Molecular Microbiology Research 2024, Vol.14, No.6, 277-289 http://microbescipublisher.com/index.php/mmr 281 disease resistance. Previous studies have shown that the first layer of immunity, PTI, is a relatively weak immune response that inhibits or prevents pathogen infestation by triggering a defense response after sensing rice blast pathogens through extracellular, transmembrane, or pattern-recognition receptors. PTI is mediated by secondary metabolite production, cell-wall thickening, and programmed cell death, by signaling of mitogen-activated protein kinases, by WRKY transcription factors, and by transcriptional recoding mediated by WRKY. Mediated transcriptional recoding, and reactive oxygen species (ROS) generation as pathways of defense against rice blast (Li et al., 2017). The second layer of immunity, ETI, is activated by highly polymorphic intracellular R proteins recognizing avirulence effectors (Avr), which has a higher level of resistance compared to PTI, and generally elicits a hypersensitivity reaction at the site of infection during the defense process, which is effective in controlling rice blast disease. It is a highly specialized disease resistance mechanism for breeding in the host (Ning et al., 2020；Oliveira-Garcia et al., 2023). The molecular mechanisms underlying blast resistance in rice involve a complex interplay of genetic and biochemical pathways. The Pi-d2 was reported to encode a B-lectin receptor kinase (Kouzai et al. 2013), while the recessive gene pi21 encodes a proline-rich protein (Fang et al. 2019), Bsr-d1 encodes a C2H2-type transcription factor protein (Li et al. 2017), and Bsr-k1 encodes a tetratricopeptide repeats-containing protein (Zhou et al. 2018). One key mechanism is the interaction between R genes and their corresponding avirulence (Avr) genes in the pathogen, which triggers a defense response in the plant. For instance, the Pita2 gene has been shown to recognize specific AvrPita isolates, leading to a robust resistance response (Meng et al., 2020). Additionally, non-race-specific resistance, which is often more durable, has been linked to natural alleles of transcription factors such as bsr-d1, a single nucleotide change in the promoter of the bsr-d1 gene, resulting in reduced expression of the gene through the binding of the repressive MYB transcription factor and consequently, enhanced disease resistance by inhibiting H2O2 degradation (Li et al., 2017). The identification of differentially expressed genes (DEGs) in response to blast infection further elucidates the molecular pathways involved in resistance. For example, transcriptome analysis in upland rice revealed DEGs that are functionally annotated to catalytic responses against disease stimuli, providing insights into the cellular mechanisms of resistance (Tan et al., 2022). The genetic basis of blast resistance in rice is multifaceted, involving a combination of R genes, QTLs, and intricate molecular mechanisms. These insights are crucial for developing durable and broad-spectrum resistant rice varieties through advanced breeding strategies. 4 Genetic Diversity in Upland Rice 4.1 Adaptation and cultivation conditions of upland rice Upland rice is primarily cultivated in rainfed areas with limited water availability, making it crucial for these varieties to possess traits that enable them to thrive under drought conditions. Upland rice has evolved distinct morphological and physiological adaptations to cope with water scarcity, such as deeper root systems and efficient water use mechanisms (Xia et al., 2019). The study represents the first genomic investigation in a large sample of upland rice, providing valuable gene list for understanding upland rice adaptation, especially drought-related adaptation, and its subsequent utilization in modern agriculture (Lyu et al., 2014) (Figure 3). These adaptations are a result of bi-directional selection processes that have shaped the genetic makeup of upland rice, allowing it to maintain productivity even under drought stress (Wang et al., 2023). The cultivation of upland rice is predominantly practiced by smallholder farmers in regions like Latin America and Africa, where the risk of dry spells is high (Lanna et al., 2021). 4.2 Identified blast resistance genes in upland rice Elite upland rice cultivars have the advantages of less water requirement along with high yield but are usually susceptible to various diseases. Blast disease, caused by the fungus M. oryzae, is also a significant threat to upland rice production. To date, only a few genes conferring non-race-specific resistance have been isolated in rice, act as recessive alleles. For instance, Pi21 encodes a proline-rich protein containing a metal-binding domain and a loss-of-function allele (pi21) confers non-race specific, durable resistance (Fukuoka et al., 2009). Bsr-d1, from
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