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"Soilborne pathogens"
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Wilted : pathogens, chemicals, and the fragile future of the strawberry industry
\"Wilted tells how, in the face of emergent soil pathogens, the California strawberry industry came to rely on the use of highly toxic soil fumigants. Once widely adopted, fumigation reverberated throughout the rest of the production system--in plant breeding, land access, labor practices, marketing, and more, bringing tremendous productivity. Yet, the very entanglements of plants, soils, chemicals, climate, and laboring bodies that once made strawberry production so lucrative in the Golden State have now turned into a set of interlocking threats, especially as social and ecological conditions beyond the industry's control bear down on growers\"--Provided by publisher.
Book
Chlorine and mefenoxam sensitivity of Phytophthora nicotianae and Phytopthora citrophthora from South African citrus nurseries
Phytophthora nicotianae and P. citrophthora isolates were subjected to mefenoxam and chlorine sensitivity evaluations at different concentrations, and for chlorine, different exposure times. Based on mefenoxam sensitivity, the isolates of the two species were divided in six sensitivity groups with EC50 values ranging from sensitive (0.04 ppm mefenoxam) to highly insensitive (greater than 123.69 ppm mefenoxam), with 86% of isolates being sensitive to mefenoxam. Chlorine sensitivity testing indicated strong interactions between chlorine concentration and exposure time for both species. Increased mortality was observed with increased concentration and exposure time to chlorine. For some isolates, close to 100% mortality was only reached at 6 ppm active chlorine and at an exposure time of 60 min. Because highly mefenoxam-insensitive isolates were detected from South African citrus nurseries, this fungicide should be used with care as a curative method for management of diseases caused by Phytophthora spp. It is recommended that chlorination of irrigation water, at 6 ppm active chlorine and exposure of more than 60 min, is used to eliminate P. nicotianae and P. citrophthora propagules from irrigation water as a preventative measure for these diseases.
Journal Article
Methods for Management of Soilborne Diseases in Crop Production
The significant problems caused by soilborne pathogens in crop production worldwide include reduced crop performance, decreased yield, and higher production costs. In many parts of the world, methyl bromide was extensively used to control these pathogens before the implementation of the Montreal Protocol—a global agreement to protect the ozone layer. The threats of soilborne disease epidemics in crop production, high cost of chemical fungicides and development of fungicide resistance, climate change, new disease outbreaks and increasing concerns regarding environmental as well as soil health are becoming increasingly evident. These necessitate the use of integrated soilborne disease management strategies for crop production. This article summarizes methods for management of soilborne diseases in crop production which includes the use of sanitation, legal methods, resistant cultivars/varieties and grafting, cropping system, soil solarization, biofumigants, soil amendments, anaerobic soil disinfestation, soil steam sterilization, soil fertility and plant nutrients, soilless culture, chemical control and biological control in a system-based approach. Different methods with their strengths and weaknesses, mode of action and interactions are discussed, concluding with a brief outline of future directions which might lead to the integration of described methods in a system-based approach for more effective management of soilborne diseases.
Journal Article
The rhizosphere: a playground and battlefield for soilborne pathogens and beneficial microorganisms
The rhizosphere is a hot spot of microbial interactions as exudates released by plant roots are a main food source for microorganisms and a driving force of their population density and activities. The rhizosphere harbors many organisms that have a neutral effect on the plant, but also attracts organisms that exert deleterious or beneficial effects on the plant. Microorganisms that adversely affect plant growth and health are the pathogenic fungi, oomycetes, bacteria and nematodes. Most of the soilborne pathogens are adapted to grow and survive in the bulk soil, but the rhizosphere is the playground and infection court where the pathogen establishes a parasitic relationship with the plant. The rhizosphere is also a battlefield where the complex rhizosphere community, both microflora and microfauna, interact with pathogens and influence the outcome of pathogen infection. A wide range of microorganisms are beneficial to the plant and include nitrogen-fixing bacteria, endo- and ectomycorrhizal fungi, and plant growth-promoting bacteria and fungi. This review focuses on the population dynamics and activity of soilborne pathogens and beneficial microorganisms. Specific attention is given to mechanisms involved in the tripartite interactions between beneficial microorganisms, pathogens and the plant. We also discuss how agricultural practices affect pathogen and antagonist populations and how these practices can be adopted to promote plant growth and health.
Journal Article
Early Detection of Fusarium oxysporum Infection in Processing Tomatoes (Solanum lycopersicum) and Pathogen–Soil Interactions Using a Low-Cost Portable Electronic Nose and Machine Learning Modeling
The early detection of pathogen infections in plants has become an important aspect of integrated disease management. Although previous research demonstrated the idea of applying digital technologies to monitor and predict plant health status, there is no effective system for detecting pathogen infection before symptomatology appears. This paper presents the use of a low-cost and portable electronic nose coupled with machine learning (ML) models for early disease detection. Several artificial neural network models were developed to predict plant physiological data and classify processing tomato plants and soil samples according to different levels of pathogen inoculum by using e-nose outputs as inputs, plant physiological data, and the level of infection as targets. Results showed that the pattern recognition models based on different infection levels had an overall accuracy of 94.4–96.8% for tomato plants and between 94.81% and 96.22% for soil samples. For the prediction of plant physiological parameters (photosynthesis, stomatal conductance, and transpiration) using regression models or tomato plants, the overall correlation coefficient was 0.97–0.99, with very significant slope values in the range 0.97–1. The performance of all models shows no signs of under or overfitting. It is hence proven accurate and valid to use the electronic nose coupled with ML modeling for effective early disease detection of processing tomatoes and could also be further implemented to monitor other abiotic and biotic stressors.
Journal Article
Plastic mulch film residues in agriculture: impact on soil suppressiveness, plant growth, and microbial communities
Abstract
Plastic mulch film residues have been accumulating in agricultural soils for decades, but so far, little is known about its consequences on soil microbial communities and functions. Here, we tested the effects of plastic residues of low-density polyethylene and biodegradable mulch films on soil suppressiveness and microbial community composition. We investigated how plastic residues in a Fusarium culmorum suppressive soil affect the level of disease suppressiveness, plant biomass, nutrient status, and microbial communities in rhizosphere using a controlled pot experiment. The addition of 1% plastic residues to the suppressive soil did not affect the level of suppression and the disease symptoms index. However, we did find that plant biomasses decreased, and that plant nutrient status changed in the presence of plastic residues. No significant changes in bacterial and fungal rhizosphere communities were observed. Nonetheless, bacterial and fungal communities closely attached to the plastisphere were very different from the rhizosphere communities with overrepresentation of potential plant pathogens. The plastisphere revealed a high abundance of specific bacterial phyla (Actinobacteria, Bacteroidetes, and Proteobacteria) and fungal genera (Rhizoctonia and Arthrobotrys). Our work revealed new insights and raises emerging questions for further studies on the impact of microplastics on the agroecosystems.
Plastic mulch film residues did not change soil suppressiveness level in short-term experiment but created a new niche “plastisphere” that harbors a distinct microbial community dominated by potential fungal pathogens.
Journal Article
A microbial consortium in the rhizosphere as a new biocontrol approach against fusarium decline of chickpea
Background and aim: Chickpea (Cicer arietinum L.) is an important crop worldwide. Fungi of the genus Fusarium are among the most aggressive pathogens of chickpea, causing plant wilt and/or root rot. The incidence of soilbome pathogens can be reduced by increasing the microbial diversity in the rhizosphere. To improve soil suppressiveness against Fusarium spp., we optimized a microbial consortium consisting in a mixture of bacterial isolates selected from the naturally occurring microflora in the chickpea rhizosphere. Methods: Beneficial rhizobacteria were selected based on i) their mutual compatibility when grown in mixture, ii) antagonistic activity against F. oxysporum f. sp. ciceris race 0 and F. solani f. sp. pisi and iii) growth promoting capacity on chickpea. Results: The best results were obtained by using a consortium consisting of a mixture of four bacterial isolates: Serratia marcescens isolate 59, Pseudomonas fluorescens isolate 57, Rahnella aquatilis isolate 36 and Bacillus amyloliquefaciens isolate 63. Conclusions: This microbial consortium efficiently controlled both Fusarium pathogens, with a consistently higher efficacy compared to those of bacteria applied individually. The putative mechanisms involved in the interaction between antagonists, plant and Fusarium are discussed.
Journal Article
Grafting Snake Melon Cucumis melo L. subsp. melo Var. flexuosus (L.) Naudin in Organic Farming: Effects on Agronomic Performance; Resistance to Pathogens; Sugar, Acid, and VOC Profiles; and Consumer Acceptance
The performance of snake melon [Cucumis melo var. flexuosus (L.)] in organic farming was studied under high biotic and salt stress conditions. Soilborne diseases (mainly caused by Macrophomina phaseolina and Neocosmospora falciformis), combined with virus incidence [Watermelon mosaic virus (WMV), Zucchini yellow mosaic virus (ZYMV), and Tomato leaf curl New Delhi virus (ToLCNDV)] and Podosphaera xanthii attacks, reduced yield by more than 50%. Snake melon susceptibility to M. phaseolina and Monosporascus cannonballus was proved in pathogenicity tests, while it showed some degree of resistance to Neocosmospora keratoplastica and N. falciformis. On the contrary, salt stress had a minor impact, although a synergic effect was detected: yield losses caused by biotic stress increased dramatically when combined with salt stress. Under biotic stress, grafting onto the melon F1Pat81 and wild Cucumis rootstocks consistently reduced plant mortality in different agroecological conditions, with a better performance compared to classic Cucurbita commercial hybrids. Yield was even improved under saline conditions in grafted plants. A negative effect was detected, though, on consumer acceptability, especially with the use of Cucurbita rootstocks. Cucumis F1Pat81 rootstock minimized this side effect, which was probably related to changes in the profile of sugars, acids, and volatiles. Grafting affected sugars and organic acid contents, with this effect being more accentuated with the use of Cucurbita rootstocks than with Cucumis. In fact, the latter had a higher impact on the volatile organic compound profile than on sugar and acid profile, which may have resulted in a lower effect on consumer perception. The use of Cucumis rootstocks seems to be a strategy to enable organic farming production of snake melon targeted to high-quality markets in order to promote the cultivation of this neglected crop.
Journal Article
Diversity of Phytophthora Species Detected in Disturbed and Undisturbed British Soils Using High-Throughput Sequencing Targeting ITS rRNA and COI mtDNA Regions
Disease outbreaks caused by introduced Phytophthora species have been increasing in British forests and woodlands in recent years. A better knowledge of the Phytophthora communities already present in the UK is of great importance when developing management and mitigation strategies for these diseases. To do this, soils were sampled in “disturbed” sites, meaning sites frequently visited by the public, with recent and new plantings or soil disturbances versus more “natural” forest and woodland sites with little disturbance or management. Phytophthora diversity was assessed using high-throughput Illumina sequencing targeting the widely accepted barcoding Internal Transcribed Spacer 1 (ITS1) region of rRNA and comparing it with the mitochondrial cytochrome c oxidase I (COI) gene. Isolation of Phytophthora was run in parallel. Nothophytophthora spp. and Phytophthora spp. were detected in 79 and 41 of the 132 locations of the 14 studied sites when using ITS or COI, respectively. A total of 20 Phytophthora amplicon sequence variants (ASVs) were assigned to known Phytophthora species from eight clades (1a, 2, 2b, 3a, 5, 6b, 7a, 8b, 8c, 8d, 10a, and 10b) and 12 ASVs from six clades (1a, 2c, 3a, 3b, 6b, 7a, 8b, 8c, and 8d) when using ITS or COI, respectively. Only at two locations were the results in agreement for ITS, COI, and isolation. Additionally, 21 and 17 unknown Phytophthora phylotypes were detected using the ITS and COI, respectively. Several Phytophthora spp. within clades 7 and 8, including very important forest pathogens such as P. austrocedri and P. ramorum, were identified and found more frequently at “disturbed” sites. Additionally, eight ASVs identified as Nothophytophthora spp. were detected representing the first report of species within this new genus in Britain. Only three species not known to be present in Britain (P. castaneae, P. capsici, and P. fallax) were detected with the ITS primers and not with COI. To confirm the presence of these or any potential new Phytophthora species, sites should be re-sampled for confirmation. Additionally, there is a need to confirm if these species are a threat to British trees and try to establish any eradication measures required to mitigate Phytophthora spread in Britain.
Journal Article
DISEASES CAUSED BY SOILBORNE PATHOGENS: BIOLOGY, MANAGEMENT AND CHALLENGES
Soilborne pathogens cause severe diseases in many crops. They have common features based on their close connection with the soil, which has a strong influence on their survival and capacity to cause disease. The latter stems from interactions between the pathogen and the host, which both in turn interact with the biotic and abiotic components of the environment. Soilborne pathogens produce resting structures which, in the absence of a host, are inactive, and are therefore protected from the soil's hostile activities due to fungistasis. However, in the presence of root exudates of a susceptible host in the rhizosphere, or an adequate nutrient source, they germinate and infect the plant, pending suitable conditions. In addition, soilborne pathogens may colonize the roots of plants that are not their major host, without inducing visible symptoms. Soilborne pathogens have many mechanisms for their spatial dispersal, e.g., through infected propagation material. Basic management strategy involves disruption of one or more of the disease components, at any stage of disease development, to achieve an economic reduction in disease with minimal disturbance to the environment. This is achieved by chemical, physical, biological, cultural, physiological and genetic approaches, using soil disinfestation (fumigation, soil solarization, biofumigation, anaerobic soil disinfestation), biocontrol, organic amendments, resistant cultivars and grafting, fungicides, cultural practices, induced resistance and others. These should be carried out in the framework of integrated pest-management programs. Many challenges remain. We need to study the gap between the promising results obtained under controlled conditions and the modest results obtained under realistic ones. A better understanding of the mechanisms and modes of action of the involved processes should provide new tools for disease management.
Journal Article