Bioprospecting of Plant Growth-Promoting Rhizobacteria for the Management of Late Leaf Spot Disease

Abstract

Late leaf spot (LLS), caused by Nothopassalora personata, is one of the most destructive foliar diseases limiting groundnut productivity worldwide. The present study aimed to isolate and characterise plant growth-promoting rhizobacteria (PGPR) from the rhizosphere of healthy groundnut plants and evaluate their antagonistic potential against N. personata under in vitro conditions. Rhizospheric soil samples collected from healthy groundnut plants at ICRISAT were used to isolate PGPR using the serial dilution and spread plate techniques. A total of 12 morphologically distinct bacterial isolates were obtained and screened for antagonistic activity using the dual-culture assay. Significant variation was observed among the isolates, with inhibition of mycelial growth ranging from 59% to 92%. The highest inhibition was recorded by isolate IC-PGPR-1 (92%), followed by IC-PGPR-6 (90%). Based on their superior antagonistic activity, these two isolates were selected for molecular identification. Amplification of the 16S rRNA gene using universal primers 27F and 1492R produced an approximately 1,500 bp amplicon in both isolates. BLASTn analysis identified isolate IC-PGPR-1 as Bacillus cereus (99.65% sequence similarity; GenBank accession no. PZ770073) and isolate IC-PGPR-6 as Pseudomonas aeruginosa (99.73% sequence similarity; GenBank accession no. PZ770288). Maximum Likelihood phylogenetic analysis further confirmed the taxonomic identity of both isolates by clustering them with authenticated reference strains. The results demonstrate that indigenous PGPR associated with the groundnut rhizosphere possess promising antagonistic activity against N. personata and represent potential candidates for the development of environmentally sustainable management strategies for late leaf spot disease.