Pathogenesis study of blood disease bacterium in local bananas of Malaysia

Abstract

Banana blood disease (BBD), a banana wilt disease caused by blood disease bacterium (BDB), Ralstonia syzygii subsp. celebesensis (RSC), was first reported in Malaysia in 2007. BDB results in wilting appearance and internal bleeding-like symptoms, which eventually leads to entire crop loss including ready-harvested fruit bunch. Understanding the pathogenesis of BDB in local common banana cultivars provides good foundation to tailor disease management plan to mitigate BBD. To address this need, our study was performed to characterize BDB isolated from locally grown banana plants and to compare the pathogenesis of the bacterium in four most common local banana cultivars. In this study, BDB isolated from Malaysia's plantation was identified and characterized via the molecular and phenotypic method. The pathogenicity of characterized virulent BDB isolate was determined in four local banana cultivars via disease rating that was newly developed specifically for BDB-infected bananas. The identity of the isolated strains was first confirmed as Blood Disease Bacterium using Sanger sequencing analysis of 16s rRNA gene. Standard biochemical tests and growth curve study showed that the BDB isolates were Gram-negative, non-motile rod-shaped, catalase-positive, oxidase-positive bacterium, and had an optimum growth rate at 35 °C. The pathogenicity of a selected virulent BDB isolate was then determined via Koch's Postulates in four local banana cultivars. Recognizing the lack of a specific disease rating scale to quantify the pathogenesis of BDB in bananas, we developed a disease rating scale specifically to BDB-infected bananas in this study. Based on the pathogenicity test, local banana cultivars (cv.) in Malaysia included cv. Berangan, cv. Nipah, cv. Awak and cv. Nangka demonstrated disease severity index (DSI) higher than 95%, indicating their susceptibility towards to BDB. In conclusion, our results showed that the four most common banana cultivars in Malaysia were highly susceptible to infection by virulent BDB.