Standard Differential Blast Isolates Research Articles

Pathogenicity Analyses of Rice Blast Fungus (Pyricularia oryzae) from Japonica Rice Area of Northeast China.

In order to understand the pathogenicity differentiation of rice blast fungus (Pyricularia oryzae Cavara), a total of 206 isolates of P. oryzae were collected from three Japonica rice regions in Jilin Province, northeast China. Pathogenicity test showed that the reaction pattern of 25 monogenic differential varieties (MDVs) of rice (Oryza sativa L.) demonstrated a wide pathogenic diversity among the isolates. Those MDVs harbor 23 resistance (R) genes with the susceptible variety Lijiangxintuanheigu (LTH) as control. Virulent isolates of MDVs harboring R genes Pish, Pit, Pia, Pii, Pik-s, Pik, Pita (two lines), and Pita-2 (two lines) had high frequencies ranging from 80 to 100%, to MDVs harboring R genes Pib, Pi5(t), Pik-m, Pi1, Pik-h, Pik-p, Pi7(t), Piz, Piz-5, and Piz-t showed intermediate frequencies ranging from 40 to 80%, and to MDVs with R genes Pi3, Pi9(t), Pi12(t), Pi19(t) and Pi20(t) presented low frequencies ranging only from 0 to 40%. The U-i-k-z-ta pattern of race-named criteria categorized the 206 isolates into 175 races. Sub-unit U73 for Pib, i7 for Pi3 and Pi5(t), k177 for Pik-m/Pik-h/Pik-p, z17 for Pi9(t), and ta332 for Pi20(t) were crucial on pathogenic differences in regions. Twenty-seven standard differential blast isolates (SDBIs) were selected to characterize resistance in rice accessions. This study could help to build a durable identification system against blast in the Japonica rice area of northeast China and enhance our understanding of the differentiation and diversity of blast races in the world.

Genetic Variation of Blast (Pyricularia oryzae Cavara) Resistance in the Longistaminata Chromosome Segment Introgression Lines (LCSILs) and Potential for Breeding Use in Kenya.

In Kenya's rice-growing areas, Basmati varieties have been produced in monoculture since the late 1980s. This has resulted in the breakdown of the resistance (R) gene-mediated response of the local Basmati varieties to blast disease caused by Pyricularia oryzae. To improve blast resistance in Kenyan Basmati varieties, continuous identification of R genes and suitable breeding materials for Basmati are necessary. Longistaminata chromosome segment introgression lines (LCSILs) with the Kernel Basmati genetic background, developed using a rice line called potential low-input adaptable-1 (pLIA-1) derived from a cross between Taichung 65 (T65) (a rice variety in the Japonica Group) and O. longistaminata, are expected to contain useful blast R genes derived from O. longistaminata or T65. In this study, we investigated the genetic variation of blast R genes in LCSILs and their parents by using a new international differential system for designating blast races based on the gene-for-gene theory and molecular characterization using single nucleotide polymorphism (SNP) markers. LCSILs and their parents were classified into three groups-A, B1, and B2-based on reaction patterns to the standard differential blast isolates (SDBIs). Group A, including pLIA-1, showed the highest resistance in all groups, followed by groups B1 and B2. Kernel Basmati in group B1 was considered to possess Pik-p or Pi7(t), Pi19(t), and other unknown R genes. In addition to these R genes, LCSIL 6, 12, 27, 28, and 40, in group A, were determined to possess one of Pish, Piz-t, or both genes that confer resistance to the Kenyan blast races. These lines can be used for efficiently pyramiding blast R genes in the local Basmati varieties.

A unique genetic variation with respect to blast (Pyricularia oryzae Cavara) resistance in rice (Oryza sativa L.) varieties in Vietnam.

A unique genetic variation with respect to blast resistance was clarified in 201 rice accessions from Vietnam. These accessions were classified into three clusters-A, B1, and B2-based on their reactions to 26 standard differential blast isolates selected in Vietnam. Cluster A was the dominant cultivar group in Vietnam and the most susceptible of the three clusters. Cluster B1 was the smallest group and the most resistant. Cluster B2 was the second-most dominant group and of intermediate resistance between clusters A and B1. The percentages of accessions comprising each cluster varied by region and area. Accessions in cluster A were distributed widely throughout Vietnam and had the highest frequencies in both the Central and North regions. Accessions in cluster B2 were found with highest frequencies in the mountainous and intermediate areas of the North region. Accessions in cluster B1 were found with highest frequencies in the Central region and Red River Delta area (North region). These results suggest that rice accessions in Vietnam were basically susceptible (cluster A) or of intermediate resistance (cluster B2), and that high-resistance cultivars were mainly distributed in the low altitude areas, such as the Red River Delta area and Central region.

Characterization of Six Partial Resistance Genes and One Quantitative Trait Locus to Blast Disease Using Near Isogenic Lines with a Susceptible Genetic Background of Indica Group Rice (Oryza sativa)

Seven near isogenic lines (NILs) for six partial blast-resistance genes— Pi35, pi21, Pi37(t)( Pi37-KRIL17), Pb1, and Pi34 (two: Pi34-Chubu32 and Pi34-Chugoku40, originating from different Japonica Group rice lines, ‘Chubu 32’ and ‘Chugoku 40’, respectively)—and one quantitative trait locus (QTL), PiPHL9, derived from Japonica Group line ‘Hokkai PL9’, were developed in rice ( Oryza sativa L.). These NILs have the genetic background of an Indica Group susceptible line ‘US-2’, which does not harbor complete resistance genes and can clarify the effects of partial resistance genes and the QTL. These NILs and US-2 were used to determine the effects of the partial resistance genes and the QTL based on the results of an inoculation test for leaf blast using international standard differential blast isolates in the young seedling stage and a natural infection test in the mature stage after heading at a blast field. The NILs produced mainly moderate reactions in the inoculation test and rarely exhibited “resistant” and “susceptible” reactions. Each of the partial resistance genes and the QTL had different effects in panicle blast. Two genes, Pi35 and Pb1, were the most effective with respect to resistance, followed by Pi37-KRIL17. Pi34-Chugoku40 was the weakest. The effects of pi21, Pi34-Chubu32, and PiPHL9 varied among cultivation seasons and could be easily affected by environmental conditions. This is the first report clarifying the effects of partial resistance genes without the major complete genes, which will be helpful for advanced genetic and pathological studies and as a source of genes for rice breeding. [Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Lines for blast resistance genes with genetic background of Indica Group rice as international differential variety set

AbstractTwenty‐one near‐isogenic lines (NILs) for 18 resistance genes—Pia, Pii, Pi3, Pi5(t), Pik‐s (two lines from two donors), Pik‐m, Pi1, Pik‐h, Pik, Pik‐p, Pi7(t), Pi9(t), Piz, Piz‐5, Piz‐t, Pita‐2, Pita (three donors) and Pi20(t)—to blast disease were developed through introduction into the genetic background of a semi‐dwarf susceptible rice line, US‐2, by recurrent backcross breeding. US‐2 is derived from a cross between an Indonesian Tropical Japonica Group cultivar, 'Kencana', and an improved high‐yielding and semi‐dwarf Indica Group cultivar, 'Takanari', bred in Japan. The reactions of US‐2 NILs to standard differential blast isolates were clearly defined than previous differential varieties (DVs) such as monogenic lines. US‐2 and its NILs are adapted well to wide environmental conditions from temperate to subtropical regions. They will be useful and easier to handle and manage as the first DV set with genetic background of Indica Group rice for pathology studies and as gene sources for rice breeding programme.

Near-isogenic lines for resistance to blast disease, in the genetic background of the Indica Group rice (Oryza sativa L.) cultivar IR64

We developed 21 near-isogenic lines (NILs) in the genetic background of the Indica Group rice ( Oryza sativa L.) cultivar IR64, with each containing one of the 11 blast resistance genes: Pish , Piz , Piz-5 , Pi9 (t), Pii , Pi3 , Pik , Pik-h , Pik-p , Pi1 , and Pi7 (t). The NILs were confirmed to harbor these genes by their reaction patterns to standard differential blast isolates and by analyses for graphical genotypes using DNA markers located on the same chromosome regions as the target resistance genes. The agronomic traits of these NILs, such as days to heading and yield components, were also investigated and found to be very similar to those of IR64, even when grown under the dramatically different environmental conditions of the temperate and subtropical regions of Japan. These NILs and their genetic information will be used as gene sources for Indica Group rice breeding programs, to improve resistance to blast disease, and as a multiline variety that will also be useful as an alternative approach to the development of the durability of rice resistance to blast disease in tropical areas, especially in irrigated lowland ecosystems.

Pathogenicity of Isolates of the Rice Blast Pathogen (Pyricularia oryzae) From Indonesia.

A total of 201 isolates of Pyricularia oryzae (the causal agent of rice blast) were collected from three rice ecosystems (upland, lowland, and swampy) in five regions of Indonesia (West Java, Lampung, South Sumatra, Kalimantan, and Bali). Their pathogenicities were characterized based on the patterns of reaction of 25 differential varieties (DVs) and the susceptible control Lijiangxintuanheigu (LTH), which was susceptible to all blast isolates. A high proportion of isolates (>80.0%) were virulent to DVs for resistance genes Pib, Pit, Pia, Pik-s, and Pi12(t), and a low proportion of isolates (<12.9%) were virulent to DVs for Pik-m, Pi1, Pik-h, Pik, Pik-p, and Pi7(t). Virulence to the other DVs for Pish, Pii, Pi3, Pi5(t), Pi9(t), Piz, Piz-5, Piz-t, Pita-2 (two lines), Pita (two lines), Pi19(t), and Pi20(t) showed intermediate frequencies from 20.0 to 80.0%. These isolates were classified into three cluster groups, Ia, Ib, and II, and the frequencies of cluster groups varied between the three ecosystems and the five regions. The frequencies of cluster groups varied between ecosystems and regions, and races varied according to the ecosystems. A total of 27 standard differential blast isolates (SDBIs) were selected from the 201 isolates collected. The set of 25 DVs and these 27 SDBIs will be used as a new differential system for analysis of the pathogenicity of blast isolates and analysis of resistance genes in rice cultivars, which will contribute to building a durable protection system against blast disease in Indonesia.

Genetic Variation of Rice Blast (Pyricularia oryzae) Isolates in Laos

The pathogenicity of 192 blast isolates collected from regions across the whole of Laos from 2007 to 2009 showed a wide variation in terms of the frequencies of virulence toward differential varieties (DVs) and the susceptible control cultivar Lijiangxintuanheigu. High frequencies of virulence (&gt;50%) were found in the reactions of DVs for Pit, Pia, Pi3, Pi5(t), Pik-s, Piz-t, Pi19(t), and Pi20(t); intermediate values (from 10 to 50%) were found in DVs for Pib, Pii, Pik-m, Pi1, Pik-h, Pik, Pik-p, Pi7(t), Piz-5, Pita (two lines), Pita-2 (two lines), and Pi12(t); and low frequencies (&lt;10%) were found in DVs for Pish, Piz, and Pi9(t). The blast isolates were classified into three cluster groups: Ia and Ib (low virulence) and II (high virulence), based on the patterns of reaction to them. The blast isolates in cluster group Ia were dominant in rainfed lowland areas, those in Ib were dominant in irrigated lowland areas, and those in II were dominant in upland areas. Cluster groups Ia, Ib, and II were dominant in the Southern, Central, and Northern regions, respectively. Blast races in Laos were distributed according to ecosystems for rice cultivation and geographical regions from south to north with different virulence. These isolates were categorized into 156 races, and the numbers of blast isolates were few in each race. A total of 15 representative isolates were selected from among them as standard differential blast isolates, to develop a differential system.

Genetic variation of blast (Pyricularia oryzae Cavara) resistance in rice (Oryza sativa L.) accessions widely used in Kenya.

A total of 47 rice accessions collected from Kenya were investigated the genetic variations and classified into two cluster groups, A and B, by polymorphism data of 65 simple sequence repeat (SSR) markers. Clusters A and B corresponded to Japonica and Indica Groups, respectively. The number of Japonica Group accessions was limited in comparison with those of the Indica Group. Based on their patterns of reaction to standard differential blast isolates (SDBIs), these accessions and 57 control cultivars including differential varieties and several accessions harboring partial resistance genes were classified again into three cluster groups: Ia (high resistance), Ib (intermediate resistance) and II (susceptible). The rice accessions from Kenya were classified only into groups Ia and Ib. The accessions from Kenya were finally classified into three categories, A-Ia, B-Ia and B-Ib, based on the two classifications of polymorphism of SSR markers and resistance. The Indica Group accessions had wider genetic variation for blast resistance than did the Japonica Group accessions. The three leading cultivars (Basmati 217, Basmati 370 and ITA 310) categorized into Cluster group Ia were susceptible to some SDBIs from Kenya. The genetic variation for blast resistance in Kenya was demonstrated as the first report using SDBIs.

Genetic variation in blast resistance in rice germplasm from West Africa.

The genetic variation in resistance to blast (Pyricularia oryzae Cavara) in 195 rice accessions comprising 3 species of the AA genome complex (Asian rice [Oryza sativa L.], African rice [Oryza glaberrima Steud.] and wild rice [Oryza barthii]) was investigated based on their patterns of reaction to standard differential blast isolates (SDBIs) and SSR marker polymorphism data. Cluster analysis of the polymorphism data of 61 SSR markers identified 3 major clusters: cluster A (mainly Japonica Group or upland accessions), cluster B (mainly Indica Group or lowland accessions) and cluster C (O. glaberrima and O. barthii). The accessions were classified again into 3 resistance groups based on reactions to SDBIs: group Ia (susceptible), group Ib (middle resistance) and group II (high resistance). Group Ia included only a few differential varieties, susceptible controls and the Japonica Group cultivar Nipponbare. Accessions in clusters A and B included all 3 resistance groups and showed a wide variation in blast resistance, but cluster C contained only group Ib. These results demonstrated that variations in Asian rice (O. sativa) accessions in West Africa were skewed toward high resistance and that variations in O. glaberrima and O. barthii were limited and lower than the Asian rice accessions.

Genetic variation in resistance to blast (Pyricularia oryzae Cavara) in rice (Oryza sativa L.) germplasms of Bangladesh.

Genetic variation in blast resistance was clarified in 334 Bangladesh rice accessions from 4 major ecotypes (Aus, Aman, Boro and Jhum). Cluster analysis of polymorphism data of 74 SSR markers separated these accessions into cluster I (corresponding to the Japonica Group) and cluster II (corresponding to the Indica Group). Cluster II accessions were represented with high frequency in all ecotypes. Cluster II was further subdivided into subclusters IIa and IIb. Subcluster IIa accessions were represented with high frequency in only Aus and Jhum ecotypes. Cluster I accessions were more frequent in the Aman ecotype than in other ecotypes. Distinct variations in resistance were found, and accessions were classified into 4 groups (A1, A2, B1 and B2) based on their reactions to standard differential blast isolates. The most susceptible group was A2 (which included susceptible variety Lijiangxintuanheigu, most of the differential varieties, and a few Bangladesh accessions), followed in order by A1, B2 and B1 (the most resistant). Accessions from 4 ecotypes fell with different frequencies into each of these resistance groups. These results demonstrated that Japonica Group accessions were found mainly in Aman, and Indica Group accessions were distributed across all ecotypes. Susceptible accessions were limited in Aus and Aman.

Diversity and Distribution of Rice Blast (Pyricularia oryzae Cavara) Races in Bangladesh

The pathogenicity of 331 blast isolates (Pyricularia oryzae Cavara) collected from different regions and ecosystems for rice cultivation in Bangladesh was evaluated by compatibility on 23 differential varieties (DV), each harboring a single blast resistance gene, and susceptible 'Lijiangxintuanheigu' (LTH). A wide variation in virulence was found among the isolates, and 267 races were classified using a new designation system. Virulence of blast isolates against DV carrying the resistance genes Pia, Pib, Pit, Pik-s, Piz-t, Pi12(t), Pi19(t), and Pi20(t), as well as avirulence against those carrying Pish, Pi9, Pita-2, and Pita, was distributed widely in Bangladesh. Cluster analysis of the compatibility data on the DV initially classified the isolates into groups I and II. The virulence spectra of the two groups differed mainly according to the reactions of the DV to Pii, Pi3, Pi5(t), Pik-m, Pi1, Pik-h, Pik, Pik-p, and Pi7(t). Group I isolates were distributed mainly in rainfed lowlands, whereas group II isolates were found mainly in irrigated lowlands; however, there were no critical differences in geographic distribution of the blast isolates. In total, 26 isolates, which could be used to identify the 23 resistance genes of the DV on the basis of their reaction patterns, were selected as a set of standard differential blast isolates. To our knowledge, this is the first clear demonstration of the diversity and differentiation of blast races in Bangladesh. This information will be used to develop a durable blast protection system in that country.

Diversity and Distribution of Rice Blast (Pyricularia oryzae Cavara) Races in Vietnam.

A total of 239 isolates of blast (Pyricularia oryzae Cavara) collected from northern and central Vietnam showed a wide variation in pathogenicity based on the reaction patterns to 25 differential varieties (DVs) harboring 23 resistance genes and susceptible cultivar Lijiangxintuanheigu (LTH). The frequencies of isolates virulent toward DVs for Pish, Pik-m, Pi1, Pik-h, Pik, Pik-p, Pi7(t), Pi9(t), Piz-5, Pita-2, and Pita were low, but they were high for DVs for Pib, Pit, Pia, Pii, Pi3, Pi5(t), Pik-s, Piz, Piz-t, Pi12(t), Pi19(t), and Pi20(t). Isolates were classified into three cluster groups Ia, Ib, and II based on reaction patterns to DVs and LTH. The frequencies of isolates virulent toward 11 DVs for Pik-m, Pi1, Pik-h, Pik, Pik-p, Pi7(t), Pi9(t), Piz, Piz-5, Pita-2, and Pita in cluster II and DV for Piz-t were higher and lower than those of Ia and Ib, respectively. The frequencies to DVs for Pii, Pi3, Pi5(t), and Piz-t were different between clusters Ia and Ib. Clusters Ia and Ib were distributed with similar frequencies in the northeast, north central, and south central coast regions, but the frequencies among three cluster groups in the Red River Delta and northwest regions were different. This means that the blast races in these two regions were different from the others. Overall, the blast isolates were categorized into 153 races. Among them, 26 were selected as a set of standard differential blast isolates for characterizing 23 resistance genes and developing a differential system in Vietnam.

Detection of novel blast resistance genes, Pi58(t) and Pi59(t), in a Myanmar rice landrace based on a standard differential system

The use of broad-spectrum R genes is an effective way to achieve durable resistance against rice blast (Magnaporthe oryzae Couch, anamorph: Pyricularia oryzae Cavara) in rice (Oryza sativa L.). We previously surveyed the diversity of blast resistance in 948 rice varieties and found a Myanmar rice landrace, Haoru (International Rice Research Institute genebank acc. no. IRGC33090), with broad-spectrum resistance against the standard differential blast isolates. Here, we examined the genetic basis of Haoru’s broad-spectrum resistance by using the standard blast differential system consisting of the standard isolates and differential varieties. For genetic analysis, we used a BC1F1 population and BC1F2 lines derived from crosses of Haoru with a susceptible variety, US-2. Co-segregation analysis of the reaction pattern in the BC1F1 population against the 20 standard isolates suggested that Haoru harbors three R genes. By using bulk-segregant and linkage analysis, we mapped two of the three R genes on chromosomes 12 and 6, and designated them as Pi58(t) and Pi59(t), respectively. Pi58(t) and Pi59(t) were differentiated from other reported R genes using the standard differential system. The estimated resistance spectrum of Pi58(t) corresponded with that of Haoru, suggesting that Pi58(t) is primarily responsible for Haoru’s broad-spectrum resistance. In addition, Pi59(t) and the third gene were also proven to be new and useful genetic resources for studying and improving blast resistance in rice.

Characterization of Rice Blast Isolates by the Differential System and their Application for Mapping a Resistance Gene, Pi19(t)

To facilitate resistance gene characterization in the present study, the pathogenicities of newly collected blast isolates from rice fields in the Philippines were characterized using international blast differential varieties consisting of 31 monogenic lines that target 24 resistance genes. To classify and designate the blast isolates, we used a new international blast designation system, which has been proposed as a suitable naming system for comparing blast races among different studies. A total of 23 rice blast isolates collected from the Philippines were classified into 16 pathotypes, which showed reaction patterns different from those seen in the standard isolates. Among the blast pathotypes, 11 had differentiating ability for four Pik alleles (Pik, Pik-m, Pik-h, and Pik-p) and Pi1, whereas the standard blast isolates from the Philippines were not able to differentiate these genes. In addition, several blast isolates were avirulent to IRBLt-K59, IRBL19-A, and Lijiangxintuanheigu, although the standard differential blast isolates were virulent to these lines. Moreover, two blast isolates were virulent to a monogenic line, IRBL9-W, which harbours Pi9 and was resistant to all standard differential blast isolates. By using the isolates avirulent to IRBL19-A, Pi19(t) was successfully mapped in the centromeric region on chromosome 12 with simple sequence repeat markers RM27937 and RM1337. These markers are useful for marker-assisted Pi19(t) introgression worldwide.

Characterization of Pi13, a blast resistance gene that maps to chromosome 6 in indica rice (Oryza sativa L. variety, Kasalath)

Characterization of resistance genes is essential for the development of a new variety resistant to blast (Magnaporthe grisea) in rice (Oryza sativa L.). In this study, we found that an indica variety, Kasalath, harbored a resistance gene that showed a broad spectrum of resistance reactions against standard differential blast isolates from the Philippines and Japan. Quantitative trait locus (QTL) analysis was conducted using backcross inbred lines derived from crosses between Kasalath and the japonica cultivar, Koshihikari, to detect the QTL for blast resistance. QTLs were detected on chromosomes 6 and 8. Further, QTL analysis of chromosome segment substitution lines of Kasalath in the Koshihikari genetic background revealed that the Kasalath allele at the QTL on chromosome 6 strongly contributed to blast resistance. These results suggested that the gene locus might be identical to Pi13(t) that had already been reported. By marker-assisted breeding, a near-isogenic line, Koshihikari Toyama BL7, with a Kasalath chromosome segment containing Pi13(t) introduced into Koshihikari genetic background, was developed. The reaction of Koshihikari Toyama BL7 to the differential blast isolates indicated that Pi13(t) was a broad-spectrum and moderate resistance gene. Since Pi13(t) showed single-gene segregation and was characterized, the gene was re-designated as Pi13.

Genetic analysis of resistance genes in an Indica-type rice (Oryza sativa L.), Kasalath, using DNA markers

We searched for blast resistance genes in an Indica-type rice (Oryza sativa L.) cultivar, Kasalath. The resistance gene was estimated based on the reaction patterns to standard differential blast isolates from Japan and Philippines against the monogenic lines as differential varieties targeting 24 kinds of resistance genes. Kasalath showed complete resistance only to a Japanese isolate, Hoku1, which was avirulent to genotypes containing the Piz allele genes and virulent to genotypes containing Pia and Pish. Kasalath was susceptible, or only moderately resistant, to the Philippine isolates. A QTL analysis for resistance to Hoku1 was performed in backcross inbred lines derived from crosses between Kasalath and a Japonica-type cultivar, Nipponbare (recurrent parent), harboring Pia and Pish. A resistance QTL with the Kasalath genotype was detected in the same region as Pia on chromosome 11. Association analysis in 50 chromosome segment substitution lines detected three associations, on chromosomes 6, 8 and 11; the association located in the same region as the QTL on chromosome 11 had a strong resistance effect. These reaction patterns indicated that Kasalath did not harbor Pia and that the QTL on chromosome 11 was the other allele of Pia or a novel resistance gene.

Diversity analysis for resistance of rice (Oryza sativa L.) to blast disease [Magnaporthe grisea (Hebert) Barr.] using differential isolates from the Philippines

AbstractA wide variation in resistance to blast disease caused by Magnaporthe grisea (Hebert) Barr. (Rossman et al. 1992) was found using 922 rice (Oryza sativa L.) varieties collected mainly from Asia. These were classified into six varietal groups, termed clusters A–F, according to Ward’s hierarchical cluster analysis, based on the reaction pattern to 20 standard differential blast isolates from the Philippines. The most susceptible two clusters, B and C, dominated in varieties from the Far East (Japan). Varieties from East Asia and Southeast Asia occurred less frequently in B and C clusters than those of Japan, and more frequently in E and F clusters, which were the most resistant of the cluster groups. Varieties from South Asia showed the widest variation, occurring in all clusters but less frequently in cluster B. The cluster B varieties dominated in Japan and showed a high frequency of isozyme type VI, corresponding to Japonica type. In contrast, the frequency of cluster B was low in the groups with isozyme types I, II, III and V, which dominated in South Asia. Isozyme type I corresponds to Indica type varieties. The distribution of resistance corresponded to the geographical distribution of rice varieties and might be related to differentiation into Indica and Japonica types. These findings will provide useful information for understanding the variation in blast resistance at the global level.