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Article

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

by
Dongyuan Wang
1,2,
Feng Zhu
1,
Jichun Wang
1,*,
Hongguang Ju
3,*,
Yongfeng Yan
4,
Shanyan Qi
1,2,
Yuping Ou
1,2 and
Chengli Tian
1
1
Plant Pathology Division, Institute of Plant Protection, Jilin Academy of Agricultural Sciences, Changchun 130033, China
2
Plant Pathology Division, College of Plant Protection, Jilin Agricultural University, Changchun 130118, China
3
Rice Breeding Division, College of Agriculture, Yanbian University, Yanji 130002, China
4
Rice Breeding Division, Institute of Rice Research, Jilin Academy of Agricultural Sciences, Changchun 130033, China
*
Authors to whom correspondence should be addressed.
Pathogens 2024, 13(3), 211; https://doi.org/10.3390/pathogens13030211
Submission received: 24 December 2023 / Revised: 26 February 2024 / Accepted: 26 February 2024 / Published: 28 February 2024
(This article belongs to the Special Issue The Remaining Threat of Magnaporthe oryzae)
Browse Figures
Review Reports Versions Notes

Abstract

:
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.

1. Introduction

Blast, caused by the fungus Pyricularia oryzae Cavara (formerly Magnaporthe oryzae B. C. Couch), is the most damaging disease in rice worldwide [1]. The interaction between host resistance and fungus virulence in the pathosystem can be explained by a “gene for gene” theory: for every resistance gene in the host variety, there is a corresponding avirulence gene in the blast pathogen [2,3]. Based on the theory, a large number of differential varieties (DVs) with special resistance genes have been developed [4,5,6,7,8,9,10,11,12]. Since 2000, two sets of DVs originated from Japonica Lijiangxintuanheigu (LTH) and Indica CO39 have been reported [13,14]. The Japonica monogenic DVs are produced by introducing single resistance genes into a Chinese Japonica cultivar LTH one by one. The introduced R genes include Pib, Pit, Pia, Pii, Pi3, Pi5(t), Pik-s, Pik-m, Pi1, Pik-h, Pik, Pik-p, Pi7(t), Pi9(t), Piz, Piz-5, Piz-t, Pita-2 (two lines), Pita (two lines), Pi12(t), Pi19(t), and Pi20(t). These DVs are the latest and have been broadly utilized in many countries or regions in the world, including China [15], Japan [16], Kenya [17], and Indonesia [18].
Blast isolates have played a critical role in the identification of resistant germplasm in rice breeding. Each standard differential blast isolate (SDBI) has special avirulent characteristics, so SDBIs have been developed and broadly used in resistance breeding programs [13,18,19,20]. Pathogenically diverse isolates with different avirulence gene proportions have been reported in Cambodia [21], West Africa [22], Bangladesh [19], and Vietnam [20]. However, there is no report about SDBIs originating from the DVs in the Japonica rice production area of China.
There are two sets of DVs used successively in northeast China, where Japonica rice is produced [23]. The first set of DVs has been used since 1976, including 7 DVs of Tetep, Zhenlong13, Sifeng43, Dongnong363, Guandong51, Hejiang18, and LTH [5]. Because their genetic backgrounds on R genes are poorly understood, their identified race information has poorly helped blast-resistance breeding. The second set of DVs contains 25 monogenic differential varieties (MDVs), which harbor 23 resistance genes originating from Japonica LTH. Wang et al. [15] were the first to use this set of MDVs, then followed by others [17,18]. Nowadays, the second set of MDVs has been applied to evaluate the pathogenic diversity of isolates, exchange resistant germplasm, understand resistance genetics of germplasm by artificial inoculation, and guide resistance breeding. For example, the Japonica variety Qinglin511 is bred from Jiudao44 as a gene donor, which harbors the R gene Piz, and the local elite variety Jijing88 as a recurrent parent. Field selection in each generation is assisted by blast isolate JLavrPiz-20220817 as an SDBI. As a result, Qinglin511 is resistant to blast with high-yielding and super grain quality [24].
It is well known that planting blast-resistance varieties is the most economical, effectual, and environment-friendly method for controlling rice blast [1,2,25]. Blast-resistance breeding is based on a suitable understanding of the pathogenic characteristics of local pathogens. Therefore, our goal in this study was to comprehensively understand the pathogenic characteristics of rice blast isolates in Jilin Province so as to serve blast-resistance breeding. In northeast China, including Heilongjiang, Liaoning, and Jilin provinces, plus nearby Russia, Japan, and North Korea, Japonica rice is planted on five million hectares, where blast is the most severe disease [23,26]. Therefore, this study focused on rice blast isolates, aiming to (1) understand virulence diversity and isolate frequency in the Japonica rice area of northeast China; (2) clarify predominant pathogenic types; and (3) select SDBIs for screening accessions to a special pathogen.

2. Materials and Methods

2.1. P. oryzae Single Spore Isolation and Conservation

During 2019–2021, we collected P. oryzae-infected rice panicles and leaves from three regions in Jilin Province, China: the west drought region (Region I), including Song-Yuan and Bai-Cheng; the central semi-humid region (Region II), including Chang-Chun, Ji-Lin, and Si-Ping; and the east semi-mountain humid region (Region III), including Yan-Ji, Tong-Hua, and Liao-Yuan (Figure 1, Table 1). To obtain a single spore of P. oryzae, the collected samples were incubated on moist filter paper in a Petri dish for 24 h with the protocol described by Wang et al. [15]. The incubated samples were shaken off on water–agar medium at 25 °C for 24–36 h until single spores could be noticed with long hyphae under the optical microscope. Each single spore was picked up using small hooks and cultured in a PDA slant medium at 25 °C for 5–7 d. Then, a single colony was transferred to rice straw agar medium covered with filter paper of 9 cm in diameter at 25 °C for 10 d. Finally, these cultures of all single isolates carrying mycelia and conidia were stored at −20 °C in sterile glass vials after necessary drying.
Note: Three regions were classified based on the climate differentiation in Jilin Province, northeast China. The west drought region includes Bai-Cheng City and Song-Yuan City; the center semi-humid region, including Chang-Chun City, Ji-Lin City, and Si-Ping City; and the east semi-mountain humid region, including Yan-Ji City, Tong-Hua City, and Liao-Yuan City. Two groups occurred in all three regions, and two subgroups were divided into Ia and Ib in both the central and east regions.
Table 1. Blast isolates and frequencies in three regions of Jilin Province, northeast China.
Table 1. Blast isolates and frequencies in three regions of Jilin Province, northeast China.
Number of Blast Isolates and Frequency (%)
Cluster Group
RegionIaIbIITotal
West drought region6 (18.75)0 (0.00)26 (81.25)32 (100.00)
Central semi-humid region17 (20.99)1 (1.23)63 (77.78)81 (100.00)
East semi-mountain humid region24 (25.80)1 (1.08)68 (73.12)93 (100.00)
Total47 (22.82)2 (0.97)157 (76.21)206 (100.00)

2.2. Differential Varieties and Growth Conditions

Our study used 25 rice monogenic lines with a highly susceptible check variety, Menggudao (CK). These monogenic differential varieties (MDVs) harbor 23 single R genes, respectively, including IRBLsh-B(Pish), IRBLt-K59(Pit), IRBLb-B(Pib), IRBLa-A(Pia), IRBL-F5(Pii), IRBL3-CP4(Pi3), IRBL5-M[Pi5(t)], IRBLks-F5(Pik-s), IRBLkm-Ts(Pik-m), IRBL1-CL(Pi1), IRBLkp-K60(Pik-p), IRBLk-k[LT](Pik), IRBLkh-K3[LT](Pik-h), IRBL7-M[Pi7(t), IRBL9-W[Pi9(t)], IRBLz-Fu(Piz), IRBLz5--CA(Piz-5), IRBLzt-T(Piz-t), IRBLta2-Re(Pita-2), IRBLta2-Pi(Pita-2), IRBL12-M[Pi12(t)], IRBLta-K1(Pita), IRBLta-CP1(Pita), IRBL19-A[Pi19(t)], IRBL20-IR24[Pi20(t)], and the backcross parent LTH [27,28,29]. Seeds of the monogenic lines and LTH were generously provided by Cailin Lei from the Institute of Crop Sciences, Chinese Academy of Agricultural Sciences (ICS-CAAS). LTH is a Japonica-type local variety from Yunnan Province, China, which is broadly susceptible to rice blast isolates. The Menggudao is used as a super-susceptible control variety or induce variety susceptible to blast disease in disease nurseries in China. Five seeds of each MDV and CK were planted in a plastic tray (68 × 34 × 7 cm) containing local clay soil that had been treated with 0.1% carbendazim fungicide for 3 d. The tray was kept at 20 °C for the night and 28 °C for the day for about four weeks until seedlings were at the 4th–5th leaf stage [15].

2.3. Inoculation and Evaluation

Each isolate was inoculated on an oat agar medium with a standard method [30]. After 2 weeks, each conidial suspension was standardized to a concentration of 1 × 105 spores/mL, then 200 mL standardized spore suspension was sprayed to each tray (1 square meter) with seedlings at the 4th–5th leaf stage using an atomizer. The trays were kept in the dark for 16 h before being transferred to a greenhouse at 25–28 °C with 95% relative humidity. At 6–7 d after inoculation, blast reaction was classified on a scale of 0–5, where 0 means no evidence of infection; 1 means brown specks smaller than 0.5 mm, no sporulation; 2 means brown specks about 0.5–1.0 mm in diameter, no sporulation; 3 means roundish to elliptical lesion about 1–3 mm in diameter with a gray center surrounded by brown margins, lesions capable of sporulation; 4 means typical spindle-shaped lesions capable of sporulation, longer than 3 mm with necrotic gray centers and water-soaked or reddish brown margins, little or no coalescence of lesions; and 5 means the same as type 4 but with half of one or two leaf blades killed by the coalescence of lesions as described by Hayashi and Fukuta [31] using Menggudao as susceptible check. The inoculation and evaluation were performed twice sequentially for each rice line and each blast isolate, and the most severe lesion type on the leaf was recorded according to the compatible reaction type. Scales 0–2 were classified as R (Resistant) and 3–5 as S (Susceptible).

2.4. Characterization of the Blast Isolates

The R and S reaction patterns of each MDV to the blast isolates were characterized according to the U-i-k-z-ta pattern criteria and pathogenic proportion to MDVs [18]. The diversity in the collection was measured with Simpson’s diversity index [32]. The index values range from 0 to 1, where 0 presents no diversity and 1 maximum diversity [19].

2.5. Selection of Standard Blast Isolates

A compatible reaction pattern between MDVs and blast isolates was used to select standard blast isolates (SDBIs). An SDBI had no pathogenicity to one of the MDVs but had very strong pathogenicity to all other MDVs. Based on the gene-for-gene theory, there is a corresponding avirulence gene existing in isolates, which could be used to identify the genetic background of rice accessions resistant to P. oryzae according to the interaction-compatible phenotype. Furthermore, we selected some super-virulent isolates for screening super-resistant germplasm.

2.6. Dendrogram Construction and Cluster Analysis

Cluster analysis was performed via Ward’s [33] hierarchical method, based on the data of infection scores of the 25 DVs and LTH by blast isolates, in the MEGA11 computer program, aligned using clustalw implemented with the maximum likelihood method.

3. Results

3.1. Race Information by U-i-k-z-ta Pattern Criteria and Cluster Groups

We identified 206 blast isolates from collected samples originating in three ecosystems: 93 isolates from Region I—the west drought; 81 from Region II—the central semi-humid; and 32 from Region III—the semi-mountain humid (Table 1; Figure 1). In accordance with the race name criteria of the U-i-k-z-ta pattern, the 206 isolates were categorized into 175 races based on the phenotype data (Supplementary Table S1; Supplementary Figure S1). Race U73-i5-k177-z11-ta330 contained five isolates and proved to be predominant among all races, followed by four isolates in race U53-i7-k177-z17-ta330, U73-i7-177-z17-ta733, and U73-i5-k103-z00-ta330, three isolates in race U53-i1-k101-z02-ta330, U73-i5-k177-z07-ta330, and U73-i7-k177-z17-ta731, and two isolates in 12 races of U53-i7-k177-z07-ta330, U53-i7-k175-z07-ta730, U53-i7-k177-z17-ta733, U73-i1-k101-z01-ta330, U73-i1-k101-z01-ta332, U73-i5-k101-z01-ta330, U73-i1-k101-z00-ta330, U73-i5-k177-z11-ta332, U73-i7-k177-z03-ta330, U73-i5-k177-z01-ta730, U73-i7-k177-z17-ta333, and U73-i7-k177-z17-ta732. Each of the remaining 156 races contained one of the remaining 156 isolates.
The 206 isolates from three regions were classified into two groups, and Group I was divided into subgroups Ia and Ib (Supplementary Figure S1). Group I had 49 isolates, while Group II had 157 isolates. In Group I, Subgroup Ia had 47 isolates. (Table 1; Figure 1). It was obvious that Group II was the dominant among the three regions. Moreover, there were no isolates belonging to Subgroup Ib in the west region.
Among the three regions, the east region had the largest isolate number (93), followed by the central region (81) and the west region (32). Similarly, among cluster Group II, the east region had the largest isolate number (68), followed by the central region (63) and the west region (26), and the frequencies were 73.12%, 77.18%, and 81.25%, compared to Group I (Table 1). The details of pathogenic characteristics were presented in the dendrogram (Supplementary Figure S2).

3.2. Frequencies of Isolate Virulence toward MDVs

Analyses of the virulence frequency of blast isolates to 25 MDVs and LTH in three regions showed that 5 MDVs (Pi3, Pi9(t), Pi12(t), Pi19(t), and Pi20(t)) had low frequency (<40%), 10 MDVs (Pib, Pi5(t), Pik-m, Pi1, Pik-h, Pik-p, Pi7(t), Piz, Piz-5, and Piz-t) had moderate virulence frequencies (40–80%), and 10 MDVs (Pish, Pit, Pia, Pii, Pik-s, Pik, Pita (two lines), and Pita-2 (two lines)) had high virulence frequencies (>80%) (Figure 2a–d). Thirty-six isolates were avirulent to LTH, while check variety Menggudao was susceptible to all isolates. Isolate frequencies to MDVs were similar in three regions, but the MDVs harboring Piz-5 and Piz-t had lower frequency in Region III of east semi-mountain than in Region I of west drought and Region II of central semi-humid (Figure 2a–c).

3.3. Subgroup Reaction Type of MDVs

Among 206 isolates, race reaction types were diverse. In MDVs Subgroup “U”, there were 21 reaction types (U01, U03, U11, U13, U21, U22, U23, U31, U32, U33, U40, U43, U52, U53, U61, U62, U63, U70, U71, U72, and U73). Among them, U73 had the most types of 100 (48.5%), which were virulent to four MDVs of Pish, Pib, Pit, Pia, and LTH. Subgroup U53 had 44 types (21.4%), which were virulent to three MDVs of Pish, Pit, Pia, and LTH but not virulent to Pib. The avrPib existed in many isolates (Table 2).
In MDVs Subgroup “i”, there were eight reaction types: i7, i6, i5, i4, i3, i2, i1, and i0. Among them, three were major types, with i5 having the dominant types of 65 (31.6%) virulent to Pii and Pi5(t), followed by i7, with 63 types (30.6%) virulent to all three MDVs of Pii, Pi3, and Pi5(t), and i1, with 45 types (21.8%) virulent to Pii. Pii was more susceptible to Pi3 and Pi5(t) (Table 2).
MDVs Subgroup “k” had 45 reaction types. Among them, k177 was the predominant reaction type in Jilin Province, containing 85 isolates (41.4% of all 206 isolates), and was virulent to MDVs for Pik-s, Pik-m, Pi1, Pik-h, Pik, Pik-p, and Pi7(t) (Table 2).
In MDVs Subgroup “z”, z17 and z07 had more types than others, with 40 (19.4%) and 30 (14.6%), respectively. Both had different virulent and avirulent reactions to MDV for Pi9(t) and largely influenced the pathogenic diversity in “z” (Table 2).
MDVs Subgroup “ta” had 28 reaction types, including ta000, ta010, ta021, ta030, ta031, ta120, ta130, ta132, ta220, ta221, ta230, ta232, ta233, ta300, ta312, ta320, ta322, ta330, ta331, ta332, ta333, ta431, ta620, ta713, ta730, ta731, ta732, and ta733. Among them, ta330 was dominant with 87 isolates (42.2%), virulent to Pita-2(Pi), Pita-2(Re), Pita(K1), and Pita(CP1), but avirulent to Pi12(t), Pi19(t), and Pi20(t) (Table 2). The avrPi12(t), avrPi19(t), and avrPi20(t) were predominant avirulence genes in Jilin Province (Table 2).
Evidently, from the above MDVs subgroup results, U73, U53, i7, i5, i1, k177, and ta330 were predominant reaction types, and their frequency was more than 20%. Like z17 and z07 were affected by Pi9(t) reaction phenotype, ta330 was affected by Pi12(t), and all of them crucially influenced isolate characterization (Table 2).

3.4. Standard Differential Blast Isolates (SDBIs) Characterization

Based on the race type information, we selected 25 blast isolates as standard differential blast isolates (SDBIs) for screening resistance accessions (Table 3). These SDBIs differentiated the 23 kinds of resistance genes among the 25 DVs. Specifically, the strains of LY1, TH11, SP11, and SY15 corresponded to the broad-spectrum resistance genes of Pi19(t), Pi20(t), Pi12(t), and Pi9(t), respectively (Figure 2d), which could be used to identify the accessions resistant to P. oryzae according to targeted genes. Among them, four isolates, TH20, JL19, LY23, and YJ9, showed different reaction patterns between IRBLta2-Pi and IRBLta2-Re, the same resistance gene Pita-2. And, two isolates, CC13 and SY1, showed different reaction patterns between IRBLta-K1 and IRBLta-CP1, which harbored the same resistance genes Pita (Table 3). Furthermore, two strong virulence isolates, JL27 and SY5, were selected because they were pathogenic to all MDVs harboring all resistance genes (Table 3). The existence of super-virulent isolates indicated a severe threat to rice production. Meanwhile, super-virulent isolates could be used to digest some broad-spectrum resistant accessions to fill special shortcomings in the region.

4. Discussion

Based on the reaction patterns of 25 DVs harboring 23 resistance genes, backcross parent LTH, and check variety Menggudao, we identified 206 isolates from samples collected in three regions in Jilin Province, northeast China (Figure 1 and Table 1). Based on the criteria of the U-i-k-z-ta pattern, we clarified 175 races among 206 isolates, whereas race U73-i5-k177-z11-ta330 included 5 isolates, which were predominant among the races. Furthermore, among MDVs subgroups, U73(100 reaction types, 48.5%) and U53(44, 21.4%); i7(63, 30.6%), i5(65, 31.6%), and i1(45, 21.8%); k177(85, 41.3%); and ta330 (87, 42.2%) were predominant (Table 2). Thirty isolates demonstrated no virulence to LTH, suggesting that there were some resistance genes existing in the LTH variety, and the same events occurred in Kenya, where four isolates showed no virulence [17].
Among 25 MDVs and LTH, those harboring resistance genes Pish, Pit, Pia, Pii, Pik-s, Pik, Pita(two lines), and Pita-2(two lines) had the highest virulence frequency of P. oryzae ranging from 80 to 100%, followed by intermediate, 40–80%, for Pib, Pi5(t), Pik-m, Pi1, Pik-h, Pik-p, Pi7(t), Piz, Piz-5, and Piz-t, and low, 0–40%, for Pi3, Pi9(t), Pi12(t), Pi19(t), and Pi20(t). Compared with the previous 44 isolates studied, the resistance frequencies of Pi9(t), Pi19(t), Piz, Piz-5, Piz-t, Pi12(t), Pi5(t), and Pik-h were all more than 60% [15]. But, besides the Pi9(t), Pi12(t), Pi19(t), and Pi3, the Pi20(t) was more than 60% in this study, and the pathogenic characteristics of the isolates changed. The complex situation of the blast population might be related to the rice cultivars or the number of blast samples collected in different regions [17].
We divided the identified isolates into two groups (I and II) based on their reaction pattern on 25 MDVs. Those predominant races had high frequencies of reaction types. The frequency variation of blast isolates to DVs is essential for race diversity. For example, in race Subgroup Ib, the U63, the major difference from IRBLb-B(Pib), occurred twice in total, and the frequency was 66.7%. This was the major reason attributable to the Ib group. Similarly, the presence and absence of U53, z07, and k177 were major differences between Group I and Group II. Altogether, the diversity of all the major reaction types corresponded to the distribution of isolates of the cluster. The diversity index of DVs Groups z and k, which was calculated by the Simpson method [32], was higher than that of the other three groups. The diversity of avirulence genes for the blast isolates was important to differentiate the cluster groups.
Even though the set of MDVs has been used for pathogenic study in China, we were the first to use the U-i-k-z-ta criterion for naming each race of MDVs and screening SDBIs of blast fungus. Based on the gene-for-gene theory, every resistance gene in the host crop corresponds to an avirulence gene in the pathogen [3]. Wang et al. [15] were the first to inoculate 44 blast fungal isolates originated from Jilin to 23 monogenic line varieties. Isolate frequencies to MDVs of Pi9(t), Pi19(t), Piz, Piz-5, Piz-t, Pi12(t), Pi5(t), and Pik-h were 94.2%, 84.1%, 81.8%, 81.8%, 79.5%, 72.7%, 68.2%, and 68.2%, respectively, which clarified that avrPi9(t), avrPi19(t), avrPiz, avrPiz-5, avrPiz-t, avrPi12(t), avrPi5(t), and avrPik-h were the predominant avirulence gene types. In Hunan Province, China, Xing et al. [34] inoculated the same rice monogenic lines using their local isolates and demonstrated that avrPi9(t), avrPiz-5, avrPik-h, and avrPik-m were predominant with a frequency of 91.6%, 91%, 87.9%, and 87.3%, respectively. In Chongqing, China, Li [35] reported that avrPik-m and avrPik-h were the predominant avirulence genes, both frequency with 82.18%, followed by avrPi9(t), avrPik, and avrPi7(t) with 76.24%, 73.27%, and 70.30%, respectively. In Heilongjiang Province, China, Zhang et al. [36] found that avrPi12(t), avrPi9(t), avrPi19(t), avrPi20(t), and avrPiz-t had high frequency with 74.69%, 72.28%, 68.67%, 68.07%, and 60.24%, respectively. Altogether, isolate frequency to the DVs contained Pi9(t) is low, but to the DVs contained Pi12(t) varies differently according to the areas, which suggests that Pi9(t) is the most stable resistance gene. The structure of a pathogen population is strongly influenced by the structure of its host population [37]. The complex situation of the blast population might be related to the rice cultivars that are cultivated in certain regions [17].
Also, this same set of MDVs have been used in many countries, including China [15], Western Africa [22], Cambodia [21], the United States [30], Japan [16], Bangladesh [19], Kenya [17], Vietnam [20], and Indonesia [18]. This set of MDVs in our study could be an effective tool to clarify the pathogenic characteristics of blast fungus, search for resistance germplasm, and develop cultivars resistant to blast worldwide. The virulences of isolates to some MDVs are similar across many countries, such as the MDVs harboring Pia, Pii, and Pit are all high, but Pi9(t), Piz, and Pib are low in almost all the countries. However, the virulences of the MDVs harboring other resistance genes are different. For example, Pi12(t), Pi19(t), and Pi20(t) isolates have low virulence in Jilin Province, northeast China, but Pi12(t) and Pi20(t) isolates have similar virulence in northeast China and Japan [16]. But, Pi19(t) and Pi20(t) isolates have higher virulence frequency in Bangladesh, Kenya, and Cambodia than in other countries. In Indonesia, Pi12(t) isolates have high virulence, but Pi19(t) and Pi20(t) isolates have moderate virulence. Pita (two lines) and Pita-2 (two lines) isolates have higher virulence frequency and greater differentiation in Cambodia than in other Asian countries (Supplementary Table S2; Supplementary Figure S2).
We selected 27 SDBIs based on the distinct non-pathogenic reaction patterns corresponding to 25 MDVs (Table 3). These SDBIs could be used as the basic tool to evaluate rice germplasm for resistance to blast. Assisted with those strong virulent isolates such as JL27 and SY5, we will mine novel resistance genes to blast. We identified some virulent isolates with high frequency, which may break the existing resistance and bring about an epidemic of blast in the Japonica rice-planting area. Those SDBIs could be used to develop a durable system against blast disease in the Japonica area in northeast China, and the isolates could be replaced according to the modification abilities or virulence stability. Furthermore, the designation system for 25 MDVs in our study could be used to compare blast races in different regions and countries so as to help understand the differentiation and diversity of blast races in the world [16,17,18,19,20,21,22,30,31].

5. Conclusions

Using the U-i-k-z-ta pattern criteria, we first named 175 race types among 206 virulent isolates of P. oryzae in China. A total of 27 SDBIs were selected, and the set of strains would help us to develop a durable system against rice blast disease in northeast China. This study described the pathogenic diversity of blast isolates in the Japonica rice area of northeast China and compared the pathogenic diversity of isolates with other countries, which could help us to develop cultivars resistant to blast around the world.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/pathogens13030211/s1, Figure S1: Deprogram structure of physiological race based on the U-i-k-z-ta criteria of a total of 206 rice blast fungi isolates; Figure S2: Section value of virulent frequencies of isolates to DVs in different countries; Table S1: 1. Races information on 206 identified isolates according to the U-i-k-z-ta pattern named criteria; Table S2: Virulence differentials of rice blast isolates in many counties.

Author Contributions

Conceptualization, J.W.; methodology, J.W.; software, D.W.; validation, D.W., F.Z. and J.W.; formal analysis, D.W. and J.W.; investigation, D.W., J.W., S.Q., Y.O., Y.Y. and C.T.; resources, D.W., J.W., H.J., S.Q., Y.O. and Y.Y.; data curation, D.W. and J.W.; writing—original draft preparation, D.W. and J.W.; writing—review and editing, D.W.; visualization, D.W.; supervision, J.W.; project administration, H.J. and Y.Y.; funding acquisition, J.W. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the International Cooperation Project PJ014815 from the Rural Development Administration of South Korea, the Agricultural Innovation Project CXGC2021TD002 from Jilin Province, China, and the overseas training projects P162009007 and P192009006 from the Jilin Provincial Bureau of Foreign Experts Affairs.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

All the data generated during the current study are included in the manuscript.

Acknowledgments

We would like to thank Wengui Yan, who worked at the United States Department of Agriculture, Dale Bumpers National Rice Research Center; Erxun Zhou, who works at South China Agricultural University; and Yoshimichi Fukuta, who worked at Tropical Agricultural Research Front, Japan International Research Center for Agricultural Sciences, for their help in providing suggestions and revising this manuscript.

Conflicts of Interest

The authors declare no conflict of interest.

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Pathogens 13 00211 g001
Figure 1. Distribution of blast isolates identified from three regions in Jilin Province, northeast China.
Figure 1. Distribution of blast isolates identified from three regions in Jilin Province, northeast China.
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Pathogens 13 00211 g002
Figure 2. Pathogenic frequencies of blast isolates to differential varieties (DVs) in Japonica rice samples collected from three regions in Jilin Province, northeast China. (a) frequency of virulent blast isolates in west drought region; (b) frequency of virulent blast isolates in central semi-humid region; (c) frequency of virulent blast isolates in east-semi-mountain humid region; (d) frequency of virulent blast isolates of total isolates.
Figure 2. Pathogenic frequencies of blast isolates to differential varieties (DVs) in Japonica rice samples collected from three regions in Jilin Province, northeast China. (a) frequency of virulent blast isolates in west drought region; (b) frequency of virulent blast isolates in central semi-humid region; (c) frequency of virulent blast isolates in east-semi-mountain humid region; (d) frequency of virulent blast isolates of total isolates.
Pathogens 13 00211 g002
Table 2. Reaction types of differential varieties (DVs) in each subgroup.
Table 2. Reaction types of differential varieties (DVs) in each subgroup.
Reaction to Resistance Gene in Differential VarietyCluster Group
Reaction typePishPibPitLTHPia----Ia (n = 47)Ib (n = 2)II (n = 157)Total (n = 206)
U73vvvvv----3906110048.5
U63avvvv----02131.5
U53vavvv----00444421.4
OthersU72, U71, U70, U62, U61, U52, U43, U40, U33, U32, U31, U23, U22, U21, U13, U11, U03, U0180515928.6
Diversity index 0.310.000.760.71
Reaction typePiiPi3Pi5(t)------
i7vvv------20616330.6
i5vav------150506531.6
i1vaa------222214521.8
Others i6, i4, i3, i2, i080253316
Diversity index 0.680.000.730.76
Reaction typePik-s--Pik-mPi1Pik-hPikPik-pPi7(t)
k177v--vvvvvv00858541.3
k101v--aaavaa15062110.2
Others k176, k175, k174, k173, k171, k167, k165, k163, k157, k156, k154, k147, k145, k143, k137, k131, k127, k123, k121, k117, k114, k113, k112, k111, k107, k106, k103, k102, k100, k077, k067, k057, k055, k047, k032, k020, k017, k012, k010, k003, k002, k001, k0003226610048.5
Diversity index 0.871.000.700.81
Reaction typePi9(t)--PizPiz-5Piz-t---
z17v--vvv---30374019.4
z07a--vvv---00303014.6
z01a--vaa---151284421.4
z00a--aaa---21062713.11
Othersz16, z15, z14, z13, z12, z11, z10, z06, z05, z04, z03, z0281566531.55
Diversity index 0.701.000.860.87
Reaction typePita-2 (Pi)Pita-2 (Re)Pi12(t)Pita (K1)Pita (CP1)-Pi19(t)Pi20(t)-
ta332vvavv-av-20212311.2
ta330vvavv-aa-252608742.2
Others ta733, ta732, ta731, ta730, ta713, ta620, ta431, ta333, ta331, ta322, ta320, ta312, ta300, ta233, ta232, ta230, ta221, ta220, ta132, ta130, ta120, ta031, ta030, ta021, ta010, ta00020076960.47
Diversity index 0.710.000.820.79
Note: a, avirulent; v, virulent.
Table 3. Standard differential blast isolates (SDBIs) collected in three regions of Jilin Province.
Table 3. Standard differential blast isolates (SDBIs) collected in three regions of Jilin Province.
Monogenic Lines Varieties Harboring Resistance Genes
Isolate CodeIRBLsh-B(Pish)IRBLb-B(Pib)IRBLt-K59(Pit)IRBLa-A(Pia)IRBL-F5(Pii)IRBL3-CP4(Pi3)IRBL5-M[Pi5(t)]IRBLks-F5(Pik-s)IRBLkm-Ts(Pik-m)IRBL1-CL(Pi1)IRBLkh-K3[LT](Pik-h)IRBLk-k[LT](Pik)IRBLkp-K60(Pik-p)IRBL7-M[Pi7(t)IRBL9-W[Pi9]IRBLz-Fu(Piz)IRBLz5—CA(Piz-5)IRBLzt-T(Piz-t)IRBLta2-Pi(Pita-2)IRBLta2-Re(Pita-2)IRBL12-M[Pi12(t)]IRBLta-K1(Pita)IRBLta-CP1(Pita)IRBL19-A[Pi19]IRBL20-IR24[Pi20(t)]LTH
CC24avvavavvvvavvvvvvvvvvvvavv
SY4vavvvvvvvvvvvvvvvvvvvvvvvv
YJ33vvavvvavvavvvvvvvvvvvvvaav
CC31avvavvvvvvvvvvvvvvvvavvaav
LY7vavvavvavvvvvvvvvvavavvaav
SY7vavvvavvvvvvvvvvvvvvvvvvvv
SY12vvvvvvavvvvvvvavvvvvavvaaa
YJ23vavvvvvavvvvvvvvvvvvvvvvav
TH20vvvvvaavavvvvvavvvavavvaaa
JL19vavvvavvvavvvvavvvvvavvaav
CC12vavvavvvvvavvvaavvvvavvaav
YJ15vavvvavvvvvaavavaavvavvaav
YJ39vvvvvvvvavvvavavaavvvvvvav
TH19vvvvvvvvvvvvvaavvvvvavvavv
SY15vvvvvvvvvvvvvvavvvvvvvvvvv
YJ31vvavvvavvvvvvvvaavvvvvvaav
YJ14vvvvvvvvvvvvvvvvavvvavvvav
TH10vvavvavvvvvvvvvvvavvvvvaav
LY23vvvvvvvvvvvvvvvvvvaavvvvav
YJ9vvvvvvvvvvvvvvvvvavaaavaav
SP11vvvvvvvvvvvvvvvvvvvvavvvvv
CC13vavvvavvvvavaaavvvavvavaav
SY1vvvvvavavvaavaaavavvvvavvv
LY1vvvvvvvvvvvvvvvvvvvvvvvavv
TH11vvvvvvvvvvvvvvvvvvvvvvvvav
JL27vvvvvvvvvvvvvvvvvvvvvvvvvv
SY5vvvvvvvvvvvvvvvvvvvvvvvvvv
Note: CC is the abbreviation of Chang-Chun; SY, Song-Yuan; TH, Tong-Hua; JL, Ji-Lin; SP, Si-Ping; LY, Liao-Yuan; YJ, Yan-Ji; v, virulent; a, avirulent.
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Wang, D.; Zhu, F.; Wang, J.; Ju, H.; Yan, Y.; Qi, S.; Ou, Y.; Tian, C. Pathogenicity Analyses of Rice Blast Fungus (Pyricularia oryzae) from Japonica Rice Area of Northeast China. Pathogens 2024, 13, 211. https://doi.org/10.3390/pathogens13030211

AMA Style

Wang D, Zhu F, Wang J, Ju H, Yan Y, Qi S, Ou Y, Tian C. Pathogenicity Analyses of Rice Blast Fungus (Pyricularia oryzae) from Japonica Rice Area of Northeast China. Pathogens. 2024; 13(3):211. https://doi.org/10.3390/pathogens13030211

Chicago/Turabian Style

Wang, Dongyuan, Feng Zhu, Jichun Wang, Hongguang Ju, Yongfeng Yan, Shanyan Qi, Yuping Ou, and Chengli Tian. 2024. "Pathogenicity Analyses of Rice Blast Fungus (Pyricularia oryzae) from Japonica Rice Area of Northeast China" Pathogens 13, no. 3: 211. https://doi.org/10.3390/pathogens13030211

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