Isolation and Identification of Antagonistic Rhizobacteria and In vitro Evaluation of their Effectiveness against Postharvest Fungal Rot Pathogens of Apple (Malus domestica)

Aims: Isolation and identification of rhizospheric bacteria with antifungal potential against four postharvest rot fungi of apple fruits were investigated.

Study Design: Completely Randomized Design (CRD) laid out in 10 (rhizospheric bacteria) by 4 (rot fungi) factorial, replicated three times.

Place and Duration of Study: Microbiology Laboratory, Department of Biological Sciences, Bells University of Technology, Ota Ogun State, Nigeria, between 2022 and 2023.

Methodology: Rhizobacteria were isolated from soils using serial dilution and pour plate method. The bacteria were identified using morphological, biochemical, and molecular approaches targeting16S rRNA partial gene sequences. Antagonistic activity of the bacterial isolates were assessed in vitro against Lasiodiplodia theobromae (Lt), Fusarium equiseti (Fe), Pennicillium species (Ps) and Curvularia aeria (Ca) isolated from apple fruits using dual culture procedure. Data were collected on percentage inhibition of radial growth (PIRG). The PIRG data were analyzed using analysis of variance (ANOVA).

Results: Ten rhizobacteria viz: Pseudomonas lactis, Neobacillus kokaensis, Paenibacillus pabuli, Cryseobacterium indologens, Calidifontibacillus erzurumensis, Rossellomorea marisflavi, Bacillus aerius, Brevibacillus reusreri, Stenotrophomonas pavanii and Cytobacillus firmus were isolated. The inhibitory potential of these rhizobacteria against postharvest rot fungi varied (p =.01), with Calidifontibacillus erzurumensis producing highest inhibition of radial growth of Fe (74.5±16.2%), Lt (60.0±4.7%), Ps (60.6±5.2%) and Ca (52.9±5.9%).

Conclusion: Calidifontibacillus erzurumensis has the highest antifungal property against postharvest rot fungi of apple fruits indicating its potential for a sustainable postharvest pest management.