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Rice blast is a major plant disease that occurs worldwide and significantly reduces rice yields. Rice blast disease occurs periodically in Korea, causing significant socio-economic damage due to the unique status of rice as a major staple crop. A disease outbreak prediction system is required for preventing rice blast disease. Epidemiological investigations of disease outbreaks can aid in decision-making for plant disease management. Currently, plant disease prediction and epidemiological investigations are mainly based on quantitatively measurable, structured data such as crop growth and damage, weather, and other environmental factors. On the other hand, text data related to the occurrence of plant diseases are accumulated along with the structured data. However, epidemiological investigations using these unstructured data have not been conducted. The useful information extracted using unstructured data can be used for more effective plant disease management. This study analyzed news articles related to the rice blast disease through text mining to investigate the years and provinces where rice blast disease occurred most in Korea. Moreover, the average temperature, total precipitation, sunshine hours, and supplied rice varieties in the regions were also analyzed. Through these data, it was estimated that the primary causes of the nationwide outbreak in 2020 and the major outbreak in Jeonbuk region in 2021 were meteorological factors. These results obtained through text mining can be combined with deep learning technology to be used as a tool to investigate the epidemiology of rice blast disease in the future.

The genome of the rice blast fungus Magnaporthe oryzae contains several types of transposable elements (TEs), and some TEs cause genetic variation that allows M. oryzae to evade host detection. We studied how five abundant TEs in rice pathogens, Pot3, Pot2, MAGGY, Line-like element (MGL) and Mg-SINE, are expressed under diverse conditions related to growth, development, and stress. Expression of Pot3 and Pot2 was activated in germinated conidia and mycelia treated with tricyclazole. Retrotransposon MAGGY was highly expressed in appressoria and tricyclazole-treated mycelia. MAGGY and Pot2 were also activated during the early and late stages of perithecia development. MGL was up-regulated in conidia and during conidial germination but not during appressorium formation. No noticeable expression of Mg-SINE was observed under most conditions. Our results should help investigate if and how condition-specific expressions of some TEs contribute to the biology and evolution of M. oryzae.

Rice blast disease caused by Magnaporthe oryzae is the most important disease of rice in both South and North Korea. Cultivation of disease-resistant cultivar is the best way to prevent this notorious disease, but M. oryzae races have been continuously changed to adapt a new cultivar. Therefore, it is important to get the information about the race and avirulence genes of the pathogen for developing blast-resistant rice cultivar. Since the entrance of North Korea was prohibited, the information about the races of M. oryzae in North Korea border areas and South Korea was collected to get the information about the diversity of rice blast pathogen in North Korea. The disease occurrence on monogenic lines carrying single resistant gene was investigated in Jeonju, Suwon, Cheorwon, Goseong, and Baengnyeongdo in Korea, and Dandong in China. The monogenic lines in Jeonju and Suwon showed diverse ranges of the response, while those in Baengnyeongdo and Dandong showed relatively high resistant responses to rice blast. All the field isolates of M. oryzae were characterized for rice blast races by the Korean differential varieties and screened for known avirulence genes to determine the spatial distribution of avirulence genes and the population of M. oryzae.

Almost 30% of arable lands of North Korea are covered with paddy rice. In rice cultivation of North Korea, rice blast disease is the most important fungal disease and bacterial leaf blight is the most important bacterial disease. Seven North Korean rice cultivars had been tested for the disease resistance against rice blast pathogen, Magnaporthe oryzae and bacterial leaf blight pathogen, Xanthomonas oryzae pv. oryzae. The responses of seven cultivars against 17 different M. oryzae races from South Korea had been quite different. Among seven cultivars, Giljoo1ho was very resistant to all 18 different M. oryzae isolates from South Korea, nevertheless KI or KJ. Pyungdo5ho was very susceptible, it showed susceptible responses to 8 out of 10 KI races and 7 out of 8 KJ races of M. oryzae isolated in South Korea. However, the response to bacterial leaf blight was different from the response to rice blast pathogen. Gijoo1ho, Wonsan69ho, Onpo1ho, and Pyungdo15ho were susceptible to KXO42 (K1) and KXO90 (K2), respectively. Pyungdo5ho was resistant to KXO85 (K1) and KXO19 (K3), and Pyungyang21ho was resistant to K1 races. Based on these results, Giljoo1ho can be a good resource for the breeding of resistant rice cultivar against M. oryzae isolates from South Korea.

The rice blast fungus, Magnaporthe oryzae, is one of the most economically important crop diseases. In addition, rice-M. oryzae interaction is a classical gene-for-gene host-pathogen system. Race variation in pathogen groups was proposed as the main mechanism for rapid break-down of resistance in newly introduced rice cultivars. These new pathogen race variations may be caused by changes in an avirulence gene, such as point mutations, insertion of transposons, and frame shifts. The avirulence gene AVR-Pita1 is representative avirulence gene in which all of these mutations are reported. In this review, we present a useful information for avirulence gene AVR-Pita1 and its homologous genes AVR-Pita2 and AVR-Pita3. We also review examples that cause mutations in these evolutionarily significant genes.

The fungal species contain diverse transposable elements and repetitive sequences up to ~10% of their genome. It has been reported that distribution of transposable elements tends to correlate with the host range of the pathogen. Moreover, transposable elements cause the loss of an avirulence gene in the pathogen, which resulted in disease on a resistance cultivar. Thus, the transposable elements in the fungal pathogens may be one of the key factors driving the plant-fungus interactive evolution. In this article, we reviewed classification and biological functions of transposable elements in Magnaporthe species.

The rice blast fungus is a representative model phytopathogenic fungus in which Gene-for-Gene interaction with host rice is applicable. After 1980, eight differential varieties have been constructed and classified to analyze the race of rice blast isolates in Korea. However, since there is limited information about the genetic background of rice blast resistance genes within the Korean differentials, scientific analysis on the emergence of new race or resistance break down was difficult. Recently, a differential system has been developed using monogenic resistance lines to understand the interactions of pathogen race and rice resistance genes. In this study, a total of 50 isolates were selected from four different races isolated in Korea, and they were inoculated into monogenic lines. As a result, the isolates in the same race classified by the Korean differential system reacted differently in single monogenic lines. This suggests that the isolates categorized as the same race group contains different avirulence genes and furthermore, it is presumed that the Korean differential system is difficult to provide useful information for breeding program. For this reason, introduction of differential system using monogenic resistance lines is required in addition to the current system.

Isolates of the rice blast fungus show a range of tissue-specificities infecting leaves, nodes, neck and panicles. Although neck and panicle blast cause significantly greater yield losses than the leaf blast, virulence tests of the blast isolates have been performed only rice leaves instead of neck and panicles. In this study, we have developed a virulence test method for neck and panicle blast. We selected three representative isolates from each of leaf, neck, and panicle blast. We observed that severe disease lesions developed on the neck and the panicles when the infected rice plants were incubated in a dew chamber for 48 h instead of 24 h when tested on leaves. Unlike the leaf blast, a typical lesion on the neck and panicles appeared after 14 days post-infection as opposed to 7 days with leaf blast. This method will be applied to examine tissue-specificity of the rice blast fungus isolates.

A sequential planting method was developed to screen rice plants with durable resistance against rice blast in a short time, and applied for several years in Korean rice breeding program. In this study, we showed the advantages of a sequential planting method compared to other pathogenicity tests. The correlation analysis among three pathogenicity tests and other factors demonstrated that durable resistance depended on the average of diseased leaf area and the number of compatible pathogens. Significant correlations were found in the nursery test but not in the field test result. In addition, we traced changes in the pathogen population during sequential planting stages through re-isolation of the pathogen. The portion of compatible pathogens was increased during sequential planting. Through this study, we provide an effective sequential planting method and direction of durable resistance in a breeding program.

Blast resistance of 29 rice cultivars confirmed as a durable resistance in the evaluation of sequential planting from 2004 to 2006 was evaluated to nursery screening in 14 test sites during 11 years in Korea. The average disease severity (ADS) of 29 rice varieties against rice blast showed 3.5 degree; however, the difference of disease severity among the varieties was from 1.9 to 4.8. The 29 varieties were grouped into resistance less than 3.0 ADS degree including 12 varieties and moderate resistance over 3.1 ADS degree including 17 varieties. Among the 12 rice cultivars presented low ADS, 4 rice cultivars, Ungwang, Pungmi 1, Sinunbong 1, and Dasan 1 were constantly appeared high resistant reaction during 11 years in all test sites and the others were showed various diseases severity across the test years and the test sites. Twenty-one rice cultivars including Gopum were more variable among the test sites while the others were higher variable among the test years. These results indicated that durable resistance test against rice blast using sequential planting is a very efficient screening method to predict durability and nursery test for long periods and also useful method to predict indirectly durable resistance of rice cultivars. [ABSTRACT FROM AUTHOR]

Rice is a source of food supply as the staple food. The narrow genetic diversity of Korean Japonica cultivars is prone to be susceptible to abiotic and biotic stresses such as rice blast, bacterial blight, and brown planthopper (BPH). The best approach for prevention of the breeding and extermination of disease and insect pest would be the development of rice cultivars harboring multiple disease and insect pest resistance genes. National Institute of Crop Science (NICS) in Korea developed a mutant line, Namil(EMS)-bl10,bph1, by using ethyl-methane-sulfonate (EMS) as the chemical mutagen on the wild type, Namil. The mutant line exhibits strong resistance levels against rice blast and brown planthopper. To localize favorable mutated allele types, two mapping populations were constructed by using F2 progenies derives crosses between Namil(EMS)-bl10,bph1 and Milyang23 and Namil (wild type) and Milyang23. Each F2 progenies were evaluated in terms of DNA marker genotype as well as agronomic traits measured, and for rice blast and BPH resistance, virulent blast isolate 94-254 and Korean biotype of BPH were used to screen F2:3 seedlings to conduct association analysis between marker genotype and evaluated phenotype of progeny lines. Through comparisons on major loci between two mapping populations, the putative major loci for rice blast resistance (RM1337, R2=54.4%) and BPH (RM0277, R2=55.1%) were primarily localized on chromosome 12. [ABSTRACT FROM AUTHOR]

Rice is not only one of major crops grown in the world but also the staple food in Asia. However, in modern agriculture, the genetic diversity in rice gene pool is diminishing by selection breeding. Hence, rice is readily threatened by biotic and abiotic stresses. Rice blast is one of the major threats to stable rice production. The best approach to prevent rice blast is development of rice cultivars harboring resistance gene against blast disease. National Institute of Crop Science (NICS) in Korea developed a mutant line, Namil(SA)-bl5, which has inherited short culm and rice blast resistance by treatment of sodium azide (SA). To localize favorable mutated allele types, two mapping populations were constructed by using F2 progenies derives crosses between Namil(SA)-bl5 and Milyang23 and Namil (wild type) and Milyang23. Each F2 progenies were evaluated in terms of culm length and resistance level against a rice blast isolate, 94-254 along with their parental lines. Association analyses between marker genotype on 68 SSR anchor markers and evaluated phenotype of progeny lines were adopted to localize the putative chromosomal locations involved to culm length and blast resistance. Association analyses localized two major loci on the chromosomes of middle-low region of 6 (R2=15.8%) and the distal region of 7 (R2=20.0%), and a major locus on the middle of chromosome 12 (R2=46.6%) for the reduced culm length and increased resistance level against rice blast, respectively. [ABSTRACT FROM AUTHOR]

Rice blast is one of the major threats to stable rice production. In modernized rice breeding system, development of rice cultivars harboring resistance gene is one of the most efficient approaches against blast disease. Wild rice species, to the context, have been recognized as valuable genetic resources in improving resistance or tolerance level of modern commercial rice cultivars against biotic or abiotic stresses. National Institute of Crop Science (NICS), Korea developed an introgression line, ‘Suweon 506', which has inherited the rice blast resistance from a BBCC genome wild Oryza species, O. minuta (Acc. 101141). Genetic analysis was carried out to localize the chromosomal region responsible for the rice blast resistance of ‘Suweon 506' by using F2 progenies from ‘Suweon 506' × ‘Milyang 23'. Association analysis between marker genotypes and their inferred resistance levels of F2 progenies against a Korean blast isolate, ‘93-072' localized the target genetic region on rice chromosome 12. Further association analysis with increased number of DNA markers, and e-Landings on the rice pseudomolecule 6, the segment of ‘RM101-S10704-RM1337' was identified to be tightly linked to the rice blast resistance gene from O. minuta at the 8.8∼11.9 Mbp physical region of rice chromosome 12, where at least 9 rice blast resistance genes have been also identified. The 3.1 Mb equivalent virtual contig, composed with 31 BAC/PAC clones will be further analyzed for fine mapping and gene identification. [ABSTRACT FROM AUTHOR]