Isolation and Enumeration of Soil Bacterial Population Associated with Rhizosphere Soils of Yellow Leaf Disease of Arecanut
K. Premalatha *
Centre of Excellence on Watershed Management, University of Agricultual Sciences, Bangalore, India.
Gangadhara Naik
Department of Plant Pathology, Keladi Shivappa Nayaka University of Agricultural and Horticultural Sciences, Shivamogga, India.
K. M. Satish
Keladi Shivappa Nayaka University of Agricultural and Horticultural Sciences, Shivamogga, India.
B. C. Dhananjaya
Department of Soil Science, Keladi Shivappa Nayaka University of Agricultural and Horticultural Sciences, Shivamogga, India.
K. Hariprasad
University of Agricultual Sciences, Mandya, India.
*Author to whom correspondence should be addressed.
Abstract
Yellow Leaf Disease (YLD) is one of the most destructive diseases affecting arecanut, causing severe yield reduction and a decline in palm vigour. The present study was undertaken to isolate, enumerate, and characterise culturable rhizosphere bacterial communities associated with healthy and YLD-affected arecanut palms. Rhizosphere soil samples were collected from healthy and diseased gardens, and bacterial colonies were isolated using serial dilution and the spread-plate technique on nutrient agar medium. The purified isolates were characterised based on colony morphology, Gram reaction, and cell morphology. A total of 33 bacterial isolates were obtained and characterised. Of these, 29 isolates (87.88%) were Gram-positive, whereas only four isolates (12.12%) were Gram-negative, indicating the predominance of Gram-positive bacteria in the arecanut rhizosphere. Colony morphology exhibited considerable diversity in colour and shape, with predominantly circular (73%) and serrated (27%) colonies. Microscopic examination revealed both cocci and rod-shaped bacterial cells. The predominance of Gram-positive bacteria and the higher culturable bacterial population in healthy rhizosphere soils suggest the presence of microbial communities that may contribute to nutrient cycling, plant growth promotion, and the suppression of soil-borne pathogens. These findings provide baseline information on culturable bacterial diversity associated with healthy and YLD-affected arecanut rhizospheres.
Keywords: Arecanut, Areca catechu, yellow leaf disease, rhizosphere bacteria, culturable bacteria, bacterial enumeration, gram staining, colony morphology, healthy rhizosphere, diseased rhizosphere