Large-Scale Genome Scanning within Exonic Regions Revealed the Contributions of Selective Sweep Prone Genes to Host Divergence and Adaptation in Magnaporthe oryzae Species Complex

The Role of Genetic Resistance in Rice Disease Management

Rice (Oryza sativa) is a crucial staple crop for global food security, particularly in Asia. However, rice production faces significant challenges from various diseases that can cause substantial yield losses. This review explores the role of genetic resistance in rice disease management, focusing on the molecular mechanisms underlying plant-pathogen interactions and strategies for developing resistant varieties. The paper discusses qualitative and quantitative resistance, emphasizing the importance of resistance (R) genes, defense-regulator genes, and quantitative trait loci (QTLs) in conferring broad-spectrum disease resistance. Gene-for-gene relationships in rice-pathogen interactions are examined, particularly for Xanthomonas oryzae pv. oryzae and Magnaporthe oryzae. The review also covers recent advancements in breeding techniques, including marker-assisted selection, genetic engineering, and genome editing technologies like CRISPR-Cas. These approaches offer promising avenues for enhancing disease resistance in rice while maintaining yield potential. Understanding and exploiting genetic resistance mechanisms is crucial for developing durable and broad-spectrum disease-resistant rice varieties, essential for ensuring sustainable rice production and global food security in the face of evolving pathogen threats and changing environmental conditions.

Chinese Populations of Magnaporthe oryzae Serving as a Source of Human-Mediated Gene Flow to Asian Countries: A Population Genomic Analysis

Magnaporthe oryzae, a filamentous heterothallic ascomycete fungus that serves as the causative agent of rice blast disease, is globally distributed in rice-growing regions. Populations shaped by environmental factors and human intervention play important roles in the formation of genetic structure. In this study, population structures and spatiotemporal dynamics were investigated based on large-scale whole genomic sequences of rice-infecting M. oryzae around the world. By analyzing these genetic structures, we identified divergent clades that crossed geographic boundaries. While we observed associations between the isolates and their geographic origins, we also found that there were frequent migration events occurring across Asia in main rice cultivation regions. Within Asia, China was the migration origin, facilitating gene flows to Japan and South Korea. Since the 1970s, the genetic diversity of M. oryzae populations in China has also shown a steadily increasing trend, continuing through to the 2020s. Additionally, our analysis of the evolutionary history of Asian M. oryzae populations provided insights into the population expansion that has taken place in recent decades. Overall, our findings indicate that human-mediated gene flows played a pivotal role in shaping the genetic structure of M. oryzae.

Allelic variation in rice blast resistance: a pathway to sustainable disease management

Rice blast is a major problem in agriculture, affecting rice production and threatening food security worldwide. This disease, caused by the fungus Magnaporthe oryzae, has led to a lot of research since the discovery of the first resistance gene, pib, in 1999. Researchers have now identified more than 50 resistance genes on eight of the twelve chromosomes in rice, each targeting different strains of the pathogen.These genes are spread out across seventeen different loci. These genes, which primarily code for nucleotide-binding and leucine-rich repeat proteins, play an important part in the defense of rice against the pathogen, either alone or in combination with other genes. An important characteristic of these genes is the allelic or paralogous interactions that exist within these loci. These relationships contribute to the gene's increased capacity for evolutionary adaptation. The ability of resistance proteins to recognize and react to novel effectors is improved by the frequent occurrence of variations within the domains that are responsible for recognizing pathogen effectors. The purpose of this review is to summarize the progress that has been made in identifying these essential genes and to investigate the possibility of utilizing the allelic variants obtained from these genes in future rice breeding efforts to increase resistance to rice blast.

Emergence and spread of the barley net blotch pathogen coincided with crop domestication and cultivation history

Fungal pathogens cause devastating disease in crops. Understanding the evolutionary origin of pathogens is essential to the prediction of future disease emergence and the potential of pathogens to disperse. The fungus Pyrenophora teres f. teres causes net form net blotch (NFNB), an economically significant disease of barley. In this study, we have used 104 P. teres f. teres genomes from four continents to explore the population structure and demographic history of the fungal pathogen. We showed that P. teres f. teres is structured into populations that tend to be geographically restricted to different regions. Using Multiple Sequentially Markovian Coalescent and machine learning approaches we demonstrated that the demographic history of the pathogen correlates with the history of barley, highlighting the importance of human migration and trade in spreading the pathogen. Exploring signatures of natural selection, we identified several population-specific selective sweeps that colocalized with genomic regions enriched in putative virulence genes, and loci previously identified as determinants of virulence specificities by quantitative trait locus analyses. This reflects rapid adaptation to local hosts and environmental conditions of P. teres f. teres as it spread with barley. Our research highlights how human activities can contribute to the spread of pathogens that significantly impact the productivity of field crops.

The use of evolutionary analyses to predict functionally relevant traits in filamentous plant pathogens

Identifying traits involved in plant-pathogen interactions is one of the major objectives in molecular plant pathology. Evolutionary analyses may assist in the identification of genes encoding traits that are involved in virulence and local adaptation, including adaptation to agricultural intervention strategies. In the past decades, the number of available genome sequences of fungal plant pathogens has rapidly increased, providing a rich source for the discovery of functionally important genes as well as inference of species histories. Positive selection in the form of diversifying or directional selection leaves particular signatures in genome alignments and can be identified with statistical genetics methods. This review summarises the concepts and approaches used in evolutionary genomics and lists major discoveries related to plant-pathogen adaptative evolution. We underline the significant contribution of evolutionary genomics in discovering virulence-related traits and the study of plant-pathogen ecology and adaptive evolution.