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"Soilborne plant pathogens Control."
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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
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
Major Soilborne Pathogens of Field Processing Tomatoes and Management Strategies
Globally, tomato is the second most cultivated vegetable crop next to potato, preferentially grown in temperate climates. Processing tomatoes are generally produced in field conditions, in which soilborne pathogens have serious impacts on tomato yield and quality by causing diseases of the tomato root system. Major processing tomato-producing countries have documented soilborne diseases caused by a variety of pathogens including bacteria, fungi, nematodes, and oomycetes, which are of economic importance and may threaten food security. Recent field surveys in the Australian processing tomato industry showed that plant growth and yield were significantly affected by soilborne pathogens, especially Fusarium oxysporum and Pythium species. Globally, different management methods have been used to control diseases such as the use of resistant tomato cultivars, the application of fungicides, and biological control. Among these methods, biocontrol has received increasing attention due to its high efficiency, target-specificity, sustainability and public acceptance. The application of biocontrol is a mix of different strategies, such as applying antagonistic microorganisms to the field, and using the beneficial metabolites synthesized by these microorganisms. This review provides a broad review of the major soilborne fungal/oomycete pathogens of the field processing tomato industry affecting major global producers, the traditional and biological management practices for the control of the pathogens, and the various strategies of the biological control for tomato soilborne diseases. The advantages and disadvantages of the management strategies are discussed, and highlighted is the importance of biological control in managing the diseases in field processing tomatoes under the pressure of global climate change.
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
Non-monotonic influence of biochar dose on bean seedling growth and susceptibility to Rhizoctonia solani: the “Shifted Rmax-Effect”
AIMS: Biochar affects the progress of plant diseases caused by soilborne pathogens, frequently featuring U-shaped biochar dose/disease response curves. This study tested this phenomenon in common bean (Phaseolus vulgaris L.) with several biochars. METHODS: Four biochars prepared from two feedstocks (eucalyptus wood and greenhouse wastes) each at 350 and 600 °C were tested on bean seedling growth and infection caused by Rhizoctonia solani at concentrations of 0–3 % by weight. Biochar direct toxicity to R. solani was quantified in vitro. RESULTS: In general, lower concentrations (≤1 %) of biochar suppressed damping-off, whereas higher concentrations (3 %) were ineffective at disease protection. Plant growth in the absence of the pathogen was generally improved at all doses by the four biochars. Maximum growth response (G-Rₘₐₓ) generally occurred at higher biochar doses than maximum disease reduction (D-Rₘₐₓ). Direct toxicity to the pathogen could not explain disease reduction. CONCLUSION: Inverted U-shaped biochar dose/plant growth and biochar dose/disease reduction curves are emerging as common patterns in biochar/crop/pathogen systems. Frequently, the inflection between growth promotion and suppression occurs at different doses than the inflection between disease suppression and promotion. We term this the “Shifted Rₘₐₓ-Effect”. As there is no simple rule-of-thumb for crop/soil/biochar/dose/pathogen combinations, the possible effects of biochar on plant pathogens should not be overlooked.
Journal Article
Effective and Sustained Control of Soil-Borne Plant Diseases by Biodegradable Polyhydroxybutyrate Mulch Films Embedded with Fungicide of Prothioconazole
Soil-borne diseases and plant rhizosphere nematode have caused many crop yield losses. Increased environmental awareness is leading to more restrictions on the use of certain fumigants and root irrigation methods due to their impact on human health and soil system. Therefore, it is necessary to find alternative treatments to maintain crop economic yields and environmental sustainability. In the present work, biodegradable antifungal mulches were prepared by blending poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (PHB) with fungicide of prothioconazole (PRO), which were used for effective and sustained control of soil-borne plant diseases. To reveal the application prospect of the PHB/PRO composite films in the management of soilborne plant diseases, some physical and biological properties were evaluated. The proper mulch film of PHB/PRO was assessed based on its mechanical and optical properties, while water solubility and the film micromorphology was further characterized. The release patterns of composite films under different pH levels were investigated. Moreover, the in vitro antifungal bioassay and pot experiment showed satisfactory bioactivity of the PHB/PRO films against Sclerotium rolfsii Sacc., a soil-borne disease in peanut fields. This study demonstrated that the biodegradable mulch films containing PRO fungicide are capable of inhibiting soil-borne plant pathogenic fungi effectively, and this facile but powerful strategy may find wide applicability in sustainable plant and horticulture protection.
Journal Article
Nucleotides enriched under heat stress recruit beneficial rhizomicrobes to protect plants from heat and root-rot stresses
Background
Plants thrive under biotic and abiotic stresses with the help of rhizomicrobiota. Root exudates play a pivotal role in recruiting beneficial microbes that assist plants in surviving environmental challenges, but the mechanisms of plant-microbiome interactions to resist multiple stresses remain elusive. We investigated how heat stress alters the rhizomicrobiomes of
Panax notoginseng
and how these heat stress-regulated microbes confer enhanced heat tolerance and disease resistance.
Results
We revealed that heat stress at 36 °C caused thermal damage to plants while enhancing heat tolerance and disease resistance for the survival of subsequent plants. Specifically, the beneficial microbes
Burkholderia
sp. and
Saitozyma podzolica
were recruited by the heat-stressed
P. notoginseng
and were confirmed to be responsible for resisting multiple stresses. Heat stress-induced plant roots secrete nucleotides such as purines and pyrimidines to promote the proliferation of these two beneficial microbes rather than root-rot pathogens. The exogenous application of these nucleotides to natural soil also resulted in the enrichment of the same beneficial microbes. Cross-species validation experiments in
Capsicum annuum
(pepper) and
Solanum lycopersicum
(tomato) further demonstrated that co-application of nucleotides with beneficial microbes synergistically enhanced heat tolerance.
Conclusions
Our findings highlight a plant strategy for thriving under multiple adversities and propose a potential pathway by leveraging nucleotide-mediated recruitment of beneficial microbes for enhancing plant resilience against multiple stresses.
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Video Abstract
Journal Article
Control Strategies of Clubroot Disease Caused by Plasmodiophora brassicae
The clubroot disease caused by the soil-borne pathogen Plasmodiophora brassicae is one of the most important diseases of cruciferous crops worldwide. As with many plant pathogens, the spread is closely related to the cultivation of suitable host plants. In addition, temperature and water availability are crucial determinants for the occurrence and reproduction of clubroot disease. Current global changes are contributing to the widespread incidence of clubroot disease. On the one hand, global trade and high prices are leading to an increase in the cultivation of the host plant rapeseed worldwide. On the other hand, climate change is improving the living conditions of the pathogen P. brassicae in temperate climates and leading to its increased occurrence. Well-known ways to control efficiently this disease include arable farming strategies: growing host plants in wide crop rotations, liming the contaminated soils, and using resistant host plants. Since chemical control of the clubroot disease is not possible or not ecologically compatible, more and more alternative control options are being investigated. In this review, we address the challenges for its control, with a focus on biological control options.
Journal Article
The double life of Ceratobasidium: orchid mycorrhizal fungi and their potential for biocontrol of Rhizoctonia solani sheath blight of rice
Ceratobasidium includes orchid mycorrhizal symbionts, plant pathogens and biocontrol agents of soilborne plant pathogens. It is not known to what extent members of the first guild also can participate in the others. Ceratobasidium spp. were isolated from roots of Colombian orchids and identified by phylogeny based on nrITS sequences. Phylogenetic grouping of Ceratobasidium spp. isolates corresponded to orchid host substrate (epiphytic vs. terrestrial). Isolates were tested for virulence on rice and for biocontrol of Rhizoctonia solani, causal agent of sheath blight of rice. All Ceratobasidium spp. isolates caused some signs of sheath blight but significantly less than a pathogenic R. solani used as a positive control. When Ceratobasidium spp. isolates were inoculated on rice seedlings 3 d before R. solani, they significantly reduced disease expression compared to controls inoculated with R. solani alone. The use of Ceratobasidium spp. from orchids for biological control is novel, and biodiverse countries such as Colombia are promising places to look for new biocontrol agents.
Journal Article
Rapid real-time quantitative colorimetric LAMP methodology for field detection of Verticillium dahliae in crude olive-plant samples
Background
Verticilium dahliae
is the most important wilt pathogen of olive trees with a broad host range causing devastating diseases currently without any effective chemical control. Traditional detection methodologies are based on symptoms-observation or lab-detection using time consuming culturing or molecular techniques. Therefore, there is an increasing need for portable tools that can detect rapidly
V. dahliae
in the field.
Results
In this work, we report the development of a novel method for the rapid, reliable and on-site detection of
V. dahliae
using a newly designed isothermal LAMP assay and crude extracts of olive wood. For the detection of the fungus, LAMP primers were designed targeting the internal transcribed spacer (ITS) region of the rRNA gene. The above assay was combined with a purpose-built prototype portable device which allowed real time quantitative colorimetric detection of
V. dahliae
in 35 min. The limit of detection of our assay was found to be 0.8 fg/μl reaction and the specificity 100% as indicated by zero cross-reactivity to common pathogens found in olive trees. Moreover, detection of
V. dahliae
in purified DNA gave a sensitivity of 100% (Ct < 30) and 80% (Ct > 30) while the detection of the fungus in unpurified crude wood extracts showed a sensitivity of 80% when multisampling was implemented. The superiority of the LAMP methodology regarding robustness and sensitivity was demonstrated when only LAMP was able to detect
V. dahliae
in crude samples from naturally infected trees with very low infection levels, while nested PCR and SYBR qPCR failed to detect the pathogen in an unpurified form.
Conclusions
This study describes the development of a new real time LAMP assay, targeting the ITS region of the rRNA gene of
V. dahliae
in olive trees combined with a 3D-printed portable device for field testing using a tablet. The assay is characterized by high sensitivity and specificity as well as ability to operate using directly crude samples such as woody tissue or petioles. The reported methodology is setting the basis for the development of an on-site detection methodology for
V. dahliae
in olive trees, but also for other plant pathogens.
Journal Article