Race 2 of Verticillium dahliae infecting tomato in Japan can be split into two races with differential pathogenicity on resistant rootstocks

Verticillium dahliae infecting tomato can be differentiated into races 1 and 2 based on differential pathogenicity on tomato cultivars carrying resistance gene Ve1. Although no commercial cultivars resistant to race 2 are available, race 2‐resistant rootstock cultivars Aibou and Ganbarune‐Karis have been bred in Japan. Nevertheless, the resistance of these rootstocks appears to be unstable in commercial tomato fields. Pathogenicity assays conducted under controlled conditions revealed that these rootstock cultivars are resistant to some isolates of race 2; this resistance is controlled by a single dominant locus, denoted by V2, based on segregation of resistance in F₂ populations from selfed rootstock cultivars. However, some other isolates of race 2 can overcome this resistance. Therefore it is proposed that the current race 2 of V. dahliae should be divided into two races, i.e. ‘race 2’ (nonpathogenic on Aibou) and ‘race 3’ (pathogenic on Aibou). The distribution of these races was surveyed in 70 commercial tomato fields in Hida, Gifu Prefecture, Japan. Race 3 was found in 45 fields, indicating that race 3 had already spread throughout the region. On the other hand, 25 fields had only race 2, and thus race 2‐resistant rootstocks would be effective for disease management in these fields. Races 2 and 3 could not be identified by genomic Southern hybridization probed with a telomere sequence, nor with previously reported race‐specific PCR assays. Elucidation of race‐determining mechanisms and development of methods for quick race identification should be made in future studies.     

Success and failure of invasive races of plant pathogens: The case of Puccinia striiformis f. sp. tritici in France

Invasions of new races can have contrasting consequences on populations of Puccinia striiformis f. sp. tritici, causing yellow rust of wheat. For example, the emergence of PstS7 (Warrior race) had major impacts in Europe and in France. By contrast, PstS2 had no impact in France, while it significantly affected other parts of the world. The objective of this study was to better understand factors that govern the success of an invasive race, taking the contrasting history of PstS7 and PstS2 in France as a case study. We compared these two races for three key factors driving invasive potential: (a) virulence against local cultivars, (b) aggressiveness in local environmental conditions, and (c) competitiveness against local races. During the period when PstS2 was detected, 70% of the grown wheat area was protected against this race by at least one known Yr resistance gene. By contrast, we found that only 15% of the wheat area had a low risk of infection by PstS7. In planta competition experiments suggested a higher competitiveness of PstS7 against local isolates compared to PstS2 in optimal thermal conditions. In silico experiments, based on thermal performance curves, suggested a high competitiveness of PstS7 considering infection efficiency. PstS2 was extremely competitive against local races in all considered environments (20 French sites × 15 years) due to its short latency period. Our findings highlight the importance of considering adaptation to environmental conditions, particularly temperature, in addition to virulence spectrum, in order to understand the evolutionary trajectories of emerging strains in pathogen populations.     

Identification of resistance to new virulent races of rust in sunflowers and validation of DNA markers in the gene pool

Sunflower rust, caused by Puccinia helianthi, is a prevalent disease in many countries throughout the world. The U.S. Department of Agriculture (USDA)-Agricultural Research Service, Sunflower Research Unit has released rust resistant breeding materials for several decades. However, constantly coevolving rust populations have formed new virulent races to which current hybrids have little resistance. The objectives of this study were to identify resistance to race 336, the predominant race in North America, and to race 777, the most virulent race currently known, and to validate molecular markers known to be linked to rust resistance genes in the sunflower gene pool. A total of 104 entries, including 66 released USDA inbred lines, 14 USDA interspecific germplasm lines, and 24 foreign germplasms, all developed specifically for rust resistance, were tested for their reaction to races 336 and 777. Only 13 of the 104 entries tested were resistant to both races, whereas another six were resistant only to race 336. The interspecific germplasm line, Rf ANN-1742, was resistant to both races and was identified as a new rust resistance source. A selection of 24 lines including 19 lines resistant to races 777 and/or 336 was screened with DNA markers linked to rust resistance genes R(1), R(2), R(4u), and R(5). The results indicated that the existing resistant lines are diverse in rust resistance genes. Durable genetic resistance through gene pyramiding will be effective for the control of rust.     

中国小麦条锈菌主要流行菌系的寄生适合度研究

 为了预测我国未来小麦条锈菌的优势种群,本研究采用抗性组分法测定了我国条锈菌主要流行菌系的寄生适合度。结果表明:决定我国小麦条锈菌最重要的寄生适合度属性为条锈菌的产孢能力(繁殖力),其次为条锈菌的侵染能力,再次为扩展能力;建立了小麦条锈菌寄生适合度属性3个主成份的数学模型;在供试的菌系中,Su11-4、Su11-14和CY32相对寄生适合度较高,已经成为我国目前小麦条锈菌的优势小种(类型);CY31由于其寄生适合度较低,出现频率逐年下降,已成为次要小种,感染"中四"苗期的新菌系T4类型,由于其寄生适合度低,也不会成为今后一个时期的流行小种。     

The wheat stem rust pathogen in the central region of the Russian Federation

A total of 387 isolates of Puccinia graminis f. sp. tritici (Pgt) collected in the central region of the Russian Federation from 2000 to 2009 was analysed with North American differential sets comprising 16 genotypes for samples of 2000–2006 and 20 genotypes for samples from 2007–2009. Forty‐five races were identified. The race composition of the local population underwent changes during this period. Race MKBT was the predominant race in the earlier years, but TKNT and TKNTF were in the majority later. During 2000–2009 there were no stem rust epidemics in the region. It was assumed that the local pathogen population cycled on wild grasses (including Elytrigia, Agropyron, Festuca, Dactylis, Phleum and Lolium spp.) and not only on wheat. The existence of host communities of wheat stem rust was supported by random amplified polymorphic DNA (RAPD) markers produced with high‐GC primers. The local population of Pgt was considered to be sexual based on the relatively high diversity of races isolated from various hosts and the absence of correlation between virulence attributes and molecular markers.     

Qualitative and quantitative variation in pathogenicity of races of coffee leaf rust (Hemileia vastatrix) detected in the State of São Paulo,Brazil

Between 1977 and 1981, seven qualitatively distinct new races of coffee leaf rust (Hemileia vastatrix) were detected in breeding plots in the State of São Paulo, Brazil. Four races carry complex virulence against the resistance genes S_H1, S_H2, S_H4 and S_H5 ofCoffea arabica. Three races match unidentified resistance genes ofC. canephora. Two of these were isolated from cv. Kouillou and one from the hybrid population Icatu. Pending further identification, these races were indicated by the number of their type cultures (Is. 2, 10 and 11). Is. 2 and Is. 10 showed extra virulence to some coffee genotypes and decreased virulence to other coffee genotypes, suggesting stabilizing selection. Three rust isolates were detected which differed quantitatively from the common rust race II. Is. 1 was moderately virulent to the coffee differential for S_H3 in the laboratory but avirulent in the greenhouse, indicating a host x pathogen x environment interaction. Is. 3 and 12 showed levels of virulence intermediate between race II and Is. 2 and 10, respectively. The results show that incomplete resistance of coffee toH. vastatrix, at various levels, can be race-specific. The nature of race formation of coffee leaf rust in Brazil and breeding strategies for obtaining durable resistance are discussed.     

临麦系列春小麦品种抗条锈性分析

小麦条锈病是发生于甘肃省临夏州小麦生产上的最主要病害,种植抗病品种是防治该病最经济有效且有利于保护环境的措施。作者于2013年在甘肃省农业科学院植物保护研究所兰州低温温室和甘谷试验站进行了苗期、成株期分小种接种鉴定,并于2010-2014年对临麦系列春小麦品种‘临麦32号’~‘临麦36号’在甘肃省不同生态区的8个试验点进行成株期抗条锈性分析,结果表明:春小麦品种‘临麦32号’苗期对所有供试菌系均表现感病,成株期对CYR29和CYR32表现中抗-中感;‘临麦33号’除对CYR29苗期表现免疫、成株期表现中抗-中感外,对其余供试菌系均表现感病。对自然诱发的条锈病,两品种也表现感病;‘临麦34号’和‘临麦36号’除对新菌系G22-9、G22-14表现感病外,对其余菌系表现抗病,但自2013年开始两品种在田间也表现感病;‘临麦35号’全生育期对接种及自然诱发的条锈菌均表现抗病。苗期选用24个国内外供试条锈菌单孢菌系进行基因推导分析,发现供试临麦系品种抗性谱与已知基因载体品种的抗性谱均不一致,初步推测供试临麦系品种含有未知抗条锈基因。     

小麦条锈菌鉴别寄主和小种命名现状

 中国是世界上小麦条锈病最大的流行区之一,也是限制中国小麦生产的最严重病害之一,特别是当条件适于其发生时会造成巨大的产量损失.小麦条锈菌小种生理专化性研究及小种监测是掌握小麦条锈菌及其毒性变化动态、抗病基因有效性及病害流行预测预报的重要依据,是治理由此病原菌引起的小麦条锈病的基本环节之一.由于地域、条锈菌群体结构、研究水平和历史等的差异,目前国际上不同国家和地区采用相应的小麦条锈菌鉴别寄主和小种命名方法.中国、美国和印度均使用了各自不同的小麦条锈菌鉴别寄主,并采用了相应的小种命名体系,例如从1957至2002年,中国利用10多个鉴别寄主已鉴定和命名了32个小种和30多个致病类型,美国利用10多个鉴别寄主已鉴定和命名了80个小种;另一类是采用1972年Johnson提出的二进制国际小种命名法,这种体系包括了国际鉴别寄主和欧洲鉴别寄主,象一套鉴别寄主被整体使用,欧洲、中东、亚洲、非洲和南美国家及澳大利亚和新西兰均采用此体系监测小麦条锈菌变化,是一套被最为广泛接受和使用的小麦条锈菌小种鉴别方法和命名系统,但随着研究深入和各国实际情况差异等原因,不同研究人员加入了不同的辅助鉴别寄主,以更能准确和实际地反映本国和地区的现实情况,为生产服务,本文对此现状进行了分析和比较.由于此病菌具有长距离气传和扩散的特点(地区间、国家间和洲际间),因而也讨论了未来小麦条锈菌鉴别寄主组成、小种命名方法和研究结果的交流和比较等实际问题.     

Phenotypic and genotypic changes in French populations of Phytophthora infestans: are invasive clones the most aggressive?

The main objective of this investigation was to test the ‘always more aggressive’ hypothesis, often advocated to explain lineage replacements in clonal populations of the potato late blight oomycete Phytophthora infestans. To this end, genotypic and pathogenicity data on 1274 French isolates of P. infestans, collected over the period 2001–2008, were analysed. Overall, the populations sampled showed limited genetic diversity, with four multilocus lineages (1_A1, 2_A1, 8_A1 and 13_A2) accounting for over 80% of the isolates collected. As in other West European countries, drastic changes in these dominant clonal lineages were observed over the course of the 8 years, particularly in the appearance and propagation of the clone 13_A2. However, invasiveness of clones was not associated with higher aggressiveness; on the contrary, dominant clones had generally low or moderate aggressiveness relative to others present at the same time within the same populations. This finding challenges the link between invasive behaviour and increased aggressiveness often assumed for this biotrophic pathogen, and could reflect the existence of a trade‐off between intra‐season and inter‐season transmission. This would be consistent with the concept of inclusive fitness, which involves the abilities to both reproduce and survive.     

Thermal generalist behaviour of invasive Puccinia striiformis f. sp. tritici strains under current and future climate conditions

Yellow rust is a devastating wheat disease. Since 2000, Puccinia striiformis f. sp. tritici strains PstS1 and PstS2 have become adapted to high temperatures and have spread worldwide. By 2011, Warrior strains had invaded both warm and cold areas of Europe. This study questioned whether thermal aptitude promoted the spread of Warrior strains, similar to PstS1/PstS2, by comparing infection efficiency (IE) at five temperatures and latent period (LP) under warm and cold regimes for Warrior isolates and pre‐2011 reference strains on two susceptible wheat varieties. The Warrior isolates showed a range of IE and LP responses to temperature that was intermediate between the northern reference isolates adapted to cold conditions and both the southern and invasive PstS2 isolates adapted to warm conditions. Warrior isolates had the highest IE under optimal temperatures of 10 and 15 °C, and displayed reduced infectivity under the warmest (20 °C) and coldest (5 °C) temperatures. Warrior strains acted as thermal generalists and the reference isolates acted as specialists. An IE thermal response was used to simulate the development of each isolate under future climate scenarios in a temperate and Mediterranean region. Isolates had the same ranking for yearly IE over the three 30‐year periods (1971–2000, 2021–2050, 2071–2100) and both locations, with a slight infection increase in the future. However, in the future IEs increased in earlier months. The thermal generalist profile of Warrior isolates for IE was confirmed, with an intermediate capacity to tolerate warming climate, whereas the southern isolates are better adapted to warm conditions, but do not have the virulences necessary to develop on current varieties.     

小麦持久抗条锈病品种Champlein的抗性遗传分析

小麦条锈病是小麦生产中最重要的病害,培育抗病品种是防治条锈病最经济、有效、安全的措施。‘Cham-plein’引自法国,对条锈菌生理小种表现良好持久抗性。为了明确其抗性遗传特点,以感病品种‘铭贤169’与其杂交、自交和回交获得了F1、F2、F3和BC1代,人工接种小麦条锈菌生理小种CY32,在温室和田间对‘Champlein’进行遗传分析。结果表明:苗期‘Champlein’对CY32的抗病性由1对显性基因控制;成株期‘Champlein’对CY32的抗病性由2对显性和1对隐性抗条锈病基因以互补方式控制;系谱分析表明基因可能来源于‘Vilmorin27’。     

Virulence analysis of Puccinia graminis f.sp. tritici populations in Ethiopia with special consideration of Ug99

Wheat stem rust samples were collected in 2006 and 2007 in the Arsi, Bale, Shewa and northwest regions of Ethiopia to determine virulence diversity and race distribution in Puccinia graminis f.sp. tritici populations. Stem rust incidence was high in Arsi, Bale and east Shewa. In northwest Ethiopia, and north and west Shewa, stem rust was prevalent at low levels. A total of 152 isolates was analysed and 22 races were identified. Races TTKSR (Ug99), TTHSR and RRTTR were predominant, with frequencies of 26·6, 17·7 and 11·1%, respectively. These races were also detected in all regions. The highly virulent race designated Ug99 was present throughout the country and dominated in all regions except northwest Ethiopia. A variant of Ug99 virulent against the stem rust resistance gene Sr24 was not detected in this study. Four stem rust resistance genes ( Sr13, Sr30, Sr36 and SrTm p) were found to confer resistance to most of the races prevalent in Ethiopia. With the exception of Sr30 , which is not effective against Ug99, these genes could be used in breeding for resistance to stem rust in Ethiopia.     

Pathogenic variability in Ethiopian isolates of Fusarium oxysporum f. sp. ciceris and reaction of chickpea improved varieties to the isolates

Twenty-four isolates of Fusarium oxysporum f. sp. ciceris were isolated from wilted chickpea plants obtained from different districts and ‘wilt sickplots’ of central Ethiopia to assess variability in pathogenecity of the populations. Each isolate was tested on 10 different chickpea lines and eight improved chickpea varieties. Isolates showed highly significant variation in wilt severity on the differential lines and improved varieties. Based on the reaction types induced on differential lines, isolates were grouped into four corresponding races. Of the 24 isolates, F13, F20 and F22 were the most virulent. Isolates of race 3 were found in all of the districts and ‘wilt sickplots’ studied. Improved chickpea varieties also showed differential reactions to the isolates. All varieties were resistant to isolates of race 3, while varieties Arerti and DZ-10-4 were resistant to all isolates tested, showing the lowest mean wilt severity. Varieties DZ-10-11 and Maryie were susceptible to isolates F13, F20 and F22 and showed the highest mean wilt severity. Identification of races can be useful in breeding chickpea varieties resistant to wilt. The differential reactions of the improved varieties against different races might be important in managing chickpea wilt through gene deployment.     

Characterization of Puccinia graminis f. sp. tritici isolates derived from an unusual wheat stem rust outbreak in Germany in 2013

An unusual stem rust infestation occurred in German wheat fields in summer 2013. This study analysed 48 isolates derived from 17 Puccinia graminis f. sp. tritici (Pgt) samples and six races were identified: TKTTF, TKKTF, TKPTF, TKKTP, PKPTF and MMMTF. Infection type and genotypic data confirmed that none of these races belonged to the TTKS (Ug99) race group. German isolates of race TKTTF are phenotypically different to the ones responsible for the stem rust epidemic in Ethiopia in 2013–2014. Forty isolates were genotyped using a custom SNP array. Phylogenetic analysis showed that these 40 isolates represented two distinct lineages (clade IV and clade V). Thirty‐eight isolates clustered into clade IV, which previously was defined by Ethiopian isolates of race TKTTF. Race TKKTP is of special concern due to its combined virulence to stem rust resistance genes Sr24, SrTmp and Sr1RS^Amigo. The vulnerability to race TKKTP in US and international winter wheat was confirmed as 55% of North American and international cultivars and breeding lines resistant to race TTKSK (Ug99) became susceptible to TKKTP. Races identified in Germany in 2013 confirmed the presence of virulence to important resistance genes that are effective against race TTKSK. This information should be useful for breeders to select diverse and effective resistance genes in order to provide more durable stem rust resistance and reduce the use of fungicides.     

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.     

The role of aggressiveness and competition in the selection of Phytophthora infestans populations

Selection within populations of Phytophthora infestans was investigated by comparing the aggressiveness of single‐lesion isolates on detached leaflets of four potato cultivars with differing levels of race‐nonspecific resistance to P. infestans. The isolates included 23 representative of Northern Ireland genotypes from the early 2000s, used to inoculate previously reported field trials on competitive selection (2003–2005), plus 12 isolates recovered from the 2003 trial. The cultivars were those planted in the previous trials: Atlantic (blight‐susceptible) and Santé, Milagro and Stirling (partially resistant). Very highly significant variation for latent period, infection frequency and lesion area was found between genotypes and cultivars; differences between genotypes were more marked on the more resistant cultivars, but no one genotype was the most aggressive across all. Detached leaflets were also inoculated with mixtures of isolates from each genotype group at three sporangial concentrations: differences in aggressiveness between genotypes were more apparent at lower concentrations and on the more resistant cultivars. Genotype groups that were the most aggressive on the more resistant cultivars tended to be those selected by the same cultivars in the field. A mixture of all isolates of all genotypes was used to inoculate detached leaflets of the same cultivars. With one exception, single spore isolates recovered from any one leaflet belonged to a single genotype, but different genotypes were recovered from different cultivars. Phytophthora infestans isolates from Northern Ireland showed significant variation for foliar aggressiveness, and pathogen genotypes exhibited differential aggressiveness to partially resistant cultivars and interacted competitively in genotype selection.     

Methodology of virulence screening and race characterization of Plasmopara halstedii,and resistance evaluation in sunflower – a review

Sunflower downy mildew is a disease of high global economic impact as well as a causal agent that is extremely difficult to eradicate. During the past decades, several approaches for the determination of Plasmopara halstedii (Ph) races have been used worldwide and are discussed in this review. Procedures of isolation, cultivation and maintenance of Ph isolates, as well as the screening of sunflower for resistance, are also critically reviewed. The predominant, globally used resistance screening protocol is a ‘whole seedling immersion’ inoculation. ‘Soil drench’ inoculation allows more precise control of the number of Ph zoosporangia applied to a single sunflower seedling. A detached leaf assay has been described, but it has been used mainly for Ph subcultivation and fungicide tests. For race determination, a differential set consisting of nine sunflower genotypes has been used since 1988, coupled with a numerical triplet code for virulence phenotyping of Ph. The increasing variability in global Ph populations has demonstrated the inadequacy of the current set of differentials, and several researchers have proposed additional public lines as new differentials. Furthermore, bulk isolates may show different results in repeated tests, as Ph may contain genetically distinct zoospores within a single zoosporangium. For precise race determination, single zoosporangia or single zoospore isolates are advisable. However, due to low success of isolation, approximately 1–2%, this method cannot be applied in routine Ph race screening. Methods surveyed in this review have a broad spectrum of applications, including taxonomic studies.     

Occurrence of races and pathotypes of cucurbit powdery mildew in southeastern Spain

The causal agent of cucurbit powdery mildew in southeastern Spain has been investigated since 1996. Of the 139 single-spore isolates obtained, all were identified asSphaerotheca fusca. Four physiological races (1, 2, 4 and 5) of the pathogen were detected. During the survey, a population shift ofS. fusca was observed: race 1 was progressively replaced by other races. In addition, race coexistence was observed in several cucurbit greenhouses. Four host range patterns or pathotypes were distinguished among the isolates ofS. fusca. All isolates were highly aggressive on melon and especially on zucchini cultivars. No clear relationships between races and pathotypes could be established, although isolates virulent on watermelon were preferentially associated with race 1. These data show an apparent heterogeneity ofS. fusca populations in southeastern Spain that should be analyzed further. http://www.phytoparasitica.org posting Aug. 9, 2002.     

Diversity of Phytophthora Clandestina Isolated From Subterranean Clover in Southern Australia: Analysis of Virulence and RAPD Profiles

The virulence spectrum of 112 isolates of Phytophthora clandestina collected from 56 sites in four subterranean clover-growing states in southern Australia was determined using differential cultivars of subterranean clover. Five races were detected, with race 0 in all states except New South Wales, race 1 in all states, race 2 only in Victoria, race 3 only in New South Wales, and race 4 in Victoria and Western Australia. The level of genotypic diversity among the different P. clandestina populations was investigated using five RAPD primers. Among 30 bands amplified, only two were polymorphic. This enabled identification of four multilocus RAPD genotypes. Three of the four genotypes occurred in all four states. Races 2 and 3 occurred with RAPD genotypes 1 and 2 only whereas races 0 and 1 occurred in all four multilocus RAPD genotypes. These results indicate that the pathogenicity spectrum of P. clandestina can change rapidly.     

小麦抗源武汉2号和品冬34的抗条锈性遗传分析

为明确小麦品种武汉2号和品冬34对小麦条锈菌流行小种的抗病性及抗病遗传规律,用小麦条锈菌生理小种CYR29、CYR31、CYR32、CYR33以及致病类型Su11-4、Su11-5、Su11-11、PST-Ch42在苗期接种小麦品种武汉2号和品冬34进行抗病性鉴定,并用武汉2号和品冬34分别与感病亲本铭贤169进行杂交,对F₂群体和F_2：3家系在温室进行苗期遗传分析。结果表明：武汉2号对CYR29和CYR32表现感病,对其它小种和致病型均表现抗病,且对CYR31的抗性由1对隐性基因控制;品冬34对所测试的小种和致病类型均表现高抗,且对CYR32的抗性由1对显性基因控制。