Crown Rust Research Articles

Field Application of Benzothiadiazole (BTH) to Oats (Avena sativa): Effects on Crown Rust Resistance and Avenanthramide Production

Avenanthramides are phenolic antioxidants produced in oat (Avena sativa L.) in response to fungal infection and, as shown in greenhouse experiments, by treatment with plant defense activators, such as benzothiadiazole (BTH). Presented here are the results of application of BTH under field conditions. Field trials were conducted in 2013 using four application rates, approximating manufacturer's recommendations, on two oat cultivars and in 2014 using three application rates on three oat cultivars. The results showed a subtle but demonstrable effect of increased avenanthramide production in vegetative tissue and mature grain and enhanced resistance to crown rust infection. Gene expression of pathogenesis related protein‐1 (PR‐1), phenylalanine ammonia lyase (PAL) and hydroxycinnamoyl‐CoA:hydroxyanthranilate hydroxycinnamoyl‐CoA transferase (HHT) was also monitored by RT‐qPCR. Both PR‐1 and PAL expression were demonstrably up‐regulated in the field trials; HHT was not. However, greenhouse experiments showed all three genes to be elicited with 63‐, 9‐, and 3‐fold increases, respectively. Thus, field application of plant defense activators can effectively enhance crown rust resistance and avenanthramide production in oat by up‐regulating certain metabolic pathways; their practical application, however, will require substantial investigative efforts.

Identification of Genes in a Partially Resistant Genotype of Avena sativa Expressed in Response to Puccinia coronata Infection.

Cultivated oat (Avena sativa), an important crop in many countries, can suffer significant losses through infection by the fungus Puccinia coronata, the causal agent of crown rust disease. Understanding the molecular basis of existing partial resistance to this disease might provide targets of interest for crop improvement programs. A suppressive subtractive hybridization (SSH) library was constructed using cDNA from the partially resistant oat genotype MN841801-1 after inoculation with the pathogen. A total of 929 genes returned a BLASTx hit and were annotated under different GO terms, including 139 genes previously described as participants in mechanisms related to the defense response and signal transduction. Among these were genes involved in pathogen recognition, cell-wall modification, oxidative burst/ROS scavenging, and abscisic acid biosynthesis, as well genes related to inducible defense responses mediated by salicylic and jasmonic acid (although none of which had been previously reported involved in strong responses). These findings support the hypothesis that basal defense mechanisms are the main systems operating in oat partial resistance to P. coronata. When the expression profiles of 20 selected genes were examined at different times following inoculation with the pathogen, the partially resistant genotype was much quicker in mounting a response than a susceptible genotype. Additionally, a number of genes not previously described in oat transcriptomes were identified in this work, increasing our molecular knowledge of this crop.

Resistance to Puccinia coronata f. sp. avenae in Avena magna, A. murphyi, and A. insularis.

Wild oat tetraploids of the section Pachycarpa have already been proven to be a rich source of useful genes but have largely been unexploited for Puccinia coronata resistance. In this study, accessions of Avena magna, A. murphyi, and A. insularis gathered from European and North American gene banks were evaluated at the seedling stage for crown rust reaction using the host-pathogen test and six highly diverse and virulent P. coronata isolates. Of the 92 Avena accessions analyzed, 58.7% were resistant to at least one crown rust race. In all, 37% of the tested accessions reacted nonuniformly, which indicated their heterogeneity. The highest level of resistance was observed in three of the accessions, one of which was verified by flow cytometry as being hexaploid and two of which were verified as being tetraploids. The infection profiles of 19 accessions corresponded to resistance determined by the genes Pc14, Pc39, Pc40, Pc48, Pc50, Pc54, Pc55, Pc61, Pc67, Pc68, Pc97, Pc101, or Pc104. The patterns of infection of the remaining resistant A. magna and A. murphyi accessions allowed us to postulate the presence of potentially novel crown rust resistance genes.

Yield Losses Due to Crown Rust in Winter Oats in Alabama

Crown rust is a common disease on winter oats in Alabama. While considered the most destructive disease of oats, little has been done in recent years, with current cultivars, to demonstrate yield losses due to crown rust. Field studies were conducted to determine the effect of fungicides and application timing on crown rust severity and yield. All fungicides reduced crown rust and improved yield. Two fungicide applications were better than a single fungicide application for reducing crown rust. Relative to yield, a single fungicide application during flag leaf development (FS 8-9) was better than a single application during head extension (FS 10.3). When compared with the non-treated control, significant yield gains were obtained with Tilt and Headline in all four years and Stratego YLD in three of four years. Fungicide programs resulted in a broad range of crown rust severities; disease levels were highly related to decreases in yield in each of four years. In two study years, ‘Coker 227’ was more damaged by crown rust, with about 10% yield loss for each unit disease, than was ‘Horizon 270,’ with 2.5 to 4.5% loss. However, in 2013, virulence patterns of the crown rust pathogen shifted and disease on Horizon 270 was greater than that on Coker 227; relative yield losses were also much lower in 2013. Accepted for publication 15 April 2016. Published 4 May 2016.

Registration of ‘FL PE’, a Later‐Maturing Diploid Annual Ryegrass

‘FL PE’ (Reg. No. CV‐280, PI 675350) diploid annual ryegrass (Lolium multiflorum Lam.) is a synthetic cultivar selected for later maturity, excellent cold tolerance, and resistance to crown rust (caused by Puccinia coronate Corda) and gray leaf spot (caused by Pyricularia grisea Sacc.) It offers sufficient cold tolerance to be grown in the northern part of the annual ryegrass region of the United States. It also has sufficient disease resistance to be grown in the southern annual ryegrass belt. FL PE was produced from cold‐tolerant germplasm jointly produced in Scottsbluff, NE, Gainesville, FL, and Marianna, FL. The beginning seed sources for this selection program were composited in 2003 from FL/NEX2003 (new3) LRCT, FLX2003 (new3), NE/FL 2003 (new4) LRCT, NE/FLX2002 (new2) LRCT, and M/FL 2003 (new4) LRCT. Eight cycles of recurrent mass selection for crown rust resistance, gray leaf spot resistance, and mid‐late seed maturity were completed at Gainesville. FL PE showed high dry matter yields at Gainesville and was among the higher‐yielding lines at Tifton and Calhoun, GA (total of 14 location‐years data reported). Maturity ratings at Gainesville show that FL PE was among the later‐maturing lines evaluated. Late maturity can be beneficial in years with limited early summer perennial grass production; however, late maturity can also delay early summer production of these grasses, such as bermudagrass [Cynodon dactylon (L.) Pers.]. FL PE had excellent levels of resistance to crown rust disease at Gainesville.

Role of Alternate Hosts in Epidemiology and Pathogen Variation of Cereal Rusts.

Cereal rusts, caused by obligate and biotrophic fungi in the genus Puccinia, are important diseases that threaten world food security. With the recent discovery of alternate hosts for the stripe rust fungus (Puccinia striiformis), all cereal rust fungi are now known to be heteroecious, requiring two distinct plant species serving as primary or alternate hosts to complete their sexual life cycle. The roles of the alternate hosts in disease epidemiology and pathogen variation vary greatly from species to species and from region to region because of different climatic and cropping conditions. We focus this review on rust fungi of small grains, mainly stripe rust, stem rust, leaf rust, and crown rust of wheat, barley, oat, rye, and triticale, with emphases on the contributions of alternate hosts to the development and management of rust diseases.

Genetic diversity and crown rust resistance of oat landracesfrom various locations throughout Turkey

Ziya DUMLUPINAR*, Eric N. JELLEN, J. Michael BONMAN, Eric W. JACKSON Department of Agricultural Biotechnology, Faculty of Agriculture, Kahramanmaras Sutcu Imam University, Kahramanmaras, Turkey Department of Plant and Wildlife Science, Brigham Young University, Provo, Utah, USA USDA, Agricultural Research Service, Small Grains and Potato Germplasm Research Unit, Aberdeen, Idaho, USA General Mills Crop Bioscience, Wheat Innovation Center, Manhattan, Kansas, USA

A Greenhouse-based Inoculation Protocol for Fungi Causing Crown Rust and Stem Rust Diseases of Kentucky Bluegrass Turf

Rusts are destructive fungal diseases that can cause severe thinning and unattractive discoloration of kentucky bluegrass (KBG; Poa pratensis L.). Currently, turfgrass breeding programs rely on field evaluations to screen KBG germplasm for rust resistance; methods that are expensive, labor intensive, and require large turf areas. The availability of a greenhouse-based assay to perform prescreening of KBG germplasm for resistance to rust diseases before field trials would allow breeders to remove the poorest performing plants before field evaluations thus enhancing breeding efficiency. In this study, we set out to develop a reliable, low-cost greenhouse inoculation protocol for the two most common rust pathogens of KBG in temperate growing regions: Puccinia coronata and Puccinia graminis, the causal agents of crown and stem rust, respectively. Using a modified inoculation assay and custom-built plexi-glass chambers adapted from protocols used for cereal rust pathogens, urediniospores of crown and stem rust fungi developed on inoculated plants 10 to 14 days postinoculation. Real-time polymerase chain reaction (PCR) assays, disease symptomology, and morphology of urediniospores confirmed the presence and identity of both rust pathogens from inoculated host tissue. The inoculation protocols described here represent an effective method to accelerate screening of KBG germplasm for resistance to crown and stem rust diseases. Infection of KBG plants in the greenhouse will also allow breeders to maintain populations of crown and stem rust fungi throughout the year, providing a reliable and ongoing source of pathogen inoculum for experimentation and screening in the future.

Estimating genomic heritabilities at the level of family-pool samples of perennial ryegrass using genotyping-by-sequencing.

KeymessageBy using the genotyping-by-sequencing method, it is feasible to characterize genomic relationships directly at the level of family pools and to estimate genomic heritabilities from phenotypes scored on family-pools in outbreeding species.Genotyping-by-sequencing (GBS) has recently become a promising approach for characterizing plant genetic diversity on a genome-wide scale. We use GBS to extend the concept of heritability beyond individuals by genotyping family-pool samples by GBS and computing genomic relationship matrices (GRMs) and genomic heritabilities directly at the level of family-pools from pool-frequencies obtained by sequencing. The concept is of interest for species where breeding and phenotyping is not done at the individual level but operates uniquely at the level of (multi-parent) families. As an example we demonstrate the approach using a set of 990 two-parent F2 families of perennial ryegrass (Lolium Perenne). The families were phenotyped as a family-unit in field plots for heading date and crown rust resistance. A total of 728 K single nucleotide polymorphism (SNP) variants were available and were divided in groups of different sequencing depths. GRMs based on GBS data showed diagonal values biased upwards at low sequencing depth, while off-diagonals were little affected by the sequencing depth. Using variants with high sequencing depth, genomic heritability for crown rust resistance was 0.33, and for heading date 0.22, and these genomic heritabilities were biased downwards when using variants with lower sequencing depth. Broad sense heritabilities were 0.61 and 0.66, respectively. Underestimation of genomic heritability at lower sequencing depth was confirmed with simulated data. We conclude that it is feasible to use GBS to describe relationships between family-pools and to estimate genomic heritability directly at the level of F2 family-pool samples, but estimates are biased at low sequencing depth.Electronic supplementary materialThe online version of this article (doi:10.1007/s00122-015-2607-9) contains supplementary material, which is available to authorized users.

Virulence of crown rust isolates (Puccinia coronata f.sp. lolii) on genotypes of Italian and perennial ryegrass (Lolium multiflorum and L. perenne)

Crown rust samples were collected in 2004 on rust infected Italian and perennial ryegrass leaves at 28 sites in 11 European countries. Out of these 28 rust collections, 112 single-pustule isolates were produced to determine virulence frequency and complexity on 32 ryegrass genotypes. A high level of virulence diversity was observed within and between individual sampling sites. In total, 107 pathotypes with different virulence combination were found. Of these, just five combinations occurred twice. All 32 individuals were susceptible to at least two single-pustule isolates using a detached-leaf segment test. In the field, the 32 genotypes differed greatly in their susceptibility to crown rust. Nevertheless, the correlation between mean susceptibility in the field and virulence frequency of the 32 differentials was significant. The three most resistant genotypes in the field were also the genotypes with the lowest virulence frequency. Genetic analysis of resistance to crown rust in three genotypes of perennial ryegrass led to the identification of three dominant resistance genes: Pclol1, Pclol2 and Pclol3. Each of the three genes conferred resistance to a limited number of single-pustule isolates and was ineffective against at least one single-pustule isolate. The patterns of resistance reaction to specific single-pustule isolates provide evidence that the three R-genes represent distinct crown rust resistance genes in ryegrass. Moreover, the data demonstrate clearly the existence of pathotype specificity in crown rust of Lolium species.

Mapping genes in barley for resistance to Puccinia coronata from couch grass and to P. striiformis from brome, wheat and barley

AbstractBarley (Hordeum vulgare L.) mapping populations have been developed that are useful to study the inheritance of quantitative resistance to adapted and unadapted rust fungi. In a recent host range study, we found that the parents of those mapping populations also differed in their resistance to the crown rust Puccinia coronata (PcE) of couch grass (Elymus repens), as well as three isolates of P. striiformis, representing formae speciales hordei (Psh), tritici (Pst) and bromi (Psb). Available mapping populations were phenotyped at the seedling stage to map the genes conferring resistance to these rust isolates. Resistances to PcE, Psb and Pst inherit quantitatively. This contrasted with reports that barley nonhost resistance to unadapted formae speciales of P. striiformis is based on major genes. We mapped QTLs effective against PcE using relative latency period and relative infection frequency. Some QTLs for resistance were contributed by ‘Vada’ and ‘Cebada Capa’, others by SusPtrit. One PcE-resistance QTL on 3H, contributed by ‘Cebada Capa’, co-localised with a QTL effective against four unadapted grass rust species, indicating either a single gene with broad-spectrum effectiveness or a cluster of rather specific genes. Chromosome arm 7HL from Vada seems particularly rich in genes for resistance to rust fungi. Resistance to Pst and Psb, measured as the number of uredinia, tended to co-localise with each other and mapped to 1HS, 2HL and 7HL. The nearly complete resistance of Ethiopian line L94 to Psh was due to a major gene mapped on chromosome 4H. That gene is likely the recessive gene rpsGZ, which was previously reported in the Ethiopian line Grannenlose Zweizeilige.

Genetic analysis of seedling resistance to crown rust in five diploid oat (Avena strigosa) accessions.

Crown rust, caused by Puccinia coronata Corda f. sp. avenae Eriks., is a serious menace in oats, for which resistance is an effective means of control. Wild diploid oat accessions are a source of novel resistances that first need to be characterised prior to introgression into locally adapted oat cultivars. A genetic analysis of resistance to crown rust was carried out in three diverse diploid oat accessions (CIav6956, CIav9020, PI292226) and two cultivars (Saia and Glabrota) of A. strigosa. A single major gene conditioning resistance to Australian crown rust pathotype (Pt) 0000-2 was identified in each of the three accessions. Allelism tests suggested that these genes are either the same, allelic, or tightly linked with less than 1 % recombination. Similarly, a single gene was identified in Glabrota, and possibly two genes in Saia; both cultivars previously reported to carry two and three crown rust resistance genes, respectively. The identified seedling resistance genes could be deployed in combination with other resistance gene(s) to enhance durability of resistance to crown rust in hexaploid oat. Current diploid and hexaploid linkage maps and molecular anchor markers (simple sequence repeat [SSR] and diversity array technology [DArT] markers) should facilitate their mapping and introgression into hexaploid oat.

Free polyamine and polyamine regulation during pre‐penetration and penetration resistance events in oat against crown rust (Puccinia coronata f. sp. avenae)

During recent years a wealth of studies has focused on the role of polyamines in plant–environment stress interaction. However, less is known about the role of these compounds in plant disease resistance, and most of this knowledge is related to the hypersensitive response. Here the involvement of polyamines in the oat–crown rust interaction is examined, focusing on the mesophyll cell pre‐penetration and penetration resistance mechanisms. Two different oat cultivars were used, one resistant (Saia) and the other susceptible (Araceli) to crown rust (Puccinia coronata f. sp. avenae). Differential increases in polyamines between oat cultivars upon rust inoculation were observed and associated with increased pre‐penetration and penetration resistance. Elevated levels of spermidine and spermine, together with increases in the cell wall‐bound diamine‐ and polyamine oxidase activities, and concomitant increases in the polyamine oxidation product 1,3‐diaminopropane, were observed in the resistant cultivar at early stages of the infection process. This suggests an involvement of polyamines and derived H2O2 during penetration resistance. The putative role of polyamines in oat resistance to crown rust is supported by the increased resistance observed in the susceptible cultivar Araceli, as a result of reduced appressorium formation, after treatment with exogenous polyamines. Because arginine decarboxylase (ADC) has been reported as a key polyamine biosynthesis enzyme in plants exposed to stress, ADC transcript levels and enzyme activity were also evaluated, revealing an increase in ADC activity in cv. Saia at the key time points for the pre‐penetration and penetration resistance responses, which suggest an involvement of this enzyme in the resistance response.

Genome-wide association study for crown rust (Puccinia coronata f. sp. avenae) and powdery mildew (Blumeria graminis f. sp. avenae) resistance in an oat (Avena sativa) collection of commercial varieties and landraces.

Diseases caused by crown rust (Puccinia coronata f. sp. avenae) and powdery mildew (Blumeria graminis f. sp. avenae) are among the most important constraints for the oat crop. Breeding for resistance is one of the most effective, economical, and environmentally friendly means to control these diseases. The purpose of this work was to identify elite alleles for rust and powdery mildew resistance in oat by association mapping to aid selection of resistant plants. To this aim, 177 oat accessions including white and red oat cultivars and landraces were evaluated for disease resistance and further genotyped with 31 simple sequence repeat and 15,000 Diversity Arrays Technology (DArT) markers to reveal association with disease resistance traits. After data curation, 1712 polymorphic markers were considered for association analysis. Principal component analysis and a Bayesian clustering approach were applied to infer population structure. Five different general and mixed linear models accounting for population structure and/or kinship corrections and two different statistical tests were carried out to reduce false positive. Five markers, two of them highly significant in all models tested were associated with rust resistance. No strong association between any marker and powdery mildew resistance at the seedling stage was identified. However, one DArT sequence, oPt-5014, was strongly associated with powdery mildew resistance in adult plants. Overall, the markers showing the strongest association in this study provide ideal candidates for further studies and future inclusion in strategies of marker-assisted selection.

Reactive Oxygen Species are not Increased in Resistant Oat Genotypes Challenged by Crown Rust Isolates

AbstractCrown rust (Puccinia coronata Corda f.sp. avenae) can devastate oats (Avena sativa). Oxidative stress is part of the resistance mechanism in several pathosystems, but in the oat–crown rust system, it is unclear, especially regarding partial resistance. We evaluated the effects of P. coronata on oxidative stress in oat cultivars: URS 21 (partially resistant), Leggett (race‐specific resistant), URS22 and Clintland 64 (susceptibles). Seedlings and plants were inoculated with P. coronata uredospores. Cultivars were assessed for antioxidant enzyme activity and the reactive oxygen species (ROS) hydrogen peroxide and superoxide. Due to the importance of the partial resistance of URS21, this cultivar and URS 22 were also appraised for total phenolics and the relative expression of oxidative stress genes. Postinoculation, Leggett and URS 21 showed no increased peroxide levels. The susceptible cultivars increased ROS and ascorbate peroxidase activity. Clintland 64 increased also catalase activity, whereas URS 22 increased glutathione reductase and the expression of genes encoding antioxidant enzymes. URS 21 showed almost no antioxidant enzyme induction. Shortly after inoculation, URS 21 showed increased expression of genes encoding lipoxygenase and peroxidase. Cultivars URS 21 and Leggett accumulated cell wall fluorescent compounds, phenolics being detected in the former. Oxidative stress appears not to cause the hypersensitive response in this pathosystem, but late ROS accumulation did occur in the susceptible cultivars. Cultivar URS 21 may, differently from other known mechanism to date, reduce ROS accumulation by increasing the level of phenolics, resulting in later pathogen and cell death, showing non‐specific resistance to races of the pathogen also at seedling stage.

Quantitative Trait Loci from Two Genotypes of Oat (Avena sativa) Conditioning Resistance to Puccinia coronata.

Developing oat cultivars with partial resistance to crown rust would be beneficial and cost-effective for disease management. Two recombinant inbred-line populations were generated by crossing the susceptible cultivar Provena with two partially resistant sources, CDC Boyer and breeding line 94197A1-9-2-2-2-5. A third mapping population was generated by crossing the partially resistant sources to validate the quantitative trait locus (QTL) results. The three populations were evaluated for crown rust severity in the field at Louisiana State University (LSU) in 2009 and 2010 and at the Cereal Disease Laboratory (CDL) in St. Paul, MN, in 2009, 2010, and 2011. An iSelect platform assay containing 5,744 oat single nucleotide polymorphisms was used to genotype the populations. From the 2009 CDL test, linkage analyses revealed two QTLs for partial resistance in the Provena/CDC Boyer population on chromosome 19A. One of the 19A QTLs was also detected in the 2009 LSU test. Another QTL was detected on chromosome 12D in the CDL 2009 test. In the Provena/94197A1-9-2-2-2-5 population, only one QTL was detected, on chromosome 13A, in the CDL 2011 test. The 13A QTL from the Provena/94197A1-9-2-2-2-5 population was validated in the CDC Boyer/94197A1-9-2-2-2-5 population in the CDL 2010 and 2011 tests. Comparative analysis of the significant marker sequences with the rice genome database revealed 15 candidate genes for disease resistance on chromosomes 4 and 6 of rice. These genes could be potential targets for cloning from the two resistant parents.

Genetic analysis and molecular mapping of a seedling crown rust resistance gene in oat.

Genetic analysis and genome mapping of a major seedling oat crown rust resistance gene, designated PcKM, are described. The chromosomal location of the PcKM gene was identified and linked markers were validated. Crown rust (Puccinia coronata Corda f. sp. avenae Eriks) is the most important foliar disease of oats and can cause considerable yield loss in the absence of appropriate management practices. Utilization of novel resistant genes is the most effective, economic and environmentally sound approach to control the disease. Crown rust resistance present in the cultivar 'Morton' was evaluated in a population developed from the cross OT3019 × 'Morton' to elucidate the genetic basis of resistance. Crown rust reaction evaluated in field nurseries and greenhouse tests demonstrated that resistance provided by 'Morton' was controlled by a single gene, temporarily designated as PcKM. The gene was initially linked to a random amplified polymorphic DNA band and subsequently converted into a sequence characterized amplified region (SCAR) marker. Genotyping with the PcKM SCAR on the 'Kanota' × 'Ogle' population, used to create the first oat chromosome-anchored linkage map, placed the PcKM gene on chromosome 12D. Consensus map markers present in the same region as the PcKM SCAR were tested on the OT3019 × 'Morton' population and two additional phenotyped populations segregating for PcKM to identify other markers useful for marker-assisted selection. Three markers were perfectly linked to the PcKM phenotype from which TaqMan and KBioscience competitive allele-specific PCR assays were developed and validated on a set of 25 oat lines. The assays correctly identified PcKM carriers. The markers developed in this study will facilitate fine mapping of the PcKM gene and simplify selection for this crown rust resistance.

A major quantitative trait locus conferring adult plant partial resistance to crown rust in oat.

BackgroundCrown rust, caused by Puccinia coronata f. sp. avenae, is the most important disease of oat worldwide. Adult plant resistance (APR), based upon partial resistance, has proven to be a durable rust management strategy in other cereal rust pathosystems. The crown rust APR in the oat line MN841801 has been effective for more than 30 years. The genetic basis of this APR was studied under field conditions in three recombinant inbred line (RIL) populations: 1) AC Assiniboia/MN841801, 2) AC Medallion/MN841801, and 3) Makuru/MN841801. The populations were evaluated for crown rust resistance with the crown rust isolate CR251 (race BRBB) in multiple environments. The 6 K oat and 90 K wheat Illumina Infinium single nucleotide polymorphism (SNP) arrays were used for genotyping the AC Assiniboia/MN841801 population. KASP assays were designed for selected SNPs and genotyped on the other two populations.ResultsThis study reports a high density genetic linkage map constructed with oat and wheat SNP markers in the AC Assiniboia/MN841801 RIL population. Most wheat SNPs were monomorphic in the oat population. However the polymorphic wheat SNPs could be scored accurately and integrated well into the linkage map. A major quantitative trait locus (QTL) on oat chromosome 14D, designated QPc.crc-14D, explained up to 76% of the APR phenotypic variance. This QTL is flanked by two SNP markers, GMI_GBS_90753 and GMI_ES14_c1439_83. QPc.crc-14D was validated in the populations AC Medallion/MN841801 and Makuru/MN841801.ConclusionsWe report the first APR QTL in oat with a large and consistent effect. QPc.crc-14D was statistically significant in all environments tested in each of the three oat populations. QPc.crc-14D is a suitable candidate for use in marker-assisted breeding and also an excellent target for map-based cloning. This is also the first study to use the 90 K wheat Infinium SNP array on oat for marker development and comparative mapping. The Infinium SNP array is a useful tool for saturating oat maps with markers. Synteny with wheat suggests that QPc.crc-14D is orthologous with the stripe rust APR gene Yr16 in wheat.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-014-0250-2) contains supplementary material, which is available to authorized users.

The jack of all trades is master of none: a pathogen's ability to infect a greater number of host genotypes comes at a cost of delayed reproduction.

A trade-off between a pathogen's ability to infect many hosts and its reproductive capacity on each host genotype is predicted to limit the evolution of an expanded host range, yet few empirical results provide evidence for the magnitude of such trade-offs. Here, we test the hypothesis for a trade-off between the number of host genotypes that a fungal pathogen can infect (host genotype range) and its reproductive capacity on susceptible plant hosts. We used strains of the oat crown rust fungus that carried widely varying numbers of virulence (avr) alleles known to determine host genotype range. We quantified total spore production and the expression of four pathogen life-history stages: infection efficiency, time until reproduction, pustule size, and spore production per pustule. In support of the trade-off hypothesis, we found that virulence level, the number of avr alleles per pathogen strain, was correlated with significant delays in the onset of reproduction and with smaller pustule sizes. Modeling from our results, we conclude that trade-offs have the capacity to constrain the evolution of host genotype range in local populations. In contrast, long-term trends in virulence level suggest that the continued deployment of resistant host lines over wide regions of the United States has generated selection for increased host genotype range.

Are fungicide applications to control crown rust of oat beneficial?

May, W. E., Ames, N., Irvine, R. B., Kutcher, H. R., Lafond, G. P. and Shirtliffe, S. J. 2014. Are fungicide applications to control crown rust of oat beneficial? Can. J. Plant Sci. 94: 911–922. Crown rust (Puccinia coronata Corda f. sp. avenae Eriks.) negatively impacts seed quality and yield in oat (Avena sativa L.) in rust-prone areas of eastern Saskatchewan, Manitoba, Ontario, and Quebec. Genetic resistance is the primary means for controlling this disease, but early seeding and fungicide applications have been suggested to reduce yield losses. Trials were conducted in six locations in Saskatchewan and Manitoba in 2009–2011 to determine the interactions between cultivar, fungicide application, crown rust and seeding date. The cultivars were chosen to represent a range of resistance to the current races of crown rust: AC Morgan, very susceptible; CDC Orrin, susceptible; CDC Boyer, partially resistant; and Leggett, resistant. Crown rust severity varied among locations and cultivars. The sprayed flag and penultimate leaves of AC Morgan tended to have similar amounts of crown rust as the unsprayed leaves of CDC Boyer and CDC Orrin regardless of the level of crown rust infection. Leggett's yield and quality did not respond to fungicide application. Only AC Morgan consistently benefited from a fungicide application. At high crown rust sites fungicide application improved AC Morgan's yield by 17 to 27% (690 kg ha−1 to 781 kg ha−1). Delayed seeding reduced grain yield from 8 to 26% with 8% occurring at low crown rust sites and the largest reductions occurring at high crown rust sites in susceptible cultivars. The test weight of AC Morgan increased from 242 g 0.5 L−1 to 255 g 0.5 L−1 when fungicide was applied at high crown rust sites seeded in mid-May. Fungicide application did not change the test weight of Leggett. The β-glucan level was affected more by seeding date (0.4%) and cultivar (0.4%) than fungicide application (0.1%). Seeding a cultivar with better crown rust resistance than AC Morgan in mid-May eliminated most of the benefits derived from fungicide application. These results indicate that prophylactic fungicide applications are unlikely to provide yield improvement when early planting is combined with even a moderately disease-resistant cultivar.