Epidemiological and histological components of crown rust resistance in oat genotypes

Crown rust, caused by Puccinia coronata f. sp. avenae, can cause significant damage in all regions where oats (Avena sativa L.) are cultivated. The primary means of controlling crown rust has been through genetic resistance, although in most cases resistance has been quickly overcome by the pathogen. More durable partial or non-specific resistance may possess different mechanisms from those underlying genes with specific effects. We studied the epidemiological and histological components of crown rust resistance with potential use in plant protection. Among the components evaluated, pustule density showed the clearest effect on resistance, while the latent period was not an important component. Cell death associated with the accumulation of autofluorescent and phenolic compounds was common in the resistant genotypes, but temporally distinct for the genotypes studied. Genotype Pc68/5*Starter, which has race-specific resistance, showed rapid cell death that prevented the development of pathogen colonies. Conversely, with cultivar URS 21 and genotypes 04B7113-1 and 04B7119-2, cell death and associated accumulation of autofluorescent and phenolic compounds was delayed until pathogen colonies were already established. Pathogen colonies developed normally in susceptible plants genotypes, and had usually produced sporogenic tissue by 5 days after inoculation. The data suggest that the resistance mechanisms, especially hypersensitivity and phenolic compound production, active in resistant plants are similar but may be differently expressed over time. The temporal variation in the expression of hypersensitivity and phenolic compound production reflects the level of field resistance in these genotypes.     

Rhamnus lycioides in Tunisia is a new aecial host of oat crown rust

Puccinia coronata was not previously described on Rhamnus spp. in Tunisia. Three sites in the northwest of Tunisia, where Rhamnus is reported to be abundant, were surveyed for the presence of pycnia and aecia of oat crown rust caused by Puccinia coronata f. sp. avenae. Two Rhamnus species (R. lycioides and R. alaternus) were encountered in the sites. Pycnia with viable pycniospores and aecia with viable aeciospores were found on R. lycioides. However, no characteristic structures of crown rust were found on R. alaternus. Aeciospores collected from leaves of R. lycioides were used to inoculate oat plants usually susceptible to oat crown rust. Typical uredinia containing oat crown rust urediniospores appeared on the leaves of these plants. Moreover, the sixteen Pc-gene differential oat lines, used by oat researchers to study the virulence pattern in oat crown rust populations, were artificially inoculated with aeciospores from R. lycioides. These inoculated lines showed resistance/susceptibility similar to the registered resistance level of these lines to crown rust under field conditions in Tunisia. These results indicate that R. lycioides, a common and endemic part of the vegetation in the northwest of Tunisia, is a new aecial host of oat crown rust. The aeciospores produced on this forest plant could constitute the source of the virulence diversity already detected via the Pc-gene line trials.     

Characterization and mapping of oat crown rust resistance genes using three assessment methods

ABSTRACT Resistance is the primary means of control for crown rust of oat (Avena sativa L.), caused by Puccinia coronata f. sp. avenae, and better knowledge of the genetics of resistance will enhance resistance breeding. Disease data were generated in the field and greenhouse for parents and recombinant inbred lines of the Ogle/TAM O-301 (OT) oat mapping population using (i) a new quantitative assay that employs quantitative real-time polymerase chain reaction (q-PCR) to estimate fungal growth in the host, (ii) digital image analysis, and (iii) visual ratings. The objectives of this study were to evaluate each assessment method's ability to map a major gene from cv. Ogle and potential quantitative trait loci (QTL) contributed by Ogle and TAM O-301. All three assessment methods identified the major gene in Ogle, which was mapped to linkage group OT6. The resolution produced by q-PCR, however, enabled more precise mapping of the major gene. Quantitative analysis indicated that 64% of the phenotypic variation was accounted for using q-PCR, whereas 41 and 52% were accounted for using visual and digital assessments, respectively. Data generated by q-PCR permitted identification of QTL on linkage groups OT32, accounting for 6% of the phenotypic variation, and OT2, accounting for 4% of the variation. QTL on both OT32 and OT2 were conferred by TAM O-301, one of which (OT2) was indiscernible using data from the visual and digital assessments. The new method of precisely phenotyping crown rust resistance provided a more accurate and thorough means of dissecting resistance in the OT mapping population. Similar methods could be developed and applied to other important cereal rust diseases.     

Occurrence of oat stem rust in west Wales

The first significant occurrence of stem rust ( Puccinia graminis Pers, ssp, graminis var, stakmanii Guyot, Massenot & Saccas ex, Urban) on spring oats ( Avena sativa L.) in west Wales, UK is reported.     

Sources and genetics of crown rust resistance in barley

ABSTRACT Crown rust, caused by Puccinia coronata var. hordei, is a new disease threat to barley in the Great Plains region of the United States. Deployment of resistant cultivars is the only economically viable option for the control of this disease. Thus, the objective of this study was to investigate the sources and genetics of crown rust resistance in barley. A geographically diverse sample of barley germ plasm collected around the world (526 accessions total) was evaluated at the seedling stage to P. coronata var. hordei, and only 10 accessions (1.9% of the total) were found resistant. These 10 accessions were also resistant at the adult plant stage in a greenhouse test. Three F(2) populations (Bowman x Hor2596, MR x Hor2596, and MD x Hor2596) were developed to study the inheritance of crown rust resistance in the resistant line Hor2596 (CIho 1243). A close fit to a 3:1 ratio of resistant/susceptible plants was observed in all three populations and is consistent with the segregation of a single resistance gene. F(1) plants from the Bowman x Hor2596 population exhibited slightly higher infection types than the resistant parent, indicating incomplete dominance. The locus symbol Rpc1 and allele symbol Rpc1.a were recommended for the crown rust resistance gene in Hor2596. An attempt was made to associate the Rpc1 locus with one of the seven barley chromosomes by analyzing linkage data with previously mapped morphological markers in crosses with multiple recessive (MR) and multiple dominant (MD) morphological marker stocks. However, no close linkages were detected between Rpc1 and the 20 morphological markers present in the marker stocks. The resistant accessions identified in this study should be useful to breeders for developing barley germ plasm with crown rust resistance.     

Molecular mapping of the crown rust resistance gene rpc1 in barley

ABSTRACT Crown rust of barley, caused by Puccinia coronata var. hordei, occurs sporadically and sometimes may cause yield and quality reductions in the Great Plains region of the United States and Canada. The incompletely dominant resistance allele Rpc1 confers resistance to P. coronata in barley. Two generations, F(2) and F(2:3), developed from a cross between the resistant line Hor2596 (CIho 1243) and the susceptible line Bowman (PI 483237), were used in this study. Bulked segregant analysis combined with random amplified polymorphic DNA (RAPD) primers were used to identify molecular markers linked to Rpc1. DNA genotypes produced by 500 RAPD primers, 200 microsatellites (SSRs), and 71 restriction fragment length polymorphism (RFLP) probes were applied to map Rpc1. Of these, 15 RAPD primers identified polymorphisms between resistant and susceptible bulks, and 62 SSR markers and 32 RFLP markers identified polymorphisms between the resistant and susceptible parents. The polymorphic markers were applied to 97 F(2) individuals and F(2:3) families. These markers identified 112 polymorphisms and were used for primary linkage mapping to Rpc1 using Map Manager QT. Two RFLP and five SSR markers spanning the centromere on chromosome 3H and one RAPD marker (OPO08-700) were linked with Rpc1 and, thus, used to construct a 30-centimorgan (cM) linkage map containing the Rpc1 locus. The genetic distance between Rpc1 and the closest marker, RAPD OPO08-700, was 2.5 cM. The linked markers will be useful for incorporating this crown rust resistance gene into barley breeding lines.     

Virulence of Puccinia triticina in Turkey and leaf rust resistance in Turkish wheat cultivars

Leaf rust caused by Puccinia triticina is a common disease on wheat in the coastal regions of Turkey. Collections of P. triticina from infected wheat leaves were obtained from the main wheat production zones of Turkey in 2009 and 2010. A total of 104 single uredinial isolates were tested for virulence on 20 lines of Thatcher wheat that differ for single leaf rust resistance genes. Forty-four different virulence phenotypes were identified over both years. Four phenotypes were found in both years. Phenotype FHPTQ found in 2009, with virulence to genes Lr2c, Lr3, Lr16, Lr26, Lr3ka, Lr17a, Lr30, LrB, Lr10, Lr14a, Lr18, Lr3bg, and Lr14b, was the most common phenotype at 15.4 % of the total isolates. Forty-three winter and spring wheat cultivars from Turkey were tested as seedlings with 13 different P. triticina virulence phenotypes from Canada, the US and Turkey. The infection types on the cultivars were compared with infection types on the Thatcher near isogenic lines to postulate the presence of seedling leaf rust resistance genes in the cultivars. Resistance genes Lr1, Lr3a, Lr10, Lr14a, Lr17a, Lr20, Lr23, and Lr26 were postulated to be present in the Turkish wheat cultivars. DNA of the wheat cultivars was tested with PCR markers to determine the presence of the adult plant resistance genes Lr34 and Lr37. Marker data indicated the presence of Lr34 in 20 cultivars and Lr37 in three cultivars. Field plot evaluations of the wheat cultivars indicated that no single Lr gene conditioned highly effective leaf rust resistance. Resistant cultivars varied for combinations of seedling and adult plant resistance genes.     

Usefulness of gene pg10 as a source of stem rust resistance in oat breeding

ABSTRACT Infection types produced by Puccinia graminis f. sp. avenae on plants of Avena sativa with the stem rust resistance gene Pg10 are characterized by moderate-sized uredinia surrounded by an area of chlorosis and a larger variable zone of dark brown necrosis. This study was undertaken to assess the effectiveness of gene Pg10 as a source of resistance to stem rust and to determine the interactions of this gene with other common Pg genes. A derived Pg10 line was tested with 58 distinct pathotypes of P. graminis f. sp. avenae and was crossed to substituted single-gene lines carrying the resistance gene Pg1, Pg2, Pg3, Pg4, Pg8, Pg9, Pg13, Pg15, Pg16, or Pga. The Pg10 line showed moderate resistance to all 58 patho-types, and there was no indication of specificity in virulence by any isolate. Gene Pg10 was inherited independently of the other Pg genes and had a complementary effect on the expression of resistance by these genes. An effective level of resistance conferred by Pg10 was demonstrated in a field nursery artificially inoculated with P. graminis f. sp. avenae. It was concluded that Pg10 is a potentially useful source of stem rust resistance in oat breeding, with its main attributes being an apparent broad base of resistance, ease of combining with other Pg genes, and complementary effects on the expression of other Pg genes.     

Development and validation of a quantitative PCR assay method of assessing relative resistance of oat (Avena sativa) to crown rust (Puccinia coronata f. sp. avenae)

Evaluation of oat crown rust resistance is usually based on visual assessment of disease severity or infection types. Visual assessment is subjective, prone to rater bias and requires expert knowledge. PCR-based quantitative assays can overcome challenges associated with visual assessment. New TaqMan primers and probes were designed from Puccinia coronata f. sp. avenae (Pca) sequences. The primer–probe sets were specific to Pca, amplified using as little as 0.5 pg fungal DNA (fDNA) and allowed for scaling to variation in sample total DNA quantity. The quantitative PCR (qPCR) assay was validated using oat recombinant inbred lines (RILs) from the Provena × 94197A1-9-2-2-2-5 cross evaluated under a controlled environment. For comparison with fDNA load, inoculation with the Pca race LCBB provided segregation data on the hypersensitive response, while Pca race LSLG provided data on segregation for reduced pustule number. fDNA content was positively correlated with both pustule number and infection type (IT). Composite interval mapping identified two quantitative trait loci (QTLs) on oat linkage groups Mrg12 and Mrg20 using visual and qPCR assessments (pustule number, IT and fDNA). In this study a qPCR assay method that can be used to assess the relative resistance of oat to crown rust was refined and validated, and single nucleotide polymorphisms (SNPs) closely linked with two QTLs derived from the crown rust resistant line 94197A1-9-2-2-2-5 were identified.     

Virulence gene distribution and dynamics of the white pine blister rust pathogen in Western north america

ABSTRACT We assayed the distribution and frequency of two genes of the blisterpathogen with specific virulence to major resistance genes in sugar pine and western white pine in inoculum from extensive parts of the hosts' ranges. The genes, vcr1 and vcr2, differentially neutralize the cognate resistance alleles Cr1 and Cr2 of the two respective hosts and are clearly marked by their interaction phenotypes. Basidiospores from each inoculum source were cast over Cr1 and Cr2 host genotypes simultaneously, and interaction phenotypes scored when developed. vcr1 was confined to sites with high concentrations of Cr1 (mostly plantations) where frequencies tended toward fixation. vcr2 showed a similar tendency, except high frequencies were occasionally observed from natural and planted stands of western white pine with very low frequencies of Cr2. Otherwise, no pattern was evident for either allele: frequencies were very erratic from site to site within short distances (<1 to 7 km) of each other and oscillated with high amplitudes at the same sites measured in consecutive years. Intense selection for virulence by Cr alleles occurs locally, but spread of vcr alleles over the landscape is mitigated by remarkably low gene flow. Absence of heterozygotes among single telia inoculum on Cr2 genotypes indicated cytoplasmic inheritance of vcr2, similar to vcr1(previously reported).     

中国小麦条锈病菌CYR32和CYR33的毒性及基因型多样性

为明确我国小麦条锈病菌当前主要流行生理小种CYR32和CYR33的毒性及基因型特征,从全国11个省(区)随机选取29个CYR32菌株和39个CYR33菌株,利用近等基因系及辅助鉴别寄主对其进行毒性鉴定,利用SSR分子标记技术对其进行基因型分析,并对其进行聚类分析。结果显示,CYR32和CYR33菌系各有17种毒性表型,而且在抗病基因Yr2、Yr17、Yr27、Yr32、Yr43、Yr Sp、Yr Exp2、Yr28、Yr V23上都发生了毒性分化,CYR32和CYR33菌系的多样性指数分别为0.089、0.097;CYR32和CYR33菌系的香农信息指数均值分别为0.44和0.45;当相似性系数为0.93时,CYR32和CYR33菌系分别被聚为5个和8个毒性类群;当相似性系数为0.84时,CYR32和CYR33菌系分别被聚为10个和16个基因型类群。表明在中国鉴别寄主上具有相同毒性谱特征的CYR32和CYR33菌系在近等基因和SSR分子标记中发生了不同程度的毒性和基因型分化。     

冀西北地区燕麦主栽品种（系）抗秆锈病鉴定

2011-2012年,在2个试验点,采用孕穗期接种混合菌种的方法,对冀西北地区40个燕麦主栽品种（系）抗秆锈病进行了鉴定。结果表明：9个皮燕麦品种中,‘冀张燕5号’、‘冀张燕2号’、‘坝燕1号’、‘冀张燕1号’和‘定燕1号’等5个品种,31个裸燕麦品种（系）中,‘白燕2号’、‘白燕11号’、‘冀张莜6号’、‘冀张莜12号’、‘花晚6号’、‘晋燕14号’和‘燕科1号’等7个品种,至少在1个试验点表现免疫、抗病或慢病,其中大多在温度较低的试验点1更抗病,认为与大多数燕麦抗秆锈病基因表现低温抗病性有关;其余28个品种（系）均表现感病或高度感病。     

燕麦DNA在小麦抗条锈病育种中的利用

以健壮燕麦Avena sativa L.为供体,以普通小麦品种宁春4号为受体,利用花粉管通道将燕麦总DNA导入小麦中。对供体、受体、导入后代各变异株系进行连续4年的成株期混合菌种的抗病性鉴定和2年的分生理小种鉴定。结果显示:供体对小麦条锈菌免疫,受体对小麦条锈菌各生理小种严重感染,导入后代中有6个株系对小麦条锈菌各生理小种均表现高抗。表明燕麦DNA上可能携有抗小麦条锈菌的新基因,并已通过花粉管通道进入小麦,整合到小麦的染色体组中,稳定地表达。     

源自陕、甘野生小檗的小麦条锈菌有性生殖后代的毒性分析

 小麦条锈病是我国最具毁灭性的小麦病害之一,其流行常常造成小麦严重减产。种植抗病品种是防治该病害最经济、有效和环保的措施。但是,由于新毒性菌系的出现,抗病品种在种植短短数年内便“丧失”其抗病性。研究证实病原菌毒性变异产生新菌系是导致小麦品种抗病性“丧失”的根本原因。近年来,随着小麦条锈菌转主寄主小檗的确定,发现自然条件下我国小麦条锈菌在野生小檗上可以完成有性生殖。本研究通过对2015年自然发病小檗小麦条锈菌的分离及其单夏孢子堆纯化,利用中国鉴别寄主进行了毒性测定分析。从陕西、甘肃两省的3种感病小檗共分离获得小麦条锈菌菌系8个,其中有1个菌系与已知小种Su11-126的毒性完全匹配,其余7个为新菌系;93个单夏孢子堆群体可分为47个不同的致病类型,包括14个已知小种类型,33个新小种类型;有56个菌系与已知小种的毒性完全匹配,37个为新小种。本研究再次获得了条锈菌自然条件下存在有性生殖并因此导致新菌系产生的证据,证实了野生小檗在我国小麦条锈菌的生活史和病害循环中具有作用。     

Effect of crown rust on regrowth, competitive ability and nutritional quality of perennial and Italian ryegrasses

Infection of susceptible cultivars of perennial (Lolium perenne) and Italian (Lolium multiflorum) ryegrasses with crown rust (Puccinia coronata) reduced yield measured 6 weeks after infection and at two regrowth cuts. In perennial, but not Italian, ryegrass, rust infection of mixed swards of a resistant and a susceptible cultivar reduced the contribution to yield made by the susceptible cultivar and increased that of the resistant cultivar. This effect persisted for three regrowth cuts. The trend in effect on the number of tillers, but not plant height, was similar.
Infection increased leaf protein in susceptible perennial ryegrass but had little effect in Italian ryegrass. In both species, rust reduced water-soluble carbohydrate and the predicted digestibility of susceptible and resistant cultivars, but had no effect on quality of regrowth.     

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。     

Development,characterization and application of genomic SSR markers for the oat stem rust pathogen Puccinia graminis f. sp. avenae

Oat stem rust, caused by Puccinia graminis f. sp. avenae (Pga), is one of the most severe diseases of oats worldwide. Population studies are scarce for this pathogen, mainly due to the lack of polymorphic molecular markers suitable for genetic analysis. In this study, an Australian Pga isolate was sequenced, the abundance of simple sequence repeats (SSRs) was determined and PCR‐based polymorphic markers suitable for genetic diversity analysis were developed. The amplification of 194 primer pairs was initially assessed using a set of 12 isolates of different cereal rust species and their formae speciales. A high frequency of cross‐species amplification was observed for most markers; however, 36 SSRs were diagnostic for P. graminis only. A subset of 19 genome‐derived SSRs were deemed useful for genetic diversity analysis of Pga and were assessed on 66 Pga isolates from Australia, Brazil and Sweden. Brazilian and Australian isolates were characterized by one and two predominant clonal lineages, respectively. In contrast, the Swedish isolates, previously shown to undergo sexual recombination, were highly diverse (nine distinct genotypes out of 10 isolates) and divided into two subpopulations. The genome‐derived SSR markers developed in this study were well suited to the population studies undertaken, and have diagnostic capabilities that should aid in the identification of unknown rust pathogen species.