Biocontrol potential of Bacillus subtilis WL2.3 in mitigating Phytophthora infestans infection in potatoes

This research aimed to identify native biocontrol bacteria capable of suppressing Phytophthora infestans in potato crops. A total of forty bacterial strains were isolated from wheat (Triticum aestivum), sunflower (Helianthus annuus), potato (Solanum tuberosum), and cotton (Gossypium herbaceum) plants collected in Sibi, Pakistan. Out of these, ten isolates showed antagonistic effects against P. infestans, with inhibition percentages ranging from 27 to 62%. The isolate WL2.3 exhibited the strongest inhibition at 62%. Furthermore, sporangia germination tests, including those using cell-free supernatants, revealed that WL2.3 and its supernatant inhibited sporangia germination by 65% and 60%, respectively. Strain WL2.3 also showed various traits that promoted growth in plants, including solubility of phosphate, siderophores, ability to synthesize indole-3-acetic acid, cellulose lysis, and generation of hydrogen cyanide. The phylogenetic analysis based on 16S rRNA demonstrated a match of 98.80% with Bacillus subtilis with the GenBank accession number of PQ764123.1. The efficacy of WL2.3 was also experimented in pot experiments to determine its agronomic and pathological effects to potato plants infested with P. infestans. Of the 11 parameters that were considered, eight of them showed a significant improvement: percentage disease index, number of tubers, weight of tubers, length of the shoot, number of leaves, weight of roots, number of roots, and number of shoots. These results indicate that WL2.3 successfully reduced the effects of the oomycete pathogen, as shown by a decrease in the percentage disease index to 46% in the group treated with WL2.3. Thus, WL2.3 is a promising biocontrol agent for plant disease management and growth promotion.