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Abstract
Finger millet (Eleusine coracana (L) Gaertn) is a highly nutritious staple crop grown in eastern Africa and India. Although it has been historically neglected by researchers, its climate resilience and nutritional qualities deem it a crop worthy of consideration for improving food security challenged by climate change. The top biotic constraint to finger millet production is blast disease caused by Magnaporthe oryzae, which is responsible for blast in over 50 grasses. In my dissertation, I focused on characterizing genetic factors in both the pathogen and host that are associated with finger millet blast resistance. In Chapter 2, I characterized host and pathogen dynamics during early infection of two eastern African blast strains which have different infection potential on the relatively resistant finger millet cultivar TZA1637 through whole-plant and leaf sheath assays, coupled with confocal microscopy. Upon conducting RNA-Seq at three early infection timepoints of leaf sheath tissue of TZA1637 infected with a highly (U2) and lowly infectious strain (E36), I identified differentially expressed genes and co-expression clusters which can support identifying candidate avirulence (AVR) genes. In Chapter 3, I validated EcAVR-Pik, orthologous to AVR-Pik in rice blast, as a functional AVR gene in finger millet blast. Given that the cognate resistance (R) genes for AVR-Pik seem to be absent in fingermillet, I conducted RNA-Seq on host plants infected with strains isogenic for EcAVR-Pik to identify genes involved in the resistance response, including putative host R genes. Of genes which were differentially expressed between the incompatible (resistant) and compatible (susceptible) interactions, many were involved in jasmonic acid (JA) signaling and turnover. A pilot acidic hormone profiling study demonstrated an increase in JA accumulation during the compatible versus the incompatible response in TZA1637. Collectively, our data suggest that repression of JA-response genes by MYC2 is important for resistance. The homoeologous EcRPS2-like genes, nucleotide binding site (NBS) - leucine-rich repeat (LRR) genes which were upregulated during the incompatible versus compatible interactions, were identified as candidate R genes. Upon validation, EcRPS2-like can be used to improve finger millet for blast resistance. This gene might also be exploitable in other crops such as rice for which the ortholog of EcRPS2-like is nonfunctional.