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Ho, Jinn Shyuan (2025) Transcriptome, physiological and biochemical analyses of the systemic resistance of banana (Musa acuminata cv. Berangan) induced by plant-growth-promoting rhizobacterium against blood disease bacterium. PhD thesis, University of Nottingham Malaysia.

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Abstract

Bananas and plantains are the global top produced fruit with a total 135 million tonnes of production in 2022. Banana blood disease (BBD) is a deadly bacterial wilt disease in banana and caused by Ralstonia syzygii subsp. celebesensis (Rsc), also known as blood disease bacterium (BDB). BDB results in wilting appearance, brownish-red discoloration of internal vascular tissues, and eventually entire crop loss including ready-harvested fruit bunch. Despite being the third highest valued fruit crop in Malaysia, prevalence of banana blood disease has been part of the factor in impacting banana’s production since 2007 and its relapse draws attention to the need of effective long-term management strategy. Using biological control agent (BCA) such as plant-growth-promoting rhizobacterium (PGPR) has emerged as the preferred approach due to its environment friendly and sustainable properties. Therefore, understanding the pathogenesis of BDB supports the study on the applicability of PGPR to induce systemic resistance (ISR) in banana against BBD. In this project, BDB was firstly isolated from Malaysia’s plantation followed by identification and characterisation through molecular and phenotypic method. The identity of BDB isolated strains was first confirmed as Blood Disease Bacterium via Sanger sequencing analysis of 16s ribosomal ribonucleic acid (rRNA) gene. Standard biochemical tests and growth curve study manifested the BDB isolates were non-motile rod-shaped, Gram-negative, catalase-positive, oxidase-positive bacterium, and had an optimum growth rate at 35 °C. The pathogenesis of the characterised virulent BDB isolate (P1) was then studied via Koch’s Postulates in four local banana cultivars using disease rating scale that was newly developed. The pathogenicity test result showed that these four local banana cultivars (cv.) including cv. Berangan, cv. Nipah, cv. Awak and cv. Nangka demonstrated disease severity index (DSI) higher than 95%, indicating their susceptibility towards BDB. To determine the applicability of PGPR (MyIPO application no. PI2020006647) obtained from Malaysia Agricultural and Research Development Institute (MARDI) as BCA in banana against BDB, cv. Berangan and cv. Nipah was selected as plant model. Upon demonstrating promising growth-promoting effect in both cv., PGPR-induced plantlets challenged by BDB showed significantly lower DSI as compared to the non PGPR-induced plantlets in both cv., indicating the feasibility of PGPR (MyIPO application no. PI2020006647) as disease management approach to manage BBD. Hence, the mechanism of PGPR in inducing systemic resistance in banana plantlets was studied in cv. Berangan from the physiological, biochemical and molecular perspectives. Significant improvements were shown in the growth of leaf number, leaf area, pseudostem height and girth diameter in PGPR-induced plantlets by 14.22%-18.42% meanwhile DSI of PGPR-induced plantlets was significantly reduced by 18.41%. In the aspect of biochemical analysis, increased activities of defence-related enzymes such as polyphenol oxidase (PPO), peroxidase (POD), β-1,3-glucanase, phenylalanine ammonia lyase (PAL) along with the increased total phenolic content (TPC) in PGPR-induced plantlets, highlights the role of PGPR in constructing disease resistance through the upregulation of biosynthesis of secondary metabolites against BDB infection. Furthermore, the ability of PGPR in inducing oxidative burst of reactive oxygen species (ROS) included hydrogen peroxide (H2O2) and superoxide anion (O2-) to combat BDB infection while malondialdehyde (MDA) content remained at low level. This further proposed the ability of PGPR in inducing appropriate amplitude of defence response to prevent activation of programmed cell death. Differentially expressed genes (DEGs) of PGPR-induced plantlets were determined through the leaf transcriptomic profiling of PGPR-induced cv. Berangan upon BDB infection on 0, 1 and 3 dpi via Next Generation Sequencing. Out of 5328 DEGs, 565 upregulated and 755 downregulated DEGs were uniquely identified in the PGPR-induced plantlets against BDB on 0, 1 and 3 dpi. Kyoto Encyclopaedia Genes and Genomes (KEGG) pathway enrichment analysis further revealed the significant involvement of these DEGs in regulating metabolic pathways, starch and sucrose metabolism, biosynthesis of secondary metabolites, protein processing in endoplasmic reticulum, MAPK signalling pathway, plant-pathogen interactions, plant hormone signal transduction and lipid metabolism. Quantitative PCR (qPCR) further validated the RNA-seq results for nine genes selected from different signalling pathways in view of their significant regulations by PGPR in PGPR-induced plantlets. This included GBSSI-2 from starch and sucrose metabolism, LRR gene like PLA-I, PR proteins such as acidic-endochitinase, E3 ubiquitin protein ligase ATL42-like and sHSP from the defence signalling pathway, transcription factors (TF) including MYB protein-like, WRKY22 and ethylene-responsive TF ERF119-like, and ABA receptor PYL4-like from the plant hormone signal transduction. Taken together, the outcome of this project confirmed the growth-promoting effect of PGPR and highlighted the biocontrol ability of PGPR in ISR through the regulation of metabolic, plant hormone signal transduction and plant defence signalling pathways. Nevertheless, the set of validated genes contributing to the disease resistance by PGPR against BBD could serve as potential genetic biomarkers for developing BBD-free banana cultivars, thereby constructing resilience in banana production in Malaysia.

Item Type:	Thesis (University of Nottingham only) (PhD)
Supervisors:	Ho, Wan Yong Yeap, Swee Keong Chin, Chiew Foan
Keywords:	Banana; Ralstonia syzygii subsp. Celebesensis; induced systemic resistance; PGPR; blood disease; biocontrol
Subjects:	S Agriculture > SB Plant culture
Faculties/Schools:	University of Nottingham, Malaysia > Faculty of Science and Engineering — Science > Division of Biomedical Sciences
Item ID:	79935
Depositing User:	Ho, Jinn
Date Deposited:	08 Feb 2025 04:40
Last Modified:	08 Feb 2025 04:40
URI:	https://eprints.nottingham.ac.uk/id/eprint/79935

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