Cold plasma treatment to improve banana growth and disease tolerance against fusarium wilt / Priya Rajakumar

Priya , Rajakumar (2024) Cold plasma treatment to improve banana growth and disease tolerance against fusarium wilt / Priya Rajakumar. Masters thesis, Universiti Malaya.

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Abstract

Banana (Musa spp.) is a valuable fruit crop due to its high nutrition and availability throughout the year. Being among the top 10 staple food by production, banana serves millions of lives worldwide. However, banana production is threatened by a destructive disease called Fusarium wilt, caused by the hemi-biotrophic soil-borne pathogen Fusarium oxysporum f. sp. cubense (Foc). Developing disease-tolerant banana varieties through conventional breeding or genetic engineering is complicated by the parthenocarpic nature of bananas, which lack seeds for traditional breeding methods. An alternative to these methods is using an eco-agricultural technology called cold plasma (CP) treatment. CP treatment is a non-ionizing radiation that uses electricity and reactive carrier gases (nitrogen, oxygen, helium) to inactivate enzymes, microbial decontamination and for food preservation. Besides, CP treatment also plays a role in crop improvement via growth and disease tolerance improvement. For consistency, the term ‘cold plasma’ will be generally referred as ‘plasma’ throughout the thesis. This study aimed to investigate the plasma effects on the growth performances and Fusarium wilt disease tolerance in banana plants. In this study, tissue culture derived ‘Berangan’ banana plantlets were treated with plasma followed by two months acclimatization in the greenhouse. Growth performances in terms of height, leaf number and stem diameter were measured and evaluated over a three-month duration for the plasma-treated plants in comparison with the untreated plants. Plasma treatment exhibited a favourable impact on plant growth, with no observed negative effects. In addition, a bioassay experiment was conducted by inoculating both plasma-treated and untreated plants with Foc Tropical Race 4 (Foc TR4) to study the plasma effect on Foc tolerance. Controls were also prepared (non-Foc inoculated plants comprises of plasma-treated and untreated). Disease severity index (DSI) and disease progression were recorded throughout five weeks post-Foc inoculation. Plasma-treated plants displayed delayed disease progression at week four compared to the untreated plants that started exhibiting severe wilting symptoms in week three. Nevertheless, the plasma-treated plants were found to be highly susceptible to Foc infection just like the untreated (non-plasma). However, DSI values in terms of leaf symptom index (LSI) and rhizome discoloration index (RDI) for the plasma-treated plants were slightly lesser (LSI: 4.0, RDI: 6.0) compared to the untreated plants (LSI: 4.2, RDI: 6.6). To understand the regulatory mechanism underlying CP treatment which influences the growth and defence in banana plants, several Foc-responsive genes involved in defence and growth were selected for this study including defence-related (PR1, WRKY22, WRKY50, PAL, CEBiP, ChiH) and growth-related (Cytochrome P450, NAC68, CAT) genes. qPCR analysis of root samples collected at 2-, 24-, 48- and 72-hours post-inoculation (hpi) revealed differential expression of those genes following CP treatment and Foc TR4 inoculation. CP treatment was found to differentially induce the defence and growth genes, particularly in conjunction with Foc TR4 infection. The findings not only shed light on the potential use of CP to increase yield by improving growth and tolerance against Fusarium wilt but offer insights into the possible mechanisms contributing to the improved traits.

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