Temperature-sensitive wheat stem rust resistance gene Sr15 is effective against Puccinia graminis f. sp. tritici race TTKSK

The wheat stem rust fungus, Puccinia graminis f. sp. tritici (Pgt), race TTKSK and related races pose a serious threat to world wheat production. Knowing the effectiveness of wheat stem rust resistance (Sr) genes against Pgt race TTKSK is fundamental in mitigating this threat through resistance breeding. Sr15 was previously identified as being ineffective against Pgt race TTKSK. Here, multirace disease phenotyping data, linkage analyses, allelism testing and haplotype analyses are presented to support the conclusion that Sr15 is effective against Pgt race TTKSK. Resistance to race TTKSK was mapped to Sr15 in a biparental population. Thirty-two accessions with Sr15 displayed seedling resistance phenotypes against race TTKSK. However, these accessions were susceptible as seedlings at high temperatures (22–25 °C), consistent with previous reports that the interaction between avirulent Pgt isolates and Sr15 is temperature-sensitive. Markers STS638, wri4 and KASP_IWB30995 were found to predict the presence of Sr15, suggesting the utility of these assays for marker-assisted selection in breeding programmes. The effectiveness of Sr15 to specific Pgt races and temperatures makes it a less-desirable TTKSK-effective gene. Wheat lines assayed as resistant to race TTKSK at the seedling stage may possess Sr15 and breeders should be aware of the limitations of Sr15 for conferring stem rust resistance.     

小麦秆锈菌新型小种Ug99的研究进展

Ug99(TTKS)为1999年在乌干达首次发现的秆锈菌新小种,对小麦抗秆锈病基因Sr31具有强毒力.此小种致病性极强,传播迅速,给全球小麦生产带来威胁.在肯尼亚用Ug99对我国118个小麦生产品种和材料进行抗病性鉴定结果表明,高感品种占98.3%.该小种一旦传入我国,将对小麦生产造成严重损失.笔者对国内外关于小麦抗Ug99遗传研究、抗病基因分子标记研究现状及我国应对措施进行了概述.     

我国小麦秆锈菌种群动态分析

１９９５～１９９６年间,在我国７省区６２个县点共收集标样２８３份,涉及品种１１７个,分离到菌株４５５份,鉴定出１５个致病类型,其出现类型的发生频率分别是２１Ｃ３ＣＫＲ为１７．５％,２１Ｃ３ＣＦＨ９．６％,２１Ｃ３ＣＫＨ８．８％,２１Ｃ３ＣＦＲ６．０％,２１Ｃ３ＣＴＲ２２．０％,２１Ｃ３ＣＰＲ９．４％,２１Ｃ３ＣＴＨ８．８％,２１Ｃ３ＣＰＨ１１．９％,３４ＭＫＧ１．３％,３４Ｃ２ＭＫＨ０．２％,３４Ｃ２ＭＫＫ０．１％,３４Ｃ２ＭＦＨ３．６％,３４Ｃ２ＭＦＫ０．４％,３４Ｃ１ＭＫＲ和３４Ｃ１ＭＦＲ为０．２％。１９９６年２１Ｃ３ＣＫＲ的出现频率上升为第１位,对Ｓｒ１１有毒力的致病类型出现频率有所下降。     

Comparison of Puccinia graminis f.sp. tritici from South America and Europe

Twenty isolates of Puccinia graminis f.sp. tritici from South America were compared with 19 from Europe using virulence, isozymes and random amplified polymorphic DNA (RAPD) markers. The isozyme and virulence patterns for these isolates were also compared with those of 11 isolates representative of the common race clusters in North America. All three types of marker showed a level of similarity between the South American and European isolates comparable with that between isolates from the same continent. The average similarity coefficients between the South American and European isolates were 0.65 for virulence, 0.67 for isozymes, and 0.70 for RAPD markers. Among South American isolates the values were 0.63 for virulence, 0.64 for isozymes and 0.72 for RAPDs. For the South American and European isolates, correlation between the similarity matrices based on RAPDs and on isozyme markers, respectively ( r  = 0.52), was higher than that between the RAPD and virulence matrices ( r  = 0.32) or between isozyme and virulence matrices ( r  = 0.16). The North American isolates had a comparable level of similarity for virulence and isozymes to both the South American and European populations. There was no clear distinction between the South American, North American and European isolates, which is consistent with the hypothesis that these populations may have had a common origin.     

小麦秆锈菌新小种Ug99及其对我国的影响分析

Ug99(TTKS)是1999年在乌干达首次发现的对最重要小麦抗秆锈病基因Sr31有强毒力的秆锈菌新小种。大量证据显示:该小种不仅具有极其特殊的毒力组合而且传播十分迅速,除在中非乌干达、东非肯尼亚、埃塞俄比亚、苏丹流行外,Ug99现已越过红海、传到了阿拉伯国家也门,以及巴基斯坦的沿海地区,越来越逼近我国。Ug99堪称我国的超毒小种,我国最典型的秆锈菌小种只能分别克服或Sr5或Sr9 e或Sr11单基因抗性,而Ug99不仅具有Sr5、Sr9 e、Sr11的联合毒力,而且还具有Sr21、Sr31、Sr38的联合毒力,而我国从未有小种能克服后者的抗性。1B/1L(含Sr31)易位系曾是我国使用的重要秆锈抗源,必对Ug99高度脆弱,我国118份小麦品种在KARI的测定结果表明,高感品种频率98.3%。一旦Ug99入侵我国,其他流行条件也完全具备。因此,充分作好防范Ug99流行的准备十分必要。     

The expression of components of seedling resistance to Erysiphe graminis f.sp. tritici in Triticum timopheevii and a hexaploid derivative

The expression of components of resistance to three isolates of Erysiphe graminis f.sp. tritici was investigated on the primary seedling leaves of nine lines of Triticum timopheevii, one line of the wild ancestor T. araraticum, and a hexaploid derivative from T. timopheevii, CI 12633. Wheat cv. Nord Desprez was used as a susceptible control with no known major gene for powdery mildew resistance. The expression of resistance was studied 72 h after inoculation to investigate the efficiency of a sequence of barriers to fungal penetration and development: cuticle; papilla; epidermal cell hypersensitivity; and the hypersensitive necrotic reaction of mesophyll cells underlying the infection area. Production of conidia was assessed after 10 days. Neither the profuse epidermal hairs nor the leaf cuticle contributed directly to resistance in T. timopheevii. However, both T. araraticum and T. timopheevii exhibited papilla-mediated resistance and, in addition, T. araraticum showed epidermal hypersensitivity. T. timopheevii may possess a gene or genes for resistance additional to those already transferred to, and expressed in. the hexaploid derivative CI 12633, particularly those which condition the hypersensitive necrotic reaction of the mesophyll cells surrounding the infection area.     

2007年我国部分麦区小麦白粉菌对三唑酮的抗药性监测

采用拌种离体叶段法测定了我国9个省（市）的112个小麦白粉菌株对三唑酮的抗性。结果表明,供试菌株的平均EC50为57.25mg/L,平均抗性水平为27.39倍,其中86.61%供试菌株已经产生抗性,抗药性比敏感菌株高出10~40倍的菌株占47.32%,四川、山东、甘肃和贵州等地菌株的抗性高于其他地区。此结果可为三唑类杀菌剂在我国的推广应用和制定合理的抗药性治理措施提供依据。     

2010年西藏小麦条锈菌生理小种群体结构与分析

西藏地区是中国相对独立的小麦种植区,小麦条锈病是西藏冬小麦上最重要的病害.长期以来,对西藏小麦条锈菌生理小种群体结构缺乏全面系统的了解.为了弄清西藏小麦条锈菌生理小种群体结构,本研究从西藏地区小麦条锈病发生的关键地区采集并鉴定了小麦条锈菌标样261份.西藏地区小麦条锈菌群体结构复杂,小种类型数多,主要优势小种以CYR32和CYR33为主,水源11类群为优势类群,Hybrid46类群结构简单,未发现CYR32以外的类型;CYR32之前的小种数较多、其中CYR17、CYR20、CYR31出现频率较高;西藏小麦条锈菌群体结构与内地有着较大的相似性,同时也有其自身的独特性,表现西藏小麦条锈菌优势小种组成与四川、云南两省相似,与青海省差异较大.推测西藏地区小麦条锈菌与四川和云南省存在较密切的菌源交流,与青海省交流较少.     

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.     

Comparison of resistance-inducing abilities of virulent and avirulent races of Erysiphe graminis f.sp. hordei and a race of Erysiphe graminis f.sp. tritici in barley

Resistance to powdery mildew was induced in barley by preinoculation with virulent and avirulent races of barley powdery mildew ( Erysiphe graminis f.sp. hordei ), and with a race of wheat powdery mildew ( E. graminis f.sp. tritici ). Four inducer densities were tested in 13 different induction periods between 1 and 24 h. Generally, the resistance induced by barley powdery mildew increased up to 10-12 h of induction and was maintained in longer induction periods. The inducing abilities of virulent and avirulent races could not be distinguished up to 10-12 h of induction, after which the inducing ability of avirulent races increased significantly in relation to virulent races. Wheat powdery mildew was able to induce more resistance than barley powdery mildew in induction periods up to 8 h. In a single inoculation procedure the number of haustoria developing from virulent barley powdery mildew decreased as inoculum density increased. The effect was ascribed to induction of resistance. This reduction of infection efficiency in the compatible interaction was compared to induced resistance. However, the inoculum density needed for 50% resistance induction in the double inoculation procedure was approximately 40 times higher than the inoculum density needed for 50% reduction in infection efficiency in the single inoculation procedure.     

Resistance responses of albino leaves of Triticum timopheevii mutants inoculated with Erysiphe graminis f.sp. tritici

Albino chlorophyll mutants induced in Triticum timopheevii by γ-irradiation were used to study the influence of photosynthetic activity on the development of two isolates of Erysiphe graminis f.sp. tritici , and host resistance responses, 72 h after inoculation. The results showed that the percentage of pathogenic units inhibited by papilla response and epidermal cell hypersensitivity was lower on albino primary seedling leaves than on normal green seedling leaves. On albino leaves, the development of pathogenic units which established a successful penetration was either decreased or retarded, depending on the isolate used. This effect could be attributed to the limited supply of assimilates from the albino host due to the lack of photosynthetic activity.     

小麦白粉病菌对氟唑菌酰羟胺的敏感基线建立

氟唑菌酰羟胺是一种新型琥珀酸脱氢酶抑制剂(succinate dehydrogenase inhibitor, SDHI)类杀菌剂,2019年在我国登记在小麦上防治赤霉病,为明确其对小麦白粉病的潜在防治效果,以及为监测小麦白粉病菌群体对其是否产生抗药性,本文采用离体叶段法测定了2000年前和2019年采自我国河南、山东等9省市的110株小麦白粉病菌菌株对氟唑菌酰羟胺的敏感性。结果表明,采自2019年的88株菌株,其EC50范围为0.010 2~0.766 8 μg/mL,平均EC50为(0.224 3±0.179 6)μg/mL;采自2000年前的22株菌株,其EC50范围为0.052 1~0.882 4 μg/mL,平均EC50为(0.356 3±0.279 6)μg/mL;两组菌株群体间的敏感性无显著差异。氟唑菌酰羟胺对110株菌株的EC50范围为0.010 2~0.882 4 μg/mL,平均EC50为(0.250 7±0.210 3)μg/mL,敏感性频率分布呈单峰曲线,可作为小麦白粉病菌对氟唑菌酰羟胺的敏感基线。本研究结果可为氟唑菌酰羟胺防治小麦白粉病以及未来监测该病原菌对药剂的抗性提供参考依据。     

新疆伊犁州小麦条锈菌生理小种鉴定及毒性分析

伊犁州是新疆小麦条锈病重灾区, 对该地区开展小麦条锈菌生理小种监测意义重大?本研究通过对2020年采自新疆伊犁4县的149份小麦条锈菌样品进行生理小种监测, 以期明确该地区小麦条锈菌生理小种组成及毒性情况?结果表明, 共监测到28个生理小种, 其中CYR 33?Su 11-1?Su 11-12?CYR 32及CYR 34出现频率较高, 分别为14.09%, 12.75%, 8.05%, 8.05%和7.38%; 水源11类群为优势类群, 出现频率高达44.30%?对抗条锈病基因Yr1?YrA?Yr3?Yr6?YrSu?Yr9的毒性频率均大于70%, 表明这些基因在伊犁州抗性基本丧失?新疆伊犁州4县小麦条锈菌毒性多样性分析显示, Nei’s 遗传多样性指数为0.34, Shannon 信息指数为0.50, 表明伊犁州条锈菌毒性多样性水平较高, 毒性组成丰富; 小麦条锈菌毒性相似系数在0.92~1.00, 其中伊宁县和巩留县的样品遗传距离最近, 察布查尔县与其他3县样品遗传距离最远?因此, 新疆伊犁州地区抗锈育种应以抗CYR 33和Su 11-1为主, 兼顾抗Su 11-12?CYR 32和贵农22类群中其他类型?另外不同县区应合理进行抗病基因布局, 以期实现小麦条锈病的区域间联合防治?     

Comparison of Virulence and Isozyme Phenotypes of Pgt-QCCJ and Great Plains Races of Puccinia graminis f. sp. tritici

ABSTRACT Stem rust race Pgt-QCCJ was first found in the Great Plains of the United States in 1989, collected primarily from barley. This race became a major part of the Puccinia graminis f. sp. tritici population, even though it is virulent to only a few hard red winter wheat cultivars in the central Great Plains and to barley in the northern Great Plains. It threatens barley production in the northern Great Plains of the United States and Canada due to virulence to Rpg-1. Six differences in virulence and two in isozyme banding patterns from the most similar stem rust races make it unlikely that QCCJ arose as a mutant. Thus, QCCJ likely arose through sexual or parasexual recombination. Sexual recombination in the Great Plains is unlikely, as it has not been detected in many years. Avirulence to 'McNair 70l' is only known from the Pacific Northwest of the United States and adjacent Canada. The rust population in this area is of sexual origin, and the pattern of virulence/avirulence and isozyme banding for QCCJ occurs there. Pgt-QCCJ likely originated in the Pacific Northwest during or before 1989 and was wind-transported into the Great Plains.     

Differential response of phytohormone signalling network determines nonhost resistance in rice during wheat stem rust (Puccinia graminis f. sp. tritici) colonization

Stem rust caused by Puccinia graminis f. sp. tritici is one of the most devastating diseases of wheat. Breakdown of host resistance under field conditions triggered by the evolution of new pathogenic races and pathotypes is a perennial threat for wheat cultivation. Rice, often grown in a rice–wheat cropping system, is immune to rust infection. Our microscopic studies revealed that P. graminis f. sp. tritici, although displaying nearly identical uredospore germination, stomatal entry, and epi- and endophytic mycelial growth in rice and wheat, failed to sporulate to cause rust disease in rice. We identified 18 key defence signalling genes in rice and unravelled their elicitation dynamics in time-course studies during infection. ICS1, NPR1-3, PRs, EDS1, PAD4, FMO1 (salicylic acid [SA] signalling), and ethylene-related genes (ACO4 and ACS6) were strongly elicited in rice. However, genes from the jasmonic acid (JA) signalling pathway (LOX2, AOS2, MYC2, PDF2.2, JAZ8, JAZ10) showed a delayed response during colonization in rice compared to an early or no induction in wheat. However, the JA/ethylene marker gene PDF2.2 was strongly induced in wheat as early as 12 hr postinoculation. Furthermore, rice and wheat displayed specific profiles of accumulation of various phenolic acids during P. graminis f. sp. tritici 40A infection. We propose a model where a differential modulation of the SA/JA-dependent defence network may modulate nonhost resistance. A deeper understanding of the molecular mechanism governing differential elicitation of defence signalling may provide a novel resistance mechanism for the sustainable management of rust diseases.     

Genetics of avirulences in Erysiphe graminis f.sp. hordei

The genetics of avirulences towards barley mildew resistances were analysed in crosses of the Ervsiphe graminis f.sp. hordei isolate DH14 with CC107 and with CC138. Nine avirulences, Av r_a9, Avr _a10, Avr _a11, Avr _a12, Avr _Ab, Avr _CP, Avr _h, Avr _k and Avr _La, segregated as single genes in one or other cross. However. F₁ segregation data were consistent with avirulence matching the Mla7 resistance gene being controlled by two genes, designated Avr _a7 1 and Avr _a7 2. Infection types of avirulent isolates differed on varieties in which Mla7 had been derived from each of the four known sources of that resistance. Linkage was detected between Avr _a7 1 and Avr _h in the cross CC107 × DH14, and between Avr _a10 and Avr _k, Avr _a11 and Avr _La, and Avr _h and the triadimenol response gene Tdl2 in CC138 × DH14.     

Genetic Diversity in Australian Populations of Puccinia graminis f. sp. avenae

ABSTRACT Sequence-tagged microsatellite profiling was used to develop 110 microsatellites for Puccinia graminis f. sp. tritici (causal agent of wheat stem rust). Low microsatellite polymorphism was exhibited among 10 pathogenically diverse P. graminis f. sp. tritici isolates collected from Australian cereal growing regions over a period of at least 70 years, with two polymorphic loci detected, each revealing two alleles. Limited cross-species amplification was observed for the wheat rust pathogens, P. triticina (leaf rust) and P. striiformis f. sp. tritici (stripe rust). However, very high transferability was revealed with P. graminis f. sp. avenae (causal agent of oat stem rust) isolates. A genetic diversity study of 47 P. graminis f. sp. avenae isolates collected from an Australia-wide survey in 1999, and a historical group of 16 isolates collected from Australian cereal growing regions from 1971 to 1996, revealed six polymorphic microsatellite loci with a total of 15 alleles. Genetic analysis revealed the presence of several clonal lineages and subpopulations in the pathogen population, and wide dispersal of identical races and genotypes throughout Australian cereal-growing regions. These findings demonstrated the dynamic population structure of this pathogen in Australia and concur with the patterns of diversity observed in pathogenicity studies.     

Biochemical characteristics of sporelings of Puccinia graminis f. sp. tritici and protoplasts from wheat isolines of potential significance in specificity

The affinity of various lectins for protoplasts from isolines of wheat differing in their reaction to Puccinia graminis Pers. f. sp. tritici , Ericks and E. Henn. race 21 and for infection structures of the fungus was studied. Protoplasts of both isolines were agglutinated by concanavalin A and soybean lectin and lysed by wheat germ agglutinin. Pokeweed mitogen and wheat germ agglutinin bound to fungal germ tubes and appressoria but not to uredospore walls, substomatal vesicles or infection hyphae.
Viability of protoplasts from either isoline was not affected when they were incubated with uredospores, germlings with and without infection structures or with an extract of the susceptible line, heavily infected by the fungus. No differences between polypeptide fractions prepared from protoplasts of the isolines were detected by sodium dodecyl sulphate polyacrylamide gel electrophoresis.     

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.