Phenotyping Kariega × Avocet S doubled haploid lines containing individual and combined adult plant stripe rust resistance loci

The bread wheat cultivar Kariega has maintained its stripe rust resistance since the first detection of Puccinia striiformis f. sp. tritici (Pst) in South Africa during 1996. Doubled haploid mapping population (MP) lines derived from a Kariega × Avocet S cross, carrying consistently detected adult plant resistance (APR) quantitative trait loci (QTLs)/gene combinations, were phenotyped at macroscopic and microscopic levels. Field data obtained over four seasons revealed that MP lines carrying a combination of any two of the APR loci QYr.sgi-2B.1, QYr.sgi-4A.1 or Yr18 displayed low coefficients of infection. Lines MP 45 and MP 65, carrying all three gene regions, showed leaf area infected and host reaction type ratings similar to Kariega. The microphenotype of lines was studied in flag leaves sampled from field plots during two seasons using fluorescence microscopy. Pst colony length, number of haustorial mother cells per colony and hypersensitivity index supported the phenotypic data. All three microscopy variables attested to low levels of disease in lines containing multiple stripe rust resistance loci. Lines MP 51 and MP 223 with a single QYr.sgi-2B.1 and Yr18, respectively, also showed adequate resistance, in contrast to lines carrying only QYr.sgi-4A.1 which showed significantly more disease symptoms. Host cell necrosis and lignification were revealed as mechanisms of resistance in some lines.     

四川省100个小麦品种(系)抗条锈病基因的 分子检测

 为了解四川省近年小麦生产品种和后备品种对条锈菌致病类型G22-83和流行小种CYR32、CYR33的抗性水平,明确已知的主要抗条锈基因在该地区小麦品种中分布状况,利用小麦条锈菌G22-83、CYR32和CYR33对四川省100个小麦品种(系)进行苗期抗病性鉴定;采用已知基因Yr5、Yr9、Yr10、Yr15、Yr18 和Yr26的分子标记,对供试小麦材料进行抗性基因检测。结果表明,100个供试材料中,对CYR32 表现抗病的58份,占58%;对CYR33 表现抗病的63份,占63%;对G22表现抗病的43份,占43%;对CYR32、CYR33和G22均表现抗病性的品种(系)28个,占28%。供试小麦品种(系)中携带Yr9、Yr10、Yr15 和Yr26基因的材料分别有24份(24%)、9份(9%)、5份(5%)和26份(26%),所有供试品种(系)中未检测到Yr5和Yr18基因。     

四川58个小麦品种苗期抗条锈基因推导及成株期抗性表现

为了解四川小麦品种所含抗条锈基因及其在田间的抗性表现,将29个毒性谱各异的小麦条锈菌鉴别菌株于苗期接种35个已知抗条锈基因载体品系和58份四川小麦品种（系）,通过抗病谱对比分析和各品种（系）系谱分析,推导了四川小麦品种（系）的抗条锈基因型。在田间,选用中国小麦条锈菌优势小种CY32、CY33、Su-4和对Yr10、Yr24和Yr26致病的贵农22致病类型田间突变株进行混合接种,在乳熟期对各品种（系）的抗条锈性进行了鉴定。结果显示,Yr2、Yr5、Yr7、Yr9、Yr10、Yr24、Yr27、YrSpp、YrAlba等9个基因以单基因或基因组合的形式存在于44个四川小麦品种（系）中。有6个品种（系）含有Yr9基因,10个品种（系）含有Yr10基因,11个品种（系）含有Yr24基因,其中1个同时含有Yr10和Yr24基因。23个品种（系）含有未知基因及其组合。共有19个小麦品种（系）成株期对包含上述混合菌种在内的田间流行菌系表现抗病,其中5个品种抗性受成株抗性基因控制。     

中国不同春麦区小麦地方种质抗条锈病评价及抗性基因分析

为明确中国不同春麦区小麦地方种质对当前小麦生产上流行的条锈病菌Puccinia striiformis f.sp.tritic的抗性水平及其所含抗性基因，利用条锈病菌生理小种条中32（CYR32）和条中34（CYR34）及混合生理小种（致病类群）对来自5个春麦区的196份小麦地方种质进行苗期、成株期抗性鉴定，并通过6个已知条锈病抗性基因Yr9、Yr18、Yr26、Yr48、Yr65和Yr67对其所含重要抗性基因进行分子标记检测。结果显示，在苗期，有11份小麦地方种质对CYR32表现出抗性，有12份对CYR34表现出抗性，分别占供试种质总数的5.61%和6.12%；有6份对CYR32和CYR34均表现出抗性；在成株期，有59份小麦地方种质在5个田间诱导环境下表现出稳定的抗性。有119份小麦地方种质检测到含抗性基因，其中有3份携带Yr9，有50份携带Yr18，有43份携带Yr48，有54份携带Yr65，所有供试种质均未检测到Yr26和Yr67，抗性基因的组合分析发现，共有31份小麦地方种质携带4种抗性基因组合类型Yr9+Yr18、Yr18+Yr48、Yr18+Yr65和Yr48+Yr65。表明来自中国5个春麦区的小麦地方种质条锈病抗性表型呈多样性，且携带目前在小麦抗病育种和生产上有效的条锈病抗性基因（组合），建议加大对小麦地方种质的保护和应用力度。     

Mapping of Aegilops umbellulata‐derived leaf rust and stripe rust resistance loci in wheat

Aegilops umbellulata, a non‐progenitor diploid species, is an excellent source of resistance to various wheat diseases. Leaf rust and stripe rust resistance genes from A. umbellulata were transferred to the susceptible wheat cultivar WL711 through induced homoeologous pairing. A doubly resistant introgression line IL 393‐4 was crossed with wheat cultivar PBW343 to develop a mapping population. Tests on BC₂F₇ RILs indicated monogenic inheritance of seedling leaf rust and stripe rust resistance in IL 393‐4 and the respective co‐segregating genes were tentatively named LrUmb and YrUmb. Bulked segregant analysis placed LrUmb and YrUmb in chromosome 5DS, 7.6 cM distal to gwm190. Aegilops geniculata‐derived and completely linked leaf rust and stripe rust resistance genes Lr57 and Yr40 were previously located in chromosome 5DS. STS marker Lr57/Yr40MAS‐CAPS16 (Lr57/Yr40‐CAPS16), linked with Lr57/Yr40 (T756) also co‐segregated with LrUmb/YrUmb. Seedling infection types differentiated LrUmb from Lr57. Absence of leaf rust‐susceptible segregants among F₃ families of the intercross (IL 393‐4/T756) indicated repulsion linkage between LrUmb and Lr57. YrUmb expressed a consistently low seedling response under greenhouse conditions, whereas Yr40 expressed a higher seedling response. Based on the origin of LrUmb/YrUmb from the U genome and Lr57/Yr40 from the M genome, as well as phenotypic differences, LrUmb and YrUmb were formally named Lr76 and Yr70, respectively. These genes have been transferred to Indian wheat cultivars PBW343 and PBW550, and advanced breeding lines are being tested in state and national trials.     

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.     

云南小麦条锈菌群体对18个抗条锈近等基因系的毒性分析

为监测云南省小麦条锈菌群体毒性及小麦抗条锈基因的有效性动态,2016年采用18个抗条锈近等基因系鉴别寄主对云南省9个州市的136个小麦条锈菌株进行毒性分析,并按八进制法对小种进行命名。结果表明,云南省小麦条锈菌群体毒性丰富,共鉴定出64个小种类型,其中居于前2位的小种是550273和550073,出现频率分别为28.68%和11.76%,是本年度优势小种;其它小种出现频率均在4.41%以下,为次要小种。条锈菌群体对Yr5、Yr10、Yr15、Yr32四个抗条锈基因的毒力频率均为0,对Yr24、Yr Tr1、Yr8、Yr17四个抗条锈基因的毒力频率在0.74%~11.76%之间,表明这8个基因是云南省当前有效的抗条锈基因;对Yr27的毒力频率为52.94%,对Yr1、Yr6、Yr7、Yr9、Yr43、Yr44、Yr SP、Yr Exp2、Yr Tye九个抗条锈基因的毒力频率为77.94%~91.91%,表明这10个抗条锈基因的抗性已减缓或丧失,说明这些基因在云南省已失效。     

中国75个国审小麦品种抗条锈基因推导

为明确通过国家农作物品种审定委员会审定的75个小麦品种对条锈病抗病基因状况,根据供试品种与21个来自不同国家或地区条锈菌菌系的互作反应,与已知基因载体品种侵染型进行比较。结果显示,在已知抗条锈病基因中,Yr1、Yr2、Yr3、Yr5、Yr6、Yr7、Yr8、Yr9、Yr17、Yr27、YrA、Yr25、YrSu、YrSp、YrSk等基因以单基因或基因组合形式分布在49个小麦品种（系）中,Yr3所占比例为26.7%,Yr2为20.0%,Yr2、Yr3以基因组合形式存在的占14.7%;其次,携带Yr9的品种有12个,占16.0%;携带Yr1、YrSp的品种各10个,均占13.6%;其余推导出的抗条锈病基因比例均在10.0%以下。镇麦8号、宁麦15和生选6号感染所有菌系,推导其不含有已知抗条锈病基因。     

部分小麦抗条锈基因及生产品种在云南的抗性表现

为掌握部分小麦已知抗条锈基因及我国小麦当前主要生产品种的抗条锈性变异状况,为其合理利用提供依据,2012-2013年,采用田间病圃自然诱发鉴定法,对21个抗条锈单基因系、15个聚合基因品系及67个小麦生产品种在云南6个地点进行抗性监测。结果表明:Yr27、Yr(7,22,23,Le1,Le2)和Yr(30,Sk,QYR3,QYR4,QYR5,QYR6,QYR7)在云南2年6点都表现稳定的抗性;Yr15、Yr25、YrSu92和Yr(27,Slk)在2年6点中,仅1个点感病且病情指数较低;Yr17、Yr18、Yr24、Yr26、Yr30、Yr32、YrA、YrSp、Yr(1,Ky1,Ky2)、Yr(3a,V23,+)、Yr(A,H)、Yr(Ab,Alb)、Yr(Gui1,Gui2,Gui3)、Yr(8,19,Com)或2年在相同或不同点表现感病,或1年在2点以上表现感病,表明这些基因抗性有丧失趋势;Yr1,Yr2,Yr5,Yr6,Yr7,Yr8,Yr9,Yr10,YrSu,Yr(3a,4a,16),Yr(3a,ND,+),Yr(10,Mor),Yr(17,29,P1,P2),Yr(Ju1,Ju2,Ju3,Ju4),在2年2点以上都表现感病,表明这些基因抗性可能已经丧失。当前在国内被认为有效的抗条锈基因Yr5,Yr10,Yr15和Yr26中,除Yr15抗性相对稳定外,其余3个田间抗性已逐渐丧失。67个国内生产品种或抗源,或多或少,或1年或2年都表现感病,条锈病抗性水平很低,寻找新的抗源并培育新的抗病品种已迫在眉睫。     

Temperature adaptation in Australasian populations of Puccinia striiformis f. sp. tritici

Stripe rust, caused by Puccinia striiformis f. sp. tritici, is one of the major fungal pathogens of wheat. A new pathotype was introduced to Australia in 2002 and several derivative pathotypes were detected in subsequent seasons. It has been suggested that the severity of stripe rust outbreaks in Australia since 2002 could be as a result of traits other than virulence in the pathogen population. This study was conducted to investigate the hypothesis that the stripe rust pathogen population dominant in Australia since 2002 was better adapted to warm temperature conditions compared to previous pathogen populations. Sixteen pathotypes were selected to examine the influence of two contrasting temperature regimes during the 24 h incubation (10°C and 15°C) and the subsequent post‐inoculation (17°C and 23°C) periods on latent period and infection efficiency on four susceptible wheat cultivars. In addition, the effect of two contrasting incubation temperatures on urediniospore germination was examined. The results indicated that pathotypes of P. striiformis f. sp. tritici detected after 2002 did not show evidence of adaptation to high temperatures, which suggests that other factors contributed to the observed increased aggressiveness.     

以Taichung29为背景的小麦抗条锈病近等基因系转育进展

自1988年起,系统开展了以Taichung29为背景的小麦抗条锈病近等基因系转育及其基础性研究。采用回交法和系谱法相结合的转育方法,以春性品种Taichung29为轮回亲本作母本,分别与25个抗性供体即中国小麦条锈病菌鉴别寄主和国际上重要的抗条锈基因载体品种杂交、回交和自交。通过基因推导分析、单体分析和SSR标记技术检测目的基因,选育抗条锈近等基因系,现已获得重要进展,成功选育出8个以Taichung29为背景的抗条锈病单基因近等基因系,即Taichung29*6／Yr1、Taichung29*6／Yr2、Taichung29*6／Yr5、Taichung29*6／Yr7、Taichung29*6/Yr9、Taichung29*6／Yr10、Taichung29*6/YrSpP、Taichung29*6/YrKy2。另有9个组合转育获得343个抗性稳定株系,正检测其目的基因,3个组合转至BC₆F₃,自交纯合筛选抗性稳定株系,5个组合转至BC₅,继续回交转育。     

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。     

Pathotype diversification in the invasive PstS2 clonal lineage of Puccinia striiformis f. sp. tritici causing yellow rust on durum and bread wheat in Lebanon and Syria in 2010–2011

Yellow rust is the major wheat disease in central West Asia and North Africa. Recently, severe epidemics have occurred, with major yield losses in 2010–2011 in Lebanon and Syria. We conducted an extensive field survey, with a collection of 273 samples of Puccinia striiformis f. sp. tritici, to explore the origin of these epidemics. All samples were genotyped with 20 microsatellite markers, and 54 isolates were pathotyped. The population was dominated by the PstS2 lineage, which has spread worldwide since 2000 and displays considerable pathotype diversity (10 pathotypes). The 22 multilocus genotypes (MLGs) detected corresponded to variants of the clonal lineage PstS2, but they differed from the common PstS2 genotype found in the worldwide study conducted between 1981 and 2010. No strong differentiation was observed between Lebanon and Syria. The dominant MLG in Syria was common to both countries. Nine MLGs were found exclusively in the Syrian population and four were restricted to the Lebanese population, including the dominant MLG in Lebanon. The predominant MLG-11 was found in nine pathotypes, at high frequency. The dominant pathotype in Syria was virulent against widely deployed resistance genes (Yr2, Yr6, Yr7, Yr9, Yr25, and Yr27); virulence against Yr3, Yr8, Yr17, and YrSP occurred at various frequencies, but Yr1, Yr4, Yr5, Yr10, Yr15, and Yr32 were effective against all isolates. No host effect was detected. The presence of diverse host populations consisting of landraces and elite varieties, and diverse climatic conditions may account for the unexpectedly high diversity of this clonal population.     

远缘杂交后代转育的小麦抗源材料抗病及抗旱性研究

郑麦9023和豫麦66分别与野生二粒小麦和野燕麦远缘杂交后代进行杂交和回交,经过7代筛选、鉴定,获得了20个抗病性和农艺性状稳定的高代系。在陕西杨凌设置条锈菌流行小种（CYR32和CYR33）病圃,在甘肃天水设置自然发病圃对筛选的小麦高代系进行异地抗病性鉴定,同时对其进行分小种CYR32、CYR33、CYR31和CH42苗期鉴定;分别选用Yr5、Yr9、Yr10、Yr15、Yr17、Yr18和Yr26等7个已知抗条锈病基因的分子标记进行基因检测;对高代系进行萌发干旱胁迫试验,从而对其抗旱性进行评价;并调查其农艺性状并进行评价。抗病、抗旱和农艺性状调查结果显示：参试的20个高代系中,符合抗病耐旱且农艺性状较好,可用于作为抗源亲本的高代系有8个分别是郑野-2、郑野-3、郑野-6、豫野-1、豫野-2、豫野-4、豫野-5、豫野-6。研究结果表明,在抗病、耐旱综合性状优良育种目标指导下,将郑麦9023和豫麦66作为基因累加的库容,利用系谱选择法,结合育种分子标记检测辅助选择,可不断对品种郑麦9023和豫麦66进行改良与创新;并且可依次对其抗病性、抗旱性、成熟期等农艺性状基因及来源不同的优良基因进行累加转育。     

Genetic diversity of Puccinia striiformis from cereals in Alberta,Canada

Stripe rust of wheat caused by Puccinia striiformis f. sp. tritici has recently become a production problem on wheat in Alberta, Canada, and stripe rust of barley caused by P. striiformis f. sp. hordei occurs regularly. A total of 261 isolates of P. striiformis were collected from wheat, barley, Hordeum jubatum and triticale plants in Alberta, Canada from 2007 to 2012, and compared to isolates from other provinces and the USA. The genetic diversity of the pathogen was assessed using 11 simple sequence repeat (SSR) markers and by examining a length polymorphism in the ribosomal DNA (rDNA) intergenic spacer 1 (IGS1) region. A total of 28 SSR genotypes were detected within Alberta. The 13 genotypes common on wheat (P. striiformis f. sp. tritici) were distinct from the 15 genotypes common on barley (P. striiformis f. sp. hordei). Four SSR genotypes, two within each forma specialis, represented 85% of the isolates recovered. Genotypic diversity was low, population genetic analysis indicated a clonal structure, and the genotypes were widely dispersed. In both formae speciales, the dominant genotype varied between years. The second most common P. striiformis f. sp. hordei genotype was found to be more closely related to older P. striiformis f. sp. tritici genotypes from the USA than to other P. striiformis f. sp. hordei genotypes.     

Reference gene selection for qPCR gene expression analysis of rust-infected wheat

Real-time PCR (qPCR) is an effective method to quantify mRNA levels, but requires validated reference genes for data normalisation. The GeNorm-Plus algorithm was used to examine the expression stability of six candidate reference genes in resistant Avocet Yr1 wheat infected with Puccinia triticina, Puccinia striiformis and Puccinia graminis f.sp. tritici respectively. Results indicated that within the first 48 h after inoculation, the expression stability of the candidate reference genes differed between the three incompatible interactions. The geometric mean of ARF and RLI showed the best stability in P. triticina-infected wheat, CDC and RLI in P. striiformis-infected wheat and CDC, 18S and TUBB in P. graminis f.sp. tritici-infected wheat respectively. This clearly emphasised the need for reference gene validation for each different plant–pathogen interaction.     

African wheat germplasm – a valuable resource for resistance to rust diseases

Known and unknown genes conferring seedling and adult plant resistance (APR) to leaf rust, stem rust and stripe rust were detected either singly or in combination in a set of 136 African wheat genotypes using multi-pathotype tests with characterized Australian Puccinia triticina (Pt), P. graminis f. sp. tritici (Pgt) and P. striiformis f. sp. tritici (Pst) pathotypes. Lines Beladi 132, IYN 68/9.44, Kenya Kifaru and Kenya Mbweha were postulated to carry resistance against multiple pathotypes of Pt, Pgt and Pst, whereas IAR/W/163-3, Grano Di Moggio Tipo 44 and Trigo 48 had resistance against all pathotypes tested in the current study. Field evaluation with the three rust pathogens detected low to high APR in more than 50% of lines, and while most tested positive with markers linked to known APR genes (csLV34, csLV46G22, TM10KASPAR, csGS, Cfb5006 and csSr2), many carried unidentified and useful resistance to all three rusts. Genetic analysis of F₃ mapping populations based on seven genotypes showed either monogenic or digenic inheritance of APR to leaf rust, stem rust and stripe rust. The lines postulated to carry effective uncharacterized seedling genes and APR genes are of great potential value in diversifying resistance to help achieve durable control of all three rust diseases of wheat.     

Selection pressure effects on the proportion and movement of resistance alleles introgressed from wheat in Aegilops cylindrica

In winter wheat in the USA, Aegilops cylindrica is one of the most troublesome weeds, while the pathogen Oculimacula spp. causes foot rot disease. Imazamox‐resistant (IR) and foot rot‐resistant (FR) wheat cultivars represent effective tools to control the weed and prevent disease infection. However, resistance allele (RA) movement between wheat and A. cylindrica facilitates the introgression process under herbicide and disease selection pressure. Field experiments using IR and FR A. cylindrica plants intermixed with susceptible plants were conducted to measure the proportion of the RAs in the progeny and RA movement with and without herbicide and disease selection. Yield components of A. cylindrica plants were determined across treatments. The herbicide RA proportion in the progeny was greater when plants were treated with the herbicide imazamox in both years. Disease RA proportion was greater with disease occurrence only in one year. Herbicide RA movement from resistant to susceptible plants was greater with herbicide than without it only in one year. Plants carrying the RAs had greater total spikelet weight and 1000‐spikelet weight compared with susceptible plants with or without selection. However, susceptible plants produced more spikelets than the resistant ones in the absence of selection. If plants within an A. cylindrica population acquire the herbicide RA, its proportion will increase each generation under selection. These findings contribute to the understanding of crop allele introgression into related species and the evolution of increased weediness, with weed management implications.     

Histopathology provides a phenotype by which to characterize stripe rust resistance genes in wheat

The expression of the resistance phenotypes of QPst.jic‐2D and QPst.jic‐4B, two quantitative trait loci (QTL) for stripe rust resistance in wheat cv. Alcedo, were assessed relative to plant growth stage, while a histopathology analysis was undertaken to characterize the cellular interaction between Puccinia striiformis f. sp. tritici (the causal agent of stripe rust) and each QTL. QPst.jic‐2D expressed a partial resistant phenotype at seedling growth stages, with the level of resistance increasing as the wheat plant matured, conferring a disease‐free phenotype at heading. QPst.jic‐4B, however, did not express a resistant phenotype until booting (growth stage 41 on the Zadoks scale), displaying its full resistant phenotype at heading. Microscopic examination in flag leaves showed that infection sites formed in all genotypes tested, with full infection‐site establishment being observed by 36 h post‐inoculation (hpi). In lines carrying both QPst.jic‐2D and QPst.jic‐4B, as well as the parental cv. Alcedo, no microcolony formation, defined by the appearance of runner hyphae, was observed. Microcolony formation was observed in lines carrying only one, or neither QTL. Cell death associated with infection sites was observed for all genotypes, although the timing of first appearance and the extent of the cell death response varied considerably. In lines carrying both QPst.jic‐2D and QPst.jic‐4B cell death did not extend beyond one to three cells. In lines carrying only one QTL more extensive cell death was observed and cell death appeared later in lines with QPst.jic‐4B than QPst.jic‐2D. Cell death was also occasionally observed in lines without either QTL, although only at 264 hpi.     

A high virulence and pathotype diversity of Puccinia striiformis f.sp. tritici at its centre of diversity,the Himalayan region of Pakistan

Information on the pathogen virulence profile and diversity across locations is crucial for host germplasm improvement and deployment. The rapid acquisition of virulence to host resistance by the wheat yellow/stripe rust pathogen (Puccinia striiformis f.sp. tritici: PST), makes it crucial to know about its virulence and pathotype diversity. Recent studies have shown the plausible centre of origin of the pathogen in the Himalayan region, with Pakistan being the most ancestral to all other worldwide populations. To assess the status of virulence and pathotype diversity in the Himalayan region of Pakistan, a set of 127 PST infected wheat samples from eight locations were collected, multiplied and pathotyped using a set of 36 differential lines from the world set, European and Chinese sets, and 9 Avocet Yr isolines. Virulence (Vr) was recorded to 18 out of 24 tested yellow rust resistance (Yr) genes, while a total of 53 pathotypes were detected out of 127 isolates tested. Virulence was found to the resistance genes rarely deployed in Pakistan (Vr8) or even worldwide level (Vr5), while virulence to Vilmorin 23 (Yr3+) was absent in Pakistan, which is common in Europe. None of the pathotypes was dominant across all locations, however, no clear spatial structuring was observed for the studied locations. Our results suggested a high virulence and pathotype diversity in line with the previously proposed potential role of sexual recombination in the temporal maintenance of PST in the Himalayan region of Pakistan. This information should be useful in host resistance gene improvement and deployment.