Identification of in planta bioprotectants against Fusarium wilt in Medicago sativa L. (lucerne) from a collection of bacterial isolates derived from Medicago seeds

Fusarium wilt caused by <i>Fusarium oxysporum</i> f. sp. <i>medicaginis</i> (Fom) is an important disease affecting lucerne/alfalfa cultivations worldwide. <i>Medicago sativa</i> L. (lucerne) is one of the major legume crops in global forage industry. This study aimed to identify bacteria capable of biologically controlling the wilt pathogen through a comprehensive screening of bacterial isolates obtained from domesticated and wild growing <i>Medicago</i> seeds. Using a multi-tiered evaluation pipeline, including <i>in vitro</i>, soil-free and potting mix-based pathogenicity and bioprotection assay systems, the bioprotection efficacy of 34 bacterial isolates derived from <i>Medicago</i> seeds was initially evaluated against six <i>Fusarium</i> strains <i>in vitro</i>. <i>Fusarium oxysporum</i> (Fo) F5189, which has previously been characterized as a <i>Fusarium oxysporum</i> f. sp. <i>medicaginis</i> isolate causing <i>Fusarium</i> wilt in lucerne was selected for <i>in planta</i> assays. Lucerne cultivars Grazer and Sequel, representing susceptible and resistant genotypes were chosen to assess the disease progression. Pathogenicity and bioprotection time-course studies were conducted to understand the temporal dynamics of host-pathogen interactions and efficacy of the bioprotectants. The disease symptoms were scored using a disease rating index developed in this study. The results indicated variability in bioprotection efficacy across bacterial isolates, with some strains suppressing disease in both soil-free and potting mix-based systems. <i>Paenibacillus</i> sp. (Lu_MgY_007; NCBI: PQ756884) and <i>Pseudomonas</i> sp. (Lu_LA164_018; NCBI: PQ756887) were identified as promising bioprotectants against Fusarium wilt under tested growth conditions. The time-course studies highlighted the critical role of persistent biocontrol activity and precise timing of biocontrol application for achieving long-term disease suppression. Overall, the observed reduction in disease severity underscores the potential of these bioprotectants as sustainable strategies for managing Fusarium wilt in lucerne cultivars. However, comprehensive molecular-level analyses are warranted to elucidate the underlying pathogenicity and bioprotection mechanisms, offering valuable insights for the development of more precise and effective future biocontrol strategies in agricultural systems.