Crown Rust Severity Research Articles

Predictive ability of perennial ryegrass spaced‐plant nurseries for turfgrass and seed production swards in Minnesota

AbstractTurf‐type perennial ryegrass (Lolium perenne L.) success depends on adequate turfgrass quality and economical seed yield. In most breeding programs, spaced plants are the initial unit of selection in which observations of related individuals dictate the selection of superior germplasm for further testing. Therefore, spaced plants must be predictive of seed production and turfgrass growing environments. This study investigated the effectiveness of standard (three plants m−2) and competitive (23 plants m−2) spaced‐plant nurseries as selection environments with respect to two sward environments as well as applying a novel image analysis technique for several key traits. Seed production, turfgrass, and the two spaced‐plant growing environments were tested at two locations in Minnesota. Turfgrass quality traits were measured in 2017 and 2018 and seed production traits were measured in 2018. Automated image analysis was able to predict the traditional visual scoring values at both locations for crown rust (Puccinia coronata f.sp. lolii) severity [Pearson's correlation (rp) > 0.79, P < .001], winter injury (rp > 0.89, P < .001), and turfgrass texture (rp > 0.88, P < .001). Increasing the competition among spaced plants altered the plant phenotype and improved accuracy for vegetative biomass, crown rust severity, seed yield, and, at one location, turfgrass quality. There was no benefit of increasing competition for several traits such as genetic color, fertile tillers, and spikelet number. Although the competitive design was not useful for all traits, pragmatically, the competitive design used less space and often made measurements and observations easier for bunch‐type grasses.

The fungal endophyte Epichloë festucae var. lolii plays a limited role in mediating crown rust severity in perennial ryegrass

AbstractPerennial ryegrass (Lolium perenne L.) is an important turf and forage species that often becomes infected with Puccinia coronata f. sp. lolii, the causal pathogen of crown rust. Disease control through clavicipitaceous endophytes has been proposed as a potential biocontrol. Two field experiments were designed to determine the influence of native Epichloë endophyte infection on natural rust development across a diverse panel of perennial ryegrass germplasm. Experiment 1 used an isogenic population design in which infected (E+) or endophyte‐free (E−) clonal plants were nested within 14 perennial ryegrass entries. Experiment 2 consisted of isofrequent E+ and E− progeny from isogenic parents. Results showed the endophyte had no consistent main effect on crown rust severity among or within entries; however, several isogenic host pairs did show either favorable or antagonistic effects. Despite these sporadic effects, no differences were found between isofrequent family pairs, indicating the presence of a host × endophyte interaction. Genotypic and phenotypic data revealed that endophyte isolates were similar within entry, indicating that host genotype could be responsible for the highly specific endophyte effect on crown rust. The preponderance of host resistance in mediating rust severity was supported by large broad (>.75) and narrow‐sense (.76) heritability estimates. These findings support the conclusion that endophyte infection does not play a substantial role in mediating crown rust severity on a population scale in perennial ryegrass.

Preserving Spring Oat Yields in New York Through Varietal Resistance to Crown Rust

Crown rust is the principal disease of spring oat in New York. Management with resistance genes is effective but contingent on understanding varietal responses to local pathogen populations. Field studies were conducted from 2015 to 2018 to assess the crown rust susceptibility of commercial cultivars and public breeding lines under natural conditions in New York. Three of the 10 commercial varieties trialed were determined to be resistant, and breeding lines from five different states also exhibited resistance. On average, yield was reduced by 34.56 kg/ha for every 1% increase in crown rust severity, whereas the impact on test weight was negligible. A race differential panel was deployed in 2018 at a central screening nursery to determine the range of pathogen virulence present. Susceptible interactions were observed on only five crown rust differentials, and virulence on all five has been recorded at high levels across the country. Crown rust may be a limiting factor to oat production in New York, but yield potential and crop value can be preserved by planting an appropriately resistant variety.

Using R‐Based Image Analysis to Quantify Rusts on Perennial Ryegrass

Core Ideas An automated open‐source analysis system was developed to rate crown and stem rust. The system was validated against manual measurements and visual rater ability. Consistency in rater (n = 9) ability was excellent for crown rust and fair to good for stem rust. Agreement in rater scores for individual images was low and showed high levels of variation. The automated system can replace visual rating of crown rust in the field but not stem rust. Crown and stem rust are major diseases of perennial ryegrass (Lolium perenne L.). Plant breeders and pathologists often rate rust severity in the field using the modified Cobb scale, but this method is subjective and labor intensive. A novel, open‐source system using ImageJ and R was developed to quantify pustule number and area using digital images collected from spaced plants in the field. The computer‐processing pipeline included development of training data for prediction of pixel identity using random forest and noise reduction spatial processing. Raters and the computer scored rust severity on plant images of varying complexity including whole‐plant (WP), five‐leaf (FL), and single‐leaf (SL) image series. Computer accuracy was determined using the SL, while the FL series gave insight into the true value of WP severity. Rater ability was assessed using a panel of nine scientists with varying levels of disease rating experience. Results showed rater perceptions of crown rust severity were very consistent across images, but agreement on severity values for a given image were low. Rater consistency for stem rust severity was low and FL scores were not strongly correlated with WP scores (r = 0.36, P = 0.03), indicating low rater accuracy. The computer‐processing pipeline was able to accurately discriminate, count, and quantify crown and stem rust pustules on leaf samples. Correlations between computer and the median rater score for crown rust were excellent (r > 0.90, P < 0.001) for all image series. Similar to raters, there was a lack of correlation between WP and FL series (r = 0.20, not significant) indicating that this technique is limited to leaf or stem samples for stem rust and not applicable to WP. However, the computer‐processing pipeline shows promise in replacing visual rating of WP for crown rust.

Multi-Environmental Trials Reveal Genetic Plasticity of Oat Agronomic Traits Associated With Climate Variable Changes.

Although oat cultivation around the Mediterranean basin is steadily increasing, its yield in these regions lags far behind those of Northern Europe. This results mainly from the poor adaptation of current oat cultivars to Mediterranean environments. Local landraces may act as reservoirs of favorable traits that could contribute to increase oat resilience in this region. To aid selection of suitable agro-climate adapted genotypes we integrated genome-wide association approaches with analysis of field assessed phenotypes of genetic variants and of the weight of associated markers across different environmental variables. Association models accounting for oat population structure were applied on either arithmetic means or best linear unbiased prediction (BLUPs) to ensure robust identification of associations with the agronomic traits evaluated. The meta-analysis of the six joint environments (mega-environment) identified several markers associated with several agronomic traits and crown rust severity. Five of these associated markers were located within expressed genes. These associations were only mildly influenced by climatic variables indicating that these markers are good candidates to improve the genetic potential of oat under Mediterranean conditions. The models also highlighted several marker-trait associations, strongly affected by particular climatic variables including high rain pre- or post-heading dates and high temperatures, revealing strong potential for oat adaptation to specific agro-climatic conditions. These results will contribute to increase oat resilience for particular climatic conditions and facilitate breeding for plant adaptation to a wider range of climatic conditions in the current scenario of climate change.

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.

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.

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.

Screening for Resistance to Crown Rust in Oat Genotypes through Morphological and Molecular Parameters

A collection of 20 oat genotypes from different sources were evaluated in small isolated field plots for crown rust severity in natural epidemics with virulent P. coronata isolates and further screened with linked molecular markers. Large variation was observed for disease severity under field conditions in spreader plot. Genotypes with partial resistance due to a reduction of disease severity in spite of a compatible interaction (rust score 3) and moderate susceptibility were identified. The twenty genotypes displaying the variable disease severity with visible necrosis were selected for further studies regarding presence or absence of major genes (Pc91 and Pc68) for resistance to crown rust. In field nurseries, on the basis of latency period and disease severity (DS) none of the twenty genotypes fell into the resistant pool (score 1). Most of them showed a prolonged latency period, reduced infection frequency and colony size, and increased percentage of early aborted colonies not associated with host cell necrosis. Result on screening for crown rust resistance in field screening and by linked markers showed the absence of major resistance gene in the target population, several advance lines were identified as moderately resistant to crown rust reaction.

Crown Rust Development and Selection for Virulence in Puccinia coronata f. sp. avenae in an Oat Multiline Cultivar.

Crown rust, caused by Puccinia coronata f. sp. avenae is the most important disease of cultivated oat in North America. Numerous race-specific (Pc) genes for crown rust have been found in Avena spp. but this type of resistance has not been durable when used in oat cultivars. Increasing diversity for resistance within a crop by the use of multiline cultivars or varietal mixtures has been proposed as a means of achieving durable resistance to highly variable pathogens such as P. coronata f. sp. avenae. Multiline cv. E77 was evaluated over multiple seasons in the University of Minnesota buckthorn nursery in St. Paul. Buckthorn (Rhamnus cathartica, the alternate host of P. coronata) supports a sexually recombining, highly diverse crown rust population in the St. Paul nursery. Crown rust severity on flag leaves was measured multiple times on E77 and its 10 component lines during grain filling. Single-urediniospore isolates taken from crown rust samples during early stages of the epidemic and at the end of the epidemic were tested for virulence on the 10 component lines of E77 in greenhouse seedling tests. Crown rust development was reduced in E77 compared with the weighted mean of the component lines at all stages of the crown rust epidemics. The mean virulence of single-urediniospore isolates tended to increase late in the epidemic on E77. These data suggest that multilines may select for complex virulence or "super races" and any resistance effect may not be durable.

Physiologic specialization of Puccinia coronata f. sp. avenae, the cause of oat crown rust, in Canada from 1999 to 2001

Crown rust [Puccinia coronata f. sp. avenae] of oat (Avena sativa) was light in southern Manitoba in July in all 3 years during 1999–2001, but by mid-August in 1999 and 2001, heavy crown-rust infections (up to 90% severity) were found in late-planted fields of susceptible oat cultivars and in wild oat (Avena fatua) in Manitoba and eastern Saskatchewan. An important change in 2001 from previous years was the large increase in crown-rust severity (up to 90%) in late-planted fields of 'Triple Crown'. Crown-rust severity remained low on 'AC Assiniboia' during 1999–2001. Using 18 differential oat lines, the number of virulence phenotypes identified in the eastern prairies was 113 from 316 isolates in 1999, 111 from 260 isolates in 2000, and 112 from 217 isolates in 2001. From Ontario, 11 virulence phenotypes were identified from 25 isolates in 1999, 26 from 60 isolates in 2000, and 17 from 26 isolates in 2001. The Ontario and prairie rust populations were dominated by isolates having virulence to Pc38 and Pc39 combined. Virulence frequency to genes Pc68 and Pc96 ranged between 0.9% and 2.8% in the eastern prairies. Virulence to Pc48 increased from 3.8% in 1999 to 22.6% in 2001 in the eastern prairies and decreased from 28.0% in 1999 to 7.7% in 2001 in Ontario. No virulence was detected to Pc94 in Ontario or in the eastern prairies and to Pc58 in Ontario in all 3 years. Isolates with virulence to gene combinations Pc68, Pc96 and Pc48, Pc68 were identified for the first time in the eastern prairie region in 1999 and 2000, respectively.

Oat Lines with Effective Adult Plant Resistance to Crown Rust.

Race-specific resistance in oat does not provide adequate protection against crown rust because new virulent races of the pathogen often arise within a few years after cultivars with race-specific resistance are released. This study assessed levels of partial resistance in a series of experimental oat lines that showed reduced crown rust severity over 30 years of exposure to a diverse crown rust population. Oat breeding lines with putative adult plant slow-rusting resistance to Puccinia coronata were evaluated in small isolated field plots for crown rust severity in natural epidemics and in controlled inoculations in the greenhouse for infection efficiency with a single virulent P. coronata isolate. Lines were also tested as seedlings against isolates from a local P. coronata population to detect race-specific resistance. In field tests, areas under the disease progress curves for all 14 experimental lines tested were significantly less than for cv. Starter, the susceptible check, and values for nine of the lines were significantly less than for Portage, a standard slow-rusting cultivar. Four lines with good field resistance were susceptible as seedlings to >85% of the local P. coronata population. One of the lines, MN841801, remained relatively free of rust in field plots over 7 years of tests, even in the 3 years when Starter was destroyed by crown rust. In greenhouse inoculations, adult plants of MN841801 developed only 7% as many uredinia as Starter. MN841801 can be an excellent source of effective, durable adult plant resistance to crown rust.

Severidade da ferrugem-da-folha e seus efeitos sobre caracteres da panícula de aveia

A ferrugem-da-folha (Puccinia coronata f.sp. avenae) foi quantificada em quatro populações F3 de aveia (Avena sativa L.) com o objetivo de estudar a severidade dessa moléstia e seus efeitos sobre seis caracteres da panícula. As populações utilizadas foram UFRGS 881920 x UFRGS 7, UFRGS 881920 x UFRGS 14, UFRGS 15 x UFRGS 7 e UFRGS 15 x UFRGS 14, sendo os genótipos UFRGS 881920 e UFRGS 15 resistentes à moléstia e os demais suscetíveis. A ferrugem-da-folha foi quantificada na época do florescimento, e próximo à maturação foram colhidas, em cada população, 10 plantas ao acaso por nota de ferrugem nas quais foram feitas as seguintes determinações: número de panículas, peso médio de panículas, número de grãos por planta e por panícula, peso de grãos e peso de mil grãos. A variabilidade em relação à severidade da ferrugem-da-folha foi analisada mediante a distribuição de freqüências das notas em cada população. A avaliação dos efeitos da moléstia sobre os caracteres da panícula foi feita pela análise de variância, análise de regressão polinomial e correlações fenotípicas. Os resultados obtidos demonstram haver ampla variação com respeito à severidade da moléstia nas populações estudadas, e os caracteres mais afetados foram o peso médio de panículas e o peso de mil grãos.

Yield Loss in Two Spring Oat Cultivars due toPuccinia coronataf. sp.avenaein the Presence or Absence of Barley Yellow Dwarf Virus

Individual studies were done to estimate yield loss due to Puccinia coronata f. sp. avenae (crown rust) in the presence or absence of barley yellow dwarf virus (BYDV-PAV-IL) for two spring oat cultivars at two locations. Crown rust disease severity was assessed several times and related to yield and yield components. Linear critical point regression models were developed with analysis of covariance. Yield loss for each percent increase in crown rust severity (modified Cobb scale A) was 56,7 kg/ha for cv. Noble and 46.0 kg/ha for cv. Ogle. Test weight decrease for each percent increase in crown rust severity was 1.2 kg/m 3 for Noble and 1.1 kg/m 3 for Ogle. Ogle exhibited tolerance to yield loss from crown rust [...]

Effect of Crown Rust on Protein and Groat Percentages of Oat Grain 1

Lines of oats (Arena sativa L.) in breeding nurseries at Madison, Wis. ranged from highly resistant to highly susceptible to infection by crown rust (Puccinia coronata Cda.). The correlation between crown rust severity (as percentage of leaf area affected) and the protein percentage of the grain averaged −0.470 over a 3-year period. Forty oat lines at Ames, Iowa ranged from moderate to high in susceptibility, as measured by the relative reduction in yield and seed weight caused by crown rust. With extremely high levels of infection, these strains showed significant variation in response of protein and groat percentages to infection. A significant reduction in protein percentage occurred in one strain and significant increases in protein percentages occurred in five other strains. Overall, the effect of crown rust on protein percentage was negatively correlated with its effects on yield (r=−0.362) and seed weight (r=−0.421). The effects crown rust on protein and groat percentages of the different lines, as measured in diseased plots, were not significantly correlated with either the inherent yields or the inherent protein percentages of the lines in unrusted control plots. This suggests that selection in breeding programs for high yield and high protein percentage could be carried out readily in conjunction with selection for crown rust resistance. The heritabilities of the effects of crown rust on protein and groat percentages were 81 and 91%, respectively.