Exploring the diversity and antimicrobial activity of endophytic microorganisms from Nagpur mandarin leaves

Abstract:

This study was conducted from June 2024 to March 2025 at the AICRP on Fruits Scheme Laboratory and the Department of Plant Pathology, Post Graduate Institute, Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Akola. The study aimed to investigate endophytic microorganisms associated with Nagpur mandarin (Citrus reticulata) leaves and evaluate their antimicrobial activity against Colletotrichum gloeosporioides. Endophytic microorganisms were isolated from healthy, asymptomatic leaves of C. reticulata. The isolates were subcultured on fresh media and identified based on their cultural and morphological characteristics, including colony features, hyphal type, and reproductive structures. Molecular identification was performed by ITS rDNA sequencing for fungal isolates and 16S rRNA gene sequencing for the bacterial isolate. Six fungal species were identified from mandarin leaves: Colletotrichum siamense, Diaporthe miriciae, Colletotrichum gigasporum, Aspergillus oerlinghausenensis, Lasiodiplodia curvata, and Aspergillus fumigatus. One bacterial isolate, Pseudomonas fluorescens, was also identified. Cultural and morphological observations of the fungal isolates focused on the mycelium and conidia. Antimicrobial activity was evaluated in vitro using dual-culture assays against the citrus twig blight pathogen C. gloeosporioides. Pseudomonas fluorescens produced the lowest pathogen colony diameter (29.12 mm) and the highest growth inhibition (67.64%). In contrast, A. oerlinghausenensis and L. curvata showed no inhibitory activity (0.00%). Among the effective isolates, C. siamense recorded the lowest inhibition (61.94%). These findings indicate that selected endophytes have potential for the biological control of citrus twig blight and are candidates for further greenhouse and field evaluation.

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