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0INTERNATIONAL SCIENTIFIC AND PRACTICAL CONFERENCE "STATUS AND DEVELOPMENT PROSPECTS OF FUNDAMENTAL AND APPLIED MICROBIOLOGY: THE VIEWPOINT OF YOUNG SCIENTISTS" _25-26 SEPTEMBER, 2024_
POTENTIAL AND APPLICATIONS OF ACTINOBACTERIA IN AGRICULTURAL BIOCONTROL MANAGEMENT
*Syed Khalida Izhar, 2Shareen Fatima Rizvi, 3Uzma Afaq, 4Saba Siddiqui
Research Scholar, Dept. of Biosciences, Integral University, 2Research Scholar, Dept. of Biosciences, Integral University, 3Assistant Professor, Dept. of Biosciences, Integral University, 4Professor, Dept. of Agriculture, Integral Institute of Agricultural Science and Technology,
Integral University https://doi.org/10.5281/zenodo.13827540
Abstract. Microbial pathogens that impact plant health pose a significant risk to global agricultural output. The persistent use of pesticides for the control of plant diseases has resulted in significant ecological damage and the emergence of pathogen resistance. Moreover, the increasing expenses associated with chemical-based management techniques and the consumer's desire for chemical-free agricultural products have led to the adoption of alternative and sustainable approaches. Naturally existing non-pathogenic microorganisms offer a highly promising and environmentally friendly approach for controlling plant diseases. The effectiveness of Bacillus subtilis and Trichoderma spp. as biocontrol agents has prompted researchers to explore other biocontrol agents. Recently, the filamentous Actinobacteria has emerged as a highly promising other option. Like other biocontrol agents and plant growth-promoting rhizobacteria, Actinobacteria depend on roughly same processes to control plant diseases and stimulate plant growth. The well acknowledged processes of biocontrol encompass competition for a specific niche or substrate, application of lytic enzymes, and synthesis of inhibitory compounds that counteract plant diseases. These helpful microorganisms simultaneously enhance the immune response of host plants against a wide range of diseases and other abiotic stressors. This chapter elucidates the intricate methods by which Actinobacteria function as biocontrol agents in the biological control of plant diseases.
Keywords: Actinobacteria, Rhizosphere, PGPR, agriculture sustainability.
Introduction
The rhizosphere microbiota has a crucial function in both the pathogenesis of plant illnesses and the defence of plants against detrimental pathogens. The efficient management of plant diseases by rhizospheric soil bacteria, especially those with antagonistic characteristics, makes them a promising candidate for the creation of biological control agents (BCAs) [1]. Furthermore, the ability of plants to survive and thrive in challenging environmental conditions is frequently ascribed to the protection provided by endophytic microbes against soil-borne diseases and the stimulation of plant growth. Microbial species, namely actinobacteria, also referred to as actinomycetes, obtained from the rhizosphere and phyllosphere of plants, have been identified as possible agents that can eliminate fungi and bacteria that inflict harm upon agriculturally significant plants [2]. In the realm of bacteria, actinobacteria, also referred to as actinomycetes, have been identified as promising agents for eliminating fungi and bacteria when obtained from both rhizospheres and the phyllosphere. Therefore, actinobacteria have emerged as a very promising reservoir of biochemically active compounds (BCAs), and their use as BCAs has greatly grown in the past twenty years. A study was conducted to investigate the antagonistic characteristics of actinobacteria against Pythium-causing illness in sugarcane. Subsequently, a
INTERNATIONAL SCIENTIFIC AND PRACTICAL CONFERENCE "STATUS AND DEVELOPMENT PROSPECTS OF FUNDAMENTAL AND APPLIED MICROBIOLOGY: THE VIEWPOINT OF YOUNG SCIENTISTS" _25-26 SEPTEMBER, 2024_
comprehensive examination was carried out to assess the biocontrol features of actinomycetes against various microorganisms, including soil-borne plant infections such as Phytophthora spp. In subsequent studies, the biocontrol properties of actinomycetes were investigated in relation to soil-borne plant diseases, namely Phytophthora spp. [3], These findings have been convincingly shown in multiple investigations. Moreover, Actinobacteria indirectly contribute to disease suppression in soil by enhancing root nodulation efficiency, facilitating plant growth in the legume Pisum sativum, and bolstering plant immunity in many plants including Arabidopsis and apple trees [4]. Actinobacteria-derived commercial pharmaceuticals, such as Mycostops (Streptomyces griseoviridis strain K61) and Actinovate (Streptomyces lydicus strain WYEC108), have shown effective in controlling plant diseases, particularly crop damping-off [5]. Infections caused by Fusarium and Alternaría have been treated with biofungicides derived from S. griseoviridis. Other research has shown that actinomycetes belonging to the genus Streptomyces are being commercially employed for the purpose of controlling diverse plant diseases [3]. The primary factors attributable to the antibacterial and plant growth enhancement by Actinobacteria are their capacity to synthesise a diverse range of secondary metabolites. In addition, actinomycetes are recognised for their ability to stimulate plant development post colonisation of interior plant tissues, without inducing any adverse effects. The antimicrobial activity of Micromonospora sp. obtained from healthy tomato plants against Fusarium oxysporum sp. lycopersici has been investigated. The endophytic strains of actinomycetes are presumed to synthesise antibacterial compounds within the plants they inhabit [6]. Moreover, the endophytic actinomycetes have been clearly shown to enhance the development of host plants and alleviate disease symptoms in different climatic conditions. Further exploration of the physiological and molecular relationships between endophytic actinomycetes and plants could reveal more advantageous applications in promoting plant growth. Consequently, the implementation of biocontrol measures can be highly beneficial when combined with chemical management strategies [7]. Thus far, a significant proportion (50%) of the many compounds derived from microorganisms have been extracted from actinomycetes. Among actinobacteria, the species Streptomyces alone has produced 60% of the agricultural compounds, followed by Micromonospora. Additionally, these compounds exhibit insecticidal properties [3]. A comprehensive knowledge of the interaction processes, namely the intimate relationship between actinobacteria and plants as both endophytes and free-living organisms in the rhizosphere, moreover, their capacity to stimulate plant development will be advantageous for their future utilisation in agriculture.
Biocontrol mechanisms of Actinobacteria to control plant diseases
Similar to other biological control agents (BCAs) as Trichoderma and plant growth-promoting fungi (PGPRs), actinomycetes are linked to enhancing root length and seedling immune response. Various studies have shown the potent plant growth-promoting effects of actinomycetes on tomato seedlings [5]. Research has documented the promotion of plant growth by the strains of Streptomyces sp. CA-2 and AA-2, as well as their capacity to furnish plant defence against harmful fungus. The crucial significance of their capacity to dissolve inorganic phosphate and fix nitrogen is well recognised. Their efficacy as inhibiting agents against different phytopathogens has been ascribed to the synergistic use of hydrolytic enzymes and antibiotic synthesis [8]. As an illustration, the severity of root-rot in Banksia grandis caused by Phytophthora cinnamomic was reduced by combining cellulose and P-glucosidase-producing isolate of Micromonospora carbonacea with an antagonistic antibiotic-producing strain of Streptomyces violascens. This
INTERNATIONAL SCIENTIFIC AND PRACTICAL CONFERENCE "STATUS AND DEVELOPMENT PROSPECTS OF FUNDAMENTAL AND APPLIED MICROBIOLOGY: THE VIEWPOINT OF YOUNG SCIENTISTS" 25-26 SEPTEMBER, 2024
reduction may be attributed to the pathogen's susceptibility to antibiotics and the action of the hydrolytic enzyme.
Fig.1 Biocontrol mechanism of Actinobacteria
CONCLUSION
The widespread application of pesticides in the control of several plant diseases has resulted in the emergence of resistance to these substances. Moreover, the detrimental impacts of chemicals on the environment are amplifying worries and prompting calls for sustainable and environmentally friendly methods. Utilising antagonistic microorganisms to control plant diseases seems to be a viable and ecologically sound approach to address this problem. To this end, microorganisms, namely actinobacteria, have emerged as a highly promising option. The biosynthesis of several secondary metabolites and antimicrobial enzymes by these microorganisms makes them very valuable not only in the pharmaceutical and commercial industries, but also in terms of agricultural significance. Enhanced comprehension of the processes implicated in the antagonistic activities and advantages provided to the host plant by stimulation of resistance and growth promotion will facilitate the development of sustainable, superior, and more effective plant disease control systems. Contemporary molecular techniques, such as in vivo expression technology (IVET), recombination in expression technology (RIVET), and transgenic development, are used to evaluate the functionality of genes, Further research will enhance our comprehension of antagonistic mechanisms and the molecular repertoire employed by these advantageous microorganisms to infiltrate, outcompete, establish colonies, and inhibit pathogens. The establishment of roots is a crucial determinant of the effectiveness of biological control agents (BCAs). Although actinobacteria have shown great promise in laboratory and greenhouse experiments , vegetability and root colonisation, competition from indigenous microflora, impact of environmental conditions on these advantageous microorganisms, and biocontrol activity of these microorganisms linked to the synthesis of antibiotic arsenal, both lytic enzymes and secondary metabolites have the potential to undergo resistance development similar to that of synthetic chemicals produced by humans in natural environments. This issue requires attention.
INTERNATIONAL SCIENTIFIC AND PRACTICAL CONFERENCE "STATUS AND DEVELOPMENT PROSPECTS OF FUNDAMENTAL AND APPLIED MICROBIOLOGY: THE VIEWPOINT OF YOUNG SCIENTISTS" _25-26 SEPTEMBER, 2024_
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