Genetic diversity and trichothecene chemotypes of the Fusarium graminearum clade isolated from maize in Nepal and identification of a putative new lineage

On smallholder farms in the foothills of the Himalayan Mountains in Nepal, fungi of the Fusarium graminearum clade cause Gibberella ear rot of maize and contamination with the 8-ketotrichothecenes nivalenol and deoxynivalenol. Previous DNA marker analyses of the F.?graminearum clade from maize in Nepal found a high level of genetic diversity but were limited in detail or scope. The present study incorporated a collection of 251 field strains from a wide geographic distribution in Nepal and utilized sequencing of the MAT1-1-3 gene of the mating type locus to determine the number and frequency of lineages and species of the F. graminearum clade. The frequency of nivalenol and deoxynivalenol chemotypes was determined by chemical analysis and by TRI13 deletion-marker analysis. We found that Gibberella ear rot of maize in Nepal is associated with a complex of species of the F. graminearum clade - mainly Fusarium asiaticum and Fusarium meridionale, but also Fusarium boothii and a putative new lineage, which we have designated the 'Nepal lineage'. Fusarium graminearum sensu stricto, which dominates in maize elsewhere in Asia and worldwide, was not detected in Nepal. Although nivalenol production has been associated experimentally with lower virulence in maize ear rot and wheat head blight, this collection of the F. graminearum clade from maize in Nepal is dominated (4:1) by nivalenol producers, suggesting that traits other than crop plant pathogenesis affect population structure in this complex agroecosystem.     

Genetic Diversity and Fitness of Fusarium graminearum Populations from Rice in Korea

Fusarium graminearum is an important fungal pathogen of cereal crops and produces mycotoxins, such as the trichothecenes nivalenol and deoxynivalenol. This species may be subdivided into a series of genetic lineages or phylogenetic species. We identified strains of F. graminearum from the Republic of Korea to lineage, tested their ability to produce nivalenol and deoxynivalenol, and determined the genetic composition and structure of the populations from which they were recovered. Based on amplified fragment length polymorphism (AFLP), PCR genotyping, and chemical analyses of trichothecenes, all 249 isolates from southern provinces belonged to lineage 6, with 241 having the nivalenol genotype and 8 having the deoxynivalenol genotype. In the eastern Korea province, we recovered 84 lineage 6 isolates with the nivalenol genotype and 23 lineage 7 isolates with the deoxynivalenol genotype. Among 333 lineage 6 isolates, 36% of the AFLP bands were polymorphic, and there were 270 multilocus haplotypes. Genetic identity among populations was high (>0.972), and genotype diversity was low (30 to 58%). To test the adaptation of lineage 6 to rice, conidial mixtures of strains from lineages 3, 6, and 7 were inoculated onto rice plants and then recovered from the rice grains produced. Strains representing lineages 6 and 7 were recovered from inoculated spikelets at similar frequencies that were much higher than those for the strain representing lineage 3. Abundant perithecia were produced on rice straw, and 247 single-ascospore isolates were recovered from 247 perithecia. Perithecia representing lineage 6 (87%) were the most common, followed by those representing lineage 7 (13%), with perithecia representing lineage 3 not detected. These results suggest that F. graminearum lineage 6 may have a host preference for rice and that it may be more fit in a rice agroecosystem than are the other lineages present in Korea.Fusarium graminearum (teleomorph: Gibberella zeae) causes head blight of small grains, including rice, wheat, and barley (23). The fungus was first reported on rice in Italy by Cattaneo (4) as Botryosphaeria saubinetii Niessland. This rice disease has since been recorded in other countries, including Brazil, China, India, Japan, Nepal, and Uganda (11, 31). The disease usually does not cause heavy damage, but under conditions that favor disease development, e.g., high humidity, it may be severe. Chung et al. (7) found that an isolate from wheat could infect rice and other plants and also could cause a postemergence blight in rice. Wheat isolates of F. graminearum can cause significant disease on rice, but under greenhouse conditions no trichothecenes were detected in the infected rice florets (14). In addition, Nepalese rice contained no detectable contamination with trichothecenes even though F. graminearum occurs in Nepal (11).The fungus can produce the 8-ketotrichothecene mycotoxins nivalenol (NIV) and deoxynivalenol (DON). Most of the biosynthetic genes for the synthesis of 8-ketotrichothecenes are tightly linked in the TRI gene cluster (9). TRI7 and TRI13 are required for acetylation and oxygenation of the oxygen at C-4 to produce NIV and 4-acetyl nivalenol (4-ANIV), respectively, from DON. PCR-based methods to identify polymorphisms in both genes were developed as simple, reliable diagnostic tools for differentiating strains with DON and NIV chemotypes (20, 21). There are regional differences in the distribution of the two chemotypes. Maize and wheat in North America and Europe commonly are contaminated with DON (9), while strains with NIV chemotypes are commonly recovered from cereal crops in Asia (15, 17). In the Republic of Korea, strains with the DON chemotype often cause maize ear rot, while strains with the NIV chemotype commonly are recovered from barley (17, 35). A severe epidemic of Fusarium head blight on wheat and barley occurred in 1963 in southern Korea (5, 6). Humans and farm animals consuming moldy cereals exhibited typical signs of trichothecene intoxication involving vomiting, dizziness, nausea, abnormal pain, and diarrhea (9). The natural occurrence of NIV and DON has been reported in barley and maize in Korea (17, 35, 41), but there have been few surveys of Fusarium mycotoxins in Korean rice.O''Donnell et al. (30) divided F. graminearum into seven phylogenetic lineages based on the genealogical concordance of six genes. The phylogenetic separation has been used to raise these seven and four additional lineages to species status (36). The geographic location often influences the lineage present, e.g., lineage 7 is the most common in the United States, and lineage 6 dominates in China. Lineage and trichothecene chemotype are not correlated (45), and the lineages are morphologically cryptic. Members of all lineages are cross-fertile with strains belonging to lineage 7 and in some cases with strains of other lineages (1, 2, 19, 25), a pattern that suggests that the members of all of the lineages belong to a single biological species.Studies of F. graminearum populations have been made in different geographic regions, e.g., China (12), Europe (42), the United States (48, 49), and Argentina (34). Populations of F. graminearum have high levels of genotypic diversity, which suggests that recombination occurs regularly in F. graminearum populations. Most studies have focused on populations from wheat, barley, and corn, and there is little information on F. graminearum populations from rice.Severe epidemics of Fusarium head blight of rice occurred in August 2001 after heavy rainfall during the rice flowering period in southern Korea. Lesions on or discoloration of the glumes were common, with infected grains first appearing to be white and later yellow, salmon, or carmine. Sometimes the entire seed was colonized. Infected grains were lightweight, shrunken, and brittle. Our objectives in the present study were (i) to determine the frequency at which F. graminearum occurs in plants with rice head blight; (ii) to determine the number and relative frequency of the F. graminearum lineages present; and (iii) to evaluate the strains for their sexual fertility, genetic relatedness, virulence, and toxin-producing abilities. Our working hypotheses were that sexually fertile strains from lineage 6 would dominate in the population and that these strains would be the most aggressive toward rice. We expected most of the lineage 6 strains to produce NIV and for there to be a high level of genetic variation, as assessed by neutral (amplified fragment length polymorphism [AFLP]) markers. We evaluate here F. graminearum population diversity in Korea and provide new information on the pathogenic capabilities of strains belonging to several of the known lineages of this very widespread fungal species.     

Occurrence of Gibberella zeae strains that produce both nivalenol and deoxynivalenol

By single ascospore isolation, several sets of asci containing eight ascospores were isolated from perithecia of Gibberella zeae. Of these sets, seven were investigated for their ability to produce 8-ketotrichothecene mycotoxins on rice grains. Analyses were made with gas chromatography-mass spectrometry and gas chromatography with 63Ni electron capture detection. Of 56 total isolates, 11 produced nivalenol, 4-acetylnivalenol, and deoxynivalenol, 1 produced nivalenol and deoxynivalenol, 7 produced deoxynivalenol and 3-acetyldeoxynivalenol, 19 produced deoxynivalenol and 15-acetyldeoxynivalenol, and 6 produced deoxynivalenol and both 15- and 3-acetyldeoxynivalenol. The remaining 12 isolates produced nivalenol and 4-acetylnivalenol. All isolates of G. zeae that we examined could produce 8-ketotrichothecenes in this investigation. This report is the first to demonstrate the presence of G. zeae isolates producing both nivalenol and deoxynivalenol. In addition, differences in the production between 3-acetyldeoxynivalenol and 15-acetyldeoxynivalenol are discussed in relation to culture conditions.     

Chemotaxonomy of Gibberella zeae with special reference to production of trichothecenes and zearalenone

By adopting a single-spore isolation technique, 113 isolates of Gibberella zeae, the perfect stage of Fusarium graminearum, were isolated from rice stubbles in barley and wheat fields and tested for production of trichothecenes and zearalenone on rice grains. Of the isolates, 93% produced the trichothecenes, and they could be subdivided into two chemotaxonomic groups: nivalenol and fusarenon-X producers and deoxynivalenol and 3-acetyldeoxynivalenol producers. No cross production of these two types of trichothecenes was observed in these isolates. Zearalenone was detected in 68% of the isolates, but no clear relationship could be observed regarding its position with respect to the two chemotaxonomic groups.     

Chemotaxonomy of Gibberella zeae with special reference to production of trichothecenes and zearalenone.

By adopting a single-spore isolation technique, 113 isolates of Gibberella zeae, the perfect stage of Fusarium graminearum, were isolated from rice stubbles in barley and wheat fields and tested for production of trichothecenes and zearalenone on rice grains. Of the isolates, 93% produced the trichothecenes, and they could be subdivided into two chemotaxonomic groups: nivalenol and fusarenon-X producers and deoxynivalenol and 3-acetyldeoxynivalenol producers. No cross production of these two types of trichothecenes was observed in these isolates. Zearalenone was detected in 68% of the isolates, but no clear relationship could be observed regarding its position with respect to the two chemotaxonomic groups.     

Occurrence of Gibberella zeae strains that produce both nivalenol and deoxynivalenol.

By single ascospore isolation, several sets of asci containing eight ascospores were isolated from perithecia of Gibberella zeae. Of these sets, seven were investigated for their ability to produce 8-ketotrichothecene mycotoxins on rice grains. Analyses were made with gas chromatography-mass spectrometry and gas chromatography with 63Ni electron capture detection. Of 56 total isolates, 11 produced nivalenol, 4-acetylnivalenol, and deoxynivalenol, 1 produced nivalenol and deoxynivalenol, 7 produced deoxynivalenol and 3-acetyldeoxynivalenol, 19 produced deoxynivalenol and 15-acetyldeoxynivalenol, and 6 produced deoxynivalenol and both 15- and 3-acetyldeoxynivalenol. The remaining 12 isolates produced nivalenol and 4-acetylnivalenol. All isolates of G. zeae that we examined could produce 8-ketotrichothecenes in this investigation. This report is the first to demonstrate the presence of G. zeae isolates producing both nivalenol and deoxynivalenol. In addition, differences in the production between 3-acetyldeoxynivalenol and 15-acetyldeoxynivalenol are discussed in relation to culture conditions.     

PCR Analysis of the Tri13 gene to Determine the Genetic Potential of Fusarium graminearum Isolates from Iran to Produce Nivalenol and Deoxynivalenol

Fusarium graminearum trichothecene producing isolates can be broadly divided into two chemotypes based on the production of the 8- ketotrichothecenes deoxynivalenol (DON) and nivalenol (NIV). Functional Tri13 gene required for the production of NIV and 4- acetyl NIV, whereas in the isolates producing DON and its acetylated derivates, this gene is nonfunctional. In this study, a total of 57 isolates from different fields of Mazandaran province, Iran were identified as F. graminearum using classical methods and species specific primers. In order to assess the potential of isolates to produce NIV or DON, we used PCR to determine whether isolates carried a functional or nonfunctional Tri13 gene. Out of the 57 tested F. graminearum isolates with Tri13 PCR assays, 46 yielded an amplicon similar to the size predicted for nivalenol production, while 11 yielded an amplicon similar to the size predicted for deoxynivalenol production. From regions where more than one F. graminearum isolate was obtained, isolates were not exclusively of a single chemotype. It seems that genetic diversity among the isolates has relation with geographical region and wheat cultivar. The assay can provide information about the distribution of Tri13 haplotype that can be used in tracing of trichothecene contaminated samples.     

Population structure and dynamics of Magnaporthe grisea in the Indian Himalayas.

The population genetics of Magnaporthe grisea, the rice blast pathogen, were analyzed in a center of rice diversity (the Uttar Pradesh hills of the Indian Himalayas) using multilocus and single-, or low-copy, DNA markers. Based on DNA fingerprinting with the multilocus probe MGR586 and single-locus probes, 157 haplotypes clustered into 56 lineages (at >/=70% MGR586 band similarity, each with unique single-locus profiles) and high diversity indices were detected among 458 isolates collected from 29 sites during 1992-1995. Most valleys sampled had distinct populations (73% of the lineages were site specific) with some containing one or a few lineages, confirming the importance of clonal propagation, and others were very diverse. Widely distributed lineages suggested that migration occurs across the region and into the Indo-Gangetic plains. Repeated sampling at one site, Matli, (170 isolates, 1992-1995) yielded 19 lineages and diversity significantly greater than that reported from similar samples from Colombia and the Philippines. Analysis of allelic associations using pairwise comparisons and multilocus variance analysis failed to reject the hypothesis of gametic phase equilibrium. The Matli population shifted from highly diverse in 1992 to almost complete dominance by one lineage in 1995. Such population dynamics are consistent with recombination followed by differential survival of clonal descendants of recombinant progeny. At another site, Ranichauri, population (n = 84) composition changed from 2 to 11 lineages over 2 yr and yielded additional evidence for equilibrium. Sexually fertile and hermaphrodite isolates of both mating types were recovered from rice in both Matli and Ranichauri. We demonstrate that Himalayan M. grisea populations are diverse and dynamic and conclude that the structure of some populations may be affected to some extent by sexual recombination.     

Mycological survey of Korean cereals and production of mycotoxins by Fusarium isolates

The fungal species isolated from Korean cereals (barley, polished barley, wheat, rye, and malt) were Alternaria spp., Aspergillus spp., Chaetomium spp., Drechslera spp., Epicoccum sp., Fusarium spp., and Penicillium spp., etc. The number of Fusarium strains isolated was 36, and their ability to produce Fusarium mycotoxins on rice was tested. Nivalenol (NIV) was produced by Fusarium graminearum (7 of 9 isolates), Fusarium oxysporum (3 of 10 isolates), and Fusarium spp. (7 of 15 isolates). Of 15 isolates of Fusarium spp., 6 formed deoxynivalenol (DON). Fusarenon-X and 3-acetyl-DON were produced by most NIV- and DON-forming isolates, respectively. Zearalenone was produced by 3 isolates of F. graminearum, 1 isolate of Fusarium equiseti, and 11 isolates of Fusarium spp. T-2 toxin was not produced by any Fusarium isolates. The highest concentrations of mycotoxins produced by Fusarium isolates were 77.4 (NIV), 5.3 (DON), 138.3 (fusarenon-X), 40.6 (3-acetyl-DON), and 23.2 (zearalenone) micrograms/g.     

Mycological survey of Korean cereals and production of mycotoxins by Fusarium isolates.

The fungal species isolated from Korean cereals (barley, polished barley, wheat, rye, and malt) were Alternaria spp., Aspergillus spp., Chaetomium spp., Drechslera spp., Epicoccum sp., Fusarium spp., and Penicillium spp., etc. The number of Fusarium strains isolated was 36, and their ability to produce Fusarium mycotoxins on rice was tested. Nivalenol (NIV) was produced by Fusarium graminearum (7 of 9 isolates), Fusarium oxysporum (3 of 10 isolates), and Fusarium spp. (7 of 15 isolates). Of 15 isolates of Fusarium spp., 6 formed deoxynivalenol (DON). Fusarenon-X and 3-acetyl-DON were produced by most NIV- and DON-forming isolates, respectively. Zearalenone was produced by 3 isolates of F. graminearum, 1 isolate of Fusarium equiseti, and 11 isolates of Fusarium spp. T-2 toxin was not produced by any Fusarium isolates. The highest concentrations of mycotoxins produced by Fusarium isolates were 77.4 (NIV), 5.3 (DON), 138.3 (fusarenon-X), 40.6 (3-acetyl-DON), and 23.2 (zearalenone) micrograms/g.     

Toxin production by Fusarium culmorum IMI 309344 and F. graminearum NRRL 5883 on grain substrates

The production of deoxynivalenol, acetyl deoxynivalenol and zearalenone by Fusarium culmorum and F. graminearum on autoclave-sterilized grain (maize, rice, wheat and barley) was investigated. Fusarium culmorum produced significantly greater levels of toxins than F. graminearum. The four substrates examined differed in their ability to support toxin production. Toxin production on maize and rice was significantly greater than toxin production on barley or wheat.     

A simple method with liquid chromatography/tandem mass spectrometry for the determination of the six trichothecene mycotoxins in rice medium

A selective and speedy LC-MS/MS method was developed to determine six trichothecene mycotoxins (nivalenol, deoxynivalenol, fusarenon X, 15-acetyldeoxynivalenol, 3-acetyldeoxynivalenol, and T-2 toxin) in rice medium where Fusarium graminearum were cultivated for in vitro tests. The analytes were extracted from the rice medium with acetonitrile/water (85/15, v/v), and diluted with acetonitrile/water (5/95, v/v) in order to minimize the effects of matrices. Diluted solutions were analyzed by LC-MS/MS with electrospray ionization (ESI) interface in negative or positive ion mode and the multiple reaction monitoring mode. Recovery rates were 76-106% with a spiked level at 1-6 microg/kg of mycotoxins that corresponded to the limit of quantitation. The method was applied to study the time courses of trichothecene production and the biomass of fungi by three Fusarium graminearum strains. Three strains have different mycotoxin biosynthesis pathways, wFg14 and 03E-1 were DON producer, and 03N-1 was NIV producer.     

Mitochondrial cytochrome b sequence variations and population structure of Siberian chipmunk (Tamias sibiricus) in Northeastern Asia and population substructure in South Korea

Twenty-five chipmunk species occur in the world, of which only the Siberian chipmunk, Tamias sibiricus, inhabits Asia. To investigate mitochondrial cytochrome b sequence variations and population structure of the Siberian chipmunk in northeastern Asia, we examined mitochondrial cytochrome b sequences (1140 bp) from 3 countries. Analyses of 41 individuals from South Korea and 33 individuals from Russia and northeast China resulted in 37 haplotypes and 27 haplotypes, respectively. There were no shared haplotypes between South Korea and Russia--northeast China. Phylogenetic trees and network analysis showed 2 major maternal lineages for haplotypes, referred to as the S and R lineages. Haplotype grouping in each cluster was nearly coincident with its geographic affinity. In particular, 3 distinct groups were found that mostly clustered in the northern, central and southern parts of South Korea. Nucleotide diversity of the S lineage was twice that of lineage R. The divergence between S and R lineages was estimated to be 2.98-0.98 Myr. During the ice age, there may have been at least 2 refuges in South Korea and Russia--northeast China. The sequence variation between the S and R lineages was 11.3% (K2P), which is indicative of specific recognition in rodents. These results suggest that T. sibiricus from South Korea could be considered a separate species. However, additional information, such as details of distribution, nuclear genes data or morphology, is required to strengthen this hypothesis.     

Mycotoxin production and cytotoxicity of Fusarium strains isolated from Norwegian cereals

Thirty-four isolates of the eight most common Fusarium species isolated from Norwegian cereals; F. avenaceum, F. culmorum, F. equiseti, F. graminearum, F. poae, F. sporotrichioides, F. torulosum and F. tricinctum were studied for their cytotoxicity and ability to produce mycotoxins. The strains were cultivated on rice, and analysed for trichothecenes (all species), zearalenone (all species), fusarochromanone (F. equiseti), wortmannin (F. torulosum), moniliformin and enniatins (F. avenaceum, F. tricinctum and F. torulosum). The cytotoxicity of the extracts were examined with an (in vitro) MTT-cell culture assay. All F. graminearum and five of seven F. culmorum isolates belonged to chemotype IA, producing deoxynivalenol and 3-acetyl-deoxynivalenol, while the two other F. culmorum strains were nivalenol producers (chemotype II). The F. equiseti isolates and one of the F. poae isolates produced both type A and B trichothecenes, and relatively large quantities of fusarochromanone were detected in the F. equiseti cultures. All Fusarium species studied showed significant cytotoxicity, but with a large variation between species, and also within each species. F. sporotrichioides and F. equiseti showed the highest average cytotoxicity. This revised version was published online in August 2006 with corrections to the Cover Date.     

Phylogeography of the flathead mullet Mugil cephalus in the north-west Pacific as inferred from the mtDNA control region

The population genetic structure and historical demography of the flathead mullet Mugil cephalus were investigated using the mtDNA control region (CR) sequences (909–1015 bp) of 126 individuals collected from seven locations in the north-west Pacific between 2005 and 2007. Haplotype diversity ( h = 0·9333–1·000) and nucleotide diversity (π = 0·0046–0·1467) varied greatly among the sampling locations. Phylogenetic analysis of the CR sequences indicated that M. cephalus in the north-west Pacific belongs to two highly divergent lineages (lineages 1 and 2), with the inferred population structure being closely associated with the distribution of both lineages. Two populations were identified, one from the East China Sea and the other from the South China Sea. The former samples were obtained from Taiwan and Qingdao of north China and associated with lineage 1 haplotypes. The latter samples were collected from the Philippines, Pearl River of South China and two samples from Japan, all of which were associated with lineage 2. Japanese samples from Okinawa and Yokosuka had different degrees of mixing between lineages 1 and 2. Historical demographic variables in both populations indicated that Pleistocene glaciations had a strong impact on M. cephalus in the north-west Pacific, resulting in a recent demographic decline of the East China Sea population but in demographic equilibrium for the South China Sea population. Japan appears to be a contact zone between lineages 1 and 2, but it may also be indicative of coexistence between resident and migratory populations. Further global studies are required to clarify the taxonomic status of this cosmopolitan species.     

Variation in 8-ketotrichothecenes and zearalenone production by Fusarium graminearum isolates from corn and barley in Korea

A total of 214 Fusarium graminearum isolates were obtained from corn and barley which were collected from Kangwon province and the southern part of Korea, respectively, and were tested for 8-ketotrichothecenes and zearalenone (ZEA) production on rice grains. The incidences of trichothecene production by 105 isolates of F. graminearum from corn were 59.0% for deoxynivalenol (DON), 37.1% for 15-acetyldeoxynivalenol(15-ADON), 13.3% for 3-acetyldeoxynivalenol (3-ADON), 7.6% for 3,15-diacetyldeoxynivalenol (3,15-DADON), 20.0% for nivalenol (NIV), 6.7% for 4-acetylnivalenol (4-ANIV), and 1.0% for 4,15-diacetylnivalenol (4,15-DANIV). DON chemotypes frequently produced 15-ADON as the major isomer rather than 3-ADON and 9 of the 61 DON chemotypes produced low levels of NIV. On the other hand, the incidences of trichothecene production of 109 isolates by F. graminearum from barley were 24.8% for DON, 72.5% for NIV, 62.4% for 4-ANIV, and 10.1% for 4,15-DANIV. Of these isolates, 78 were NIV chemotypes and only one isolate produced DON and 3-ADON as major toxins. In addition, 26 of the 78 NIV chemotypes produced low levels of DON. ZEA was frequently produced by the trichothecene-producing isolates and the incidences of ZEA were 51.4% and 31.2% for the isolates from corn and barley, respectively. There was a great regional difference in trichothecene production by F. graminearum isolates between corn- and barley-producing areas in Korea.     

东北地区中鼩鼱遗传多样性与分子系统地理学

本研究对我国东北地区3个种群（大兴安岭、小兴安岭和长白山山脉）的中鼩鼱（99个样本）Cyt b基因全序列进行分析,共获得81个单倍型。整体单倍型多态性为0.9940,显示东北地区中鼩鼱整体遗传多样性较高,3个种群的遗传多样性无明显差异。分子变异方差分析显示3个种群之间的分化占总分化的2.48%,种群内采样地的分化占总分化的0.34%,采样地内部遗传分化占总分化的97.19%。遗传分化结果显示中鼩鼱遗传分化与地理距离存在非正相关关系。结合GenBank下载欧亚其他地区中鼩鼱Cyt b基因全序列构建系统发生树,分化为3个分支：日本北海道分布的中鼩鼱构成1个小分支;韩国济州岛的中鼩鼱构成1个小分支;我国东北地区和其他欧亚大陆的中鼩鼱构成1个大分支,在这个大支上未显现进一步的遗传分化结构。中介网络分析也暗示除日本北海道和韩国济州岛外,欧亚大陆分布的中鼩鼱没有明显的地理系统分化,表现出遗传分化与地理关联性较弱。种群历史分析显示东北地区中鼩鼱经历过种群扩张。     

稻瘟病菌群体的分子遗传学研究III.——广东省2001年度稻瘟病菌群体的遗传结构分析以及两个假说的提出

利用随机扩增多态性DNA技术(randomamplifiedpolymorphicDNA,RAPD)对广东省2001年度稻瘟病菌群体的遗传结构进行了分析。以相似性系数为0.70阈值时,可将采集于广东省三大生态稻作区、早稻和晚稻生长季节的96个菌株划分为12个遗传宗谱;其中宗谱8和9的菌株数各占总数的25%和18.8%,为优势宗谱。从稻作区来看,宗谱3和8为各个稻作区的共同宗谱;而宗谱1和2,7和11,以及9、10和12则依次是粤北、粤中和粤南稻作区的特异性宗谱。从生长季节来看,来源于早、晚季的菌株完全分属于宗谱图的上、下两个半区,彼此之间不存在共同的宗谱;而且两个优势宗谱都集中于晚季供试亚群体。结合前两次实验的结果,作者提出了如下两个假说来解释广东省稻瘟病菌群体所表现的遗传特性:一个地区或生长季节的病原菌群体,其优势宗谱所占的比例越高,该地区或生长季节病害发生就越严重;在长期的水稻栽培历史中,稻瘟病菌群体可能逐步地形成了早季宗谱(小种)和晚季宗谱(小种)的遗传分化。如何进一步验证上述两个假说是值得我们进一步探讨的重要课题。     

中国小麦赤霉病菌优势种——禾谷镰刀菌产毒素能力的研究

试验测定了分离自中国小麦赤霉病常发生地区病麦穗上的47个禾谷镰刀菌(Fusariumgraminearum)菌株的产毒紊能力。结果表明,它们可以产生25种包括单端孢霉烯族化合物(Trichothecenes)、倍半萜类化合物(sesquiterpenes)、赤霉烯酮(Zearalenone)和丁烯羟酸内酯(Butenolide)等类的已知次生代谢物。这些菌株属于化学型 I,其中,来自我国温暖麦区的菌株都属化学型IA (deoxynivalenol,3-acetyl),并在气候冷凉地区发现化学型IB(de-oxynivalenol,15-acetyl)菌株。     

Endemic or introduced? Phylogeography of Asparagopsis (Florideophyceae) in Australia reveals multiple introductions and a new mitochondrial lineage

The red seaweed Asparagopsis taxiformis embodies five cryptic mitochondrial lineages (lineage 1–5) introduced worldwide as a consequence of human mediated transport and climate change. We compared globally collected mitochondrial cox2‐3 intergenic spacer sequences with sequences produced from multiple Australian locations and South Korea to identify Asparagopsis lineages and to reveal cryptic introductions. We report A. taxiformis lineage 4 from Cocos (Keeling) Islands, Australia, and the highly invasive Indo‐Pacific Mediterranean lineage 2 from South Korea and Lord Howe Island, Australia. Phylogeographic analysis showed a clear haplotype and geographic separation between western Australian and Great Barrier Reef (GBR) isolates belonging to the recently described lineage 5. The same lineage, however, was characterized by a substantial genetic and geographic break between the majority of Australian specimens and Asparagopsis collections from South Solitary Island, Southern GBR, Lord Howe Island, Kermadec Islands, Norfolk Island, New Caledonia and French Polynesia. The disjunct geographic distribution and sequence divergence between these two groups supports the recognition of a sixth cryptic A. taxiformis mitochondrial lineage. As climatic changes accelerate the relocation of biota and offer novel niches for colonization, periodic surveys for early detection of cryptic invasive seaweeds will be critical in determining whether eradication or effective containment of the aliens are feasible.