Isolation and Morphological Characterization of Endophytic Bacteria and Fungi from Different Castor (Ricinus communis L.) Genotypes

Abstract

Aim: The present investigation aimed to isolate and morphologically characterise culturable bacterial and fungal endophytes associated with diverse castor (Ricinus communis L.) genotypes. Study Design: CRD Place and Duration of Study: Department of Plant Pathology, ICAR-IIOR, Rajendranagar. The study was conducted from January 2025 to February 2026. Results: Healthy root and stem tissues from castor genotypes were surface sterilized and cultured on selective media for endophyte isolation. A total of 222 endophytic isolates, comprising 186 bacterial and 36 fungal isolates, were obtained. Stem tissues yielded a marginally higher number of endophytes (114 isolates) than root tissues (108 isolates), while the highest recovery of endophytes was observed from plants sampled at 30 days after sowing. Bacterial isolates exhibited substantial phenotypic diversity based on colony morphology, including variations in colour, shape, size, texture, elevation, and margin. Gram staining revealed that 137 isolates (73.66%) were Gram-positive, whereas 49 isolates (26.34%) were Gram-negative. Fungal isolates displayed distinct cultural and microscopic characteristics and were tentatively identified as Trichoderma, Aspergillus, Penicillium, and Fusarium species, with Trichoderma representing the predominant genus. The considerable diversity of endophytes observed among different castor genotypes and plant tissues indicates that the composition of the endophytic microbiome is influenced by host genotype and tissue type. Conclusion: Overall, these findings provide a strong foundation for the development of endophyte-based, environmentally sustainable strategies for the biological management of castor root rot and improved crop productivity.