Population Structure of the Rice Blast Fungus in Japan

日植病報 65: 15-24 (1999)

Ann. Phytopathol. Soc. Jpn. 65: 15-24 (1999)

Population Structure of the Rice Blast Fungus in Japan Examined by DNA Fingerprinting

Le Dinh DON*, Motoaki KUSABA*,**, Alfredo S. URASHIMA*, Yukio TOSA*, Hitoshi NAKAYASHIKI* and Shigeyuki MAYAMA*

Abstract

DNA fingerprinting with multilocus probes, MAGGY and MGR586, was conducted to investigate the population structure of the rice blast fungus Magnaporthe grisea in Japan. Two-hundred seventy-eight field isolates collected during 1993-1997 and 22 archival isolates collected in 1976 from various cultivars and locations were examined. Two fingerprint groups were identified at the 70% similarity level in each collection. A one-to-one correspondence was found between the groups in field isolates and the groups in archival isolates. These results suggest that two discrete lineages exist in the rice blast population. They were temporarily designated as JL1 and JL2 (Japanese Lineage). JL1 was a predominant lineage representing 97% and 77% of the field and archival isolates, respectively, and present throughout Japan. In addition, these two lineages corresponded to two of the five lineages previously detected in collections made before 1960, suggesting that the structure of the rice blast population in Japan had drastically changed during 1960-1976. The two lineages showed a very similar virulence spectrum, and no relation-ship could be recognized between lineages and pathotypes. MAGGY revealed robust groups which were similar to those revealed by MGR586, although the two elements differ in character and structure, suggesting that MAGGY could be used as an alternative probe for monitoring the population dynamics of the rice blast pathogen.

(Received July 29, 1998; Accepted October 26, 1998)

Key words: Magnaporthe grisea, rice blast, DNA fingerprinting, lineage.

INTRODUCTION

Rice blast disease, caused by Magnaporthe grisea

(Hebert) Barr. (anamorph, Pyricularia grisea (Cooke) Sacc.)25), has been recognized as a serious constraint to rice production in all rice-growing countries. The litera-ture is contradictory on the degree of pathogenic varia-tion for this pathogen. Ou and his coworkers23,24) have reported variation of pathogenicity among single spore isolates from a single lesion and from monoconidial cultures, whereas other studies have shown that patho-

genicity of the rice blast pathogen was rather stable, and that mutations were the exception rather than the rule1,15). In the field, however, instances of the appear-ance of new races (pathotypes) and the collapse of resistance of rice cultivars to blast have been documented3,5,21) The longevity of rice varieties with various resistance genes in Japan has been less than three years12), and virulence of blast isolates in a popula-tion tends to shift from avirulence to virulence, rather than virulence to avirulence, on a given host16). Such variability has made it difficult to point out strategies for selecting or breeding rice cultivars that show

durable resistance to a blast population in a given area.Recently, the development of molecular techniques

made it possible to analyze the structure and dynamics of rice blast populations. By using dispersal repetitive element MGR586 as a probe9), populations of the rice blast fungus in the United States19,38), Columbia4,18), the Philippines2,43), and European countries26) were grouped into a limited number of lineages whose members share common ancestry. The relationship between these line-ages and pathotypes was close in blast populations studied in the United States19) and European countries26) but more complex in others2,38). Zeigler et al.44) proposed a hypothesis (lineage exclusion hypothesis) that each lineage has a specific virulence spectrum, characterized by uniform incompatibility with one or a combination of host resistance, and that combinations of resistance

genes in a cultivar that, in sum, confer resistance to every lineage, could exclude all known lineages in a target region.

The rice blast population in Japan was analysed by

Sone et al.31) using MGR586 and pMG6015 as fingerprint-ing probes. However, the number of field isolates analysed was less than 20, and the relationship between lineages and pathotypes was not determined.

* Faculty of Agriculture, Kobe University, Rokkodai, Nada-ku, Kobe 657-8501, Japan 神戸大学農学部

** Present address: Faculty of Agriculture, Saga University, Honjo 1, Saga 840-8502, Japan 現在:佐賀大学農学部

16 日本植物病理学会報第65巻第1号平成11年2月

The objectives of the present study were to examine

genetic structure of the rice blast population in Japan

and to determine whether or not the lineage exclusion

hypothesis is applicable to the Japanese blast popula-

tion. We analysed three collections of the blast fungus

using MAGGY7,17,34) and MGR586 as probes for DNA

fingerprinting. One collection consisted of field isolates

collected in 1993-1997 from various rice cultivars in

several locations throughout Japan. The others were

collections consisting of representative isolates with

defined pathotypes collected in 1976 or before 1960.

MATERIALS AND METHODS

M. grisea isolates From 1993 to 1997, 81 rice

blast samples were collected from 69 fields in 12 prefec-

tures in Japan (Table 1). Each sample consisted of

several leaves and panicles of one cultivar collected in

one field, except for eight samples from Aichi prefecture

and six samples from Hokkaido which were collected

from eight and six different spots or cultivars in the

fields of the Mountainous Region Agricultural Research

Institute, Aichi-ken Agricultural Research Center and

Kamikawa Agricultural Experiment Station, respective-

ly. Infected tissues were cut into small pieces, placed on

moistened filter papers in petri dishes, and incubated

under light for 24hr at 25•Ž35). Conidia produced were

spread onto the surface of 3% water agar in a petri dish

with a sterilized forceps. A single spore was picked up

under a microscope, transferred to a potato-dextrose

agar slant, and maintained at 25•Ž for short-term stor-

age. For long-term storage, pure cultures were grown on

sterilized barley seeds in a vial, dried at 25•Ž and kept in

a case with silica gel at 5•Ž. One isolate was picked up

from one lesion on a leaf or a panicle. A total of 278

isolates were obtained from the 81 rice blast samples.

These field isolates were designated as Hy8.1, To3.4, and

so on. In each designation the two letters indicate the

name of the prefecture where samples were taken

(Table 1). The following numeral refers to the sample

number in each prefecture, and the numeral after the

decimal point (.) shows the isolate number in one sample.

Two collections of rice isolates with defined patho-

types were also tested. One consisted of 22 isolates

which had been collected in 15 prefectures in 1976 and

has been maintained in several laboratories (Table 2).

The other consisted of isolates collected before 1958 in

six prefectures. They were selected by Yamasaki and

Kiyosawa41) and have been used as standard test isolates

in studies on breeding for blast resistance. In this paper,

these two collections of isolates are called •garchival

isolates•h and •gstandard isolates•h, respectively.

Pathogenicity test A total of 164 isolates

selected at random from different fingerprint groups

were tested for determination of pathotypes on a set of

nine Japanese differential rice cultivars according to the

previously described procedure35).

Seedlings grown in plastic pots (15•~6•~9cm) to the

three- to four-leaf stage were uniformly sprayed with 30

ml of the spore suspension per three pots adjusted to a

concentration of 1•~105spores/ml. The inoculated seed-

lings were kept in a dew chamber for 16hr at 25•Ž, then

transferred to a greenhouse at 25 to 28•Ž.

Seven days after inoculation, blast disease symptoms

were scored in five categories: 0=no visible symptom;

1=minute, pinhead-sized spots; 2=small, brown to dark

brown lesions with no distinguishable centers; 3=small

eyespot-shaped lesions with gray centers; and 4=typical

blast lesions, elliptical with gray centers. Lesion types 0,

1 and 2 produced no or few conidia even under high

humidity, and were considered to be resistant. The

susceptible lesion types 3 and 4 produced abundant

conidia under high humidity. When several different

lesion types occurred on seedlings inoculated with the

same isolate, the infection type was based on the pre-

dominant lesion type. On average, each isolate was

Table 1. Location and year of collection of M. grisea field isolates tested in this study

a) Letters in brackets are abbreviated names of prefectures.

b) Niigata Agricultural Experiment Station.

Ann. Phytopathol. Soc. Jpn. 65 (1). February, 1999 17

Table 2. Archival isolates and standard isolates of M. grisea used in this study

tested at least twice. The pathotypes were designated

according to the race notation proposed by Yamada et

at.40).

DNA preparation and DNA fingerprinting analy-

sis Erlenmeyer flasks containing 40ml liquid

medium (yeast extract, 5.0g; KH2PO4, 0.5g; K2HPO4,

0.5g; MgSO4, 0.5g; glucose, 20g; CaCl2, trace; and

distilled water, to make 1 liter) were inoculated with

small mycelial blocks. The cultures were grown at 25•Ž

for 4 to 5 days on a rotatory shaker (110rev/min). To

harvest the mycelia, the cultures were filtered under

vacuum through a Buchner funnel, and the hyphal mass

was squeezed between filter papers to remove as much

liquid as possible. About 0.5 to 1.0g mycelia were

obtained from each isolate and stored at -80•Ž. Total

genomic DNA was extracted by a modified method of

the DNA mini-preparation procedure described by Liu

et al.20).

The 0.56kb SalI-BamHI (SB) fragment isolated from

MAGGY element (Fig. 1) was labeled with biotin using

NEBlot-Phototope Kit (New England Biolabs, Inc.), and

used as a MAGGY probe. The MGR clone (pMGR1)

containing the entire sequence of the MGR586 trans-

poson was provided by Dr. M.L. Farman, University of

Kentucky, and labeled similarly as done for the SB

Fig. 1. Restriction map of MAGGY and SB probe. E,

EcoRI; B, BamHI; H, HindIII; P, PstI; S, SaiI.

fragment.

DNA samples were digested to completion with

restriction enzyme BamHI or EcoRI (Boehringer Mann-

heim, Germany). The digests (1.0ƒÊg/lane) were subject-

ed to electrophoresis on 0.7% or 0.8% agarose gel for 30

hr at 30V in 0.5•~TBE buffer. DNA fragments were

transferred to a nylon membrane (Magna Graph, MSI),

and hybridized overnight with MAGGY or MGR probes.

After hybridization, the membrane was washed at high

stringency, with the final washes at 68•Ž in 0.1•~SSC,

0.1% SDS. DNA fingerprints were detected using Photo-

tope-Star Detection Kit (New England Biolabs, Inc.).

Cluster analysis Binary matrices generated

from fingerprinting data with each probe or both probes

were used for cluster analysis with a procedure de-


scribed previously14). Similarities between DNA finger-

printing profiles were calculated by using the Nei and Li's formula22): F=2Nxy/(Nx+Ny), where Nxy is the number of fragments shared by two isolates, and (Nx+Ny) is the total number of fragments in isolate x and y. Dendrograms were constructed based on the similarity coefficient by using the unweighted pair group method with arithmetic average clustering30). A computer pro-

gram developed by M. Okuda, Chugoku National Agri-cultural Experiment Station, was used for this purpose. The robustness of the clusters was determined by boot-strap analysis8) with 2000 replications using the program WINBOOT42).

RESULTS

Lineage structure in existing field isolatesFirst, isolates from the same prefecture were com-

pared to one another by MAGGY-DNA fingerprinting. In most cases isolates derived from the same sample showed more than 90% similarity in DNA fingerprint

profiles. Based on cluster analyses, isolates were clas-sified into preliminary groups, each of which consisted of isolates showing more than 80% similarity. Twenty-two isolates were selected as representatives of these prelim-inary groups, and again subjected to DNA fingerprinting with MAGGY and MGR586. On average, 50 resolvable BamHI fragments could be counted for each MAGGY

profile ranging from 1.3 to 12kb, and 50 resovable EcoRI fragments for each MGR profile ranging from 1.8 to 12kb (Figs. 2A and 2B). These isolates were clearly clus-

tered into two groups based on MAGGY fingerprints

(Fig. 3A). Bootstrap analysis showed that these groups were robust with 85% confidence in 2000 iterations. The similarity level between the two groups was less

than 60%. The level within groups was more than 70%. Similar results were obtained based on MGR fingerprints (Fig. 3B), although the similarity level among isolates belonging to the larger group was higher than that based on MAGGY fingerprints.

A dendrogram constructed from pooled data with both probes is shown in Fig. 3C. Two clonal lineages were differentiated at the 70% similarity level and named tentatively as Lf1 and Lf2. Lf2 consisted of eight isolates (3% of the total) collected from three prefec-tures (Hyogo, Aichi, and Nagano), and was considered to be a minor lineage present in a limited area, whereas Lf1 consisted of the rest of isolates (270 isolates, 97% of the total) collected from 12 prefectures, and was consid-ered to be a major lineage present in all rice-growing areas in Japan.

Lineage structure in isolates collected in 1976Twenty-two archival isolates collected in 1976 were

subjected to MAGGY- and MGR-DNA fingerprint analy-sis. A dendrogram obtained from pooled data with both

Fig. 2. DNA fingerprinting profiles of field isolates representing preliminary groups detected in 278 isolates. Genomic DNA of each isolate was digested with BamHlIand hybridized with SB probe (A), or digested with EcoRI and

hybridized with MGR586 (B). Lanes 1, P-2b; 2, 4203.1; 3, Ken53-33; 4, Ina168; 5, 1106.2; 6, Ho6.2; 7, Ina72; 8, Hokul; 9, 1601.3; 10, Na10.1; 11, Ka5; 12, Ken54-20; 13, Ken54-04; 14, 4603.4; 15, Ok2.2; 16, 4207.4. Kilobase markers are indicated on the right.


A B

C

Fig. 3. Dendrogram constructed by the unweighted pair group arithmetic mean analysis (UPGMA) of the binary matrix obtained from (A) MAGGY, (B) MGR586, and (C) both DNA fingerprinting profile (s) of field isolates representing

preliminary groups found in 278 isolates. Values on the branches of the clusters represent results of boostrap analysis with 2000 iterations.

probes is shown in Fig. 4. These isolates were clustered into two distinct groups at the 65% similarity level, which were tentatively named as Ls1 and Ls2. Ls1 was detected in 15 prefectures and accounted for 77% of the archival isolates, whereas Ls2 was detected in only four

prefectures (Aichi, Nagano, Saitama, and Tochigi).Comparision of DNA fingerprints of existing field isolates, archival isolates and standard isolatesFour field isolates representing Lf1 and Lf2 were

compared with five archival isolates representing Ls1 and Ls2 based on MAGGY-DNA fingerprints (Fig. 5A). At the 75% similarity level, the major field lineage (Lf1) corresponded to the large group in archival isolates

(Ls1), whereas the minor field lineage (Lf2) corresponded to the small group in archival isolates (Ls2). The result-

ing two lineages were designated as JL1 and JL2

(Japanese Lineage), respectively. On the other hand, the seven standard isolates representing the five previously reported lineages31) showed higher diversity (Fig. 5B). One of the standard isolates, Ken54-04, was classified into JL1, whereas two, Ken53-33 and Ken54-20, were clustered into JL2. Isolates Ina72 and Ina168 shared only 65% similarity to JL1, whereas Hokul shared less than 75% similarity to JL2. The remaining one, P-2b,

produced a distinct fingerprint strikingly different from those of JL1 or JL2.

Relationship between lineages and pathotypesTo examine the relationship between lineages and

pathotypes in Japanese rice blast population, we tested pathotypes of 164 field isolates recovered from 32 com-


Fig. 4. Dendrogram constructed by the unweighted pair group arithmetic mean analysis (UPGMA) of the binary matrix obtained from combined data of MAGGY- and MGR586-DNA fingerprinting profiles of 22 archival isolates. Values

on the branches of the clusters represent results of boostrap analysis with 2000 iterations.

mercial rice cultivars in 12 prefectures. A total of 12

pathotypes were detected based on disease reactions of nine Japanese differential rice cultivars. Race 007 was

predominant among them, accounting for 37% of the isolates tested, race 033 accounting for 15.8%, and race 037 for 9.7% (data not shown). JL1 consisted of 13

pathotypes, whereas JL2 consisted of five pathotypes that were also found in JL1 (Figs. 3C and 4). The viru-lence spectrum of each lineage is summarized in Table 3. Isolates virulent on cultivars containing Pi-ks, Pi-a, Pi-i, Pi-k, Pi-km and Pi-ta gene occurred in both lineages, and those virulent on a cultivar containing Pi-z occurred in neither lineage. As a whole, these lineages showed very similar virulence spectra.

DISCUSSION

In current studies on population biology of the rice blast fungus, MGR586 has been confirmed to be a useful

probe for DNA fingerprinting analysis of rice blast isolates2,4,18,19,26,38,43). In the present study, we confirmed

that MAGGY is also a useful probe for the analysis of the rice blast population. On average 50 restriction fragments could be detected with the MAGGY probe in DNA fingerprints of rice blast isolates, which made it

possible to evaluate the degree of genetic differentiation among those isolates. Two MAGGY fingerprint groups were identified in 278 field isolates collected from 12

prefectures throughout Japan. Similar results were also obtained in 22 archival isolates collected from 15 prefec-tures. Despite the difference in structure and number of copies6,7), MGR586 showed almost the same results as MAGGY did; only two fingerprinting groups were detected with MGR586 in field isolates and in archival

isolates. Note that the similarity levels among individ-uals within a group revealed by MGR586 probe were higher than those by MAGGY probe (Figs. 3A and 3B). These data suggest that MAGGY-DNA fingerprinting

gives higher resolution than MGR-DNA fingerprinting. In addition, bootstrap values of the putative groups

generated from pooled data with both probes were not always higher than those generated from the MAGGY data alone. These results indicate that fingerprinting with MAGGY is sufficient to describe clonal lineages in

populations of M. grisea. Another element called Fosbury also resolved rice blast isolates into lineage groups as MGR did28). We expect that MAGGY and Fosbury could

divide the rice blast population into the same lineage

groups because their structure and sequence are very similar27,28). Several other repetitive DNA elements identified in the genome of M. grisea, e.g., Pot211), MGR5839), and MGSR132), may have different resolution

and be used as complements to others.We used the MAGGY fingerprinting to reveal the

lineage structure of the three populations collected in different periods in the history of rice blast epidemics in

Japan. The two lineages found in the field isolates collected in 1993-1997 corresponded exactly to the two lineages found in the archival isolates collected in 1976. Consequently, they were clustered into two lineages, JL1 and JL2. JL1 was a predominant lineage present throughout Japan (Fig. 6). These results suggest that the structure of the existing rice blast population in Japan is much simpler than that in other countries2,18,26).

However, when field isolates and archival isolates were compared with the seven standard isolates col-lected before 1960, the distiction between lineages became less clear. Such differentiation as previously


A

B

Fig. 5. Relationship between lineages detected in different collections. (A) Dendrogram was constructed by UPGMA

based on MAGGY-DNA fingerprint data of isolates representing lineages found in field isolates collected in 1993-1997 (Lf1 and Lf2) and in archival isolates collected in 1976 (Ls1 and Ls2). (B) Dendrogram was constructed based

on MAGGY-DNA fingerprint data of isolates in (A) and standard isolates collected before 1960. The lineage designations given by Sone et al.31) are shown in the parentheses. Values on the branches of the clusters represent results of boostrap analysis with 2000 iterations.

defined by Sone et al.31) seemed to be somewhat difficult in the present study. JL1, accounting for 97% of field isolates and 77% of archival isolates, corresponded to

JBLA-K04, whereas JL2 corresponded to JBLA-K33 (Fig. 5B). Undoubtedly, lineages JL1 and JL2 were present before 1960, but JL1 could be amplified and has occupied all current rice-growing regions in Japan. Haplotypes represented by the other four standard iso-lates were not recovered from samples collected in 1976, 198031 or 1993-1997, even in the same prefectures where they were found before 1960, and are considered to have diminished or disappeared in the current population. These results suggest that the number of lineages or the

genetic diversity in the rice blast population has de-

creased in the agricultural environment in Japan espe-cially during 1960-1976. In contrast, the same lineages were recovered over different years and seasons in the United States and the Philippines2,19,38. Roumen et al.26) suggested that the same lineages may have been present in Italy for more than 30 years. The cause of the decrease of lineage diversity in the Japanese rice blast

population is not clear, although this decrease may be related to the extensive cultivation of a limited number of cultivars with the same genotypes, or successive breakdown of resistance genes which occurred in the 1960's13,37) as speculated by Sone et al.31). Further anal-

yses are needed using isolates collected from various locations and various years.


Fig. 6. Distribution of lineages JL1 and JL2 in Japan. The open, half-closed, and closed circles represent lineage JL1

present before 1960, in 1976, and in 1993-1997, respectively. The open, half-closed, and closed squares represent JL2 present before 1960, in 1976, and in 1993-1997, respectively. The figures in parentheses are the numbers of isolates belonging to each lineage.

Table 3. Virulence spectrum of Japanese lineages (JL) on differential rice cultivars

a) Total number of isolates tested for each lineage.b) Percentage of virulent isolates.

Multiple pathotypes occurred in each of the two line-ages and all pathotypes in JL2 were found in JL1. These results suggest that there was no relationship between lineages and pathotypes in the Japanese rice blast popu-

lation in contrast to the results in the United States19) and European countries26). Our results support the infer-ence that the evolution of virulence in M. grisea may be independent of currently detectable changes at the DNA level38). This inference seems to be reasonable because the gene-for-gene relationship29) implies that the patho-type is determined only by the limited number of avirulence loci corresponding to the resistance loci involved. Recently, a single base-pair change in aviru-lence genes has been suggested to lead to virulence of

previously avirulent isolates10,33) We suggest that the diagnosis of pathotypes of rice blast isolates by DNA fingerprinting would be impossible unless all the avir-

ulence loci involved are cloned and analyzed. The char-acterization of the avirulence gene corresponding to Pi-ta would be the first step for establishing such a technique for diagnosis36).

Based on the lineage analysis of M. guisea populations in the Philippines, Zeigler et al.43,44) proposed that a lineage of the pathogen could be reliably excluded from infection by one or more resistance gene (s), and that it would be useful to combine such invariant resistances to exclude all known lineages in a target region. We could not find JL2 isolates virulent on resistance genes Pi-zt and Pi-ta2. However, the predominant lineage JL1 in-cluded only a small proportion of isolates carrying virulence genes to Pi-zt (0.5%), or Pi-ta2 (6.2%) (Table 3), suggesting that the absence of such isolates in JL2 may be due to the small sample size of JL2 population. The resistance gene Pi-z in cv. Fukunishiki was effective


against all isolates in JL1 and JL2. However, the col-lapse of the resistance of this cultivar was recorded in 1966 in Fukushima prefecture, and in 1972 in Aichi

prefecture13,37,39) These facts are convincing that the current rice blast population in Japan includes isolates that carry the virulence gene on Pi-z or that have a

potential to overcome this resistance gene. Zeigler et al.43) suggested that the combination of resistance genes Pi-2 (t) and either Pi-l (t) or Pi-4a (t) could be effective

against all lineages tested in the Philippines. In addition, Roumen et al.26) pointed out that Pi-z and Pi-ta2 genes showed complete resistance to all isolates regardless of lineages in European countries. Taken together, we suggest that the application of the lineage exclusion hypothesis to a breeding program should be considered based on the epidemic history or virulence diversity of the blast pathogen in a certain region. At least in Japan, the existing lineages have a very similar virulence spec-trum, and the hypothesis does not seem to be applicable to the rice breeding program.

We would like to thank all people who sent us the rice blast samples used in this study. We are grateful to Dr. Y. Fujita, Hokuriku National Agricultural Experiment Station, for technical assistance in evaluation of results of patho-

genicity test; and Dr. N. Hayashi, Mountainous Region Agricultural Research Institute, Aichi-ken Agricultural Research Center, for kindly providing the standard isolates. We are indebted to Dr. M.L. Farman, University of Kentuck-

y, for providing the MGR586 probe; Dr. R.J. Nelson, Interna-tional Rice Research Institute, Manila, Philippines, for pro-viding the WINBOOT program; and Mr. M. Okuda, Chugoku National Agricultural Experimental Station, for providing the computer program used in cluster analysis. We thank Dr. H. Naito who gave us the detailed information on the ar-chival isolates. This study was supported by grants from the Ministry of Education, Japan (Nos. 10556011, 10460022).

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和文摘要

L.D. DON・草場基章・A.S. URASHIMA・土佐幸雄・中屋敷均・

眞山滋志:日本におけるイネいもち病菌個体群構造のDNAフ

ィンガープリント解析

日本におけるイネいもち病菌の個体群構造を明らかにするた

め,MAGGYおよびMGR586を用いてDNAフィンガープリ

ント解析を行った。1993～1997年に採集・単胞子分離した278菌

株(圃場菌株)および1976年に採集された22菌株(実験室保存

菌株)を解析したところ,それぞれの菌株集団が70%レベルの

相同性を有する2つのリネージ(Lineage)に分けられた。さら

に圃場菌株における2つのリネージは実験室保存菌株における

2つのリネージと1対1に対応した。以上の結果から,現在の日

本におけるイネいもち病菌集団には2つのリネージ(JL1, JL2

と仮称)が存在することが明らかとなった。JL1は圃場菌株およ

び実験室保存菌株のそれぞれ97%および77%を占める主要な

リネージで,日本全国に分布していた。一方,1960年以前に採

集された集団は少なくとも5つのリネージよりなるとされてい

るが,JL1, JL2はそのうちの2つに相当した。このことから,

日本のイネいもち病菌集団の構造は1960年から1976年の間に

大きく変化したことが示唆された。各リネージに属する菌系の

イネ判別品種に対する病原性を調べたところ,リネージと病原

性の間に関連は認められなかった。両プローブによるリネージ

分類はほぼ同じであったことから,MAGGYはイネいもち病菌

の個体群動態を解析するためのプローブとして有用と考えられ

る。

Documents

Population Structure of the Rice Blast Fungus in Japan