Role of Actinomycetes metabolites in nematode management Ch. Akhila1, K. Sankari Meena2, M.V. Deborah1, K. Pranahitha1 and P. Manju3 1. Professor Jayashankar Telangana Agricultural University, Hyderabad 2. ICAR-Indian Institute of Oilseeds Research, Hyderabad 3. Kumaraguru Institute of Agriculture, Tamil Nadu Introduction Modern agriculture faces the challenge of increasing crop productivity while conserving natural resources and protecting the environment. Although chemical fertilizers and pesticides have contributed greatly to agricultural production, their excessive or indiscriminate use can adversely affect soil and water ecosystems and may pose risks to human and environmental health. Growing awareness among farmers and consumers has therefore increased the demand for safe and sustainable crop protection technologies. Microorganism-based products offer an important alternative for reducing dependence on agrochemicals. Among beneficial microorganisms, actinomycetes, particularly members of the genus Streptomyces, are well known for producing a wide range of biologically active secondary metabolites. These microorganisms are prolific producers of antibiotics and other natural products and have considerable potential for agricultural applications. Plant-parasitic nematodes (PPNs) are major constraints to crop production. They damage plant roots, interfere with water and nutrient uptake and may interact with fungal and bacterial pathogens, resulting in disease complexes. Actinomycetes are gaining attention as biological tools for nematode management because of their ability to produce nematicidal metabolites, enzymes and volatile compounds and to stimulate plant defence mechanisms. Bioactive substances of actinomycetesActinomycetes produce diverse bioactive compounds that contribute to the suppression of plant pathogens and nematodes. Important metabolites include actinomycins, avermectins and other secondary metabolites, while enzymes such as chitinases, proteases, cellulases and lipases may contribute to the degradation of nematode eggshells and cuticular structures. Some actinomycetes also produce siderophores and plant-growth-promoting substances such as indole-3-acetic acid (IAA). Their nematicidal activity can occur through several mechanisms. Actinomycetes colonizing the rhizosphere can produce compounds that affect nematode movement, egg hatching, juvenile survival and development. Volatile compounds may inhibit nematode activity, while interaction with plants can stimulate defence responses. Thus, actinomycetes provide both direct and indirect protection against nematode damage. Actinomycetes in root-knot nematode managementRoot-knot nematodes (Meloidogyne spp.) are among the most economically important nematodes because of their wide host range and ability to establish feeding sites within plant roots. Several studies have demonstrated the potential of Streptomyces spp. to reduce root-knot nematode populations and disease severity in different crops. Application of Streptomyces to soil or the rhizosphere can reduce root galling and improve plant growth. These effects may result from direct nematicidal activity as well as activation of plant defence mechanisms. Actinomycetes can also influence the rhizosphere microbial community by enhancing beneficial microorganisms and suppressing certain harmful populations, thereby improving the biological environment around plant roots. Streptomyces avermitilis – a promising source of nematicidal metabolitesAmong actinomycetes, Streptomyces avermitilis is particularly important because of its ability to produce avermectins, macrocyclic lactone compounds with potent activity against insects and nematodes. Avermectins act mainly on glutamate-gated chloride channels in invertebrates, causing hyperpolarization of nerve and muscle cells, followed by paralysis and death. Eight naturally occurring avermectin components have been identified, comprising four major components—A1a, A2a, B1a and B2a—and four minor components—A1b, A2b, B1b and B2b. Their biological activity has contributed to the development of commercially important pest and nematode management products. Abamectin – an important avermectin-based nematicideAbamectin, consisting predominantly of avermectin B1a with a smaller proportion of B1b, is an important avermectin-based compound used against several insect and nematode pests. It acts on glutamate-gated chloride channels and disrupts neuromuscular activity, resulting in paralysis and death of susceptible nematodes. Nematicidal activity has been reported against several economically important nematodes, including Pratylenchus penetrans, Rotylenchulus reniformis, Meloidogyne incognita and cyst nematodes such as Heterodera schachtii, H. avenae and H. carotae. The development of avermectin-based compounds demonstrates the practical value of actinomycete-derived metabolites in crop protection. Streptomyces lactacystinicus against pine wood nematodeSecondary metabolites produced by Streptomyces lactacystinicus strain TCS19-048 showed strong activity against the pine wood nematode, Bursaphelenchus xylophilus. An ethyl acetate extract produced approximately 99.6% mortality of juvenile and adult nematodes at 2 mg mL⁻¹. The active fraction also inhibited nematode movement and increased leakage of body fluids, suggesting a direct toxic effect. Other Streptomyces species with nematicidal potentialSeveral other Streptomyces species have demonstrated nematicidal activity against Meloidogyne spp. Culture filtrates and metabolites of S. cacaoi, S. albogriseolus, S. rubrogriseus and S. antibioticus have shown activity against juvenile stages. Culture filtrates of S. rubrogriseus and S. cacaoi have also been reported to reduce egg hatching of M. incognita. These findings indicate that actinomycetes can affect different stages of the nematode life cycle, including egg hatching, juvenile movement, development and survival. Future prospects and conclusionActinomycetes, particularly Streptomyces spp., represent an important microbial resource for sustainable management of plant-parasitic nematodes. Their ability to produce diverse secondary metabolites, hydrolytic enzymes and volatile compounds, together with their plant-growth-promoting and defence-inducing properties, provides multiple opportunities for nematode suppression. The discovery of avermectins from S. avermitilis and their utilization in compounds such as abamectin demonstrate the practical importance of actinomycete metabolites in crop protection. Other species, including S. lactacystinicus, S. cacaoi, S. rubrogriseus, S. albogriseolus and S. antibioticus, further highlight the potential of this microbial group. Future research should focus on discovering novel nematicidal metabolites, understanding their modes of action, improving production and formulation technologies, and validating their efficacy under greenhouse and field conditions. Integration of actinomycetes with resistant cultivars, other biological control agents and suitable agronomic practices could provide effective and environmentally compatible nematode management. Harnessing the metabolic diversity of actinomycetes can contribute to reducing dependence on chemical nematicides and developing safer and sustainable approaches for managing plant-parasitic nematodes. References: 1. Solanki, M.K., Malviya, M.K. and Wang, Z. 2016. Actinomycetes bio-inoculants: A modern prospectus for plant disease management. In: Plant growth promoting Actinobacteria: a new avenue for enhancing the productivity and soil fertility of grain legumes (63-81). Singapore: Springer Singapore. 2. Zayed, M.S., Abdelhafez, A.A.M., Mahgoob, A.E. and Radwan, W.H. 2025. Streptomyces avermitilis and its metabolites for managing the plant-parasitic nematodes: A Review. Arab Universities Journal of Agricultural Sciences, 33(2): 183-197. 3. Shen, J., Zhang, C., Zhang, S., Chen, F., Pei, F., Zhou, S. and Lin, H. 2022. Screening, isolation and mechanism of a nematicidal extract from actinomycetes against the pine wood nematode Bursaphelenchus xylophilus. Heliyon, 8(11): e11717.