Isolation and Characterization of Native Fluorescent Pseudomonas Isolates from Uttarakhand Hills and Their Biocontrol Potential against Tomato Fusarium Wilt

Abstract

Pseudomonas spp. are recognized as efficient plant growth-promoting rhizobacteria (PGPR) with significant potential for the biological management of soil-borne phytopathogens. However, limited information is available regarding the diversity and biocontrol efficacy of native Pseudomonas isolates from the mid and high hill ecosystems of Uttarakhand. Therefore, the present investigation was undertaken during 2025–26 to isolate, characterize, and evaluate native fluorescent Pseudomonas isolates for their antagonistic potential against major soil-borne pathogens. A total of seventy rhizospheric soil samples were collected from seven districts of Uttarakhand covering altitudes ranging from 1370 to 3200 m above mean sea level. Twenty-three fluorescent Pseudomonas isolates were recovered on King’s B medium and characterized through morphological and biochemical assays. All isolates exhibited positive reactions for catalase activity, KOH solubility, and ammonification tests, whereas twelve isolates showed starch hydrolysis activity. In vitro antagonistic evaluation through dual culture assay revealed considerable variability among isolates against Fusarium oxysporum f. sp. lycopersici, Rhizoctonia solani, and Sclerotium rolfsii. Isolates PB1, PB4, and PS40 exhibited more than 75% inhibition of F. oxysporum f. sp. lycopersici, while PU2 showed maximum inhibition against R. solani (94.44%). Screening for biocontrol traits indicated that thirteen isolates produced hydrogen cyanide, whereas ten isolates exhibited phosphate solubilization and siderophore production. Under glasshouse conditions, seed biopriming with isolate PB1 significantly enhanced seed germination (93.33%) and reduced fusarium wilt disease incidence in tomato by 90% over the negative control. The study highlights the potential of native fluorescent Pseudomonas isolates, particularly PB1, as eco-friendly and sustainable biocontrol agents for the management of tomato Fusarium wilt and their possible future exploitation in integrated disease management programmes.