Characterization and valorization of some mycorhizospheric bacteria species as biological control agents against early blight disease of potato (Solanum tuberosum L.) in Algeria

In recent years, biocontrol has emerged as a promising strategy against early blight of potato (Solanum tuberosum L.), a major disease affecting potato crops in Algeria and other North African countries. The aim of this study was to identify native bacteria present in the mycorrhizosphere of Helianthemum ledifolium × T. boudieri and evaluate their antagonistic potential against Alternaria spp. isolates, using both in vitro and in situ assays. The results demonstrated a significant influence of cultural and morphological characteristics on the biocontrol efficacy of the bacterial strains. Specifically, Bacillus sp. and Pseudomonas sp. exhibited strong antagonistic activity, as evidenced by high inhibition rates of mycelial growth of Alternaria strains in vitro. Inhibition rates (IR) ranged from 2% to 90%, depending on the bacterial strain. In the in situ biocontrol experiments, DLA (Disease-Like Activity) assays targeting the interaction between the selected mycorrhizobacteria and Alternaria spp. on potato leaves showed a substantial reduction in disease severity, with the area of infection decreasing by approximately 80%. These findings highlight the potential of utilizing native mycorrhizobacteria as an alternative to chemical fungicides for sustainable potato disease management.