MOLECULAR MECHANISMS OF HOST DEFENSE TO POTATO POWDERY SCAB DISEASE

Samodya Kushani Jayasinghe

Powdery scab is a significant disease in potato, caused by the obligate biotrophic pathogen Spongospora subterranea f. sp. subterranea (Sss). This pathogen not only causes substantial yield and quality losses but also vectors the potato mop-top virus (PMTV), the causal agent of tuber necrosis. No effective chemical control measures currently exist, and only partially resistant cultivars are available. The available cultivars show a range of susceptibilities to the pathogen, ranging from highly susceptible to relatively tolerant. Therefore, the central hypothesis of this study is that resistance to Sss and PMTV is genetically determined at the genomic level. Understanding this genetic basis is crucial for developing fully resistant cultivars or improving the industry-standard genetic materials used in resistance breeding programs against these diseases. In this dissertation, the genetic basis and the potential molecular mechanisms underlying potato resistance to Sss are investigated. Phytohormone profiling combined with molecular genetic analyses using gain and loss-of-function approaches revealed that the salicylic acid-mediated mechanisms plays a central role in the defense response against Sss in potato. Through transcriptomics approaches with a potato hairy root culture system, multiple disease resistance (R) genes were identified that may contribute to resistance or susceptibility to Sss and PMTV infection within the first 72 hours post-infection. Furthermore, this work presents the first study to employ an in-situ capture spatial transcriptomic approach to investigate host responses in the Sss-induced root gall collected from infected roots of pot-grown potato plants. The spatial transcriptomics identified additional R genes that may be involved in host defenses during the root gall formation and Sss spore formation. Other potential defense-related genes identified include lipoxygenases, glutathione-S-transferases, and starch synthesis enzymes. The identification of these candidate genes lays the groundwork for the development of durable and complete resistance to powdery scab in potato. By integrating molecular genetics and transcriptomic techniques, this dissertation establishes a framework for deciphering complex host-protist-virus interactions and guiding the next generation of resistance-focused breeding in potato.

MOLECULAR MECHANISMS OF HOST DEFENSE TO POTATO POWDERY SCAB DISEASE

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