Virulence Phenotypes of a Worldwide Collection of Puccinia triticina from Durum Wheat

ABSTRACT A total of 78 isolates of Puccinia triticina from durum wheat from Argentina, Chile, Ethiopia, France, Mexico, Spain and the United States and 10 representative isolates of P. triticina from common wheat from the United States were tested for virulence phenotypes on seedling plants of 35 near-isogenic lines of Thatcher wheat. Isolates with virulence on lines with leaf rust resistance genes Lr10, Lr14b, Lr20, Lr22a, Lr23, Lr33, Lr34, Lr41, and Lr44 represented the most frequent phenotype. Cluster analysis showed that P. triticina from durum wheat from South America, North America, and Europe had an average similarity in virulence of 90%, whereas isolates from Ethiopia were <70% similar to the other leaf rust isolates collected from durum wheat. Of the 11 isolates from Ethiopia, 7 were avirulent to Thatcher and all near-isogenic lines of Thatcher. The isolates from common wheat had an average similarity in virulence of 60% to all leaf rust isolates from durum wheat. P. triticina from durum wheat was avirulent to many Lr genes frequently found in common wheat. It is possible that P. triticina currently found on durum wheat worldwide had a single origin, and then spread to cultivated durum wheat in North America, South America, and Europe, whereas P. triticina from Ethiopia evolved on landraces of durum wheat genetically distinct from the cultivated durum lines grown in Europe and the Americas.     

1999年我国小麦叶锈菌毒性监测

采用国际通用的小麦叶锈菌鉴别寄主和辅助鉴别寄主分析了来自1999年我国不同地区小麦叶锈菌的毒性基因,479个叶锈菌株共划分为162个毒性类型,其中23个为主要毒性类型.毒性类型中出现频率最高的为FHB、PHT、FHG、THT,它们对抗叶锈基因Lr2a、Lr2b、Lr3、Lr10、Lr14b、Lr16、 Lr26的平均毒性频率高于80%,而对Lr3ka、Lr25、Lr19、Lr24、Lr30、Lr15、Lr35的平均毒性频率低于30%;发现对Lr35有毒力的菌株,出现频率为1.04%;至今尚未发现对Lr38、Lr45抗性基因有毒力的菌株.研究同时发现,不同地区小麦叶锈菌的毒性类型不同,毒性频率存在一定的差异.Lr9、Lr15、Lr19、Lr24、Lr35、Lr38、Lr45为小麦抗叶锈育种可利用的有效抗病基因.     

Virulence and Molecular Polymorphism in International Collections of the Wheat Leaf Rust Fungus Puccinia triticina

ABSTRACT Collections of Puccinia triticina, the wheat leaf rust fungus, were obtained from Great Britain, Slovakia, Israel, Germany, Australia, Italy, Spain, Hungary, South Africa, Uruguay, New Zealand, Brazil, Pakistan, Nepal, and eastern and western Canada. All single-uredinial isolates derived from the collections were tested for virulence polymorphism on 22 Thatcher wheat lines that are near-isogenic for leaf rust resistance genes. Based on virulence phenotype, selected isolates were also tested for randomly amplified polymorphic DNA (RAPD) using 11 primers. The national collections were placed into 11 groups based on previously established epidemiological zones. Among the 131 single-uredinial isolates, 105 virulence phenotypes and 82 RAPD phenotypes were described. In a modified analysis of variance, 26% of the virulence variation was due to differences in isolates between groups, with the remainder attributable to differences within groups. Of the RAPD variation, 36% was due to differences in isolates between groups. Clustering based on the average virulence distance (simple distance coefficient) within and between groups resulted in eight groups that differed significantly. Collections from Australia-New Zealand, Spain, Italy, and Britain did not differ significantly for virulence. Clustering of RAPD marker differences (1 - Dice coefficient) distinguished nine groups that differed significantly. Collections from Spain and Italy did not differ significantly for RAPD variation, neither did collections from western Canada and South America. Groups of isolates distinguished by avirulent/virulent infection types to wheat lines with resistance genes Lr1, Lr2a, Lr2c, and Lr3 also differed significantly for RAPD distance, showing a general relationship between virulence and RAPD phenotype. The results indicated that on a worldwide level collections of P. triticina differ for virulence and molecular backgrounds.     

Physiological specialization and pathotype distribution of Puccinia recondita in western Europe, 1995

A pathogenicity survey of Puccinia recondita f.sp. tritici ( Prt ) was conducted in western Europe in 1995. Random urediospore isolates (850) of Prt were collected from the air by means of a jet spore sampler in wheat-growing regions of Austria, Belgium, France, Germany, northern Italy, Switzerland and the UK. Pathogenicity of the isolates was determined in tests of detached primary leaf segments maintained on water agar supplemented with benzimidazole (35 p.p.m.). The differential genotypes used were Thatcher, 20 near-isogenic Thatcher lines each with a single leaf rust resistance gene, and five cultivars/lines with additional resistance genes. All isolates were avirulent for the genes Lr9, Lr19, Lr21, Lr24, Lr25 and Lr29 , and both virulence and avirulence were detected for the remaining 19 genes. Fifty-three pathotypes were identified, four of which predominated (64% of isolates) and were widespread throughout western Europe. Three of the four predominant pathotypes were also identified in collections of wheat leaf rust collected in Poland, Hungary, Estonia and Finland. One pathotype, which comprised 35% of isolates in the south of France, was not detected in any other region. This pathotype was indistinguishable from several isolates obtained from Morocco, which suggested that it may have originated from northern Africa. Comparisons with previously published data suggested that the four predominant pathotypes were very similar and possibly the same as pathotypes present in the former Czechoslovakia for up to 20 years. The results obtained provide evidence of migration of Prt over considerable distances in western Europe, stressing the need for a co-ordinated approach for genetical control of the disease in this region.     

Genetics of leaf rust resistance in spring wheat cultivars alsen and norm

ABSTRACT Alsen is a recently released spring wheat cultivar that has been widely grown in the United States because it has resistance to Fusarium head blight and leaf rust caused by Puccinia triticina. Norm is a high yielding wheat cultivar that has been very resistant to leaf rust since it was released. Alsen and Norm were genetically examined to determine the number and identity of the leaf rust resistance genes present in both wheats. The two cultivars were crossed with leaf rust susceptible cv. Thatcher and F(1) plants were backcrossed to Thatcher. Eighty one and seventy three BCF(1) of Thatcher times; Alsen and Thatcher x Norm respectively, were selfed to obtain BCF(2) families. The BCF(2) families were tested as seedlings with different isolates of P. triticina that differed for virulence to specific leaf rust resistance genes. The BCF(2) families that lacked seedling resistance were also tested as adult plants in greenhouse tests and in a field rust nursery plot. Segregation of BCF(2) families indicated that Alsen had seedling genes Lr2a, Lr10, and Lr23 and adult plant genes Lr13 and Lr34. Norm was determined to have seedling genes Lr1, Lr10, Lr16, and Lr23 and adult plant genes Lr13 and Lr34. The characterization of Lr23 in the segregating populations was complicated by the presence of a suppressor gene in Thatcher and the high temperature sensitivity of resistance expression for this gene. The effective leaf rust resistance in Alsen is due to the interaction of Lr13 and Lr23, with Lr34; and the effective leaf rust resistance in Norm is due to the interaction of Lr13, Lr16, and Lr23, with Lr34.     

Distribution of pathotypes with regard to host cultivars in French wheat leaf rust populations

ABSTRACT Isolates of wheat leaf rust collected from durum and bread wheat cultivars in France during 1999-2002 were analyzed for virulence on 18 Thatcher lines with single genes for leaf rust resistance (Lr genes). Sampling focused on the five most widely grown bread wheat cultivars (two susceptible and three resistant) to allow statistical comparison of diversity indexes between the cultivars. Leaf rust populations from durum and bread wheats were different. The diversity of the bread wheat leaf rust pathotypes, as measured by the Shannon index, ranged from 2.43 to 2.76 over the 4 years. Diversity for wheat leaf rust resistance was limited in the host since we postulated only seven seedling resistance genes in the 35 cultivars most widely grown during 1999-2002. Leaf rust populations were strongly differentiated for virulence within bread wheat cultivars, and diversity was higher on those that were resistant, mainly due to a more even distribution of virulence phenotypes than on susceptible cultivars. The pathogen population on the susceptible cv. Soissons was largely dominated by a single pathotype (073100), whereas all other pathotypes virulent on cv. Soissons either decreased in frequency or remained at a low frequency during the period studied. Several pathotypes including the most complex one were found only on resistant cultivars, even though most of them were virulent on the susceptible cv. Soissons. Specific interactions were necessary, but not always sufficient, to account for pathotype distribution and frequencies on the cultivars, suggesting that selection for virulence to host resistance genes is balanced by other selective forces including selection for aggressiveness.     

Diversity,spatial variation,and temporal dynamics of virulences in the German leaf rust (<Emphasis Type="Italic">Puccinia recondita</Emphasis> f. sp. <Emphasis Type="Italic">secalis</Emphasis>) population in winter rye

A large collection of German rye leaf rust isolates was analysed to characterize the diversity, spatial variation and temporal dynamics of virulences. Virulence-avirulence phenotypes (=pathotypes) were determined on 23 host differentials. We found 93 pathotypes among 177 single-uredinial isolates in 2000, 201 pathotypes among 437 isolates in 2001, and 125 pathotypes among 213 isolates in 2002. In total, the 827 analyzed isolates represented 317 pathotypes. Frequency of virulences on the individual differentials varied from 2% to 97%. Eight of the differentials showed a high resistance level with virulence frequencies <10%. Virulence complexity of the isolates ranged from 3 to 21 with a mean of nine. The percentages of highly virulent isolates (>14 virulences) increased from 4 to 15% during the sampling period. A high level of virulence diversity was observed within and between individual sampling sites with Simpson indices around 0.9. Evenness indices ranged from 0.88 to 0.92. Four of the five most frequent pathotypes were found in each year but their frequency never exceeded 10%. Isolates with unusual virulence combinations could be clearly separated by principal component analysis. Location-specific pathotype frequencies were revealed in each year, but the frequency patterns varied across years. On four fields a considerable increase of highly virulent pathotypes occurred within 6 weeks during the epidemic. The high diversity of pathotypes as well as the fast accumulation of highly virulent pathotypes favour the adaptation of the pathogen to race-specific host resistances. More durable resistance might be achievable by combining new effective race-specific resistances with adult-plant and/or race-non-specific quantitative resistances.     

An integrated multivariate approach to net blotch of barley: Virulence quantification,pathotyping and a breeding strategy for disease resistance

Knowledge of pathotype diversity and virulence in local populations of Pyrenophora teres is a prerequisite to screening for durable resistance to net blotch. The current study aimed to quantify the virulence level of Moroccan isolates, identify and designate existing pathotypes, and select resistant genotypes. We developed a method for virulence quantification of P. teres isolates based on a conversion of infection responses into frequencies for use in correspondence analysis. Coordinates of the first axis of this analysis had a virulence spectrum and ranked isolates from virulent to avirulent. Mixed model analysis was also devised for virulence quantification. Coordinates of the first dimension of correspondence analysis were linearly correlated to BLUPs (Best Linear Unbiased Predictors) of the mixed model. A genotype by genotype by environment model (GGE) coupled with cluster analysis differentiated P. teres isolates into ten and nine pathotypes for net- and spot-forms respectively. Populations of these two forms were dissimilar in terms of classes of virulence. For P. teres f. maculata, avirulent, moderately virulent and highly virulent isolates represented one-third of the population, whereas 90% of P. teres f. teres population was composed of avirulent to moderately avirulent isolates. Barley differential sets were subsequently reduced to two new sets that simplified pathotyping through a key code based on resistant or susceptible reactions. Dendrograms of cluster analysis based on GGE analysis depicted the stability of a genotype’s reactions across all isolates, and using only resistant cultivars as sources of resistance to control net blotch disease would, based on this analysis, fail to control all pathotypes. Therefore, we propose an alternative breeding strategy to control net blotch effectively.     

国际上小麦叶锈菌生理小种鉴别寄主及其小种命名方法

由于地理生态条件、叶锈菌群体结构、研究历史和研究方法等的差异,不同国家和地区采用相应的小麦叶锈菌鉴别寄主和小种命名方法。美洲、中国、欧洲、埃及、南非等国家和地区均采用以Thatcher为遗传背景的分别含有Lr1、Lr2 a、Lr2 c、Lr3、Lr9、Lr16、Lr24、Lr26、Lr3 ka、Lr11、Lr17和Lr30基因的近等基因系或单基因系作为小麦叶锈菌鉴别寄主,但附加的辅助鉴别品种不尽相同;澳大拉西亚和印度的鉴别寄主自成体系。这种格局不利于国家间研究结果的对比和交流。因此,建立一套国际通用鉴别体系实属当务之急。     

Diversity of virulence phenotypes among annual populations of Puccinia triticina originating from common wheat in Israel during the period 2000–15

Leaf rust, caused by the fungus Puccinia triticina, is the most common rust disease of wheat in wheat-producing areas worldwide. The Israeli population of P. triticina has been consistently monitored since 1993. A total of 784 single urediniospore isolates from Triticum aestivum were analysed during 2000–15. The structure of the pathogen population has changed to a large extent since 2000. The annual populations of P. triticina were separated into two distinct groups, 2000–11 and 2012–15, while populations of 2000–5 and 2006–12 were differentiated to a lesser extent. The change in the population originating from T. aestivum during the period 2000–15 is less significant compared to changes in the 1990s described previously. Diversity within the annual populations of P. triticina was rather stable during the period studied. Three new pathotypes, characterized by virulences on Lr3ka and Lr30 genes, became dominant between 2012 and 2015, while all but one prevailing pathotypes in 2000–11 were avirulent on these two genes. Significant changes in virulence frequencies on a number of Lr genes (Lr2c, Lr3ka, Lr15, Lr21, Lr23, Lr26, Lr30) and pairwise associations of virulences (mainly with Lr2c and Lr26) were registered in 2012–15 or earlier. It is postulated that the composition and pathotype structure of the P. triticina population in Israel is determined by wind-disseminated urediniospores from neighbouring regions, where the migration of P. triticina from the eastern part of the Mediterranean Sea and from the Horn of Africa seem to have the greatest influence.     

Genetic Differentiation of Puccinia triticina Populations in Central Asia and the Caucasus

ABSTRACT Isolates of Puccinia triticina collected from common wheat in the Central Asia countries of Kazakhstan, Uzbekistan, Tajikistan, and Kyrgyzstan and the Caucasus countries of Azerbaijan, Georgia, and Armenia were tested for virulence to 20 isolines of Thatcher wheat with different leaf rust resistance genes and molecular genotype at 23 simple sequence repeat (SSR) loci. After clone correction within each country, 99 isolates were analyzed for measures of population diversity, variation at single SSR loci, and for genetic differentiation of virulence phenotypes and SSR genotypes. Isolates from Central Asia and the Caucasus were also compared with 16 P. triticina isolates collected from common wheat in North America that were representative of the virulence and molecular variation in this region and two isolates collected from durum wheat in France and the United States. Populations from the Caucasus, Uzbekistan, Tajikistan, and Kyrgyzstan were not significantly (P > 0.05) differentiated for SSR variation with F(st) and R(st) statistics. Populations from the Caucasus, Uzbekistan, Tajikistan, and Kyrgyzstan were significantly (P < 0.05) differentiated from the populations in South and North Kazakhstan for SSR variation. All populations from Central Asia and the Caucasus were significantly differentiated from the North American isolates and isolates from durum wheat for SSR variation and virulence phenotypes. There was a correlation between virulence phenotype and SSR genotype among individual isolates and at the population level. Mountain barriers may account for the differentiation of P. triticina geographic populations in Central Asia and the Caucasus.     

Comparative Analysis of Indices in the Study of Virulence Diversity Between and Within Populations of Puccinia recondita f. sp. tritici in Israel

ABSTRACT Isolates of Puccinia recondita f. sp. tritici (n = 260) obtained from bread, durum, and wild emmer wheat leaf collections throughout Israel during 1993 to 1997 were analyzed for virulence on a set of wheat differentials. The overall frequency of virulence increased on differentials possessing resistance genes Lr1, Lr2a, Lr3, and Lr26 and decreased on Lr17, Lr21, and Lr30. Genes Lr9 and Lr24 were resistant, while Lr18 was susceptible (98% in 1996) to all tested leaf rust isolates and Lr10 and Lr23 were susceptible to more than 78% of the isolates. Diversity between populations (years) was assessed using Kosman's H(KB) (based on degrees of similarity among distinct phenotypes) and H(KDis) (based on frequencies of individual virulences) and Nei's and Rogers' distances. The greatest difference occurred between the 1993 and 1994 populations. Phenotypic diversity within each population (year) was analyzed using the Shannon's, Simpson's, and Kosman's indices. The highest diversity within years was recorded in 1994 and significantly increased from 1993 to 1994 for all indices. The variance in the diversity between populations can be only partially explained by differences between corresponding diversities within population. The comparative analysis of diversity between and within populations over the 5 years enabled a detailed study of changes in the pathogen population. The results show that the different measures do not yield the same rank order of diversity.     

Diversity and distribution of pathotypes of the soybean rust fungus Phakopsora pachyrhizi in East Africa

Phakopsora pachyrhizi is a biotrophic fungus that causes rust on soybean, leading to devastating yield losses. Development of resistant cultivars for deployment in different geographic regions requires a comprehensive understanding of the prevalent P. pachyrhizi pathotypes. To determine the pathotypes existing in four East African countries, 65 isolates were tested on 11 soybean host differentials. In addition, the virulence spectrum of isolates collected from the same region over multiple years was compared. The majority of the isolates (54%) belonged to pathotype 1000, which was found in all countries. The pathotypes with the most complex virulence spectrum, which comprised isolates from Kenya and Malawi, were virulent on four differentials. All pathotypes were virulent on soybean genotypes carrying the Rpp1 resistance gene to P. pachyrhizi, but they were avirulent on cultivars carrying the Rpp1b, Rpp2, or Rpp3 gene, as well as on cultivar No6-12-1 that carries Rpp2, Rpp4, and Rpp5. Two of the pathotypes were virulent on cultivar UG 5 that carries Rpp1 and Rpp3 and on Hyuuga that carries Rpp3 and Rpp5. The isolates collected from different countries differed in their virulence spectrum across the years. Shannon's index (H) and Simpson's index (S) of diversity indicated that the isolates from Malawi were more diverse (H = 1.55, S = 0.90) while those from Uganda had lower diversity (H = 0.78, S = 0.46 ). The Rpp genes that were found to provide resistance to all pathotypes of P. pachyrhizi can be employed for soybean breeding aimed at durable rust resistance.     

我国40个小麦品种抗叶锈性研究

 选用11个具不同毒性基因组合的叶锈菌致病类型推导分析了1998~1999年度国家小麦区域试验40个品种所携带的抗叶锈病基因状况。在供试的39个已知抗叶锈基因(或基因组合)中,推导出Lr1、Lr2c、Lr3bg、Lr10、Lr13、Lr14a、Lr16、Lr23、Lr26、Lr32等10个抗叶锈基因,分布在24个品种中,有11个品种携带未知抗叶锈基因,5个品种不具有苗期抗叶锈基因。选用BBB、DHS、PGT和PHT等4个叶锈菌致病类型并设置5/10℃、15/20℃、25/30℃(黑暗/光照)3种不同的温度条件,研究了40个供试品种的抗性稳定性。结果表明,在这些品种中有15个品种的侵染型表现稳定或较稳定,3个品种表现为高温抗性,2个品种表现低温抗性,其余20个品种存在明显的品种、菌系和温度三者的相互作用;利用6个叶锈菌混合优势小种在田间进行成株期抗叶锈性鉴定结果表明,在40个供试品种中有21个品种具有良好的抗性,其中,至少有6个品种表现为慢锈性,有4个品种表现为明显的成株抗性,有4个品种可能携带成株抗性基因Lr34。文中还对几个主要抗叶锈基因的抗性特点及其利用价值等进行了讨论。     

春小麦品种沈免2063抗叶锈性遗传分析

为明确春小麦品种沈免2063所含抗叶锈病基因的对数、身份、显隐性和互作关系,以沈免2063为父本,分别与感病品种Thatcher及小麦抗叶锈病近等基因系Lr9、Lr19、Lr24、Lr25、Lr28、Lr42和Lr43的载体品系杂交,获得F1、F2和F3代群体后,分别在苗期和成株期进行抗病性测定。结果表明:沈免2063含有3对显性遗传且相互独立作用的抗叶锈病基因Lr9、Lr19和Lr25,在苗期,沈免2063对致病类型CBG/QQ的抗病性由Lr9和Lr25控制,对PHT/RP的抗病性由上述3对抗叶锈病基因控制;在成株期,沈免2063对优势致病类型PHT/RP和THT/TP等比混合菌种的抗病性由上述3对抗叶锈病基因控制。Lr9、Lr19和Lr25在育成品种中出现频率很低,目前尚很有效,但这3个基因均为典型的垂直抗病性基因,应进行基因布局、基因轮换等科学组配,才能延长其使用寿命。     

西藏小麦条锈菌群体结构与遗传多样性

为查明西藏小麦条锈菌Puccinia striiformis f. sp. tritici群体结构和遗传多样性,采用中国鉴别寄主和近等基因系鉴别寄主,以及竞争性等位基因特异性PCR-单核苷酸多态性（kompetitive al-lele specific PCR-single nucleotide polymorphism,KASP-SNP）分子标记对2017年采自西藏的150个小麦条锈菌菌系分别进行表型分析和基因型分析。表型分析结果显示,中国鉴别寄主将150个菌系区分为 12 个已知小种、6 个已知致病类型和 13 个未知致病类型,所有菌系均不能侵染中四和Triticum spelta album鉴别寄主。近等基因系鉴别寄主将150个菌系区分为88个毒性类型,这些毒性类型均不侵染携带抗性基因Yr5、Yr10或Yr15的品种。基因型分析结果显示,26对引物将150个菌系划分为73个基因型,表明西藏小麦条锈菌群体基因型丰富。基因流分析结果表明,波密县与洛扎县小麦条锈菌亚群体之间的基因流N_m最高,达5.86,米林县西部与波密县、洛扎县、巴宜县、米林县东部条锈菌亚群体之间的N_m较低,分别为0.25、0.34、0.42和0.67,表明西藏不同地区条锈菌群体之间基因交流强度差异较大。说明西藏作为我国小麦条锈病的独立流行区,条锈菌群体毒性结构复杂,遗传多样性高。     

Low pathotype diversity in a recombinant Puccinia striiformis population through convergent selection at the eastern Himalayan centre of diversity (Nepal)

Worldwide Puccinia striiformis f. sp. tritici (Pst) epidemics have been reported to be driven by few genetic lineages, while a high diversity is evident at the Pst Himalayan centre of diversity. This study investigated the relationship between pathotype diversity and genetic structure in Nepal, the eastern Himalayan region, which has been largely unexplored. Despite the high genetic diversity and recombinant structure detected through microsatellite genotyping, characterization of virulence phenotypes for 62 isolates identified only eight pathotypes, with two pathotypes predominant over all the populations. This is in contrast to the Pakistani and Chinese recombinant populations, where high pathotype diversity is associated with genetic diversity. The most prevalent Nepali pathotype was not a unique clonal lineage, but was represented by seven multilocus genotypes from four distinct genetic subgroups, suggesting strong directional selection on virulence genes, resulting in convergent pathotypes in distinct genetic groups. This convergent selection is discussed in comparison with clonal French and recombinant Pakistani populations. Additionally, the Nepali Pst population carried virulence to 17 out of 24 tested yellow rust resistance genes (Yr), with the absence of virulence to Victo and Early Premium and resistance genes Yr5, Yr10, Yr15, Yr24 and Yr26. Virulence to Yr2, Yr7, Yr27 and YrSu were fixed in all isolates, in line with the deployment of these resistance genes in Nepal. The results reflect the influence of resistance gene deployment on selection of virulence and pathotypes in a recombinant pathogen population, which must be considered in the context of durable resistance gene deployment.     

二倍体及四倍体中抗叶锈病基因在双二倍体中的表达与抑制

 通过杂交将近缘植物中的抗病基因导入普通小麦是抗病育种的常用方法。在利用二倍体和四倍体杂交合成双二倍体小麦过程中, 二倍体或四倍体携带的抗叶锈病基因在双二倍体中大多数情况下可以完全表达或部分表达其固有的抗病性, 但部分抗叶锈病基因则不能表达。四倍体波斯小麦Ps5、Ps8和野生二粒小麦D s3含有相同的抗叶锈病基因LrPs (暂定名), 在双二倍体Am1、Am2、Am3、Am5和Am7中可以表达其抗病性, 但在Am4中不能表达;二倍体粗山羊草Ae37含有Lr41和未知基因, 但Lr41在双二倍体Am2中不能表达;四倍体硬粒小麦Dr147携带Lr23和未知基因, 在双二倍体Am6中不能充分表达。抑制基因的存在是导致抗病基因不能表达或部分表达的主要原因之-。抑制基因位于AB染色体组或D染色体组上, 其抑制作用对抗病基因和病菌致病类型具有专化性, 还可能受温度等环境条件和寄主遗传背景等因素的影响。遗传分析结果表明, 在常温下, 双二倍体Am1、Am2、Am3和Am5对叶锈菌致病类型DGS/HB的抗病性均由1对相同的隐性抗病基因LrPs (暂定名)控制, 与它们具有共同的四倍体亲本Ps5有关。Am4不具有苗期抗叶锈病基因, 但含有来自粗山羊草A e39的1对隐性抑制基因SuLrPs (暂定名), 可抑制Am1、Am2、Am3和Am5中隐性抗叶锈病基因的表达。对抗病抑制基因存在原因和遗传分析验证方法等进行了讨论。     

Genetic differentiation of Puccinia triticina populations in the Middle East and genetic similarity with populations in Central Asia

Leaf rust of wheat, caused by Puccinia triticina, is a common and widespread disease in the Middle East. The objective of this study was to determine whether genetically differentiated groups of P. triticina are present in the Middle East region and to compare the population from the Middle East with the previously characterized population from Central Asia to determine whether genetically similar groups of isolates are found in the two regions. In total, 118 isolates of P. triticina collected from common wheat and durum wheat in Egypt, Israel, Turkey, Ethiopia, and Kenya were tested for virulence on 20 lines of wheat with single genes for leaf rust resistance and for molecular genotypes with 23 simple-sequence repeat (SSR) markers. After removal of isolates with identical virulence and SSR genotype in each country, 103 isolates were retained for further analysis. Clustering of SSR genotypes based on two-dimensional principal coordinates and virulence to wheat differential lines grouped the isolates into four Middle East (ME) groups. The two largest ME groups had virulence phenotypes typical of isolates collected from common wheat and two smaller ME groups had virulence typical of isolates collected from durum wheat. All pairs of ME groups were significantly differentiated for SSR genotype based on R(ST) and F(ST) statistics, and for virulence phenotype based on Φ(PT). All ME groups had observed values of heterozygosity greater than expected and significant fixation indices that indicated the clonal reproduction of urediniospores in the overall population. Linkage disequilibria for SSR genotypes was high across the entire population. The overall values of R(ST) and F(ST) were lower when isolates were grouped by country of origin that indicated the likely migration of isolates within the region. Although the two ME groups with virulence typical of isolates from common wheat were not differentiated for SSR genotype from groups of isolates from Central Asia based on R(ST), there was no direct evidence for migration between the two regions because all ME isolates differed from the Central Asia isolates for SSR genotypes.     

Diversity of virulence phenotypes among annual populations of wheat leaf rust in Israel from 1993 to 2008

Leaf rust, caused by the fungus Puccinia triticina, is the most common rust disease of wheat in wheat‐producing areas worldwide. The Israeli population of wheat leaf rust has been consistently monitored since 1993. A total of 840 single urediniospore isolates from Triticum aestivum (567), T. dicoccoides (119) and T. durum (154) were analysed during 1993–2008. The structure of the pathogen population has changed to a large extent since 1993. The annual populations of P. triticina were separated into two distinct groups: 1993–1999 and 2000–2008. Differentiation among the annual pathogen populations, as well as between the overall populations of the 1990s and 2000s, could be mainly attributed to the following forces: (i) migration of leaf rust urediniospores from neighbouring regions; and (ii) selection pressure of new yellow rust‐resistant wheat cultivars that have been introduced into Israel since 1997. Genetic multiplicity of wild emmer contributes to P. triticina variability in Israel. Leaf rust populations collected from common wheat, wild emmer and durum wheat differed. The population that originated from T. durum was rather stable during the years of the survey, whereas that from T. aestivum changed significantly from the 1990s to the 2000s. Diversity within the annual populations of P. triticina was highest in 1994 when many new pathotypes and associations between virulences were observed. Single‐step derivatives of the new pathotypes became dominant after 2000. Significant changes in virulence frequency to a number of Lr genes (e.g. Lr2a, Lr15, Lr17, Lr21, Lr26) were also registered in 2000–2008.