Culturable Rhizosphere Fungal Diversity in Healthy and Yellow Leaf Disease Affected Arecanut Palms

Abstract

Yellow leaf disease (YLD) is a destructive disease of arecanut (Areca catechu L.) that is associated with progressive yellowing, root deterioration, reduced nut production, and palm decline. This study compared culturable rhizosphere fungal populations in healthy and YLD-affected arecanut gardens and characterised the isolates using morphological and molecular methods. Twenty-five rhizosphere soil samples were processed using serial dilution plating on rose bengal agar. Fungal colonies were purified on potato dextrose agar, and genomic DNA was extracted. The internal transcribed spacer region was amplified using ITS-1 and ITS-4 primers, sequenced, and analysed through BLAST searches against the NCBI nucleotide database. Healthy rhizosphere soils contained higher populations of beneficial microorganisms than disease-affected soils. Trichoderma species were predominant, particularly T. asperellum and T. harzianum, while Fusarium, Talaromyces, Gibberella, and Diaporthe taxa were also identified. The abundance of Trichoderma isolates in healthy soils was consistent with their recognised associations with root development, nutrient mobilisation, water uptake, and suppression of soil-borne pathogens. The study demonstrates an association between palm health and the composition of culturable rhizosphere fungi and provides a basis for further functional and culture-independent investigations of the arecanut rhizosphere.