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Bacillus-Mediated-Induced Systemic Resistance (ISR) Against Fusarium Corm Rot
Abstract
Fungi constitute the largest group of plant pathogens responsible for a range of serious plant diseases wherein fungal rot is a major disease associated with the pre- and post-harvest produce of plants. One of the most widely spread rot-causing fungi is Fusarium spp. that include F. oxysporum, F. graminearum, and F. solani that infect bulbs, tubers, rhizomes, and corms and lead to the decomposition of the tissue and finally death of the plant. Under low temperature, fungal infection usually remains dormant which under favorable climatic conditions converts in to disease. As there is a large decline in the annual yield of the crop plant due to Fusarium rots, so this has been an issue of concern since long. Earlier only chemical pesticides were used to control these infections but due to their ill effects on soil fertility, the focus has shifted to the use of biological control agents (BCA). Among BCA, a group comprised of bacilli, pseudomonads, and actinomycetes, together with nonpathogenic organisms Fusarium, Trichoderma, and Streptomyces, played an important role against phytopathogens. BCA helps in plant disease control and growth mainly by two methods: (i) secretion of antimicrobial compounds and (ii) induction of systemic resistance in plants. Bacillus species have been very effective BCA due to their ability to produce heat and desiccation-resistant spores and to withstand high temperature, unfavorable pH, lack of nutrients or water, and the ease of stable formulation preparation. This species can display almost all the mechanisms of a biocontrol and bio-stimulation/fertilization agent.
... This disease severely damages saffron yields in the saffron growing belts of J&K, India. During corm rot infection, Fusarium oxypsorum penetrates the roots and colonizes vascular tissue thereby triggering necrosis and wilting (4). At present, the strategy employed for the control of this disease and for plant growth promotion is the use of chemical fertilizers [4]. ...
... During corm rot infection, Fusarium oxypsorum penetrates the roots and colonizes vascular tissue thereby triggering necrosis and wilting (4). At present, the strategy employed for the control of this disease and for plant growth promotion is the use of chemical fertilizers [4]. The use of these fertilizers is effective but, expensive and due to its overuse it is causing serious environmental problems. ...
... The importance of JA and ET in PGPM-mediated ISR has been demonstrated through the using JA and ET signaling mutants in Arabidopsis, where induction of ISR by P. fluorescens WCS417r was shown to be defective (De Vleesschauwer et al., 2008;Pieterse & Van Loon, 1999). Similar observations have been made in other plant species, such as tomato and rice, as well as with other PGPM, supporting the notion that JA and ET are dominant players in the regulation of the SA-independent systemic immunity conferred by beneficial soilborne microorganisms (De Vleesschauwer et al., 2008;Magotra et al., 2016). ...
In agriculture, the use of plant-associated microorganisms has emerged as an alternative to reduce the excessive use of chemicals and toxic fertilizers. The plant microbiome, composed of a diversity of microorganisms such as bacteria, fungi, algae, and nematodes, plays a fundamental role in plant growth and health, and the use of these microorganisms requires bioprospecting studies to isolate them from agroecosystems similar to those in which they are intended to be applied. These microorganisms can directly promote plant growth through various mechanisms, including the production of phytohormones, nitrogen fixation, phosphate solubilization, and the production of ACC deaminase enzymes. They can also exert indirect effects by combating plant pathogens through the production of antibiotics, lipopeptides, siderophores, and lytic enzymes. Advances in omics technologies have revolutionized the analysis of microbial inoculants' mechanisms of action from different perspectives. Genomics enables the determination of the genetic potential of microorganisms as plant growth promoters. The transcriptomic analysis provides insights into the physiological and metabolic status of these microorganisms. Proteomics is used to identify and quantify proteins related to plant growth-promoting traits. The metabolomic analysis examines the metabolites resulting from the interaction between the genome, transcriptome, and proteome of microorganisms. This comprehensive set of approaches allows for a deeper understanding of the metabolic mechanisms in plant-microorganism interactions which is of vital importance for the development of sustainable agricultural practices.
... The importance of JA and ET in PGPM-mediated ISR has been demonstrated through the using JA and ET signaling mutants in Arabidopsis, where induction of ISR by P. fluorescens WCS417r was shown to be defective (De Vleesschauwer et al., 2008;Pieterse & Van Loon, 1999). Similar observations have been made in other plant species, such as tomato and rice, as well as with other PGPM, supporting the notion that JA and ET are dominant players in the regulation of the SA-independent systemic immunity conferred by beneficial soilborne microorganisms (De Vleesschauwer et al., 2008;Magotra et al., 2016). ...
The microbial inoculant industry, encompassing formulation, commercialization, and use, has witnessed remarkable global growth in recent years. Legal regulations are necessary to ensure the quality of microbial inoculants, protect farmers' and consumers' rights, and guide the commercial promotion of microbial products. However, regulating microbial inoculants remains a worldwide challenge, as they are often classified under chemical fertilizer laws due to the lack of experience with microorganism-based products. The lack of a consensus on the definition of these products and insufficient communication between the scientific community and farmers have hindered their legal regularization. To establish a framework for the development of microbial inoculants, these issues must be addressed. This includes reporting the microbial quality of the products, such as identification, abundance, plant growth-promoting capabilities, and contamination levels. In addition, physical and chemical factors, mode of application, dosage, and other aspects impacting product quality should be considered. Numerous organizations in different countries are currently working towards regulating the production, commercialization, and use of organic inputs in agriculture. Therefore, efforts are needed to define microbial inoculants and standardize regulations across countries, emphasizing cooperation among scientists, producers, sellers, and farmers.
... It was observed that dipping of saffron corms in T. asperellum suspension before sowing reduces the disease by ~ 70% under field conditions (Gupta et al. 2020). One such consortium is shown providing resistance against various pathogens through induced systemic resistance (Magotra et al. 2016). Among bacteria, Bacillus are reported many times with biocontrol activity. ...
Many plant species of family Iridaceae like Crocus, Gladiolus, Iris and Freesia are grown worldwide for their commercially valued flowers and flowering product. All these plants along with other cultivated members are known to get diseases from multiple pathogens. This leads to greater damage in yield causing huge economic losses to farmers and growers. To understand the disease cycle, their cause and prophylactic measures on broader scale, fungal and bacterial pathogens causing corm rot diseases, blight diseases, leaf spot, wilt diseases and viral diseases are discussed. The survey of the reported literature and their analysis revealed that corm and rhizome rot is most devastating disease in all commercially valued species from this family, worldwide. Fungal pathogen Fusarium oxysporum found to be pathogen of major concern. Viral and bacterial disease is equally recurring problem. Yet, suitable and recommended agronomic practices along with use of fungicides and bactericides have potential in preventing spread of pathogens and diseases to nearby fields. The endeavour of the article is to provide summarised information with potential to be utilised by stakeholders for better disease management and prediction.
Fusarium species are cosmopolitan soil phytopathogens from the division Ascomycota, which produce mycotoxins and cause significant economic losses of crop plants. However, soils suppressive to Fusarium diseases are known to occur, and recent knowledge on microbial diversity in these soils has shed new lights on phytoprotection effects. In this review, we synthesize current knowledge on soils suppressive to Fusarium diseases and the role of their rhizosphere microbiota in phytoprotection. This is an important issue, as disease does not develop significantly in suppressive soils even though pathogenic Fusarium and susceptible host plant are present, and weather conditions are suitable for disease. Soils suppressive to Fusarium diseases are documented in different regions of the world. They contain biocontrol microorganisms, which act by inducing plants’ resistance to the pathogen, competing with or inhibiting the pathogen, or parasitizing the pathogen. In particular, some of the Bacillus, Pseudomonas, Paenibacillus and Streptomyces species are involved in plant protection from Fusarium diseases. Besides specific bacterial populations involved in disease suppression, next-generation sequencing and ecological networks have largely contributed to the understanding of microbial communities in soils suppressive or not to Fusarium diseases, revealing different microbial community patterns and differences for a notable number of taxa, according to the Fusarium pathosystem, the host plant and the origin of the soil. Agricultural practices can significantly influence soil suppressiveness to Fusarium diseases by influencing soil microbiota ecology. Research on microbial modes of action and diversity in suppressive soils should help guide the development of effective farming practices for Fusarium disease management in sustainable agriculture.
Twenty five isolates of Burkholderia gladioli, the causal agent of a bacterial disease recently
reported on saffron (Crocus sativus L.) grown in central Sardinia (Italy), were characterized using different
approaches. The characteristic symptoms of the disease on saffron plants were rot of emerging shoots and
leaves and spots on leaves and corms. In the field, the disease was destructive and reduced flowering by
about 80%. Two types of colonies of bacteria cultured from affected plants were selected on the basis of their
characteristic morphology and pigment production on nutrient-glucose-agar. One type was round, wrinkled,
and producing yellowish pigment; while the second was round, smooth and without pigment. All 25 selected
isolates were pathogenic on saffron leaves and corms. Ten were pathogenic on gladiolus and lily leaves.
None of the tested isolates was pathogenic on onion plants. The isolates were characterized by conventional
tests, Biolog, PCR and PCR-RFLP analysis. Conventional tests and PCR identified all isolates as B. gladioli.
PCR-RFLP analysis of 16S rDNA products digested with the three restriction enzymes Alu I, Dde I and
Bss KI, identified ten of the isolates as B. gladioli pv. gladioli. Sequencing and comparison of the 16S rDNA
PCR products confirmed that ten of the isolates were B. gladioli and the remaining 15 were an unidentified
Burkholderia species. Sequencing the gene encoding for β-subunit polypeptide of DNA gyrase (gyrB) did not
assist identification of these isolates. This study suggests that other Burkholderia species are involved with
bacterial softrot of saffron in Sardinia, and further studies are in progress to verify this hypothesis.
Fusarium is a genus of filamentous fungi that contains many agronomically important plant pathogens, mycotoxin producers, and opportunistic human pathogens. Comparative analyses have revealed that the Fusarium genome is compartmentalized into regions responsible for primary metabolism and reproduction (core genome), and pathogen virulence, host specialization, and possibly other functions (adaptive genome). Genes involved in virulence and host specialization are located on pathogenicity chromosomes within strains pathogenic to tomato (Fusarium oxysporum f. sp. lycopersici) and pea (Fusarium 'solani' f. sp. pisi). The experimental transfer of pathogenicity chromosomes from F. oxysporum f. sp. lycopersici into a nonpathogen transformed the latter into a tomato pathogen. Thus, horizontal transfer may explain the polyphyletic origins of host specificity within the genus. Additional genome-scale comparative and functional studies are needed to elucidate the evolution and diversity of pathogenicity mechanisms, which may help inform novel disease management strategies against fusarial pathogens.
Bacillus amyloliquefaciens NJN-6 produces volatile compounds (VOCs) that inhibit the growth and spore germination of Fusarium oxysporum f. sp. cubense. Among the total of 36 volatile compounds detected, 11 compounds completely inhibited fungal growth. The antifungal activity
of these compounds suggested that VOCs can play important roles over short and long distances in the suppression of Fusarium oxysporum.
Systemic acquired resistance is a pathogen-inducible defense mechanism in plants. The resistant state is dependent on endogenous accumulation of salicylic acid (SA) and is characterized by the activation of genes encoding pathogenesis-related (PR) proteins. Recently, selected nonpathogenic, root-colonizing biocontrol bacteria have been shown to trigger a systemic resistance response as well. To study the molecular basis underlying this type of systemic resistance, we developed an Arabidopsis-based model system using Fusarium oxysporum f sp raphani and Pseudomonas syringae pv tomato as challenging pathogens. Colonization of the rhizosphere by the biological control strain WCS417r of P. fluorescens resulted in a plant-mediated resistance response that significantly reduced symptoms elicited by both challenging pathogens. Moreover, growth of P. syringae in infected leaves was strongly inhibited in P. fluorescens WCS417r-treated plants. Transgenic Arabidopsis NahG plants, unable to accumulate SA, and wild-type plants were equally responsive to P. fluorescens WCS417r-mediated induction of resistance. Furthermore, P. fluorescens WCS417r-mediated systemic resistance did not coincide with the accumulation of PR mRNAs before challenge inoculation. These results indicate that P. fluorescens WCS417r induces a pathway different from the one that controls classic systemic acquired resistance and that this pathway leads to a form of systemic resistance independent of SA accumulation and PR gene expression.
Harvest samples of common wheat (Triticum aestivum), oats (Avena sativa), and rye (Secale cereale) from producers in western Canada were analyzed for fungal infection by toxigenic Fusarium species and contamination by trichothecenes and moniliformin (MON). Fusarium graminearum and F. avenaceum were the two most frequently isolated species from samples of rye and wheat collected in 2010. F. poae and F. sporotrichioides were more commonly detected in randomly selected oat seeds. Other toxigenic Fusarium species including F. acuminatum, F. culmorum, and E pseudograminearum as well as Phaeosphaeria nodorum (a.k.a. Septoria nodorum) were recovered primarily from fusarium-damaged kernels of wheat Pure cultures of F. avenaceum, F acuminatum, and other related species known to produce moniliformin were isolated from incubated seeds based on micro- and macromorphological criteria. The phylogenetic analysis inferred from partial DNA sequences of the acl1 and tef-1 alpha genes revealed two major clades representing F. avenaceum and F. acurninatum, respectively. These clades comprised all Canadian isolates of the two species and a number of reference cultures studied earlier for their propensity to form moniliformin in vitro and in planta. However, some reference cultures previously reported to produce significant amounts of moniliformin formed minor phylogenetic lineages that represent rather distinct but closely related species. Concomitantly, cereal samples were analyzed for the presence of deoxynivalenol and moniliformin. These two Fusarium toxins were observed most frequently in common wheat, at concentrations up to 1.1 and 4.0 mg/kg, respectively., There was no apparent relationship between moniliformin concentrations and detection of F. avenaceum and F. acuminatum in rye and oat samples. Geographical analysis of the distribution of moniliformin and F. avenaceum and F. acuminatum across the Canadian Prairies also did not indicate a strong relationship.
Fumonisins are a group of fungal toxins, occurring worldwide in maize infected mainly by Fusarium
verticillioides. This paper describes the level of fumonisins in maize seed samples and the ability of F. verticillioides strains isolated from maize seeds grown in India to produce fumonisins. Forty-three seed samples intended to be used for
consumption were collected from different regions of Karnataka and Andhra Pradesh. The samples were subjected to the agar
plate method for the detection of F. verticillioides. Identification of F. verticillioides was done based on morphological characters and further confirmed by polymerase chain reaction. The majority of the samples
were infected by F. verticillioides and infection percentage in the individual samples ranged from 5 to 51%. Twenty-three out of 35 (65%) strains were positive
for fumonisin production in high performance liquid chromatography (HPLC) and competitive direct-enzyme linked immuno sorbent
assay (CD-ELISA). Fumonisin level in seed samples ranged from 200 to 1,722μg/g using CD-ELISA. HPLC could differentiate FB1
and FB2 toxins; out of 35 strains, 14 (40%) showed both FB1 and FB2 production. These findings indicate that there may be
a risk of human exposure to fumonisins through the consumption of F. verticillioides infected corn-based foods in India.
The international programme to sequence the 4.2 Mb genome of Bacillus subtilis, a model Gram-positive bacterium, is a joint project involving European, Japanese and US research groups. To date ca. 3.0 Mb of the genome has been sequenced, with the remaining 1.2 Mb expected to be completed in 1997. The amenability of B. subtilis to genetic manipulation, combined with the availability of extensive expertise on its biochemistry and physiology, makes this bacterium a valuable organism in which to investigate the properties of genes for which functions cannot be readily ascribed by standard methods.
In the model plant Arabidopsis thaliana, several signal transduction pathways can be activated upon pathogen challenge leading to the activation of different (sets of) effector molecules. In the past it has been demonstrated that these different signal transduction pathways contribute differentially to resistance against distinct microbial pathogens. In this study, it is shown that not all pathogens activate the full set of defence responses. This indicates that depending on the particular interactions between elicitors and suppressors with their cognate plant targets, defence response cascades may or may not become activated during pathogenesis. These findings imply that current models of plant-pathogen interactions must be revised to take into account the pathogen-dependent nature of many defence responses.