An AFLP-markers based genetic linkage map of Heterobasidion annosum locating intersterility genes

A genetic linkage map of the basidiomycete Heterobasidion annosum, casual agent of root rot in conifers, was constructed from a compatible mating between isolates from the North American S and P intersterility groups. In a population consisting of 102 progeny isolates, 358 AFLP markers were scored. The linkage analysis generated 19 large linkage groups, containing 6 or more markers, which covered 1468 cM. The physical size to genetic distance was approximately 11.1 kbp/cM. Segregation of three intersterility gene loci were analysed through mating of the progeny isolates with three tester strains carrying known intersterility genotypes. The loci for the two intersterility genes (S and P) were successfully located in the map. Segregation of the mating type locus was analysed by backcrossing the progeny isolates with their parental strains. The mating type locus could not be located in the map.     

Phenotypic and Genotypic Characterization of Phytophthora infestans Isolates from China

A total of 288 (202 from potato and 86 from tomato) isolates of Phytophthora infestans were collected from 1998 to 2007 in China. The isolates were characterized based on mating type, in vitro metalaxyl sensitivity, virulence on potato differentials, allozymes of glucose-6-phosphate isomerase ( Gpi ), peptidase ( Pep ), and mitochondrial DNA (mtDNA) haplotype and examined by DNA-based simple sequence repeat (SSR) and random amplified polymorphic DNA (RAPD) fingerprinting. The majority (283 of 288) of the isolates were of the A1 mating type, the other three were the A2 mating type and two were the A1A2 mating type. Resistance to metalaxyl was frequently observed, with 248 (86.1%) resistant, 21 (7.3%) intermediate and 19 (6.6%) sensitive isolates identified. Virulence was assessed for 125 isolates on a set of 11 potato differentials and 61 races were detected. Most isolates were virulent on the differential genotype with gene R3, and all known virulence genes were found, with race 3.4.7.11 being the most common. This pattern did not appear to be associated with geographic origin, sample type, mating type or metalaxyl sensitivity. The dominant banding patterns for Gpi were 100/100/111 (176 isolates) and 100/100 (109 isolates), but genotypes 86/100 and 100/111 were also identified. All isolates tested were homozygous (100/100) at the Pep locus. The majority (205 of 288) of isolates tested was of mtDNA haplotype IIb, 76 were haplotype IIa and seven were the rare Ib haplotype. The genetic diversity of 60 representative isolates from China was assayed by two types of molecular markers, RAPD and SSR. A high level of polymorphism was found. The results demonstrated the diverse phenotypic and genotypic structure of the current populations of P. infestans in China.     

Change of Mating Type in an EU1 Lineage Isolate of Phytophthora ramorum

All Phytophthora ramorum EU1 lineage isolates tested are of A1 mating type, except for three rare isolates from 2002 to 2003 from Belgium, which were originally assigned the A2 mating type. In one of these isolates (2338), a switch from A2 to A1 mating type was observed in 2006. This observation initiated a larger study in which all cultures and subcultures of the original three EU1 A2 isolates, maintained in three laboratories under different storage conditions, were checked for mating type change. The A2 to A1 mating type switch was observed in four of seven independently maintained isolates that were derived from isolate 2338 in two laboratories, using different transfer regimes and storage conditions. Following the mating type switch to A1 in these four derived isolates, no reversion back to A2 mating was observed, even after up to 5 years of additional isolate maintenance and several more subculturing events. The three other isolates that were derived from isolate 2338 as well as the other EU1 A2 isolates collected in 2002 and 2003 and stored in the same conditions did not display such mating type change. The potential causes of the mating type conversions as well as their epidemiological implications are discussed.     

AFLP Linkage Map of the Oomycete Phytophthora infestans

Here we present the first comprehensive genetic linkage map of the heterothallic oomycetous plant pathogen Phytophthora infestans. The map is based on polymorphic DNA markers generated by the DNA fingerprinting technique AFLP (Vos et al., 1995, Nucleic Acids Res. 23: 4407-4414). AFLP fingerprints were made from single zoospore progeny and 73 F1 progeny from two field isolates of P. infestans. The parental isolates appeared to be homokaryotic and diploid, their AFLP patterns were mitotically stable, and segregation ratios in the F1 progeny were largely Mendelian. In addition to 183 AFLP markers, 7 RFLP markers and the mating type locus were mapped. The linkage map comprises 10 major and 7 minor linkage groups covering a total of 827 cM. The major linkage groups are composed of markers derived from both parents, whereas the minor linkage groups contain markers from either the A1 or the A2 mating type parent. Non-Mendelian segregation ratios were found for the mating type locus and for 13 AFLP markers, all of which are located on the same linkage group as the mating type locus. Copyright 1997 Academic Press     

掘氏疫霉同宗配合、异宗配合特性的研究

本文对掘氏疫霉的同宗配合、异宗配合特性进行了研究,发现新分离的掘氏疫霉A~2交配型菌株,不经过配对培养可以产生卵孢子;菌种在15℃下保存,自身可孕性能力逐渐减退。菌株通过接种黄瓜后,异宗配合特性可以恢复,同宗配合特性不能恢复。经过营养生长,无性繁殖,菌株后代的交配型不引起改变。通过对疫霉属有关种不同交配型与掘氏疫霉各菌株不同交配型配对培养,以及菌种不同保存时间、不同培养基、疫霉属有关种的种间和种内配对,讨论了掘氏疫霉同宗配合、异宗配合特性的影响因素。     

Intra- and Intergenomic variation of Ploidy and Clonality characterize <Emphasis Type="Italic">Phytophthora capsici</Emphasis> on <Emphasis Type="Italic">Capsicum</Emphasis> sp. in Taiwan

Phytophthora capsici is a devastating disease of pepper (Capsicum sp.) in Taiwan causing complete loss of commercial fields. The objective of this study was to characterize genetic diversity for 38 newly collected isolates and three historical isolates. Analysis of data includes whole genome sequence for two new isolates and for two isolates collected previously in 1987 and 1995. In addition, 63 single nucleotide polymorphism loci were genotyped using targeted-sequencing, revealing 27 unique genotypes. Genotypes fell into three genetic groups: two of the groups contain 90% (n = 33) of the 2016 isolates, are triploid (or higher), are exclusively the A2 mating type and appear to be two distinct clonal lineages. The isolates from 2016 that grouped with the historical isolates are diploid and the A1 mating type. Whole genome sequence revealed that ploidy varies by linkage group, and it appears the A2 clonal lineages may have switched mating type due to increased ploidy. Most of the isolates were recently race-typed on a set of differential C. annuum, and although there was no direct correlation between virulence and ploidy, many of the triploid isolates were less virulent as compared to the historical diploid isolates. The implications for breeding resistant pepper and conducting population analyses are discussed.     

Mating type, nuclear DNA content and isozyme analysis of egyptian isolates ofPhytophthora infestans

Nineteen isolatesof Phytophthora infestans from potatoes growing in the Nile Delta were analyzed. All isolates were of the A1 mating type. Intraspecific isozyme variation was evaluated for all isolates. Using 15 selected enzymes, 215 electrophoretic phenotypes were identified among 19 isolates examined. Dihydrolipoamide dehydrogenase yielded the greatest number of electrophoretic phenotypes. Based on isozyme analysis, these isolates were subsequently divided into three distinct groups. Feulgen cytophotometry was used to measure the DNA content of individual zoospore nuclei. The distribution of DNA content in the Egyptian isolates was similar to that previously observed in isolates from other regions of the world.     

AFLP Linkage Map of the OomycetePhytophthora infestans

Here we present the first comprehensive genetic linkage map of the heterothallic oomycetous plant pathogenPhytophthora infestans.The map is based on polymorphic DNA markers generated by the DNA fingerprinting technique AFLP (Voset al.,1995,Nucleic Acids Res.23:4407–4414). AFLP fingerprints were made from single zoospore progeny and 73 F1 progeny from two field isolates ofP. infestans.The parental isolates appeared to be homokaryotic and diploid, their AFLP patterns were mitotically stable, and segregation ratios in the F1 progeny were largely Mendelian. In addition to 183 AFLP markers, 7 RFLP markers and the mating type locus were mapped. The linkage map comprises 10 major and 7 minor linkage groups covering a total of 827 cM. The major linkage groups are composed of markers derived from both parents, whereas the minor linkage groups contain markers from either the A1 or the A2 mating type parent. Non-Mendelian segregation ratios were found for the mating type locus and for 13 AFLP markers, all of which are located on the same linkage group as the mating type locus.     

Mating type and sensitivity of Phytophthora nicotianae from tobacco to metalaxyl and dimethomorph in Henan province,China

Phytophthora nicotianae causes black shank, one of the most important diseases of tobacco worldwide. Metalaxyl and dimethomorph are two fungicides which have been used widely for control of this disease in Henan province, China. A study was conducted to determine the level of metalaxyl and dimethomorph sensitivity in isolates of P. nicotianae from tobacco in Henan province and mating type structure of the pathogen population. A total of 32 isolates were isolated from 11 cities in Henan province. Sensitivity of all isolates to metalaxyl and dimethomorph was tested in vitro, and mating types of all isolates were determined by pairing known A1 and A2 testers. For metalaxyl, EC₅₀ values of 32 P. nicotianae isolates ranged from 0.08 to 2.82 mg/L. Sixteen isolates were sensitive, and the rest were intermediate to metalaxyl. None were classified as resistant isolates. For dimethomorph, EC₅₀ values of 32 P. nicotianae isolates ranged from 0.07 to 0.59 mg/L. All isolates were sensitive to dimethomorph. Thirty‐one isolates were A2 mating type, and one isolate was A0 mating type. No isolate was identified as A1 mating type. These results suggested that the P. nicotianae population in Henan province has already exhibited intermediate resistance to metalaxyl and was still sensitive to dimethomorph, and asexual reproduction was the major form of reproduction for the P. nicotianae population.     

Potato late blight in Morocco: characterization of Phytophthora infestans populations (virulence and mating type)

Late blight caused by Phytophthora infestans, is the most important disease of potato in Morocco. Use of partially resistant cultivars should be an essential component of a sustainable management strategy of potato late blight, provided the durability of this form of resistance. It is therefore important to determine the nature of P. infestans Moroccan populations. Mating types were determined for 91 strains of P. infestans collected in the northern (Larache-northern plain), north western (Kénitra) and north eastern (Méknès, Middle Atlas) potato cropping areas of Morocco in 1999-2000, 2000-2001 and 2003-2004. They showed a clear regional structure of these populations, with the presence of both mating types (A1 and A2). Of all isolates collected since 1999, A2 mating type constituted 56% (54 isolates), following by A1 mating type (40.7%, 31 isolates) and A1-A2 (self-fertile) mating type (3.30%, 3 isolates). Populations from Méknès and Kénitra consisted mainly of A2 mating type, whereas populations from Larache predominantly included A1 mating type. Physiological race study revealed the presence of 19 races of P. infestans in the first collection of 25 isolates tested between 1999 and 2001. All known virulence genes were detected in western and northern Moroccan isolates, except virulence for resistance genes R2, R5, and R6 which were absent. All isolates were able to overcome two or more R genes except one isolate (5-1) corresponding to race 1.     

Characterisation of Phytophthora capsici isolates from black pepper in Vietnam

Phytophthora foot rot of black pepper caused by Phytophthora capsici is a major disease of black pepper (Piper nigrum) throughout Vietnam. To understand the population structure of P. capsici, a large collection of P. capsici isolates from black pepper was studied on the basis of mating type, random amplified microsatellites (RAMS) and repetitive extragenic palindromic (REP) fingerprinting. Two mating types A1 and A2 were detected in four provinces in two climatic regions, with A1:A2 ratios ranging from 1:3 to 1:5. In several instances A1 and A2 mating types were found to co-exist in the same farm or black pepper pole, suggesting the potential for sexual reproduction of P. capsici in the field in Vietnam although its contribution to disease epidemics is uncertain. RAMS and REP DNA fingerprinting analysis of 118 isolates of P. capsici from black pepper showed that the population was genetically more diverse where two mating types were found, although the overall genetic diversity was low with most of the isolates belonging to one clonal group. The implication of these findings is discussed. The low diversity among isolates suggests that the P. capsici population may have originated from a single source. There was no genetic differentiation of isolates from different climatic regions. In addition to the large clonal group, several isolates with unique RAMS/REP phenotypes were also detected. Most of these unique phenotypes belonged to the minority A1 mating type. This may have significant implications for a gradual increase in overall genetic diversity.     

Genotypic Analysis of Russian Isolates of Phytophthora infestans from the Moscow Region, Siberia and Far East

Phytophthora infestans samples were collected during 1997 and 1998 at multiple sites in Russia from Sakhalin Island in the Far East across Siberia (nine sites, 160 isolates) to the Moscow region (four sites, 325 isolates). In addition, 12 isolates that were obtained previously were included. All isolates were analysed for mating type, and sensitivity to metalaxyl. Isolates from within any of the nine sites outside of the Moscow region were monomorphic for mating type and nearly monomorphic for metalaxyl resistance. In contrast, both A1 and A2 isolates were detected in the Moscow region, and these isolates were also polymorphic for metalaxyl resistance. In two sites in Siberia only A2 mating type strains were detected, in the other six sites in Siberia and in Sakahlin Island, only A1 mating types were detected. A subset of isolates ( n =191) was also analysed for pathotype (virulence to 10 R-genes, each in a distinct differential genotype). All isolates were highly complex (mean number of virulences approximately 8.4 of a maximum number of 10). All isolates ( n =43) from Sakahlin Island were virulent to all 10 of the R-genes tested. A further subset of isolates ( n =70, including 12 isolates collected before 1997) was analysed for genotype at the Glucose- 6-phosphate isomerase and Peptidase loci, mtDNA haplotypes, and RFLP pattern using the RG57 probe. The US-1 clonal lineage (previously dominant) was not detected in the 1997–98 sample. The populations of P. infestans near Moscow in 1997 and 1998 was highly diverse with 15 unique genotypes (including both mating types) among a sample of 18 isolates. In contrast, the populations of P. infestans in Siberia had limited diversity, with only three multilocus genotypes detected and most populations were dominated by the SIB-1 clonal lineage. This lineage accounted for 31 of the 39 strains collected in Siberia that were assayed for multilocus genotype.     

Phytophthora infestans in Poland from 1987–1989; Nuclear DNA Content, Mating Type Distribution and Response to Metalaxyl

Isolates of Phytophthora infestans were collected from all potato growing regions of Poland during the blight seasons of 1987—1989. All 1987 isolates were of Al mating type and were sensitive to metalaxyl. In 1988 and 1989, 46.5 % and 55.3 % of the isolates were sensitive to metalaxyl, respectively. The percentage of highly resistant (R) isolates increased from 25.6 % in 1988 to 39.5 % in 1989; however the percentage of intermediately resistant (I) isolates decreased during that period from 27.9 % to 5.3 %. A significant association was observed between the A1 compatibility type and metalaxyl resistance. The A2 mating type first appeared in 1988, and its frequency increased from 4.7 % of the population in 1988 to 47.6 % in 1989. Coincident with this change in mating type frequency, changes in ploidy levels of isolates were observed. Whereas 3 % of the 1988 isolates were diploid, 90 % of the 1989 A2 isolates and 28.6 % of the 1989 Al isolates were diploid. The approximate 1:1 ratio of the two mating types encountered in 1989, and the predominance of diploidy, indicates that the Polish population of P. infestans has the potential to become sexual.     

三种致病疫霉交配型分子检测方法的比较

致病疫霉Phytophthora infestans属于异宗配合卵菌,当A1、A2两种交配型同时存在时,可以进行有性生殖,产生卵孢子。检测疫霉菌交配型的传统方法是采用对峙培养,这种方法耗时长并且需要标准的A1、A2交配型菌株作为参照。因此,人们希望开发出更加简便和快捷的可直接基于核苷酸序列差异的分子检测方法。目前,已报道了3个与致病疫霉交配型紧密连锁的分子标记可用于交配型的检测。本研究用64株致病疫霉菌比较了3种基于交配型分子标记的检测方法与传统方法检测的结果。结果显示,依据分子标记的3种分子检测方法与传统对峙培养方法测定的交配型结果一致率为61%-73%,而且3种分子检测方法都不能检测出自育菌株。因此,致病疫霉交配型的分子检测方法还有待进一步研究。     

麦根腐平脐蠕孢有性生殖生物学研究

本文报道麦根腐平脐蠕孢Bipolaris sorokiniana(有性型为Cochliobolus sativus)人工诱导形成子囊座,并获得该菌A和a两种不同交配型。子囊座形成的最佳条件是:以麦秆浸汁琼脂为培养基(pH6—6.5)。以透析袋为培养基物,24℃培养1周,移至20℃培养2周。培养中光照不是重要因素。在无培养基物的培养基上不形成子囊座。对不同地区、不同寄主植物上麦根腐平脐蠕孢72个菌株交配型测定结果,两个不同交配型在自然界分配比例为1:1,交配型菌株的分布与地理、寄主植物的差异无相关性。     

中国橡胶树疫霉种的研究*

疫病是我国植胶区的主要病害。近年来,作者从云南西双版纳和广东海南岛的橡胶树和胶园土共分离出57株疫霉菌种。通过分类研究,共鉴定出4个种:恶疫霉 Phytophthoracactorum(Leb.＆ Cohn)Schroeter,辣椒疫霉 P.capsici Leoman,柑桔褐腐疫霉 P.citrophthora(Sm.＆ Sm.)Leonian,和棕榈疫霉 P.palmivora(Butl.)Butler。其中辣椒疫霉是首次在橡胶树上发现。我国橡胶树疫霉的种群结构与东南亚和南亚的有所不同,除棕榈疫霉外,其余3种在东南亚和南亚均未发现。而东南亚常见种:簇囊疫霉(P.botryosa)、橡胶疫霉(P.heveae)和蜜色疫霉(P.meadii),在我国却迄今尚未发现或有待证实。以前报道分离自胶园土壤中的芋疫霉(P.colocasiae),可能系柑桔褐腐疫霉之误。绝大多数分离物经配对培养均可产生性器官:辣椒疫霉的A~1交配型和A~2交配型大致相等;柑桔褐腐疫霉和棕榈疫霉的A~2交配型则明显多于A~1交配型。     

中国橡胶树疫霉种的研究

疫病是我国植胶区的主要病害。近年来,作者从云南西双版纳和广东海南岛的橡胶树和胶园土共分离出57株疫霉菌种。通过分类研究,共鉴定出4个种:恶疫霉 Phytophthoracactorum(Leb.＆ Cohn)Schroeter,辣椒疫霉 P.capsici Leoman,柑桔褐腐疫霉 P.citrophthora(Sm.＆ Sm.)Leonian,和棕榈疫霉 P.palmivora(Butl.)Butler。其中辣椒疫霉是首次在橡胶树上发现。我国橡胶树疫霉的种群结构与东南亚和南亚的有所不同,除棕榈疫霉外,其余3种在东南亚和南亚均未发现。而东南亚常见种:簇囊疫霉(P.botryosa)、橡胶疫霉(P.heveae)和蜜色疫霉(P.meadii),在我国却迄今尚未发现或有待证实。以前报道分离自胶园土壤中的芋疫霉(P.colocasiae),可能系柑桔褐腐疫霉之误。绝大多数分离物经配对培养均可产生性器官:辣椒疫霉的A~1交配型和A~2交配型大致相等;柑桔褐腐疫霉和棕榈疫霉的A~2交配型则明显多于A~1交配型。     

香菇自然群体中个体间的空间分布及其遗传联系*

应用体细胞不亲和性反应、交配型因子分析和基因组ＤＮＡ的ＲＡＰＤ分析,研究了一个分布于方圆约１ｋｍ的６根倒木上的１８个香菇野生菌株间的遗传差异。结果表明,该群体大多数菌株间配对（８０．４％）体细胞不亲和,而同一倒木菌株间配对的体细胞亲和率达 ６２．５％。不同倒木菌株间未发现体细胞亲和的配对。该群体存在 １１个特异的Ａ因子和７个特异的Ｂ因子。同一倒木的菌株有的交配型因子相同,有的则不同。不同倒木的菌株大多数交配型因子不同,未发现交配型因子完全相同的菌株。ＲＡＰＤ分析显示,体细胞亲和的菌株,交配型因子完全相同的菌株,在基于ＤＮＡ相似系数的遗传相关聚类中,首先聚为小类。总起来看,在自然群体中,香菇个体间的遗传差异与其空间分布之间存在一定的联系,随着空间距离的增大,菌株间的异质性相应增高。     

Evidence of recombination in mixed-mating-type and alpha-only populations of Cryptococcus gattii sourced from single eucalyptus tree hollows

Disease caused by the pathogenic yeast Cryptococcus gattii begins with the inhalation of an infectious propagule. As C. gattii is heavily encapsulated, this propagule is most likely to be a basidiospore. However, most C. gattii strains are infertile in laboratory crosses, and population studies indicate that recombination and dispersal are very restricted. In addition, strains of the alpha mating type predominate, which would not be expected in a mating population. C. gattii comprises four genetically distinct molecular genotypes, designated VGI to VGIV. C. gattii molecular type VGI has a strong association with Eucalyptus camaldulensis and can be found in high numbers in E. camaldulensis hollows. Previous work on isolates obtained from E. camaldulensis suggested that environmental populations of C. gattii are highly fragmented, have limited ability to disperse, and are confined to individual tree hollows. In the current study, we examined large numbers of isolates from three separate hollows for evidence of recombination. In two hollows, the alpha and a mating types were present in approximately equal numbers. The third hollow had alpha cells only and was from a region where a isolates have never been found. Statistical analysis of multilocus genotypes revealed recombining subpopulations in the three Eucalyptus hollows. Recombination was equally present in the alpha-a and alpha-only populations. This is consistent with recent studies that have found evidence suggestive of alpha-alpha mating in C. gattii and Cryptococcus neoformans and raises the possibility this may be a widespread phenomenon, allowing these fungi to recombine despite a paucity of a mating partners.     

Erratum to: The Interplay Between NSAIDs and Candida albicans on the Gastrointestinal Tract of Guinea Pigs

Trichophyton rubrum is an anthropophilic species that is the most frequent etiologic agent of human dermatophytosis throughout the world. No teleomorph has been identified for T. rubrum strains. This study used PCR analysis to confirm the presence of a mating type locus in the genome of Japanese isolates of T. rubrum. To clarify the epidemiological and ecological characteristics of this fungus, mating type sequences were tested for correlation of MAT genotype to mating type. This study examined clinical isolates of T. rubrum that had been obtained from 206 human cases of tinea pedis and tinea unguium in Japan, including those from Fukuoka (29 strains), Gifu (23 strains), Kanazawa (63 strains), and Tokyo (91 strains), along with 10 isolates derived from 10 cases of canine dermatophytosis. PCR detected the presence of MAT1-1 in all of the human and animal isolates. Therefore, all isolates examined were expected to react as (?) type on the mating test and not as (+) type.