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BACKGROUND: Entomophagous fungi (EPF) not only directly kill insect pests, but also colonize plants and improve their resistance against pests. However, most previous research has focused on Beauveria bassiana and Metarhizium anisopliae, and there are few reports on whether other EPF can enhance resistance against pests via endogenous colonization. Herein, an EPF strain was isolated from diseased larvae of Spodoptera litura in a soybean field, and subjected to genome‐wide sequencing at the chromosomal level. The pathogenicity of the isolate toward various pest insects was evaluated, and the ability to colonize plants and induce resistance against phytopathogens and insect pests was tested. RESULTS: The purified isolate was identified as M. rileyi and designated MrS1Gz1–1. Biological assays revealed its strong pathogenicity toward five insect pests belonging to Lepidoptera and Hemiptera. Furthermore, the strain inhibited the growth of soil‐borne plant disease caused by Sclerotinia sclerotiorum in vitro. It colonized plants as an endophyte via soil application, thereby inducing plant resistance‐related genes against phytopathogen infection, and it disrupted the feeding selectivity of S. litura larvae. CONCLUSION: M. rileyi MrS1Gz1–1 has potential as a broad‐spectrum microbial control agent that can induce resistance against phytopathogens and insect pests feeding as an endotype. The complete genome provides a valuable resource for exploring host interactions. © 2024 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

This article in the Journal of Fish Diseases examines the effects of the fungicide dimethomorph on various species of oomycetes, which are harmful to plants and animals, including humans. The study specifically focuses on three oomycete species that cause significant economic losses in agriculture and aquaculture. Through in vitro tests and scanning electron microscopy, the researchers found that dimethomorph inhibited the growth of the oomycetes and caused morphological changes in one species. The study suggests that more research is needed to fully understand these pathogens and develop effective treatments. [Extracted from the article]

General plant diseases as well as soil‐borne pathogens severely reduce agricultural yield. The rhizosphere (the region of the soil that includes and surrounds the roots) is an important niche for microbial diversity in particular phytobeneficial bacteria including plant growth‐promoting rhizobacteria (PGPR) which have been used for a very long time to combat plant diseases. Pathogen control and crop productivity can both be improved through the use of PGPR several mechanisms, including iron‐based nutrition, antibiotics, volatile substances, enzymes, biofilm, allelochemicals, and so on. Their modes of action and molecular mechanisms have improved our comprehension of how they are used to control crop disease. Therefore, there is a lot of literal information available regarding PGPR, but this review stands out since it starts with the fundamentals: the concept of the rhizosphere and the colonization process of the latter, particularly because it covers the most mechanisms. A broad figure is used to present the study's findings. The advantages of using PGPR as bioinoculants in sustainable agriculture are also mentioned. [ABSTRACT FROM AUTHOR]

Host nutrient supply can mediate host–pathogen and pathogen–pathogen interactions. In terrestrial systems, plant nutrient supply is mediated by soil microbes, suggesting a potential role of soil microbes in plant diseases beyond soil‐borne pathogens and induced plant defenses. Long‐term nitrogen (N) enrichment can shift pathogenic and nonpathogenic soil microbial community composition and function, but it is unclear if these shifts affect plant–pathogen and pathogen–pathogen interactions. In a growth chamber experiment, we tested the effect of long‐term N enrichment on infection by Barley Yellow Dwarf Virus (BYDV‐PAV) and Cereal Yellow Dwarf Virus (CYDV‐RPV), aphid‐vectored RNA viruses, in a grass host. We inoculated sterilized growing medium with soil collected from a long‐term N enrichment experiment (ambient, low, and high N soil treatments) to isolate effects mediated by the soil microbial community. We crossed soil treatments with a N supply treatment (low, high) and virus inoculation treatment (mock‐, singly‐, and co‐inoculated) to evaluate the effects of long‐term N enrichment on plant–pathogen and pathogen–pathogen interactions, as mediated by N availability. We measured the proportion of plants infected (i.e., incidence), plant biomass, and leaf chlorophyll content. BYDV‐PAV incidence (0.96) declined with low N soil (to 0.46), high N supply (to 0.61), and co‐inoculation (to 0.32). Low N soil mediated the effect of N supply on BYDV‐PAV: instead of N supply reducing BYDV‐PAV incidence, the incidence increased. Additionally, ambient and low N soil ameliorated the negative effect of co‐inoculation on BYDV‐PAV incidence. BYDV‐PAV infection only reduced chlorophyll when plants were grown with low N supply and ambient N soil. There were no significant effects of long‐term N soil on CYDV‐RPV incidence. Soil inoculant with different levels of long‐term N enrichment had different effects on host–pathogen and pathogen–pathogen interactions, suggesting that shifts in soil microbial communities with long‐term N enrichment may mediate disease dynamics. [ABSTRACT FROM AUTHOR]

Premise: A comprehensive field‐based screening protocol is lacking for dry root rot (DRR) disease in chickpea, which is caused by Macrophomina phaseolina (formerly referred to as Rhizoctonia bataticola). Here, we describe a protocol for establishing a sick plot for DRR to enable disease assessment of a large number of chickpea plants during the natural growing season. Methods and Results: We used a chickpea plot with >30% DRR incidence, and enriched the inoculum by cultivating highly susceptible chickpea plant genotypes and incorporating infected plant material into the soil. The chickpea plants were then subjected to infection in developed sick plots with various levels of soil moisture under natural field conditions. Conclusions: Our protocol provides a robust way to impose M. phaseolina infection on chickpea plants under natural field conditions and to investigate plant responses to the infection at morphological, physiological, and molecular levels. This method can also be used to screen for other soil‐borne diseases in a variety of plants. [ABSTRACT FROM AUTHOR]

The natural bacterial communities of the soil–plant system are relevant in the process of suppressing diseases caused by soilborne plant pathogens. However, little is known regarding the structure of these communities in soils cultivated with brassica vegetables and their relationship with clubroot severity, a disease caused by Plasmodiophora brassicae. In the present study, the composition of bacterial communities in soils cultivated with cauliflower with distinct levels of disease severity was compared. The bacterial composition in soils with lower and higher clubroot severity differs in phylum and genera levels. Soils associated with plants with lower disease severity showed predominance of Kaistobacter, Flavisolibacter, Sphingobacterium, Koribacter, Nitrospira, Bradyrhizobium and Bacillus. Our study reinforces the importance of management strategies that promote improving the physical–chemical characteristics of soil, which are essential to modulate bacterial populations correlated with plant disease suppression. [ABSTRACT FROM AUTHOR]

Summary: Competition is a major type of interaction between fungi and bacteria in soil and is also an important factor in suppression of plant diseases caused by soil‐borne fungal pathogens. There is increasing attention for the possible role of volatiles in competitive interactions between bacteria and fungi. However, knowledge on the actual role of bacterial volatiles in interactions with fungi within soil microbial communities is lacking. Here, we examined colonization of sterile agricultural soils by fungi and bacteria from non‐sterile soil inoculums during exposure to volatiles emitted by soil‐derived bacterial communities. We found that colonization of soil by fungi was negatively affected by exposure to volatiles emitted by bacterial communities whereas that of bacteria was barely changed. Furthermore, there were strong effects of bacterial community volatiles on the assembly of fungal soil colonizers. Identification of volatile composition produced by bacterial communities revealed several compounds with known fungistatic activity. Our results are the first to reveal a collective volatile‐mediated antagonism of soil bacteria against fungi. Given the better exploration abilities of filamentous fungi in unsaturated soils, this may be an important strategy for bacteria to defend occupied nutrient patches against invading fungi. Another implication of our research is that bacterial volatiles in soil atmospheres can have a major contribution to soil fungistasis. [ABSTRACT FROM AUTHOR]

Various soil management strategies that use disinfestation are important in the control of soil‐borne diseases before planting. However, only a few studies pay attention to preventing pathogen reinfestation during host plant cultivation, which is also important for the stable control of soil‐borne diseases. Here we used various pre‐planting management strategies to disinfest a field severely infested with Fusarium oxysporum, and then investigated changes in the potential pathogen and microbial communities during the 11 months of host plant cultivation. The soil microbial numbers, diversity, community structure and composition varied considerably across the soils treated by dazomet fumigation and reductive soil disinfestations (RSDs) using ethanol, bagasse and bean dregs. The Fusarium inoculum decreased to the same degree in the disinfested soils with the various methods. After the cultivation of lisianthus (Eustoma russellianum (Hook.) G. Don), microbial numbers, diversity and community structure tended to be similar and Fusarium increased markedly in these soils. Furthermore, the increase in relative abundance of Fusarium, especially in the RSD‐treated soils amended with bagasse, was significantly less than in the soils amended with non‐plant residues. Further analyses showed that the increases in microbial diversity and relative abundance of Zopfiella and Mycothermus were significantly and negatively correlated with the increase in Fusarium relative abundance. The additional sources of carbon supplied in the disinfested soil positively affected the development of the soil microbiota and prevented Fusarium reinfestation resulting from host plant cultivation, which should be considered for achieving stable disease suppression in the future. Highlights: We studied Fusarium reinfestation resulting from host plant cultivation in various soil environments.Plant cultivation led to uniformity in the development of different soil microbiota.Fusarium reinfestation depended strongly on soil environment.Increased microbial diversity and specific microbial groups prevented Fusarium reinfestation. [ABSTRACT FROM AUTHOR]

Background: The phaseout of methyl bromide (MeBr) continues to stimulate research into the use of other soil fumigants for controlling soil‐borne diseases and weeds. This research evaluated tomato (Solanum lycopersicum L.) tolerance, weed emergence and the recovery of Fusarium oxysporum f.sp. lycopersici (FOL) inoculum following fumigation with various combination ratios of dimethyl disulfide plus chloropicrin (DMDS + Pic). Results: On its own, DMDS did not effectively control purple nutsedge (Cyperus rotundus L.) compared with DMDS + Pic. Control of C. rotundus and fusarium wilt increased with Pic based on weed emergence throughout the growing season and FOL inoculum recovery from soil. In all three growing seasons, 159 kg ha−1 DMDS + 379 kg ha−1 Pic provided season‐long control of C. rotundus. Conclusion: This research confirms that formulating DMDS + Pic containing a high percentage of Pic offers an effective alternative to MeBr for tomato production. © 2018 Society of Chemical Industry Formulating dimethyl disulfide plus chloropicrin (DMDS + Pic) with a high proportion of Pic offers an effective alternative to methyl bromide for Cyperus rotundus and Fusarium oxysporum control. [ABSTRACT FROM AUTHOR]

BACKGROUND: Rosemary forms an arbuscular mycorrhizal (AM) symbiosis with a group of soilborne fungi belonging to the phylum Glomeromycota, which can modify the plant metabolome responsible for the antioxidant capacity and other health beneficial properties of rosemary. RESULTS: The effect of inoculating rosemary plants with an AM fungus on their growth via their polyphenolic fingerprinting was evaluated after analyzing leaf extracts from non‐inoculated and inoculated rosemary plants by ultra‐high performance liquid chromatography‐high resolution mass spectrometry (UHPLC‐HRMS). Plant growth parameters indicated that mycorrhizal inoculation significantly increased plant height and biomass. Chemical modifications in the plant polyphenolic profile distribution were found after a principal components analysis (PCA) loading plots study. Four compounds hosting strong antioxidant properties – ferulic acid, asiatic acid, carnosol, and vanillin – were related to mycorrhizal rosemary plants while caffeic and chlorogenic acids had a higher influence on non‐mycorrhizal plants. CONCLUSION: Mycorrhization was found to stimulate growth to obtain a higher biomass of plant leaves in a short time, avoiding chemical fertilization, while analytical results demonstrate that there is an alteration in the distribution of polyphenols in plants colonized by the symbiotic fungus, which can be related to an improvement in nutritional properties with future industrial significance. © 2018 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Bacterial wilt, caused by Ralstonia solanacearum, is a devastating soilborne disease in plants that limits the production of many crops worldwide. Although management of bacterial wilt has so far been unsuccessful, enhancing host resistance to the pathogen may be an effective control strategy. Recently, magnesium oxide (MgO) was found to induce defence responses against R. solanacearum in tomato plants. Here, the mechanisms underlying MgO‐induced defence responses against R. solanacearum (MgO‐i DARS) were investigated using Arabidopsis thaliana as a host plant. MgO‐i DARS was confirmed in A. thaliana mutants deficient in jasmonic acid or ethylene signalling pathways as well as in the wildtype (Col‐0) plants. In contrast, no MgO‐i DARS was found in A. thaliana mutants deficient in the salicylic acid (SA) production (sid2‐2) and signalling pathways (tga1‐1 and npr‐1). MgO treatment led to significant accumulation of SA in both roots and shoots of Col‐0. The SA biosynthesis gene isochorismate synthase 1 (ICS1) was induced in roots and shoots of A. thaliana treated with MgO. An NADPH oxidase gene respiratory burst oxidase homolog D (AtRbohD) was up‐regulated in both roots and shoots of Col‐0 treated with MgO. No MgO‐i DARS was observed in A. thaliana mutants deficient in AtRbohD. These results suggest that SA and RBOHD‐mediated ROS are pivotal for MgO‐i DARS in A. thaliana. [ABSTRACT FROM AUTHOR]

The use of electromagnetic fields to solve issues related to agriculture is an interesting, cost‐effective, and eco‐friendly possibility to be explored. One of the most promising applications is the disinfection of soils obtained by microwave‐induced heating. This work deals with the nonlinear computational modeling of such microwave heating of soils in metal raised bed cultivations within a greenhouse. By modeling the dielectric properties of soil, in terms of composition, moisture content, and actual temperature, and accounting for the exact thermal and electromagnetic conditions in raised beds inside the greenhouse, several realistic and nonlinear multiphysics simulations were carried out. The disinfection is directed to fungi, such as Sclerotium rolfsii, and weeds, for example, ryegrass and fleabane. The effectiveness of the proposed procedure is quantified and critically discussed exploiting analytical thermal death kinetics of soilborne plant pathogens and compared to the solarization technique. Key Points: A nonlinear numerical model to investigate the feasibility of employing microwave to thermally inactivate soil pathogens is presentedPropagation in agricultural raised beds is described using transmission‐line representation and temperature dependence of soil dielectric properties is taken into accountDeath kinetics of fungi Sclerotium rolfsii is quantified from the calculated spatio‐temporal temperature distribution for different kinds of soil [ABSTRACT FROM AUTHOR]

BACKGROUND: Root‐knot nematodes (Meloidogyne spp.), soil‐borne diseases and weeds seriously reduce the commercial yield of tomatoes grown under protected cultivation in China. Allyl isothiocyanate (AITC), a natural product obtained from damaged Brassica tissues, was evaluated as a potential replacement for the fumigant methyl bromide (MB) for use in the greenhouse production of tomatoes in China. RESULTS: The dose–response assay indicates that AITC has high biological activity against major bacterial and fungal pathogens (EC50 of 0.225–4.199 mg L−1). The bioassay results indicate that AITC has good efficacy against root‐knot nematodes (LC50 of 18.046 mg kg−1), and moderate efficacy against fungal pathogens (LC50 of 27.999–29.497 mg kg−1) and weeds (LC50 of 17.300–47.660 mg kg−1). The potting test indicates that AITC significantly improved plant vigor. Field trials indicate that AITC showed good efficacy against Meloidogyne spp. and Fusarium spp. (both ∼ 80%) as well as Phytophthora spp. and Pythium spp. (both ∼ 70%), and improved plant vigor and marketable yield. CONCLUSION: AITC used as a soil fumigant (30–50 g m−2) effectively controlled major bacterial and fungal pathogens, root‐knot nematode, weeds and increased plant vigor, yield and farmers' income in tomato cultivated under protected agriculture in China. © 2018 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Abstract: Plant resource partitioning is a mechanism promoting species coexistence and ecosystem functioning. Yet, we still have limited understanding of how soil microbes, especially plant symbiotic microbes, influence resource partitioning. We hypothesized that soil‐borne microbes, in particular mycorrhizal fungi, facilitate differential performance of tree species depending on different nitrogen sources and that this leads to a positive plant diversity–community productivity relationship. We conducted two complementing glasshouse experiments. In a “monoculture experiment,” we supplied nitrogen as ammonium, nitrate or glycine and tested the growth response of three tree species associated with different root symbionts: one associated with ectomycorrhizal fungi, one associated with arbuscular mycorrhizal fungi, and the third associated with both arbuscular mycorrhizal fungi and N‐fixing bacteria. In an “intermixed experiment,” we grew the tree species at three richness levels (one, two or three species) in soil supplied with a mix of the three nitrogen forms or no added nitrogen, and with or without soil microbes. The monoculture experiment showed that in the presence of soil microbes, the ectomycorrhizal plant species grew best when supplied with glycine and the two arbuscular mycorrhizal plant species grew best with either nitrate or ammonium addition. When the different forms of nitrogen were mixed in the intermixed experiment, plant mixtures produced more biomass than plant monocultures in the presence of soil microbes, with positive complementarity effects indicating microbe‐mediated plant resource partitioning. Our results suggest that co‐existing tree species can partition soil nitrogen when grown with their particular mycorrhizal symbionts or other soil microbes, resulting in positive biodiversity effects in complex resource environments. A plain language summary is available for this article. [ABSTRACT FROM AUTHOR]

Abstract: Previously, we selected bacterial strain ISE14 through a sequential selection procedure that included radicle, seedling, and in planta assays and field tests. This strain not only suppressed a destructive soilborne disease, Phytophthora blight, caused by Phytophthora capsici but also increased fruit yields of pepper plants in the fields. This study was conducted to identify strain ISE14 by 16S rRNA gene sequence analysis and to characterise biocontrol and plant growth promotion activities of the strain in pepper plants. Strain ISE14, identified as Chryseobacterium sp., significantly reduced disease severity in plants inoculated with Ph. capsici and promoted plant growth (lengths and dry weights of shoots and roots) compared with those in plants treated with Escherichia coli DH5α (negative control) or MgSO4 solution (untreated control). This strain effectively colonised pepper plant roots as assessed by bacterial population analysis and confocal laser scanning microscopy; it enhanced soil microbial activity and biofilm formation, but not the production of indole acetic acid. Strain ISE14 also solubilised organic or inorganic phosphate by production of acid and alkaline phosphatases or reduction in pH, resulting in enhanced pepper plant growth. This strain exhibited similar or greater activity in disease control and plant growth promotion tests compared with positive control strains Paenibacillus polymyxa AC‐1 (biocontrol) and Bacillus vallismortis EXTN‐1 (plant growth). Therefore, Chryseobacterium sp. ISE14 may be a phosphate‐solubilising and plant growth‐promoting rhizobacterium (PGPR) strain that suppresses Phytophthora blight of pepper. To our knowledge, this is the first report of a phosphate‐solubilising PGPR strain of Chryseobacterium sp. that suppresses the pepper disease. [ABSTRACT FROM AUTHOR]

Summary: Phosphite (Phi) is used commercially to manage diseases mainly caused by oomycetes, primarily due to its low cost compared with other fungicides and its persistent control of oomycetous pathogens. We explored the use of Phi in controlling the fungal pathogens Puccinia emaculata and Phakopsora pachyrhizi, the causal agents of switchgrass rust and Asian soybean rust, respectively. Phi primes host defenses and efficiently inhibits the growth of P. emaculata, P. pachyrhizi and several other fungal pathogens tested. To understand these Phi‐mediated effects, a detailed molecular analysis was undertaken in both the host and the pathogen. Transcriptomic studies in switchgrass revealed that Phi activates plant defense signaling as early as 1 h after application by increasing the expression of several cytoplasmic and membrane receptor‐like kinases and defense‐related genes within 24 h of application. Unlike in oomycetes, RNA sequencing of P. emaculata and P. pachyrhizi did not exhibit Phi‐mediated retardation of cell wall biosynthesis. The genes with reduced expression in either or both rust fungi belonged to functional categories such as ribosomal protein, actin, RNA‐dependent RNA polymerase, and aldehyde dehydrogenase. A few P. emaculata genes that had reduced expression upon Phi treatment were further characterized. Application of double‐stranded RNAs specific to P. emaculata genes encoding glutamate N‐acetyltransferase and cystathionine gamma‐synthase to switchgrass leaves resulted in reduced disease severity upon P. emaculata inoculation, suggesting their role in pathogen survival and/or pathogenesis. [ABSTRACT FROM AUTHOR]

The soilborne fungi Sclerotinia sclerotiorum, Rhizoctonia solani and the oomycete Pythium ultimum are among the most destructive pathogens for lettuce production. The application of the biocontrol agent Paenibacillus alvei K165 to the transplant soil plug of lettuce resulted in reduced S. sclerotiorum, R. solani and P. ultimum foliar symptoms and incidence compared to untreated controls, despite the suppressive effect of the pathogens on the rhizosphere population of K165. In vitro, K165 inhibited the growth of S. sclerotiorum and R. solani but not P. ultimum. Furthermore, the expression of the pathogenesis‐related (PR) gene PR1, a marker gene of salicylic acid (SA)‐dependent plant defence, and of the Lipoxygenase (LOX) and Ethylene response factor 1 (ERF1) genes, markers of ethylene/jasmonate (ET/JA)‐dependent plant defence was recorded. K165‐treated plants challenged with P. ultimum showed up‐regulation of PR1, whereas challenge with R. solani resulted in up‐regulation of LOX and ERF1, and challenge with S. sclerotiorum resulted in up‐regulation of PR1, LOX and ERF1. This suggests that K165 triggers the SA‐ and the ET/JA‐mediated induced systemic resistance against P. ultimum and R. solani, respectively, while the simultaneous activation of the SA and ET/JA signalling pathways is proposed for S. sclerotiorum. [ABSTRACT FROM AUTHOR]

* Rhizoctonia solani is a soil-borne fungus causing sheath blight. In consistent with its necrotrophic life style, no rice cultivars fully resistant to R. solani are known, and agrochemical plant defense activators used for rice blast, which upregulate a phytohormonal salicylic acid (SA)-dependent pathway, are ineffective towards this pathogen. As a result of the unavailability of genetics, the infection process of R. solani remains unclear. * We used the model monocotyledonous plants Brachypodium distachyon and rice, and evaluated the effects of phytohormone-induced resistance to R. solani by pharmacological, genetic and microscopic approaches to understand fungal pathogenicity. * Pretreatment with SA, but not with plant defense activators used in agriculture, can unexpectedly induce sheath blight resistance in plants. SA treatment inhibits the advancement of R. solani to the point in the infection process in which fungal biomass shows remarkable expansion and specific infection machinery is developed. The involvement of SA in R. solani resistance is demonstrated by SA-deficient NahG transgenic rice and the sheath blight-resistant B. distachyon accessions, Bd3-1 and Gaz-4, which activate SA-dependent signaling on inoculation. * Our findings suggest a hemi-biotrophic nature of R. solani, which can be targeted by SA-dependent plant immunity. Furthermore, B. distachyon provides a genetic resource that can confer disease resistance against R. solani to plants. [ABSTRACT FROM AUTHOR]

Alternatives to soil fumigation are needed for soilborne disease control. The aim of this study was to test anaerobic soil disinfestation (ASD) as an alternative to soil fumigation for control of critical soilborne pathogens in Californian strawberry production. Controlled environment experiments were conducted at 25 and 15 °C to test different materials as carbon sources for ASD using soil inoculated with Verticillium dahliae. Field trials were conducted in three locations comparing ASD with 20 Mg ha−1 rice bran (RB) against fumigated and untreated controls, steam, mustard seed meal and fish emulsion. In ASD-treated soils, temperature and extent of anaerobic conditions were critical for control of V. dahliae, but multiple carbon inputs reduced inoculum by 80-100%. In field trials, ASD with RB provided control of a number of pathogens, and in three of four trials produced marketable fruit yields equivalent to fumigation. Little weed control benefit from ASD was found. ASD with RB also induced changes in the soil microbiome that persisted through the growing season. When equivalent yields were obtained, net returns above harvest and treatment costs with ASD RB were 92-96% of those with bed fumigation based on average prices over the previous 5 years. ASD can be a viable alternative for control of some soilborne pathogens. Growers are adopting ASD in California strawberry production, but research to determine optimal soil temperatures, anaerobicity thresholds and carbon sources for effective control of specific pathogens is needed. [ABSTRACT FROM AUTHOR]

Soilborne potato diseases and soil microbial community characteristics were evaluated over 8 years in different potato cropping systems designed to address specific management goals of soil conservation, soil improvement and disease suppression. Results were compared to a standard rotation and non-rotation control in field trials in Maine. Standard rotation consisted of barley underseeded with red clover, followed by potato (2-year). Soil-conserving system ( SC) featured an additional year of forage grass and reduced tillage (3-year, barley/timothy-timothy-potato). Soil-improving system ( SI) added yearly compost amendments to SC, and the disease-suppressive system ( DS) featured crops with known disease-suppressive capability (3-year, mustard/rapeseed-sudangrass/rye-potato). Systems were established in 2004, evaluated with and without irrigation, and actively managed until 2010, with potato also planted in 2011 and 2012 to examine residual effects. All rotations reduced soilborne diseases black scurf and common scab, and increased yield after one rotation cycle (3 years), but diseases increased overall after two rotation cycles. DS maintained lower soilborne disease levels than all other rotations, as well as high yields, throughout the study. Cropping system effects became more pronounced after multiple cycles. SI system and irrigation both resulted in higher yields, but also higher levels of soilborne disease. Cropping system and irrigation effects were significant even after systems were no longer maintained. Soil microbial community data showed significant changes associated with cropping system, and differences increased over time. Cropping system strategy had significant and lasting effects on soil microbiology and soilborne diseases, and can be used to effectively enhance potato production. [ABSTRACT FROM AUTHOR]

Rice false smut disease caused by the ascomycete fungus Villosiclava virens (Clavicipitaceae) reduces rice yield worldwide. It invades rice panicles and forms dark-green false smut balls composed of thick-walled conidia. Although the infection process during the booting stage is well studied, its infection route before this is unclear. It was hypothesized that the thick-walled conidia in soil penetrate rice roots, and the fungus latently colonizes roots and tiller buds at the vegetative stage. This hypothesis was tested using species-specific detection methods. First, real-time PCR with species-specific primers and probe was used to estimate thick-walled conidial number in the paddy field soil. Secondly, nested PCR with species-specific primers showed that fungal DNA was detected in roots and shoot apices of rice plants in the vegetative stage. Thirdly, colourimetric in situ hybridization with a species-specific oligonucleotide probe targeting 18S rRNA suggested that sparse mycelia or tightly condensed mycelia were present on the external surface of tiller buds enveloped by juvenile leaf sheaths at the vegetative stage. Thin hyphae were found around leaf axils at the surface of elongated stems at the heading stage, and the fungal hyphae grew in the rice root tissues. In addition, it was demonstrated that eGFP-tagged transformants of the fungus invaded rice roots and colonized the surface of roots and leaf sheaths under artificial conditions. [ABSTRACT FROM AUTHOR]

Clubroot, a disease of Brassicaceae species, is caused by the soilborne pathogen Plasmodiophora brassicae. High soil water content was previously described to favour the motility of zoospores and their penetration into root cells. In this study, the effect of irrigation regimes on clubroot development during the post-invasive secondary phase of infection was investigated. Three irrigation regimes (low, standard, high) were tested on two Arabidopsis accessions, Col-0 (susceptible) and Bur-0, a partially resistant line. In Col-0, clubroot symptoms and resting spore content were higher under the 'low irrigation' regime than the other two regimes, thus enhancing the phenotypic contrast between the two Arabidopsis accessions. Clubroot severity under high and low irrigation regimes was evaluated in near-isogenic lines derived from a Col-0 × Bur-0 cross, to assess the effect of soil moisture on the expression of each of four quantitative trait loci ( QTL) controlling partial resistance. The presence of the Bur-0 allele at the QTL PbAt5.2 resulted in reduced severity only under low irrigation, whereas the Bur-0 allele at QTL PbAt5.1 was associated with partial resistance only under high irrigation. QTL PbAt4 reduced the number of resting spores in infected roots, but was not associated with reduced clubroot symptoms. The results indicated that soil moisture could have consequences for the secondary phase of clubroot development, depending on plant genotype. Future genetic studies may benefit from using combinations of watering conditions during the secondary stage of infection, thus opening up the possibility of identifying genetic factors expressed under specific environmental conditions. [ABSTRACT FROM AUTHOR]

Breeding disease-resistant varieties is one of the most effective and economical means to combat soilborne diseases in pulse crops. Commonalities between pathogenic and mutualistic microbe colonization strategies, however, raises the concern that reduced susceptibility to pathogens may simultaneously reduce colonization by beneficial microbes. We investigate here the degree of overlap in the transcriptional response of the Phytophthora medicaginis susceptible chickpea variety 'Sonali' to the early colonization stages of either Phytophthora, rhizobial bacteria or arbuscular mycorrhizal fungi. From a total of 6476 genes differentially expressed in Sonali roots during colonization by any of the microbes tested, 10.2% were regulated in a similar manner regardless of whether it was the pathogenic oomycete or a mutualistic microbe colonizing the roots. Of these genes, 49.7% were oppositely regulated under the same conditions in the moderately Phytophthora resistant chickpea variety 'PBA HatTrick'. Chickpea varieties with improved resistance to Phytophthora also displayed lower colonization by rhizobial bacteria and mycorrhizal fungi leading to an increased reliance on N and P from soil. Together, our results suggest that marker-based breeding in crops such as chickpea should be further investigated such that plant disease resistance can be tailored to a specific pathogen without affecting mutualistic plant:microbe interactions. [ABSTRACT FROM AUTHOR]

This study evaluated the effect of different organic amendments on lettuce fusarium wilt caused by Fusarium oxysporum f. sp. lactucae in pots under controlled conditions. Their effects on the density of the pathogen, on the total fungi and on fluorescent Pseudomonas spp. were also evaluated after two subsequent lettuce crops. A significant reduction in the severity of the symptoms of F. oxysporum f. sp. lactucae was found after the use of Brassica carinata pellets (52-79% reduction) and compost (49-67% reduction), while Brassica green manure and cattle and chicken manure only provided partial control of fusarium wilt. However, variations in effectiveness were observed for the same treatment in repeated trials. In general, an increase was observed in Pseudomonas and a decrease in fungal populations in the growing medium, which was obtained by mixing a blonde sphagnum peat and a sandy loam soil with B. carinata pellets and compost after two consecutive cropping cycles. Prolonging the Brassica and compost treatments from 30 to 60 days did not significantly affect disease severity, plant growth or the microbial population of the total fungi or Pseudomonas. The largest lettuce biomass was obtained in the non-inoculated growing medium amended with brassica flour, chicken manure, B. carinata pellets and compost, as a consequence of fertilization. The treatment with B. juncea green manure, B. carinata (pellets and flour) and compost applied 30 days before planting led to promising results and merits further investigation for use under field conditions. [ABSTRACT FROM AUTHOR]

BACKGROUND Many orchards use fumigation to control soilborne pests prior to replanting. Controlling emissions is mandatory to reduce air pollution in California. This research evaluated the effects of plastic film type [polyethylene ( PE) or totally impermeable film ( TIF)], application rate of Telone C35 [full (610 kg ha−1), 2/3 or 1/3 rates] and carbonation at 207 kPa on fumigant transport (emission and in soil) and efficacy. RESULTS While increasing fumigant concentrations under the tarp, TIF reduced emissions >95% (∼2% and <1% of total applied 1,3-dichloropropene and chloropicrin respectively) relative to bare soil, compared with ∼30% reduction by PE. All fumigation treatments, regardless of film type, provided good nematode control above 100 cm soil depth; however, nematode survival was high at deeper depths. Weed emergence was mostly affected by tarping and fumigant rate, with no effects from the carbonation. CONCLUSION TIF can effectively reduce fumigant emissions. Carbonation under the studied conditions did not improve fumigant dispersion and pest control. The 2/3 rate with TIF controlled nematodes as effectively as the full rate in bare soil or under the PE film to 100 cm soil depth. However, control of nematodes in deeper soil remains a challenge for perennial crops. Published 2015. This article is a U.S. Government work and is in the public domain in the USA. [ABSTRACT FROM AUTHOR]

The use of inoculum of arbuscular mycorrhizal fungi ( AMF) in nursery represents a promising field in horticulture because of its known benefits in terms of plant growth and bioprotection. The present work was undertaken to determine the effect of mycorrhizal inoculation with Rhizophagus irregularis in a nursery medium on the containment of melon root rot and vine decline ( MRRVD) caused by the soil-borne pathogen Monosporascus cannonballus. The percentage of mycorrhization, biomass and yield following mycorrhizal inoculation were also evaluated. Biocontrol activity was assessed in greenhouse pot experiments upon artificial inoculation of M. cannonballus and in a two-season field experiment under production conditions in an unheated greenhouse with a history of MRRVD. On the basis of the mycorrhization parameters, the interaction appeared to be established within 30 days after inoculation. The total shoot growth in the mycorrhized plants was significantly higher when compared to the control, while the root growth was unaffected. Upon artificial inoculation of M. cannonballus, mycorrhization provided complete protection against the pathogen. Greenhouse experiments under production conditions during spring cropping season showed that pretransplanting inoculation with R. irregularis significantly decreased the severity of the disease. Also, the average fruit weight of mycorrhized plants was significantly higher than the untreated control. Nevertheless, in summer crop, the bioprotection activity of AMF failed. Present results indicate that the use of AMF in a nursery setting can contribute to the prevention of the onset of this problematic soil-borne disease within a sustainable and integrated soil-borne disease management. [ABSTRACT FROM AUTHOR]

BACKGROUND Soilborne disease management remains a great challenge in melon production with the phaseout of soil fumigant methyl bromide. Grafting has been shown to be an effective approach to control soilborne diseases. However, previous research has yielded mixed results regarding the impacts of rootstock on fruit quality. Very few studies have assessed melon quality attributes using both sensory evaluation and instrumental methods. RESULTS Galia melon 'Arava' ( Cucumis melo L. var. reticulatus Ser.) and honeydew melon 'Honey Yellow' ( C. melo L. var. inodorus Naud.) were grafted onto commercial hybrid squash ( Cucurbita maxima Duchesne × Cucurbita moschata Duchesne) rootstocks and root-knot nematode-resistant Cucumis metulifer E. Mey. ex Naud. rootstock. The grafting combinations were evaluated under different production conditions. Grafting with hybrid squash rootstocks resulted in reduced soluble solids content ( SSC) and decreased sensory ratings of 'Arava' fruit. By contrast with grafted 'Arava', grafted 'Honey Yellow' did not exhibit significant differences in sensory properties and instrumental measurements regardless of production conditions and rootstock selection. CONCLUSION The effects of grafting on fruit quality attributes differed between the two distinctive types of melon scion used. Potential negative impacts of rootstocks on melon fruit quality need to be considered in the selection and use of disease-resistant rootstocks. © 2014 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Verticillium dahliae is a destructive, soil-borne fungal pathogen that causes vascular wilt disease in many economically important crops worldwide. A polyamine oxidase ( PAO) gene was identified and cloned by screening suppression subtractive hybridisation and c DNA libraries of cotton genotypes tolerant to Verticillium wilt and was induced early and strongly by inoculation with V. dahliae and application of plant hormone. Recombinant cotton polyamine oxidase (Gh PAO) was found to catalyse the conversion of spermine (Spm) to spermidine (Spd) in vitro. Constitutive expression of Gh PAO in Arabidopsis thaliana produced improved resistance to V. dahliae and maintained putrescine, Spd and Spm at high levels. Hydrogen peroxide (H2O2), salicylic acid and camalexin (a phytoalexin) levels were distinctly increased in Gh PAO-overexpressing Arabidopsis plants during V. dahliae infection when compared with wild-type plants, and Spm and camalexin efficiently inhibited growth of V. dahliae in vitro. Spermine promoted the accumulation of camalexin by inducing the expression of mitogen-activated protein kinases and cytochrome P450 proteins in Arabidopsis and cotton plants. The three polyamines all showed higher accumulation in tolerant cotton cultivars than in susceptible cotton cultivars after inoculation with V. dahliae. Gh PAO silencing in cotton significantly reduced the Spd level and increased the Spm level, leading to enhanced susceptibility to infection by V. dahliae, and the levels of H2O2 and camalexin were distinctly lower in Gh PAO-silenced cotton plants after V. dahliae infection. Together, these results suggest that Gh PAO contributes to resistance of the plant against V. dahliae through the mediation of Spm and camalexin signalling. [ABSTRACT FROM AUTHOR]

In the past few decades, economic interest in the cultivation of chestnuts for both timber and nut production has resurfaced in the Mediterranean area. However, chestnut cultivation has suffered in recent years from the spread of exotic pests, such as the gall wasp Dryocosmus kuriphilus, and from the resurgence of previously present diseases, most likely due to anomalous climate dynamics. This is the case with chestnut ink disease, caused by the soilborne pathogens Phytophthora cinnamomi and P. cambivora. Scientific and technical support in monitoring and management, that utilizes new forecasting approaches incorporating related environmental variables, is therefore essential. The main aim of this study was to develop a mathematical model assessing the potential for the establishment of chestnut ink disease at a large scale. Towards this goal, fuzzy rule-based theory was applied to the environmental variables associated with host presence, pathogens' ecological niches and ink disease symptoms expression. The effectiveness of the rule-based modelling outcomes, provided with uncertainty maps to facilitate their correct interpretation, was confirmed by detailed field data collected from a large chestnut-growing area where ink disease has been increasing in recent years. The final model gave consistent predictions for disease presence. For this reason, it represents a flexible and valuable decision-support tool to forecast which sites are at risk from CID. [ABSTRACT FROM AUTHOR]

Compost is beneficial for agriculture fields in many ways such as soil conditioner, fertilizer, and natural pesticide and above all it helps to manage organic wastes and adds vital humic acids to soil. Four indigenous composts prepared from readily available organic wastes viz. vermicompost, banana, NADEP, and Calotropis were used in the present investigation for growth and disease suppression in mung beans. The composts were amended with Trichoderma viride in the concentration of 0.1 and 0.2% to determine their influence on length and weight of roots and shoots, disease incidence, soil moisture, and soil microflora in plants. The best results were observed in the treatment with T. viride (0.2%), followed by T. viride (0.1%) in vermicompost, while the treatment T. viride (0.1%) with Calotropis compost showed little growth and suppression of disease. All composts enhanced the soil moisture content and microbial populations in amended soil resulting in the reduction of disease incidence. Among T. viride enriched composts, the counts of fungi, bacteria, and actinomycetes were higher in the vermicompost and banana compost-amended soils. Thus, preparing these composts from readily available organic wastes and amending soil with T. viride enriched composts hold a great promise for improving soil fertility and suppressing the soil-borne plant pathogens for sustainable agriculture. [ABSTRACT FROM AUTHOR]

Botrytis cinerea causes grey mould, a disease common on many economically important crops. Although much attention is paid to the airborne inoculum of this fungus, as it sporulates abundantly in favourable conditions, knowledge on the abundance and genetic characteristics of soilborne inoculum could help improve control strategies. In this study, the soilborne inoculum of B. cinerea was quantified in two greenhouses at different times before and after the cultivation of four successive lettuce crops. Between 0 and 1177 colony-forming units ( CFU) of B. cinerea per gram of soil were recorded. There was no significant correlation between abundance of soilborne inoculum and subsequent disease incidence on lettuce ( P = 0·11). Sixty-five isolates collected from diseased plants and 66 isolates collected from the soil were investigated for their genetic diversity. The soil strains showed lower genetic diversity than the lettuce strains when considering the unbiased gene diversity within the nine microsatellite loci, the mean number of alleles per locus and the haplotypic diversity. The genetic differentiation between lettuce and soil strains decreased over three successive lettuce crops. At the same time, the genetic structure of the two groups of strains tended to become similar. These results are consistent with the hypothesis of a flow of inoculum between the lettuce crop and the soil, and vice versa. The study shows that grey mould management should pay more attention to the inoculum of B. cinerea present in the soil. [ABSTRACT FROM AUTHOR]

During transition to organic production, various strategies can be implemented to enhance soil health, including the soil property of disease suppressiveness. We previously found increased levels of diseases caused by biotrophic pathogens associated with manure application, but manure also suppressed diseases caused by necrotrophic pathogens. In an extension of that study we evaluated soils from different cropping system and organic amendment treated plots using a bioassay of suppressiveness to two soilborne diseases, Rhizoctonia root rot and sudden death syndrome (SDS) of soybean [Glycine max (L.) Merr.]. Also, the soil population levels of Pseudomonadaceae were assessed for their suitability as an indicator of disease suppressiveness. Levels of soil suppression of both Rhizoctonia root rot and SDS were found to be associated with specific cropping systems, but the associations were not consistent from year to year. There were no associations between organic amendment treatments and disease suppression in the bioassay studies. However, there was an overall increase in soil suppressiveness to Rhizoctonia solani during the 3 yr of transition, regardless of cropping system or organic amendment treatments. In contrast, there was an overall decrease in suppressiveness to Fusarium virguliforme during the transition. There was no significant effect of cropping system or organic amendment treatments on the levels of Pseudomonadaceae, indicating that this was not a good predictor of general suppression in this study. While specific treatments were not found to consistently impact soil suppressiveness, the overall increase in suppressiveness to R. solani during the 3-yr transition did show the value of the transition process. [ABSTRACT FROM AUTHOR]

Cephalosporium stripe, caused by the fungus Cephalosporium gramineum, is the only known vascular wilt disease of small grain cereals. The pathogen causes characteristic striping of leaf blades and sheaths, but can also result in seedling death, stunting, and sterile seed heads (white heads). Cephalosporium stripe is a disease of autumn (fall)-sown wheat, especially in cool and wet production regions. The disease is further favoured by early sowing, reduced tillage practices, low pH soils, and by frost heaving that damages roots. Infections occur almost entirely from spores produced on surface crop debris that are washed into the soil, although a low level of seed transmission can also occur. The pathogen colonizes root epidermis and cortical cells, subsequently moves into the vascular tissue, and eventually spreads throughout the entire plant. Production of fungal toxin(s) and extracellular polysaccharides probably play an important role in pathogenesis. Cultural practices such as delayed sowing, crop rotation, destruction of crop debris, liming of soil and fertilizer management all have potential to reduce the incidence of cephalosporium stripe. All of these cultural practices have negative economic impacts and/or increase soil erosion, and thus there is much interest in the development of resistant cultivars. There is potential for introgression of highly effective resistance from wild species into cultivated wheat. Genes for quantitatively inherited resistance can also be accumulated within cultivated wheat to attain moderate resistance. The continued use of cultivars with moderate resistance will probably be sufficient for long-term control of the disease. [ABSTRACT FROM AUTHOR]

Recently, emission of volatile organic compounds (VOCs) has emerged as a mode of communication between bacteria and plants. Although some bacterial VOCs that promote plant growth have been identified, their underlying mechanism of action is unknown. Here we demonstrate that indole, which was identified using a screen for Arabidopsis growth promotion by VOCs from soil-borne bacteria, is a potent plant-growth modulator. Its prominent role in increasing the plant secondary root network is mediated by interfering with the auxin-signalling machinery. Using auxin reporter lines and classic auxin physiological and transport assays we show that the indole signal invades the plant body, reaches zones of auxin activity and acts in a polar auxin transport-dependent bimodal mechanism to trigger differential cellular auxin responses. Our results suggest that indole, beyond its importance as a bacterial signal molecule, can serve as a remote messenger to manipulate plant growth and development. [ABSTRACT FROM AUTHOR]

Three nursery fields and three rootstock mother fields from commercial nurseries located in Comunidad Valenciana region (central-eastern Spain) were surveyed in July 2011 to detect the presence and to quantify Ilyonectria spp. in the soil. In each field, ten soil samples were taken randomly with a soil probe at a depth of 10-30 cm, and 10-20 cm from the base of the plant. Three replicate subsamples (10 g each) were taken from each soil sample. DNA was extracted and a multiplex nested PCR with species-specific primer pairs (Mac1/MaPa2, Lir1/Lir2 and Pau1/MaPa2) was used to identify the species present. Among the 180 soil DNA samples analysed, Ilyonectria spp. were detected in 172 of them. Ilyonectria macrodidyma complex was the most frequently detected, being identified in 141 samples from all the fields evaluated. However, I. liriodendri was detected in only 16 samples, but was present in all open-root field nurseries and in two rootstock mother fields. In addition, quantitative PCR ( qPCR) assays were done to assess the levels of I. liriodendri and I. macrodidyma-complex DNA in the soil samples. Detection of Ilyonectria spp. DNA using qPCR correlated with the fields found positive with the nested multiplex PCR. DNA concentrations of Ilyonectria spp. ranged from 0·004 to 1904·8 pg μL−1. In general, samples from rootstock mother fields showed the highest DNA concentrations. The ability to detect and quantify Ilyonectria spp. genomic DNA in soil samples from nursery fields and rootstock mother fields confirms soils from both field types as important inoculum sources for black-foot pathogens. [ABSTRACT FROM AUTHOR]

Ralstonia solanacearum is a Gram-negative soil-borne bacterium that causes bacterial wilt disease in more than 200 plant species, including economically important Solanaceae species. In R. solanacearum, the hypersensitive response and pathogenicity ( Hrp) type III secretion system is required for both the ability to induce the hypersensitive response ( HR) in nonhost plants and pathogenicity in host plants. Recently, 72 effector genes, called rip ( Ralstonia protein injected into plant cells), have been identified in R. solanacearum RS1000. RS1002, a spontaneous nalixidic acid-resistant derivative of RS1000, induced strong HR in the nonhost wild eggplant Solanum torvum in an Hrp-dependent manner. An Agrobacterium-mediated transient expression system revealed that Rip36, a putative Zn-dependent protease effector of R. solanacearum, induced HR in S. torvum. A mutation in the putative Zn-binding motif ( E149A) completely abolished the ability to induce HR. In agreement with this result, the RS1002-derived Δ rip36 and rip36E149A mutants lost the ability to induce HR in S. torvum. An E149 A mutation had no effect on the translocation of Rip36 into plant cells. These results indicate that Rip36 is an avirulent factor that induces HR in S. torvum and that a putative Zn-dependent protease motif is essential for this activity. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi ( AMF) can control soilborne diseases such as Fusarium oxysporum f.sp. lycopersici ( Fol). Root exudates play an important role in plant-microbe interactions in the rhizosphere, especially, in the initial phase of these interactions. In this work, we focus on (i) elucidating dynamics in root exudation of Solanum lycopersicum L. in an intercropping system due to AMF and/or Fol; (ii) its effect on Fol development in vitro; and (iii) the testing of the root exudate compounds identified in the chromatographic analyses in terms of effects on fungal growth in in vitro assays. GC- MS analyses revealed an AMF-dependent increase in sugars and decrease in organic acids, mainly glucose and malate. In the HPLC analyses, an increase in chlorogenic acid was evident in the combined treatment of AMF and Fol, which is to our knowledge the first report about an increase in chlorogenic acid in root exudates of AM plants challenged with Fol compared with plants inoculated with AMF only, clearly indicating changes in root exudation due to AMF and Fol. Root exudates of AMF tomato plants stimulate the germination rate of Fol, whereas the co-inoculation of AMF and Fol leads to a reduction in spore germination. In the in vitro assays, citrate and chlorogenic acid could be identified as possible candidates for the reduction in Fol germination rate in the root exudates of the AMF+ Fol treatment because they proved inhibition at concentrations naturally occurring in the rhizosphere. [ABSTRACT FROM AUTHOR]

The pathozone (volume of soil surrounding subterranean plant organs within which a propagule must occur if it is to have any chance of infecting the organ) is usually described by statistical models lacking biological meaning. For this reason, pathozone results might be difficult to interpret and the estimated parameters cannot be re-used in other studies. We developed a model with parameters reflecting life-history traits concerning primary infections of soilborne pathogens. The model was then fitted to experimental data obtained from eight isolates of Gaeumannomyces graminis var. tritici, causal agent of take-all disease of wheat. Our model provided not only a mechanistic description for the pathozone dynamics, but also a better fit to the data than four other models published in the literature. Although the isolates displayed phenotypic variability in terms of pathozone dynamics, these differences did not map onto the G1 and G2 genetic subgroups known to occur in Ggt populations. [ABSTRACT FROM AUTHOR]

Ralstonia solanacearum is a major soilborne pathogen that attacks > 200 plant species, including major crops. To characterize Mt QRRS1, a major quantitative trait locus ( QTL) for resistance towards this bacterium in the model legume Medicago truncatula, genetic and functional approaches were combined., QTL analyses together with disease scoring of heterogeneous inbred families were used to define the locus. The candidate region was studied by physical mapping using a bacterial artificial chromosome ( BAC) library of the resistant line, and sequencing. In planta bacterial growth measurements, grafting experiments and gene expression analysis were performed to investigate the mechanisms by which this locus confers resistance to R. solanacearum., The Mt QRRS1 locus was localized to the same position in two recombinant inbred line populations and was narrowed down to a 64 kb region. Comparison of parental line sequences revealed 15 candidate genes with sequence polymorphisms, but no evidence of differential gene expression upon infection. A role for the hypocotyl in resistance establishment was shown., These data indicate that the quantitative resistance to bacterial wilt conferred by Mt QRRS1, which contains a cluster of seven R genes, is shared by different accessions and may act through intralocus interactions to promote resistance. [ABSTRACT FROM AUTHOR]

This study was undertaken to isolate indigenous plant growth-promoting ( PGP) bacteria from solarized soil effective in the biocontrol of Monosporascus cannonballus, the cause of root rot and vine decline of melon, which is one of the most destructive soilborne diseases of this crop worldwide. The screening strategy resulted in the selection of two interesting PGP bacteria as biocontrol candidates against M. cannonballus belonging to the same microbial community. The two bacterial species, identified according to phenotypic, physiological tests and analysis of the 16 S r DNA sequence as Bacillus subtilis/amyloliquefaciens ( BsCR) and Pseudomonas putida ( Pp F4), showed PGP traits and in vitro antagonistic activity towards M. cannonballus. Antagonism by BsCR was characterized by a consistent inhibition of the pathogen in vitro growth; Pp F4 strongly inhibited the development of perithecia of the pathogen. Under greenhouse conditions, the selected bacteria were tested for their biocontrol activity in the pathosystem melon- M. cannonballus. Bs CR alone and in combination with Pp F4 determined a consistent decrease in the disease symptoms. BsCR and the combination of the bacterial strains significantly increased root biomass in both inoculated and un-inoculated plant. Upon seed treatment with BsCR, the accumulation and isoenzyme induction of peroxidase in roots as biochemical marker for induction of resistance were found, thus indicating that BsCR may reduce the disease severity also by the activation of the plant defence responses. The study highlights the synergistic biocontrol potential of B. subtilis BsCR and P. putida Pp F4 in the integrated management of root rot and vine decline of melon caused by M. cannonballus. [ABSTRACT FROM AUTHOR]

Fusarium culmorum is a ubiquitous soil-borne fungus able to cause foot and root rot and Fusarium head blight on different small-grain cereals, in particular wheat and barley. It causes significant yield and quality losses and results in contamination of the grain with mycotoxins. This review summarizes recent research activities related to F. culmorum, including studies into its population diversity, mycotoxin biosynthesis, mechanisms of pathogenesis and resistance, the development of diagnostic tools and preliminary genome sequence surveys. We also propose potential research areas that may expand our basic understanding of the wheat- F. culmorum interaction and assist in the management of the disease caused by this pathogen. Taxonomy Fusarium culmorum ( W. G. Smith) Sacc. Kingdom Fungi; Phylum Ascomycota; Subphylum Pezizomycotina; Class Sordariomycetes; Subclass Hypocreomycetidae; Order Hypocreales; Family Nectriaceae; Genus Fusarium. Disease symptoms Foot and root rot (also known as Fusarium crown rot): seedling blight with death of the plant before or after emergence; brown discoloration on roots and coleoptiles of the infected seedlings; brown discoloration on subcrown internodes and on the first two/three internodes of the main stem; tiller abortion; formation of whiteheads with shrivelled white grains; Fusarium head blight: prematurely bleached spikelets or blighting of the entire head, which remains empty or contains shrunken dark kernels. Identification and detection Morphological identification is based on the shape of the macroconidia formed on sporodochia on carnation leaf agar. The conidiophores are branched monophialides, short and wide. The macroconidia are relatively short and stout with an apical cell blunt or slightly papillate; the basal cell is foot-shaped or just notched. Macroconidia are thick-walled and curved, usually 3-5 septate, and mostly measuring 30-50 × 5.0-7.5 μm. Microconidia are absent. Oval to globose chlamydospores are formed, intercalary in the hyphae, solitary, in chains or in clumps; they are also formed from macroconidia. The colony grows very rapidly (1.6-2.2 cm/day) on potato dextrose agar ( PDA) at the optimum temperature of 25 ° C. The mycelium on PDA is floccose, whitish, light yellow or red. The pigment on the reverse plate on PDA varies from greyish-rose, carmine red or burgundy. A wide array of polymerase chain reaction ( PCR) and real-time PCR tools, as well as complementary methods, which are summarised in the first two tables, have been developed for the detection and/or quantification of F. culmorum in culture and in naturally infected plant tissue. Host range Fusarium culmorum has a wide range of host plants, mainly cereals, such as wheat, barley, oats, rye, corn, sorghum and various grasses. In addition, it has been isolated from sugar beet, flax, carnation, bean, pea, asparagus, red clover, hop, leeks, Norway spruce, strawberry and potato tuber. Fusarium culmorum has also been associated with dermatitis on marram grass planters in the Netherlands, although its role as a causal agent of skin lesions appears questionable. It is also isolated as a symbiont able to confer resistance to abiotic stress, and has been proposed as a potential biocontrol agent to control the aquatic weed Hydrilla spp. Useful websites http://isolate.fusariumdb.org/; http://sppadbase.ipp.cnr.it/; http://www.broad.mit.edu/annotation/genome/fusarium_group/MultiHome.html; http://www.fgsc.net/Fusarium/fushome.htm; http://plantpath.psu.edu/facilities/fusarium-research-center; http://www.phi-base.org/; http://www.uniprot.org/; http://www.cabi.org/; http://www.indexfungorum.org/ [ABSTRACT FROM AUTHOR]

Beet necrotic yellow vein virus ( BNYVV), vectored by Polymyxa betae, causes rhizomania in sugar beet. For disease control, the cultivation of hybrids carrying Rz1 resistance is crucial, but is compromised by resistance-breaking ( RB) strains with specific mutations in the P25 protein at amino acids 67-70 (tetrad). To obtain evidence for P25 variability from soil-borne populations, where the virus persists for decades, populations with wild-type ( WT) and RB properties were analysed by P25 deep sequencing. The level of P25 variation in the populations analysed did not correlate with RB properties. Remarkably, one WT population contained P25 with RB mutations at a frequency of 11%. To demonstrate selection by Rz1 and the influence of RB mutations on relative fitness, competition experiments between strains were performed. Following a mixture of strains with four RNAs, a shift in tetrad variants was observed, suggesting that strains did not mix or transreplicate. The plant genotype exerted a clear influence on the frequency of RB tetrads. In Rz1 plants, the RB variants outcompeted the WT variants, and mostly vice versa in susceptible plants, demonstrating a relative fitness penalty of RB mutations. The strong genotype effect supports the hypothesized Rz1 RB strain selection with four RNAs, suggesting that a certain tetrad needs to become dominant in a population to influence its properties. Tetrad selection was not observed when an RB strain, with an additional P26 protein encoded by a fifth RNA, competed with a WT strain, supporting its role as a second BNYVV pathogenicity factor and suggesting the reassortment of both types. [ABSTRACT FROM AUTHOR]

Plant roots react to pathogen attack by the activation of general and systemic resistance, including the lignification of cell walls and increased release of phenolic compounds in root exudate. Some fungi have the capacity to degrade lignin using ligninolytic extracellular peroxidases and laccases. Aromatic lignin breakdown products are further catabolized via the β-ketoadipate pathway. In this study, we investigated the role of 3-carboxy- cis,cis-muconate lactonizing enzyme ( CMLE), an enzyme of the β-ketoadipate pathway, in the pathogenicity of Fusarium oxysporum f. sp. lycopersici towards its host, tomato. As expected, the cmle deletion mutant cannot catabolize phenolic compounds known to be degraded via the β-ketoadipate pathway. In addition, the mutant is impaired in root invasion and is nonpathogenic, even though it shows normal superficial root colonization. We hypothesize that the β-ketoadipate pathway in plant-pathogenic, soil-borne fungi is necessary to degrade phenolic compounds in root exudate and/or inside roots in order to establish disease. [ABSTRACT FROM AUTHOR]

Rhizoctonia cerealis, the causal agent of sharp eyespot on wheat, was not considered to be an important pathogen for many years. Recently, the disease has become endemic in many countries except for South America. The disease has created a new threat to world wheat production because the damage of wheat sharp eyespot has become increasingly severe. In this paper, previous studies on this pathogen, including the disease geographical distribution, pathogen identification, life cycle, symptoms, favourable environmental conditions, effects on wheat yield and control strategy, are reviewed. Such information will be helpful in management of sharp eyespot. Copyright © 2011 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

BACKGROUND: Rhizobacteria have a good potential to suppress soilborne diseases, but their efficacy against sugarcane pests is rarely reported. Bacterial strains isolated from the rhizosphere of sugarcane were evaluated for their potential to suppress red rot disease on two susceptible varieties, Co-1148 and SPF-234, under field conditions. The strains were also characterised for the production of secondary metabolites associated with their antagonistic activity. RESULTS: One out of four strains, the Pseudomonas putida strain NH-50 (EU627168), reduced disease severity by 44-60% in different field trials. This potent antagonistic strain produced pyoluteorin antibiotic, as confirmed by high-performance liquid chromatography (HPLC). The PltB gene involved in pyoluteorin synthesis was amplified from the P. putida strain NH-50 and sequenced. The extracellular metabolites and volatile and diffusible antibiotics secreted by the tested strains inhibited mycelial growth of Glomerella tucumensis (Speg.) Arx & E Mull in vitro by 7-55%. CONCLUSION: The pyoluteorin-producing bacteria P. putida strain NH-50 significantly reduced disease severity on both sugarcane varieties, irrespective of fungal inoculation, i.e. either inoculated through stem or through soil. This strain also possesses other plant growth characteristics and can be used as a biopesticide for sugarcane crop. Copyright © 2011 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Summary [ABSTRACT FROM AUTHOR]

Bahiagrass ( Paspalum notatum Flueggé) is a poor host of several soilborne pests of vegetable crops; therefore vegetable crops are commonly grown in a rotation with bahiagrass pastures in Florida. The herbicide aminopyralid provides foliar and soil residual weed control and increases forage production in bahiagrass pastures; however, the soil residual activity of aminopyralid makes carryover injury likely in subsequent sensitive vegetable crops. Field research was conducted to determine the sensitivity of five vegetable crops to soil residues of aminopyralid. At an aminopyralid soil concentration of 0.2 µg kg (the limit of quantitation for aminopyralid in this research), crop injury ratings were 48% (bell pepper), 67% (eggplant), 71% (tomato), 3% (muskmelon) and 3% (watermelon), and fruit yield losses (relative to the untreated control) at that concentration were 61, 64, 95, 8 and 14% in those respective crops. The crops included in this research were negatively affected by aminopyralid at soil concentrations less than the limit of quantitation (0.2 µg kg). Therefore, it was concluded that a field bioassay must be used to determine whether carryover injury will occur when these crops are planted on a site where aminopyralid has been previously applied. Copyright © 2011 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Biofumigation, as an environment-friendly alternative to methyl bromide is gaining attention in sustainable agricultural production systems. Based on the biofumigation suppression of growth of three soil-borne filamentous fungi ( Fusarium sp., F. oxysporum and P. aphanidermatum) , Brassica oleracea var . caulorapa was selected from eight Brassica and other plant species as a potential material for the purpose. Powdered tissues of plants were confined to individual Petri dishes without physical contact with each of the following 28 fungal isolates from 16 hosts: 13 Fusarium spp., two Verticillium dahliae, two Ceratocystis fimbriata, Bipolaris sorokiniana, Gaeumannomyces graminis, Ceratobasidium cornigerum, Rhizotonia cerealis, Phytophthora parasitica, Phytophthora capsici, Botrytis cinerea, two Rhizoctonia solani, Sclerotinia sclerotiorum and Magnaporthe grisea. The level of suppression of growth 7 days after inoculation varied. Based on growth suppression, the 28 isolates were grouped into three clusters by Fuzzy clustering: Cluster I contains F. proliferatum with 20.5% suppression, Cluster II composed of 15 isolates, Fusarium sp., two V. dahliae, two C. fimbriata, B. sorokiniana, C. cornigerum, two R. solani, R. cerealis, S. sclerotiorum, P. parasitica and M. grisea, with 75.2–100% suppression and Cluster III consisted of 12 isolates; five F. oxysporum, F. solani, F. azysporum, F. moniliforme, F. graminearum, F. verticillioides, G. graminis, P. capsici with 40.7–66.2% suppression. Ceratobasidium fimbriata and V. dahliae were more sensitive to biofumigation than S. sclerotiorum and F. culmorum when different amounts of ground powder were used. One gram of powder could suppress the growth of the former two up to 68.6% and 68.7%, but the growth suppression in the latter two by 12.7% and 24.0%, respectively. These results indicated that the amount of plant tissue to be used should be considered depending on target pathogen species. The swollen root of B. oleracea var. botrytis appeared a better material than the leaf for achieving suppression of growth in pathogenic fungi. [ABSTRACT FROM AUTHOR]