interactions shapes the phytoremediation potential of S. asper. Analysis showed that intercropping may significantly change the structure of root-associated communities resulting in novel remediation properties, thus providing a basis for improving phytoremediation practices to restore contaminated soils.

The Comparison of Soil Agrochemical and Biological Properties in the Multi-Cropping Farming Systems

Multi-cropping systems play an important role in improving the quality of soil properties. A field experiment was carried at the Experimental Station of Vytautas Magnus University Agriculture Academy (Lithuania) in 2017 to 2019. The aim of the study was to compare agrophysical and biological properties of the soil in the multi-cropping systems of sole (spring barley, spring wheat, pea, caraway), binary (spring barley–caraway, spring wheat–caraway, pea–caraway) and trinary (spring barley–caraway–white clover, spring wheat–caraway–white clover, pea–caraway–white clover) crops. In the second and the third years of caraway cultivation, when solely caraway was grown, the total nitrogen content was significantly lower than in binary and trinary crops (8.5% and 17.4%, respectively). The results indicated that the highest organic carbon content was in the third year of caraway cultivation in trinary crop when caraway was grown with peas and white clover. In the third year, the highest saccharase and urease activity was found in trinary crop where caraway was grown with spring barley and white clover. A strong positive correlation was observed between the content of saccharase and urease and the total nitrogen, organic carbon, and potassium available in the soil. The results of the study suggest that multi-cropping is important for soil conservation and the sustainability of agro-ecosystems.

Plant neighbours can make or break the disease transmission chain of a fungal root pathogen

Biodiversity can reduce or increase disease transmission. These divergent effects suggest that community composition rather than diversity per se determines disease transmission. In natural plant communities, little is known about the functional roles of neighbouring plant species in belowground disease transmission. Here, we experimentally investigated disease transmission of a fungal root pathogen (Rhizoctonia solani) in two focal plant species in combinations with four neighbour species of two ages. We developed stochastic models to test the relative importance of two transmission-modifying mechanisms: (1) infected hosts serve as nutrient supply to increase hyphal growth, so that successful disease transmission is self-reinforcing; and (2) plant resistance increases during plant development. Neighbouring plants either reduced or increased disease transmission in the focal plants. These effects depended on neighbour age, but could not be explained by a simple dichotomy between hosts and nonhost neighbours. Model selection revealed that both transmission-modifying mechanisms are relevant and that focal host-neighbour interactions changed which mechanisms steered disease transmission rate. Our work shows that neighbour-induced shifts in the importance of these mechanisms across root networks either make or break disease transmission chains. Understanding how diversity affects disease transmission thus requires integrating interactions between focal and neighbour species and their pathogens.

Ecological Dynamics and Microbial Treatments against Oomycete Plant Pathogens

In this review, we explore how ecological concepts may help assist with applying microbial biocontrol agents to oomycete pathogens. Oomycetes cause a variety of agricultural diseases, including potato late blight, apple replant diseases, and downy mildew of grapevine, which also can lead to significant economic damage in their respective crops. The use of microbial biocontrol agents is increasingly gaining interest due to pressure from governments and society to reduce chemical plant protection products. The success of a biocontrol agent is dependent on many ecological processes, including the establishment on the host, persistence in the environment, and expression of traits that may be dependent on the microbiome. This review examines recent literature and trends in research that incorporate ecological aspects, especially microbiome, host, and environmental interactions, into biological control development and applications. We explore ecological factors that may influence microbial biocontrol agents’ efficacy and discuss key research avenues forward.

Organic Acid Excretion in Root Exudates as a Mechanism of Cadmium Uptake in a Sonchus Asper-Zea Mays Intercropping System

This study assessed how the Sonchus asper L.-Zea mays intercropping influenced the plant Cd level, as well as the organic acid (low molecular mass) types and concentrations in root secretions, which was accomplished by conducting pot experiments with soil that was collected from a farmland surrounding a mining area. The results showed that the oxalic and citric acids were the prevailing organic acids in the plant root secretions, and that the intercropping led to prominently elevated root exudate concentrations of the two acids for S. asper by 43.8 and 75.4%, respectively, while decreased such concentrations by 18.5 and 18.7% for Z. mays, compared to monoculture. According to observations, the root exudate concentrations of citric and oxalic acids were significantly positively related to the available rhizosphere soil Cd and plant Cd. The results indicate that changes in root exudation of oxalic acid and citric acid result in different available Cd contents of the rhizosphere soil, thereby affecting the bioavailability of soil Cd, which increases Cd uptake and accumulation in S. asper but inhibits Cd accumulation in Z. mays.

Changes in "natural antibiotic" metabolite composition during tetraploid wheat domestication

Gramineous plants protect their seeds from a variety of biotic stresses by producing toxic and deterrent secondary metabolites such as benzoxazinoids. It is unclear how the composition and abundance of these natural toxins has changed over the course of crop-plant domestication. To address this uncertainty, we characterized differences in metabolic levels of benzoxazinoids and their derivatives, between four lines of tetraploid wheat: wild emmer wheat (WEW), the direct progenitor of modern wheat; non-fragile domesticated emmer wheat (DEW), which was first domesticated about 11,000 years ago; the subsequently developed non-fragile and free-threshing durum landraces (LD); and modern durum (MD) varieties. Three-dimensional principal component analysis of mass spectrometry data of wheat metabolites showed with high resolution clear differences between metabolic profiles of WEW, DEW, and durum (LD + MD) and similarity in the metabolic profiles of the two durum lines (LD and MD) that is coherent with the phylogenetic relationship between the corresponding wheat lines. Moreover, our results indicated that some secondary metabolites involved in plant defense mechanisms became significantly more abundant during wheat domestication, while other defensive metabolites decreased or were lost. These metabolic changes reflect the beneficial or detrimental roles the corresponding metabolites might play during the domestication of three taxonomic subspecies of tetraploid wheat (Triticum turgidum).

Fungal Pathogens in Grasslands

Grasslands are major primary producers and function as major components of important watersheds. Although a concise definition of grasslands cannot be given using a physiognomic or structural approach, grasslands can be described as vegetation communities experiencing periodical droughts and with canopies dominated by grasses and grass-like plants. Grasslands have a cosmopolitan distribution except for the Antarctic region. Fungal interactions with grasses can be pathogenic or symbiotic. Herbivorous mammals, insects, other grassland animals, and fungal pathogens are known to play important roles in maintaining the biomass and biodiversity of grasslands. Although most pathogenicity studies on the members of Poaceae have been focused on economically important crops, the plant-fungal pathogenic interactions involved can extend to the full range of ecological circumstances that exist in nature. Hence, it is important to delineate the fungal pathogen communities and their interactions in man-made monoculture systems and highly diverse natural ecosystems. A better understanding of the key fungal players can be achieved by combining modern techniques such as next-generation sequencing (NGS) together with studies involving classic phytopathology, taxonomy, and phylogeny. It is of utmost importance to develop experimental designs that account for the ecological complexity of the relationships between grasses and fungi, both above and below ground. In grasslands, loss in species diversity increases interactions such as herbivory, mutualism, predation or infectious disease transmission. Host species density and the presence of heterospecific host species, also affect the disease dynamics in grasslands. Many studies have shown that lower species diversity increases the severity as well as the transmission rate of fungal diseases. Moreover, communities that were once highly diverse but have experienced decreased species richness and dominancy have also shown higher pathogenicity load due to the relaxed competition, although this effect is lower in natural communities. This review addresses the taxonomy, phylogeny, and ecology of grassland fungal pathogens and their interactions in grassland ecosystems.

Phytoremediation potential of wheat intercropped with different densities of Sedum plumbizincicola in soil contaminated with cadmium and zinc

Intercropping technology is applied widely in crop cultivation to help remediate soil polluted with heavy metals. To investigate the feasibility and potential of intercropping hyperaccumulator plants with crops in cadmium (Cd)- and zinc (Zn)-contaminated soil, a pot experiment was conducted to examine plant growth and the contents of Cd and Zn in the soil following intercropping of wheat and Sedum plumbizincicola. Five treatments were examined: control (wheat monoculture: 36 seedlings per pot), and intercropping of wheat with different planting densities of S. plumbizincicola (3, 6, 9 and 15 seedlings per pot, respectively). Results showed a decrease in soil pH, and in soil and wheat contents of Cd and Zn with increasing planting density of S. plumbizincicola, while the removal rate of Cd and Zn increased. Meanwhile, excessive planting (15 seedlings per pot) inhibited wheat growth by 27.34% compared with the control, and overall, the optimal planting density was 9 seedlings per pot, resulting in effective remediation with only a moderate effect on wheat growth. These findings highlight the value of intercropping S. plumbizincicola with wheat as a means of improving remediation of soil contaminated with heavy metals (Cd and Zn).

Nitrogen supply and intercropping control of Fusarium wilt in faba bean depend on organic acids exuded from the roots

Fusarium wilt in faba bean (Vicia faba L.) is caused by Fusarium oxysporum f. sp. fabae (FOF), which reduces the yield of crop. We used greenhouse, field and laboratory experiments to evaluate the role of organic acids in the occurrence of Fusarium wilt of faba bean to confirm the mechanism of rational application of nitrogen (N) and intercropping to alleviate Fusarium wilt. We investigated the response of organic acids exuded from the roots of faba bean to different N levels and cropping patterns (monocropping and intercropping with wheat). The results showed that the application of N and intercropping with wheat could control the Fusarium wilt of faba bean, which was closely related to the components and quantity of organic acids exuded from its roots. Among them, tartaric acid and malic acid are the most abundant and important, because they have a significant inhibitory effect on the growth and reproduction of FOF and substantially aid in the control of Fusarium wilt. The application of 90 kg ha⁻¹ of N combined with wheat intercropping significantly controlled the Fusarium wilt and increased the grain yield of faba bean. Our results suggest that 90 kg ha⁻¹ of N combined with intercropping is the most effective way to control Fusarium wilt and should be incorporated into agricultural management practices.

Social networking in crop plants: Wired and wireless cross-plant communications

The plant-associated microbial community (microbiome) has an important role in plant-plant communications. Plants decipher their complex habitat situations by sensing the environmental stimuli and molecular patterns and associated with microbes, herbivores and dangers. Perception of these cues generates inter/intracellular signals that induce modifications of plant metabolism and physiology. Signals can also be transferred between plants via different mechanisms, which we classify as wired- and wireless communications. Wired communications involve direct signal transfers between plants mediated by mycorrhizal hyphae and parasitic plant stems. Wireless communications involve plant volatile emissions and root exudates elicited by microbes/insects, which enable inter-plant signalling without physical contact. These producer-plant signals induce microbiome adaptation in receiver plants via facilitative or competitive mechanisms. Receiver plants eavesdrop to anticipate responses to improve fitness against stresses. An emerging body of information in plant-plant communication can be leveraged to improve integrated crop management under field conditions.

Diverse Intercropping Patterns Enhance the Productivity and Volatile Oil Yield of Atractylodes lancea (Thunb.) DC

Commercial cultivation of the medicinal plant Atractylodes lancea is significantly restricted by low survival rates and reduced yields. Intercropping can reasonably coordinate interspecific interactions, effectively utilize environmental resources, and increase survival and yield. We conducted a field experiment from 2014 to 2016 to analyze the advantages and effects of intercropping on A. lancea survival, growth traits, individual volatile oil content, and total volatile oil content. In addition to A. lancea monoculture (AL), five intercropping combinations were planted: Zea mays L. (ZM) + A. lancea, Tagetes erecta L. (TE) + A. lancea, Calendula officinalis L. (CO) + A. lancea, Glycine max (Linn.) Merr. (GM) + A. lancea, and Polygonum hydropiper L. (PH) + A. lancea. The survival and average rhizome weight of A. lancea was higher in the ZM, CO, and TE treatments than in the monoculture treatment, and the average plant height was higher in all intercropping treatments than in the monoculture. The volatile oil content of A. lancea from the ZM and CO treatments was significantly improved relative to that of monoculture plants. The volatile oil harvest was higher in the ZM, CO, and TE treatments than in the monoculture. We conclude that intercropping is an effective way to increase the survival and yield of A. lancea. Furthermore, intercropping with ZM, CO, and TE increases the harvest of four volatile oils from A. lancea.

Disease-Suppressive Soils-Beyond Food Production: a Critical Review

In the pursuit of higher food production and economic growth and increasing population, we have often jeopardized natural resources such as soil, water, vegetation, and biodiversity at an alarming rate. In this process, wider adoption of intensive farming practices, namely changes in land use, imbalanced fertilizer application, minimum addition of organic residue/manure, and non-adoption of site-specific conservation measures, has led to declining in soil health and land degradation in an irreversible manner. In addition, increasing use of pesticides, coupled with soil and water pollution, has led the researchers to search for an environmental-friendly and cost-effective alternatives to controlling soil-borne diseases that are difficult to control, and which significantly limit agricultural productivity. Since the 1960s, disease-suppressive soils (DSS) have been identified and studied around the world. Soil disease suppression is the reduction in the incidence of soil-borne diseases even in the presence of a host plant and inoculum in the soil. The disease-suppressive capacity is mainly attributed to diverse microbial communities present in the soil that could act against soil-borne pathogens in multifaceted ways. The beneficial microorganisms employ some specific functions such as antibiosis, parasitism, competition for resources, and predation. However, there has been increasing evidence on the role of soil abiotic factors that largely influence the disease suppression. The intricate interactions of the soil, plant, and environmental components in a disease triangle make this process complex yet crucial to study to reduce disease incidence. Increasing resistance of the pathogen to presently available chemicals has led to the shift from culturable microbes to unexplored and unculturable microbes. Agricultural management practices such as tillage, fertilization, manures, irrigation, and amendment applications significantly alter the soil physicochemical environment and influence the growth and behaviour of antagonistic microbes. Plant factors such as age, type of crop, and root behaviour of the plant could stimulate or limit the diversity and structure of soil microorganisms in the rhizosphere. Further, identification and in-depth of disease-suppressive soils could lead to the discovery of more beneficial microorganisms with novel anti-microbial and plant promoting traits. To date, several microbial species have been isolated and proposed as key contributors in disease suppression, but the complexities as well as the mechanisms of the microbial and abiotic interactions remain elusive for most of the disease-suppressive soils. Thus, this review critically explores disease-suppressive attributes in soils, mechanisms involved, and biotic and abiotic factors affecting DSS and also briefly reviewing soil microbiome for anti-microbial drugs, in fact, a consequence of DSS phenomenon.

Soil Microbiome Manipulation Gives New Insights in Plant Disease-Suppressive Soils from the Perspective of a Circular Economy: A Critical Review

This review pays attention to the newest insights on the soil microbiome in plant disease-suppressive soil (DSS) for sustainable plant health management from the perspective of a circular economy that provides beneficial microbiota by recycling agro-wastes into the soil. In order to increase suppression of soil-borne plant pathogens, the main goal of this paper is to critically discuss and compare the potential use of reshaped soil microbiomes by assembling different agricultural practices such as crop selection; land use and conservative agriculture; crop rotation, diversification, intercropping and cover cropping; compost and chitosan application; and soil pre-fumigation combined with organic amendments and bio-organic fertilizers. This review is seen mostly as a comprehensive understanding of the main findings regarding DSS, starting from the oldest concepts to the newest challenges, based on the assumption that sustainability for soil quality and plant health is increasingly viable and supported by microbiome-assisted strategies based on the next-generation sequencing (NGS) methods that characterize in depth the soil bacterial and fungal communities. This approach, together with the virtuous reuse of agro-wastes to produce in situ green composts and organic bio-fertilizers, is the best way to design new sustainable cropping systems in a circular economy system. The current knowledge on soil-borne pathogens and soil microbiota is summarized. How microbiota determine soil suppression and what NGS strategies are available to understand soil microbiomes in DSS are presented. Disturbance of soil microbiota based on combined agricultural practices is deeply considered. Sustainable soil microbiome management by recycling in situ agro-wastes is presented. Afterwards, how the resulting new insights can drive the progress in sustainable microbiome-based disease management is discussed.

Cinnamic Acid Increased the Incidence of Fusarium Wilt by Increasing the Pathogenicity of Fusarium oxysporum and Reducing the Physiological and Biochemical Resistance of Faba Bean, Which Was Alleviated by Intercropping With Wheat

BACKGROUND

Continuous cropping has resulted in the accumulation of self-toxic substances in faba beans which has restricted their global production. Intercropping is widely used to alleviate these problems.

AIMS

To explore the role of cinnamic acid stress in faba bean physiology and disease resistance, and the potential mitigating effects of intercropping the faba bean with wheat.

METHODS

Faba bean seedlings were grown with or without wheat in both field and hydroponic conditions in the presence of different cinnamic acid concentrations and Fusarium oxysporum (FOF), the occurrence of. Fusarium-mediated wilt and oxidative stress, as well as plant growth indices and the anti-pathogen defense system were analyzed.

RESULTS

Cinnamic acid significantly increased Fusarium pathogenicity, inhibited the activity of defense enzymes and reduced the ability of plants to resist pathogens, indicating the importance of cinnamic acid in the promotion of Fusarium wilt resulting in reduced seedling growth. Intercropping with wheat improved plant resistance by alleviating cinnamic acid-induced stress, which promoted crop growth and decreased the incidence and disease index of Fusarium wilt.

CONCLUSION

Cinnamic acid promotes Fusarium wilt by stimulating pathogen enzyme production and destroying the defense capability of faba bean roots. Intercropping reduces Fusarium wilt by alleviating the damage caused by cinnamic acid to the defense system of the faba bean root system.

Real-Time Visualization of Cellulase Activity by Microorganisms on Surface

A variety of methods to detect cellulase secretion by microorganisms has been developed over the years, none of which enables the real-time visualization of cellulase activity on a surface. This visualization is critical to study the interaction between soil-borne cellulase-secreting microorganisms and the surface of plant roots and specifically, the effect of surface features on this interaction. Here, we modified the known carboxymethyl cellulase (CMC) hydrolysis visualization method to enable the real-time tracking of cellulase activity of microorganisms on a surface. A surface was formed using pure CMC with acridine orange dye incorporated in it. The dye disassociated from the film when hydrolysis occurred, forming a halo surrounding the point of hydrolysis. This enabled real-time visualization, since the common need for post hydrolysis dyeing was negated. Using root-knot nematode (RKN) as a model organism that penetrates plant roots, we showed that it was possible to follow microorganism cellulase secretion on the surface. Furthermore, the addition of natural additives was also shown to be an option and resulted in an increased RKN response. This method will be implemented in the future, investigating different microorganisms on a root surface microstructure replica, which can open a new avenue of research in the field of plant root-microorganism interactions.

Phenolic Acids Released in Maize Rhizosphere During Maize-Soybean Intercropping Inhibit Phytophthora Blight of Soybean

Interspecies interactions play a key role in soil-borne disease suppression in intercropping systems. However, there are limited data on the underlying mechanisms of soil-borne Phytophthora disease suppression. Here, a field experiment confirmed the effects of maize and soybean intercropping on Phytophthora blight of soybean caused by Phytophthora sojae. Experimentally, the roots and root exudates of maize were found to attract P. sojae zoospores and inhibit their motility and the germination of cystospores. Furthermore, five phenolic acids (p-coumaric acid, cinnamic acid, p-hydroxybenzoic acid, vanillic acid, and ferulic acid) that were consistently identified in the root exudates and rhizosphere soil of maize were found to interfere with the infection behavior of P. sojae. Among them, cinnamic acid was associated with significant chemotaxis in zoospores, and p-coumaric acid and cinnamic acid showed strong antimicrobial activity against P. sojae. However, in the rhizosphere soil of soybean, only p-hydroxybenzoic acid, low concentrations of vanillic acid, and ferulic acid were identified. Importantly, the coexistence of five phenolic acids in the maize rhizosphere compared with three phenolic acids in the soybean rhizosphere showed strong synergistic antimicrobial activity against the infection behavior of P. sojae. In summary, the types and concentrations of phenolic acids in maize and soybean rhizosphere soils were found to be crucial factors for Phytophthora disease suppression in this intercropping system.

Maize/Soybean Relay Strip Intercropping Reduces the Occurrence of Fusarium Root Rot and Changes the Diversity of the Pathogenic Fusarium Species

Fusarium species are the most detrimental pathogens of soybean root rot worldwide, causing large loss in soybean production. Maize/soybean relay strip intercropping has significant advantages on the increase of crop yields and efficient use of agricultural resources, but its effects on the occurrence and pathogen population of soybean root rot are rarely known. In this study, root rot was investigated in the fields of the continuous maize/soybean strip relay intercropping and soybean monoculture. Fusarium species were isolated from diseased soybean roots and identified based on sequence analysis of translation elongation factor 1α (EF-1α) and RNA polymerase II second largest subunit (RPB2), and the diversity and pathogenicity of these species were also analyzed. Our results showed that intercropping significantly decreased soybean root rot over monoculture. A more diverse Fusarium population including Fusarium solani species complex (FSSC), F. incarnatum-equiseti species complex (FIESC), F. oxysporum, F. fujikuroi, F. proliferatum and F. verticillioides, F. graminearum and F. asiaticum was identified from intercropping while FSSC, FIESC, F. oxysporum, F. commune, F. asiaticum and F. meridionale were found from monoculture. All Fusarium species caused soybean root infection but exhibited distinct aggressiveness. The most aggressive F. oxysporum was more frequently isolated in monoculture than intercropping. FSSC and FIESC were the dominant species complex and differed in their aggressiveness. Additionally, F. fujikuroi, F. proliferatum and F. verticillioides were specifically identified from intercropping with weak or middle aggressiveness. Except for F. graminearum, F. meridionale and F. asiaticum were firstly reported to cause soybean root rot in China. This study indicates maize/soybean relay strip intercropping can reduce soybean root rot, change the diversity and aggressiveness of Fusarium species, which provides an important reference for effective management of this disease.

Reductive soil disinfestation effectively alleviates the replant failure of Sanqi ginseng through allelochemical degradation and pathogen suppression

Replant failure has threatened the production of Sanqi ginseng (Panax notoginseng) mainly due to the accumulation of soil-borne pathogens and allelochemicals. Reductive soil disinfestation (RSD) is an effective practice used to eliminate soil-borne pathogens; however, the potential impact of RSD on the degradation of allelochemicals and the growth of replant Sanqi ginseng seedlings remain poorly understood. In this study, RSD was conducted on a Sanqi ginseng monoculture system (SGMS) and a maize-Sanqi ginseng system (MSGS), defined as SGMS_RSD and MSGS_RSD, respectively. The aim was to investigate the impact of RSD on allelochemicals, soil microbiomes, and survival rates of replant seedlings. Both short-term maize planting and RSD treatment significantly degraded the ginsenosides in Sanqi ginseng-cultivated soils, with the degradation rate being higher in the RSD treatment. The population of Fusarium oxysporum and the relative abundance of genus Fusarium were dramatically suppressed by RSD treatment. Furthermore, the RSD treatment, but not maize planting, markedly alleviated the replant failure of Sanqi ginseng, with the seedling survival rate being 52.7-70.7% 6 months after transplanting. Interestingly, RSD followed by short-term maize planting promoted microbial activity restoration, ginsenoside degradation, and ultimately alleviated the replant failure much better than RSD treatment alone (70.7% vs. 52.7%). Collectively, these results indicate that RSD treatment could considerably reduce the obstacles and might also act as a potential agriculture regime for overcoming the replant failure of Sanqi ginseng. Additional practices, such as crop rotation, beneficial microorganism inoculation, etc. may also still be needed to ensure the long-term efficacy of seedling survival.

Microbial basis of Fusarium wilt suppression by Allium cultivation

Crop rotation and intercropping with Allium plants suppresses Fusarium wilt in various crops. However, the mechanisms underlying this phenomenon have not been fully elucidated. This study was designed to assess the role of microorganisms inhabiting Allium rhizospheres and antifungal compounds produced by Allium roots in Fusarium wilt suppression by Allium cultivation. Suppression of cucumber Fusarium wilt and the pathogen multiplication by Allium (Welsh onion and/or onion)-cultivated soils were eliminated by heat treatment at 60 °C, whereas those by Welsh onion-root extract were lost at 40 °C. The addition of antibacterial antibiotics eliminated the suppressive effect of Welsh onion-cultivated soil on pathogen multiplication, suggesting the contribution of antagonistic gram-negative bacteria to the soil suppressiveness. The Illumina MiSeq sequencing of 16S rRNA gene amplicons revealed that genus Flavobacterium was the predominant group that preferentially accumulated in Allium rhizospheres. Flavobacterium species recovered from the rhizosphere soils of these Allium plants suppressed Fusarium wilt on cucumber seedlings. Furthermore, confocal laser scanning microscopy revealed that Flavobacterium isolates inhibited the multiplication of the pathogen in soil. Taken together, we infer that the accumulation of antagonistic Flavobacterium species plays a key role in Fusarium wilt suppression by Allium cultivation.

Benzothiazole inhibits the growth of Phytophthora capsici through inducing apoptosis and suppressing stress responses and metabolic detoxification

Benzothiazole (BZO) is an antimicrobial secondary metabolite volatilized by many plants and microbes. However, the mechanism of BZO against phytopathogens is still unclear. Here, we found that BZO has antimicrobial activity against the oomycete pathogen Phytophthora capsici. Transcriptome and proteome analyses demonstrated that BZO significantly suppressed the expression of genes and proteins involved in morphology, abiotic stress defense and detoxification, but induced the activity of apoptosis. Annexin V-FITC/PI staining confirmed that the process of apoptosis was significantly induced by BZO at concentration of 150 mg L^-1. FITC-phalloidin actin-cytoskeleton staining combined with hyphal cell wall staining and hyphal ultrastructure studies further confirmed that BZO disrupted the cell membrane and hyphal morphology through disrupting the cytoskeleton, eventually inhibiting the growth of hyphae. These data demonstrated that BZO has multiple modes of action and may act as potential leading compound for the development of new oomycete fungicides. These results also showed that the combination of transcriptomic and proteomic approaches was a useful method for exploring the novel antifungal mechanisms of natural compounds.

Molecular Mechanisms Underlying Microbial Disease Control in Intercropping

Many reports indicate that intercropping, which usually consists of growing two species next to each other, reduces the incidence of microbial diseases. Besides mechanisms operating at the field level, like inoculum dilution, there is recent evidence that plant-centered mechanisms with identified plant molecules and pathways are also involved. First, plants may trigger the induction of resistance in neighboring plants by the well-known mechanism of induced resistance. Second, molecules produced by one plant, either above- or belowground, can directly inhibit pathogens or indirectly trigger resistance through the induction of the plant immune system in neighboring plants. Third, competition for resources such as light or nutrients may indirectly modify the expression of the plant immune system. The conceptual frameworks of nonkin/stranger recognition and competition may be useful to further investigate the molecular mechanisms underlying crop protection in interspecific plant mixtures.

Plant Bio-Wars: Maize Protein Networks Reveal Tissue-Specific Defense Strategies in Response to a Root Herbivore

In this study we examined global changes in protein expression in both roots and leaves of maize plants attacked by the root herbivore, Western corn rootworm (WCR, Diabrotica virgifera virgifera). The changes in protein expression Are indicative of metabolic changes during WCR feeding that enable the plant to defend itself. This is one of the first studies to look above- and below-ground at global protein expression patterns of maize plants grown in soil and infested with a root herbivore. We used advanced proteomic and network analyses to identify metabolic pathways that contribute to global defenses deployed by the insect resistant maize genotype, Mp708, infested with WCR. Using proteomic analysis, 4878 proteins in roots and leaves were detected and of these 863 showed significant changes of abundance during WCR infestation. Protein abundance patterns were analyzed using hierarchical clustering, protein correlation and protein-protein interaction networks. All three data analysis pipelines showed that proteins such as jasmonic acid biosynthetic enzymes, serine proteases, protease inhibitors, proteins involved in biosynthesis and signaling of ethylene, and enzymes producing reactive oxygen species and isopentenyl pyrophosphate, a precursor for volatile production, were upregulated in roots during WCR infestation. In leaves, highly abundant proteins were involved in signal perception suggesting activation of systemic signaling. We conclude that these protein networks contribute to the overall herbivore defense mechanisms in Mp708. Because the plants were grown in potting mix and not sterilized sand, we found that both microbial and insect defense-related proteins were present in the roots. The presence of the high constitutive levels of reduced ascorbate in roots and benzothiazole in the root volatile profiles suggest a tight tri-trophic interaction among the plant, soil microbiomes and WCR-infested roots suggesting that defenses against insects coexist with defenses against bacteria and fungi due to the interaction between roots and soil microbiota. In this study, which is one of the most complete descriptions of plant responses to root-feeding herbivore, we established an analysis pipeline for proteomics data that includes network biology that can be used with different types of "omics" data from a variety of organisms.

Advocating a need for suitable breeding approaches to boost integrated pest management: a European perspective

Currently, European farmers do not have access to sufficient numbers and diversity of crop species/varieties. This prevents them from designing cropping systems more resilient to abiotic and biotic stresses. Crop diversification is a key lever to reduce pest (pathogens, animal pests and weeds) pressures at all spatial levels from fields to landscapes. In this context, plant breeding should consist of: (1) increased efforts in the development of new or minor crop varieties to foster diversity in cropping systems, and (2) focus on more resilient varieties showing local adaptation. This new breeding paradigm, called here 'breeding for integrated pest management (IPM)', may boost IPM through the development of cultivars with tolerance or resistance to key pests, with the goal of reducing reliance on conventional pesticides. At the same time, this paradigm has legal and practical implications for future breeding programs, including those targeting sustainable agricultural systems. By putting these issues into the context, this article presents the key outcomes of a questionnaire survey and experts' views expressed during an EU workshop entitled 'Breeding for IPM in sustainable agricultural systems'. © 2017 Society of Chemical Industry.

Extract from Maize (Zea mays L.): Antibacterial Activity of DIMBOA and Its Derivatives against Ralstonia solanacearum

Many cereals accumulate hydroxamic acids involved in defense of plant against various fungi, bacteria, and insects. 2,4-dihydroxy-7-methoxy-1,4-benzoxazine-3-one, commonly known as DIMBOA, is one of the principal cyclic hydroxamic acids in aqueous extracts of maize. The aim of this study was to evaluate the antibacterial activity of the isolated DIMBOA and its derivatives 2-benzoxazolinone (BOA), 6-chloro-2-benzoxazolinone (CDHB), and 2-mercaptobenzothiazole (MBT) against Ralstonia solanacearum. MBT showed the strongest antibacterial activity, followed by CDHB and DIMBOA, with minimum inhibitory concentrations (MICs) of 50, 100 and 200 mg/L, respectively, better than the BOA with 300 mg/L. These compounds also significantly affect bacterial growth, reduce biofilm formation, and inhibit swarming motility within 24 h. This paper is the first to report the anti-R. solanacearum activity of DIMBOA from Z. mays. The bioassay and pot experiment results suggested that DIMBOA and its derivatives exhibit potential as a new matrix structure of designing target bactericide or elicitor for controlling tobacco bacterial wilt. Further studies must evaluate the efficacy of DIMBOA and its derivatives in controlling bacterial wilt under natural field conditions where low inoculum concentrations exist.

Plant Diseases and Management Approaches in Organic Farming Systems

Organic agriculture has expanded worldwide. Numerous papers were published in the past 20 years comparing plant diseases in organic and conventional crops. Root diseases are generally less severe owing to greater soil health, whereas some foliar diseases can be problematic in organic agriculture. The soil microbial community and nitrogen availability play an important role in disease development and yield. Recently, the focus has shifted to optimizing organic crop production by improving plant nutrition, weed control, and plant health. Crop-loss assessment relating productivity to all yield-forming and -reducing factors would benefit organic production and sustainability evaluation.

Tobacco Rotated with Rapeseed for Soil-Borne Phytophthora Pathogen Biocontrol: Mediated by Rapeseed Root Exudates

Black shank, caused by Phytophthora parasitica var. nicotianae, is a widespread and destructive disease of tobacco. Crop rotation is essential in controlling black shank. Here, we confirmed that rotating black shank-infested fields with rapeseed (Brassica napus) suppressed the incidence this disease. Further study demonstrated that rapeseed roots have a strong ability to attract zoospores and subsequently stop the swimming of zoospores into cystospores. Then, rapeseed roots secrete a series of antimicrobial compounds, including 2-butenoic acid, benzothiazole, 2-(methylthio)benzothiazole, 1-(4-ethylphenyl)-ethanone, and 4-methoxyindole, to inhibit the cystospore germination and mycelial growth of P. parasitica var. nicotianae. Thus, rapeseed rotated with tobacco suppresses tobacco black shank disease through the chemical weapons secreted by rapeseed roots.

Plant disease management in organic farming systems

Organic farming (OF) has significantly increased in importance in recent decades. Disease management in OF is largely based on the maintenance of biological diversity and soil health by balanced crop rotations, including nitrogen-fixing and cover crops, intercrops, additions of manure and compost and reductions in soil tillage. Most soil-borne diseases are naturally suppressed, while foliar diseases can sometimes be problematic. Only when a severe disease outbreak is expected are pesticides used that are approved for OF. A detailed overview is given of cultural and biological control measures. Attention is also given to regulated pesticides. We conclude that a systems approach to disease management is required, and that interdisciplinary research is needed to solve lingering disease problems, especially for OF in the tropics. Some of the organic regulations are in need of revision in close collaboration with various stakeholders.

Proteomic Analysis of the Relationship between Metabolism and Nonhost Resistance in Soybean Exposed to Bipolaris maydis

Nonhost resistance (NHR) pertains to the most common form of plant resistance against pathogenic microorganisms of other species. Bipolaris maydis is a non-adapted pathogen affecting soybeans, particularly of maize/soybean intercropping systems. However, no experimental evidence has described the immune response of soybeans against B. maydis. To elucidate the molecular mechanism underlying NHR in soybeans, proteomics analysis based on two-dimensional polyacrylamide gel electrophoresis (2-DE) was performed to identify proteins involved in the soybean response to B. maydis. The spread of B. maydis spores across soybean leaves induced NHR throughout the plant, which mobilized almost all organelles and various metabolic processes in response to B. maydis. Some enzymes, including ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), mitochondrial processing peptidase (MPP), oxygen evolving enhancer (OEE), and nucleoside diphosphate kinase (NDKs), were found to be related to NHR in soybeans. These enzymes have been identified in previous studies, and STRING analysis showed that most of the protein functions related to major metabolic processes were induced as a response to B. maydis, which suggested an array of complex interactions between soybeans and B. maydis. These findings suggest a systematic NHR against non-adapted pathogens in soybeans. This response was characterized by an overlap between metabolic processes and response to stimulus. Several metabolic processes provide the soybean with innate immunity to the non-adapted pathogen, B. maydis. This research investigation on NHR in soybeans may foster a better understanding of plant innate immunity, as well as the interactions between plant and non-adapted pathogens in intercropping systems.

Priming maize resistance by its neighbors: activating 1,4-benzoxazine-3-ones synthesis and defense gene expression to alleviate leaf disease

Plant disease can be effectively suppressed in intercropping systems. Our previous study demonstrated that neighboring maize plants can restrict the spread of soil-borne pathogens of pepper plants by secreting defense compounds into the soil. However, whether maize plant can receive benefits from its neighboring pepper plants in an intercropping system is little attention. We examined the effects of maize roots treated with elicitors from the pepper pathogen Phytophthora capsici and pepper root exudates on the synthesis of 1,4-benzoxazine-3-ones (BXs), the expression of defense-related genes in maize, and their ability to alleviate the severity of southern corn leaf blight (SCLB) caused by Bipolaris maydis. We found that SCLB was significantly reduced after the above treatments. The contents of 1,4-benzoxazine-3-ones (BXs: DIBOA, DIMBOA, and MBOA) and the expression levels of BX synthesis and defense genes in maize roots and shoots were up-regulated. DIMBOA and MBOA effectively inhibited the mycelium growth of Bipolaris maydis at physiological concentrations in maize shoots. Further studies suggested that the defense related pathways or genes in maize roots and shoots were activated by elicitors from the P. capsici or pepper root exudates. In conclusion, maize increased the levels of BXs and defense gene expression both in roots and shoots after being triggered by root exudates and pathogen from neighboring pepper plants, eventually enhancing its resistance.

Companion cropping with potato onion enhances the disease resistance of tomato against Verticillium dahliae

Intercropping could alleviate soil-borne diseases, however, few studies focused on the immunity of the host plant induced by the interspecific interactions. To test whether or not intercropping could enhance the disease resistance of host plant, we investigated the effect of companion cropping with potato onion on tomato Verticillium wilt caused by Verticillium dahliae (V. dahliae). To investigate the mechanisms, the root exudates were collected from tomato and potato onion which were grown together or separately, and were used to examine the antifungal activities against V. dahliae in vitro, respectively. Furthermore, RNA-seq was used to examine the expression pattern of genes related to disease resistance in tomato companied with potato onion compared to that in tomato grown alone, under the condition of infection with V. dahliae. The results showed that companion cropping with potato onion could alleviate the incidence and severity of tomato Verticillium wilt. The further studies revealed that the root exudates from tomato companied with potato onion significantly inhibited the mycelia growth and spore germination of V. dahliae. However, there were no significant effects on these two measurements for the root exudates from potato onion grown alone or from potato onion grown with tomato. RNA-seq data analysis showed the disease defense genes associated with pathogenesis-related proteins, biosynthesis of lignin, hormone metabolism and signal transduction were expressed much higher in the tomato companied with potato onion than those in the tomato grown alone, which indicated that these defense genes play important roles in tomato against V. dahliae infection, and meant that the disease resistance of tomato against V. dahliae was enhanced in the companion copping with potato onion. We proposed that companion cropping with potato onion could enhance the disease resistance of tomato against V. dahliae by regulating the expression of genes related to disease resistance response. This may be a potential mechanism for the management of soil-borne plant diseases in the intercropping system.