Agricultural Application of Marine Actinobacteria: A 10-Year Overview

Marine actinobacteria represent an underexplored yet highly attractive resource for sustainable agriculture. These actinobacteria, with unique adaptation to saline, oligotrophic, and environmentally fluctuating marine ecosystems, possess unique genomic and physiological properties that enable the production of diverse bioactive compounds, stress-protective metabolites, and hydrolytic enzymes. Members of genera such as Dermacoccus, Micromonospora, Salinispora, and Streptomyces have clearly demonstrated their potential in plant growth promotion, biological control of phytopathogens, and enhancement of plant tolerance to abiotic stresses, particularly salinity. Marine actinobacteria contribute to agricultural productivity through multiple mechanisms, ranging from phytohormone production (e.g., indole-3-acetic acid), siderophore-mediated iron acquisition, phosphate solubilization, nitrogen fixation, 1-aminocyclopropane-1-carboxylic acid deaminase activity, and the production of antimicrobial secondary metabolites effective against fungal pathogens. Their salt-tolerance strategies further strengthen the position of marine actinobacteria as promising bioinoculant candidates for saline degraded areas, which are expanding globally due to climate change and unsustainable agricultural practices. Despite these promising opportunities, challenges remain in strain formulation, large-scale cultivation, regulation of plant–microbe interactions, and validated field trial performance. This chapter reviews the current advancements in the agricultural applications of plant growth-promoting marine actinobacteria and their mechanisms from published literature reported within the past 10 years. Emphasis is also focused on their roles in enhancing plant growth under both biotic and abiotic stress conditions to improve crop productivity.