Abstract
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.
Highlights
Banana (Musa acuminata) is one the oldest and worldwide popular fruits with high nutritional value
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
Out of the total land area under banana cultivation, 13,000 ha are used for plantains and the rest is under the cultivation of dessert type banana (Hathrusinghe et al, 2012)
Summary
Banana (Musa acuminata) is one the oldest and worldwide popular fruits with high nutritional value. The symptoms of newly reported disease in the banana plantations in Sri Lanka do not match exactly with the available literature of soft rot diseases of banana. When analysed the nature of the symptoms developed on banana fingers, the locally-emerged disease could be hypothesised as an infection of an enterobacterial bacterium such as Erwinia spp., Dickeya spp. or Pectobacterium spp., accurate identification of the causal organism and confirmation of pathogenicity are essential prerequisites to introduce effective management measures to secure the Sri Lankan banana industry from the newly-reported disease. The present study was focused on elucidating the steps of disease development and isolation, and identification and confirmation of pathogenicity of the causal organism of banana finger rot reported from banana plantations in some districts of Sri Lanka
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