Isolation, Morphological Characterization and In Vitro Interaction Studies of Endophytic Bacteria and Fungi Associated with Pterocarpus Santalinus L.F.

Abstract Endophytic microorganisms colonise internal plant tissues without causing disease and constitute a promising reservoir of bioactive metabolites, particularly in medicinal hosts. Pterocarpus santalinus L.f. (red sanders), an endemic and endangered Indian legume with well-documented antibacterial heartwood, remains poorly explored for its endophytic community. In the present study, leaf and stem tissues of P. santalinus were collected from the Sri Venkateswara University campus, Tirupati, surface sterilised in 95% ethanol and plated on nutrient agar and potato dextrose agar. Four culturable endophytes were recovered i.e., two bacterial (PSEB-L, PaSEB-S) and two fungal (PSEF-L, PSEF-S) one of each from leaf and stem. Gram staining identified PSEB-L as a Gram-positive coccus and PSEB-S as a Gram-positive, slightly curved rod occurring in pairs. Lactophenol cotton blue mounts revealed aseptate hyphae bearing rectangular sporangia in PSEF-L and regularly septate hyphae in PSEF-S. Cross-streak assays showed mutual antagonism between the two bacterial isolates (4 mm inhibition) and marked antagonism of PSEB-S towards Bacillus subtilis (10 mm), whereas Staphylococcus aureus grew unimpeded. In dual culture the two fungal endophytes were mutually compatible, yet both restricted Aspergillus sp. and Fusarium sp.