Date of Award

5-8-2026

Thesis Type

PhD

Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Divisions

Institute for Advanced Studies

Institution

Universiti Malaya

Abstract

The growing demand for nutrient-dense fruit and vegetables presents challenges due to population growth, global climate change, limited land resources, and increasing pathogen pressure. Tomatoes, a widely consumed and nutritious fruit crop, often require high inputs of fertilisers and pesticides, raising environmental and health concerns. Ultraviolet-C (UV-C) radiation (100-280 nm), long recognised for DNA-damaging and disinfecting properties, has shown promising hormetic effects at low dosage that can enhance plant growth and post-harvest shelf-life. However, the detailed understanding of UV-C effect on flower traits, fruit quality and on molecular responses underlying plant defence remains limited. In this study, a custom UV plant treatment apparatus was developed (Patent application No: PI2024001700) to deliver precise UV-C dosage, ensuring controlled and optimised treatment conditions. Using this apparatus, this study aims to evaluate UV-C effects on flower number and size, fruit quality and on the defence-related genes expressed in the leaf transcriptome of two tomato cultivars with differing UV-C sensitivity; Red Rock (susceptible) and Super Star (comparatively tolerant). The optimal UV-C dosages were determined to be 930 J/m2 for Red Rock and 1395 J/m2 for Super Star, which showed the greatest increases in flower number, size, fruit yield, and phytochemical content compared to non-treated controls and to other UV-C doses. At the optimal dosage, both cultivars showed significant increases in flower number (1.65-1.67-fold) and flower size (1.08-1.11-fold). Fruit analysis also revealed improvement in yield (1.69-1.76-fold), weight (1.85-1.95-fold), and phytochemical contents including phenolics (1.32-1.34-fold), flavonoids (1.34-1.44-fold), anthocyanins (1.31-1.44-fold), ascorbic acid (1.29-1.40-fold), lycopene (2.54-2.62-fold) and sugars (1.13-1.17-fold). Sensory evaluation indicated enhanced acidic odour, sweetness, sourness, and juiciness, reflecting superior fruit quality. Cytotoxicity tests confirmed that fruit extracts from UV-C-treated plants were safe, showing no negative effects on normal human bronchial epithelial cells (BEAS-2B) and exhibiting a suppressing effect on lung cancer cell growth (A549), likely due to increased levels of bioactive compounds and lycopene. Gene expression analysis of fruit showed that UV-C treatment upregulated 14 R2R3-SlMYBs and 5 structural genes involved in phenylpropanoid biosynthesis. To elucidate defence mechanisms induced by UV-C treatment, RNA-seq analysis on leaves treated with the optimised UV-C dosage was conducted. The analysis identified 3,540 differentially expressed genes (DEGs) in Red Rock and 2,678 DEGs in Super Star. Gene ontology and pathway enrichment analyses revealed conserved induction of defence- and stress-associated genes, particularly within the plant-pathogen interaction pathway. RT-qPCR analysis of leaf tissue confirmed strong induction of calcium-binding and signalling genes (Solyc06g069740.1 and Solyc05g050350.2) within the plant-pathogen interaction pathway. Detached leaf assays further validated UV-C mediated defence priming, with reduced lesions and elevated defence enzyme activities against the plant pathogens; Botrytis cinerea and Sclerotinia sclerotiorum. Photoreceptor analysis revealed upregulation of UVR8 and CRYs, suggesting that UV-C perception is mediated through these photoreceptors, linking to the downstream signalling cascade involved in stress and defence responses. This study demonstrates that UV-C treatment enhances flower development, fruit quality and the plant defence response in tomato. These findings provide a foundation for integrating UV-C hormesis into sustainable agriculture practices aimed at improving crop productivity and resilience, promoting minimal use of synthetic agrochemicals.

Initial

khm

Additional Information

Thesis (PhD) – Institute for Advanced Studies, Universiti Malaya, 2026.

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