Pre-Harvest Finger Rot of Cavendish Banana (Musa acuminate) Reported from Moneragala and Badulla Districts, Sri Lanka: Identification and Confirmation of Pathogenicity of the Causal Agent

The present study was conducted to identify and confirm the pathogenicity of the causal agent of a wet finger rot of Cavendish banana, a newly reported pre-harvest disease in commercial plantations in Moneragala and Badulla districts of Sri Lanka. Bacterial species were isolated from banana fingers at three stages of symptom development: initial, middle, and late. Isolated bacterial colonies were inoculated to healthy and mature banana fingers by two methods, namely peel and pulp inoculation, to confirm the pathogenicity by Koch’s postulates. Re-isolated bacterial isolates from inoculated banana fingers showing typical symptoms were identified by biochemical tests and subjected to PCR amplification using universal primers of bacteria, B27F/1492R. Subsequent DNA sequencing of the PCR products and homology search identified the pathogen as a strain of Dickeya dadantii. Phylogenetic analysis with selected Dickeya spp. sequences available in databases identified that the D. dadantii strain of the present study groups with D. dadantii 3937 (CP002038.1), of which the complete genome has been sequenced. Cross infection studies revealed that D. dadantii isolate is more virulent on banana variety Anamalu than on Cavendish banana in terms of days taken to develop the symptoms. The findings identified the causal agent of wet finger rot of banana in the present study as a strain of D. dadantii and confirmed its pathogenicity. The present study was conducted to identify and confirm the pathogenicity of the causal agent of a wet finger rot of Cavendish banana, a newly reported pre-harvest disease in commercial plantations in Moneragala and Badulla districts of Sri Lanka. Bacterial species were isolated from banana fingers at three stages of symptom development: initial, middle, and late. Isolated bacterial colonies were inoculated to healthy and mature banana fingers by two methods, namely peel and pulp inoculation, to confirm the pathogenicity by Koch’s postulates. Re-isolated bacterial isolates from inoculated banana fingers showing typical symptoms were identified by biochemical tests and subjected to PCR amplification using universal primers of bacteria, B27F/1492R. Subsequent DNA sequencing of the PCR products and homology search identified the pathogen as a strain of Dickeya dadantii. Phylogenetic analysis with selected Dickeya spp. sequences available in databases identified that the D. dadantii strain of the present study groups with D. dadantii 3937 (CP002038.1), of which the complete genome has been sequenced. Cross infection studies revealed that D. dadantii isolate is more virulent on banana variety Anamalu than on Cavendish banana in terms of days taken to develop the symptoms. The findings identified the causal agent of wet finger rot of banana in the present study as a strain of D. dadantii and confirmed its pathogenicity.