Variability of Pectobacterium carotovorum causing rhizome rot in banana

Abstract

Abstract The rhizome rot or tip over is a major and emerging disease of banana, causing substantial economic losses. Common cultivars such as Grand Naine, Rasthali and Nendran are highly susceptible to this disease caused by different Pectobacterium species. Understanding the disease etiology and pathogen variability are essential in management programs. Bacterium Pectobacterium carotovorum was isolated from infected rhizomes from 18 locations of Kerala and Tamil Nadu states of India. Pathogenicity of all isolates were confirmed by in vitro inoculation in rhizome bits and in vivo inoculation in rhizomes of three months old plants and pseudostems of two months old tissue cultured plants of cv. Nendran. Isolates were characterized by cultural, morphological, biochemical, physiological and molecular methods. Cultural characterization was carried out on Nutrient agar (NA), Yeast Extract Glucose Calcium Carbonate (YGC), Logan's medium and Nutrient broth. Morphological characterization was carried out by Gram staining, capsule staining and flagellar staining. Biochemical characterization was done through potato and carrot soft rot test, intrinsic antibiotic resistance, growth of bacteria in three and four per cent NaCl and growth of bacteria in CVP medium. Physiological characterization was carried out by growing the bacterium at different temperatures and pH. Based on these results, 18 isolates were allocated to six groups. 16S rDNA regions of representative isolates of each group have been PCR amplified and the 1.5 kb amplicons were sequenced. Homology and phylogeny analyses had shown that all the groups belong to Pectobacterium carotovorum, and two subspecies carotovorum and brasiliense were identified.