Genetic Variation and Genotype by Environment Interaction of Crown Rust Resistance in Annual Ryegrass (\u3ci\u3eLolium multiflorum\u3c/i\u3e Lam.)

The genetic variation and genotype by environment interaction of crown rust resistance of annual ryegrass (Lolium multiflorum Lam.) was evaluated at two locations in Argentina, as part of the breeding programme in progress at our Institute. Forty half sib families originated from commercial tetraploid cultivars, were grown from seeds in a greenhouse during autumn 1999. At the stage of tillering initiation forty eight plants/familiy were randomly selected and transplanted as spaced plant trial in a randomized design with three replicates, at the two locations. All plants were scored for a range of morphological and phytopatological attributes. The severity of crown rust and the winter dry matter production were assessed on each plant. Crown rust resistance at both evaluation dates, was highly heritable and not affected by environment interaction. By contrast, winter dry matter showed a large family by location interaction and a high environmental influence. The results of the present study indicated that important progress in crown rust resistance in annual ryegrass can be achieved through phenotypic recurrent selection

Identification of genomic loci associated with crown rust resistance in perennial ryegrass (Lolium perenne L.) divergently selected populations

The inheritance of crown rust resistance in perennial ryegrass is complex with both major and minor quantitative trait loci (QTL) being detected on all seven linkage groups. However, QTL mapping populations have only few segregating alleles, limiting the transferability of results to other materials. In this study, a synthetic population was developed from four crown rust resistant and susceptible parents as starting material for a divergent selection experiment of crown rust resistance to be closer to practice in plant breeding programs, and to identify genome regions relevant across a broader range of genotypes. Following three cycles of directional selection, perennial ryegrass populations were produced with a two-fold difference in average rust resistance. Divergently selected populations were genotyped at 7 resistance gene analog-derived expressed sequence tag (RGA-derived EST) as well as 15 simple sequence repeat (SSR) loci. A test for selective neutrality (Waples test), which tests the hypothesis of genetic drift versus selection, identified significant differences in allele frequencies for 7 loci (32%). The selection effect was bidirectional with the same loci showing significant response in both positively and negatively selected populations. A region under selection represented by markers LpSSR006 and EST13 on linkage group (LG) 4 was further confirmed by colocation with two separate QTL for crown rust resistance in a VrnA, a two-way pseudo-testcross mapping population. This suggests suitability of alleles identified for introgression into perennial ryegrass germplasm, where quantitative resistance to crown rust is desired

Genetic Relationships of Crown Rust Resistance, Grain Yield, Test Weight, and Seed Weight in Oat

Integrating selection for agronomic performance and quantitative resistance to crown rust, caused by Puccinia coronata Corda var. avenae W.P. Fraser & Ledingham, in oat (Avena sativa L.) requires an understanding of their genetic relationships. This study was conducted to investigate the genetic relationships of crown rust resistance, grain yield, test weight, and seed weight under both inoculated and fungicide-treated conditions. A Design II mating was performed between 10 oat lines with putative partial resistance to crown rust and nine lines with superior grain yield and grain quality potential. Progenies from this mating were evaluated in both crown rust-inoculated and fungicide-treated plots in four Iowa environments to estimate genetic effects and phenotypic correlations between crown rust resistance and grain yield, seed weight, and test weight under either infection or fungicide-treated conditions. Lines from a random-mated population derived from the same parents were evaluated in three Iowa environments to estimate heritabilities of, and genetic correlations between, these traits. Resistance to crown rust, as measured by area under the disease progress curve (AUDPC), was highly heritable (H = 0.89 on an entry-mean basis), and was favorably correlated with grain yield, seed weight, and test weight measured in crown rust-inoculated plots. AUDPC was unfavorably correlated or uncorrelated with grain yield, test weight, and seed weight measured in fungicide-treated plots. To improve simultaneously crown rust resistance, grain yield, and seed weight under both lower and higher levels of crown rust infection, an optimum selection index can be developed with the genetic parameters estimated in this stud

Crown Rust Resistance of Italian Ryegrass Cultivar ‘Axis’ to an Isolate from Japan

Crown rust (Puccinia coronata) is one the most serious diseases of Italian ryegrass. Crown rust resistance genes in Italian ryegrass have been identified from \u27Yamaiku130\u27 and ‘Harukaze’. The aim of this study was to identify novel major resistance genes for gene pyramiding in order to develop cultivars with high levels of durable resistance to crown rus

Genomic prediction of crown rust resistance in Lolium perenne

peer-reviewedBackground Genomic selection (GS) can accelerate genetic gains in breeding programmes by reducing the time it takes to complete a cycle of selection. Puccinia coronata f. sp lolli (crown rust) is one of the most widespread diseases of perennial ryegrass and can lead to reductions in yield, persistency and nutritional value. Here, we used a large perennial ryegrass population to assess the accuracy of using genome wide markers to predict crown rust resistance and to investigate the factors affecting predictive ability. Results Using these data, predictive ability for crown rust resistance in the complete population reached a maximum of 0.52. Much of the predictive ability resulted from the ability of markers to capture genetic relationships among families within the training set, and reducing the marker density had little impact on predictive ability. Using permutation based variable importance measure and genome wide association studies (GWAS) to identify and rank markers enabled the identification of a small subset of SNPs that could achieve predictive abilities close to those achieved using the complete marker set. Conclusion Using a GWAS to identify and rank markers enabled a small panel of markers to be identified that could achieve higher predictive ability than the same number of randomly selected markers, and predictive abilities close to those achieved with the entire marker set. This was particularly evident in a sub-population characterised by having on-average higher genome-wide linkage disequilibirum (LD). Higher predictive abilities with selected markers over random markers suggests they are in LD with QTL. Accuracy due to genetic relationships will decay rapidly over generations whereas accuracy due to LD will persist, which is advantageous for practical breeding applications.This work received funding from the Irish Department of Agriculture Food and the Marine DAFM (RSF 11/S/109) and Teagasc core funding. SKA is supported by a Teagasc PhD Walsh Fellowship. SLB has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 658031

A Glucanase Gene Cosegregates with a QTL for Crown Rust Resistance in \u3cem\u3eL. Perenne\u3c/em\u3e

An important disease in Lolium spp. is crown rust caused by the fungal pathogen Puccinia coronata. In order to study the genetic background of crown rust resistance in L. perenne, a mapping study was carried out and is discussed below. To identify genomic regions or genes involved in resistance, STS markers are extremely useful. This candidate gene approach was applied in the present study

Reaction of North American Oats (Avena sativa L.) to Crown Rust

Crown rust, caused by the fungus Puccinia coronata, is a severe disease negatively impacting seed quality and yield in oat (Avena sativa). Host genetic resistance is the primary means for controlling this disease. The most extensive oat map contains nearly 2,500 genetic markers, many of which are restriction and amplified fragment length polymorphic (RFLP or AFLP) markers. However, the use of more abundant single nucleotide polymorphic (SNP) markers combined with diversity arrays technology (DArT) would be more advantageous for marker assisted breeding (MAB) and genome wide selection (GWS) applications due to the availability of high density genotyping technologies. The purpose of using this technology is to improve the competitiveness of oat by producing varieties with durable resistance to crown rust and desirable traits that will benefit oat growers in the U.S. Panels of winter and spring oat were evaluated for resistance to crown rust in four field environments in Texas, Louisiana, Minnesota, and North Dakota during a two-year study in 2010 and 2011. Plants representing 702 elite lines of oat were phenotyped for crown rust resistance and found to have highly diverse responses. The winter oat lines demonstrated the best crown rust resistance and are expected to yield the most QTL to be used in developing durable crown rust resistance. Heritability of crown rust resistance in this study ranged from 0.88 to 0.90 in spring and winter oats, respectively. Crown rust measurements were also found to be repeatable. Repeatability ranged from 0.56 to 0.88 at Castroville, TX in 2011 and 2010, respectively in spring oats and from 0.79 at St. Paul, MN in 2011 to 0.96 at Castroville, TX in 2010 in winter oats. Oat lines contributed by states along the Puccinia pathway in Texas, Louisiana, Minnesota, North Dakota, and Wisconsin on average exhibited the best crown rust resistance as compared to other areas in the country where spring and winter oat are grown. GGE biplot analysis indicated that Castroville, TX was the most representative and most ideal testing location. The above results are expected to increase knowledge of the genetic diversity of the oat germplasm, yield comprehensive genotyping and phenotyping information for North American oat breeding programs, and to promote further use of GWS and MAB for key traits regarding disease resistance in oat. Future work is to conclude the association mapping process by completing genotypic analysis

Responses to Selection for Partial Resistance to Crown Rust in Oat

Crown rust, caused by the fungal pathogen, Puccinia coronata Corda var. avenae W.P. Fraser Ledingham, reduces kernel quality and grain yield in oat (Avena sativa L.). Partial resistance is considered to be a durable form of rust resistance. This study sought to evaluate the feasibility of simultaneously improving partial resistance to crown rust, grain yield, and seed weight in an oat population, and to estimate predicted and realized heritabilities for area under disease progress curve (AUDPC) and genetic correlations between AUDPC and agronomic traits in both crown rust-inoculated and fungicide-treated plots. A single cycle of selection for partial resistance to crown rust was performed. The initial (C0) and selected (C1) generations were evaluated in a field experiment in 2001 and 2002 at two Iowa locations. Selection on an index increased the levels of crown rust resistance, grain yield, and seed weight in crown rust−inoculated plots, and seed weight in fungicide-treated plots. However, the change for the grain yield in fungicide-treated plots was not significant. In both C0 and C1 populations, AUDPC was highly heritable (H = 0.77 and 0.78 respectively), and was favorably correlated with grain yield, seed weight, and test weight measured in inoculated plots. Realized heritabilities for all traits except grain yield under fungicide treatment were consistent with predicted heritabilities. Our results suggested that index selection could increase levels of crown rust resistance, grain yield, and seed weight simultaneously

Selection for partial resistance to crown rust in oat

Crown rust, caused by the fungal pathogen, Puccinia coronata, severely reduces kernel quality and grain yield in oat. Partial resistance is considered to be a durable form of rust resistance. The objectives of this study were to evaluate the effectiveness of index selection as a method for improving partial resistance to crown rust, grain yield and seed weight in oat population, and to estimate heritabilities for area under disease progress curve (AUDPC) and genetic correlations between AUDPC and agronomic traits in both crown rust-inoculated and fungicide-treated plots. A single cycle of selection for partial resistance to crown rust was performed. The initial (CO) and selected (Cl) generations of two oat populations were evaluated in a field experiment in 2001 and 2002 at two Iowa locations. The selection, via a selection index, increased the levels of crown rust resistance and grain yield and seed weight in crown rust-inoculated plots, and seed weight in fungicide-treated plots. However, there was no significant change for the grain yield in the disease-free environment. In both CO and Cl population, AUDPC were highly heritable, and were favorably correlated with grain yield, seed weight and test weight measured in crown rust-treated plots. Realized heritabilities for all traits but grain yield under the disease-free environment were relatively high. Our results suggested that the index selection as a method for selecting oat lines with high levels of crown rust resistance, grain yield and seed weight is possible