Cataloguing Bacterial Endophytes of Calotropis procera against Potato Early Blight

Background. Potato (Solanum tuberosum L.) is a vital food crop, worldwide. It is known for its high nutritious and economic significance, for being a cash and staple crop. However, in Pakistan, its production is seriously hampered by an early blight of potato caused by Alternaria solani, leading to excessive use of fungicides for its control. The current study was conducted to isolate and characterize the endophytic bacteria from Calotropis procera and to identify the secondary metabolites produced by endophytes with the highest antagonism against A. solani. Method. C. procera samples were collected from the fields of MNS University of Agriculture Multan (MNSUAM). The endophytes were isolated from the leaves and roots of C. procera, followed by their morphological and biochemical characterization. The potato early blight samples were collected from the fields of MNSUAM and A. solani isolation was confirmed after their morphological identification. The 8 isolated endophytes were evaluated for their antagonism against potato early blight pathogen through dual culture assay. The best performing isolate was subjected to gas chromatography-mass spectrometry (GC-MS) based secondary metabolites profiling. Results. A total of 8 endophytic isolates were evaluated. Among the tested isolates, C4 exhibited the highest antifungal activity (~70%), significantly inhibiting the growth of A. solani. Endophyte C4 produced potent antimicrobial metabolites that effectively suppressed pathogen growth. Based on GC-MS analysis, the major compounds identified were phenazine-1-carboxylic acid (antibiotic, anti-biofilm), oleic acid (membrane disruptor), and others. Conclusion. The study demonstrated that endophytic bacteria isolated from C. procera, particularly isolate C4, possessed strong antagonistic activity against A. solani. The production of diverse antifungal metabolites highlights their potential as eco-friendly biocontrol agents. These findings support the evaluation of selected endophytes under greenhouse and field conditions for sustainable management of early blight in potato.