Rust Isolates Research Articles

Differential Susceptibility of Diverse Salix spp. to Melampsora americana and Melampsora paradoxa.

Melampsora spp. willow rust is the most serious disease of shrub willow bioenergy production in the northeastern United States. Recent phylogenetic studies have identified several Melampsora spp. present on willow in the Northeast; however, in-depth understanding of Melampsora spp. host susceptibility remain unresolved. In this study, a panel of 82 rust isolates collected from the northeastern United States were genotyped via ribosomal DNA sequencing and a subset of these isolates were assayed for host susceptibility. This work revealed that Melampsora americana is the most prevalent species in the sampled geographic region and that there is potential for rust resistance breeding using the Salix spp. taxa assayed. Additionally, leaf morphology traits of these Salix spp. hosts were quantified for correlation analysis, revealing that trichome density and stomata density are possible contributors to resistance. This work provides foundational rust pathology information, which is crucial for M. americana resistance breeding.

Genetic diversity of Puccinia kuehnii, the causal agent of orange rust of sugarcane, from Brazil

AbstractThe use of resistant genotypes is the preferred method to control orange rust of sugarcane (Saccharum spp) caused by Puccinia kuehnii. This approach has been adopted in Brazil but outbreaks of the disease on previously resistant varieties showed that the efficacy of this method is limited and requires a better understanding of pathogen diversity. Nevertheless, adequate molecular markers for examining pathogen diversity at population level are not available, which limits the success of orange rust control by genetic resistance. Therefore, two independent investigations were conducted to examine genetic diversity of P. kuehnii from São Paulo state, the most important sugarcane growing state of Brazil. First, simple‐sequence repeat (SSR) markers were developed in the present work and genotypic diversity of orange rust isolates from different locations investigated. Second, phenotypic diversity was examined by the single‐pustule inoculation technique on P. kuehnii isolates retrieved from three susceptible commercial sugarcane cultivars. A total of 96 SSR markers were generated and tested for this species. Subsequently, 29 isolates of P. kuehnii were fingerprinted with nine SSR markers to estimate the genotypic diversity by neighbour‐joining and 3D principal coordinates. The 29 isolates of the pathogen clustered into four main groups, which were identified by three SSR markers (NPRL_PK_108a, NPRL_PK_162_spka and NPRL_PK_221_spka). Phenotypic data at 21 days after the single‐pustule inoculation showed that P. kuehnii from highly susceptible commercial cultivars harboured a small proportion of variants capable of causing disease on resistant cultivars. A differential reaction was demonstrated for the most virulent variant in a repeated experiment confirming the existence of races within P. kuehnii in Brazil.

Near-isogenic soybean lines carrying Asian soybean rust resistance genes for practical pathogenicity validation

Asian soybean rust caused by the fungal pathogen Phakopsora pachyrhizi is the most devastating disease of soybean. The host cultivar specificity of the pathogen shows considerable differentiation depending on the area and season of its emergence. Although resistance genes for P. pachyrhizi (Rpp) have been reported in several soybean varieties, the genetic background of these varieties is highly differentiated. Furthermore, some of the varieties harbor unknown genetic factors in addition to Rpp that could influence resistance reactions against the pathogen. In order to gain a comprehensive understanding of Rpp–P. pachyrhizi interactions, homogenous plant material harboring Rpp genes is necessary. In this study, we bred Rpp-near isogenic lines (Rpp-NILs), which retained identical plant characters originating from a single genetic background, and accordingly showed low-variant compatible/incompatible reactions against the pathogen. These Rpp-NILs can be used as genetic resources for studying P. pachyrhizi epidemiology and elucidating resistance mechanisms. Compatible/incompatible relationships between the soybean rust resistance gene Rpp and isolates of the pathogen P. pachyrhizi are clearly distinguishable using the Rpp-NILs bred in this study.

Wheat leaf rust (Puccinia triticina Eriks.) virulence frequency and detection of resistance genes in wheat cultivars registered in the Czech Republic in 2016-2018

In 2016–2018 virulence of the Czech wheat leaf rust population was studied on Thatcher near-isogenic lines, carrying different Lr genes, and 130 leaf rust isolates. Virulence to Lr9 was found only sporadically. Virulence frequency to Lr2a, Lr2b, Lr2c and Lr28 was lower than in previous years. All tested isolates were avirulent to Lr19. Lr24 conditioned resistance to majority of isolates. Nineteen recently registered Czech cultivars were tested with six isolates of the pathogen and Lr genes were postulated. Presence of genes Lr1, Lr10, Lr19, Lr24, Lr26, Lr28, Lr34 and Lr37 was tested by molecular markers. Lr37 prevailed, followed by Lr genes 10, 24, 28, 1 and 26; genes Lr19 and Lr34 were not determined.

Evaluation of Variation in Switchgrass (Panicum virgatum L.) Cultivars for Rust (Puccinia emaculata) Resistance1

Abstract Eleven switchgrass cultivars (eight ornamental and three agronomic) were inoculated with 40 switchgrass rust isolates collected from the southeastern U.S. to study host resistance, rust virulence and host/pathogen interactions by measuring urediniospore germination percentage, latent period, and the number of uredia and urediniospores produced per cm2 of leaf surface. In general, ornamental switchgrass cultivars had reduced number of uredia and urediniospores produced per cm2 than did agronomic cultivars. Rust isolates were variable for virulence in culture (on grass blades in petri dishes); however they could not be segregated into groups based on collection locations or years. The results of this study will provide information concerning durable horizontal resistance in switchgrass for the ornamental industry. Index words:, Switchgrass, leaf rust, resistance. Species used in the study: switchgrass (Panicum virgatum L., rust (Puccinia emaculata).

Pyramiding three rust‐resistance genes confers a high level of resistance in soybean (Glycine max)

AbstractPyramiding Asian soybean rust (ASR) resistance (Rpp) genes in a single genotype has been shown to increase ASR resistance in soybean. However, it remains unclear which combinations of Rpp genes are superior. Therefore, here, we developed six new Rpp‐pyramided lines carrying different combinations of Rpp genes and evaluated their resistance against 13 Bangladeshi rust (Phakopsora pachyrhizi) isolates (BdRPs) alongside seven previously developed Rpp‐pyramided lines. We found that lines carrying one, two and three Rpp genes had high ASR resistance without sporulation in 13.8%, 35.2% and 73.1% of the assays, respectively. Among the new lines that were developed, those with Rpp3 + Rpp4 and Rpp3 + Rpp4 + Rpp5 had high levels of ASR resistance, while the line containing Rpp2 + Rpp4 + Rpp5 showed immunity phenotype at two weeks after inoculation by the BdRP‐22 infection. Thus, pyramiding larger numbers of Rpp genes confers soybean with a higher level of resistance to ASR pathogens and can produce an immunity phenotype at two weeks after inoculation.

دامنهی میزبانی جمعیتهای مختلف زنگ برگی گندم در ایران

In order to investigate the host range of various populations of causal agent of wheat leaf rust, Puccinia. recondita sensu lato, during 2010-2016, fifty isolates of the pathogen were collected from different hosts of Poaceae in various parts of Iran including: Ardabil, Fars, Golestan, Ilam, Kerman, Khuzestan, Khorasan Razavi, Kurdistan, Mazandaran and West Azerbaijan. Pathogenicity of all isolates on seven hosts, including bread wheat (Triticum aestivum L., cv. Boolani), durum wheat (Triticum durum Desf., cv. Karkhe & cv. Yavaroos), barley (Hordeum vulgare L., cv. Afzal), oat (Avena sativa L.), rye (Secale montanum Guss.) and triticale (Triticosecale Wittm. Ex A. Camus) was examined. Results indicated that all isolates had high disease severity on bread wheat (cv. Boolani) and triticale. Bread wheat isolates were avirulent on all hosts except for triticale, which showed a hypersensitive reaction or small, dispersed pustules. Triticale isolates were only pathogenic on triticale and bread wheat. Durum wheat isolates were virulent on bread wheat, durum wheat, and triticale, and were avirulent on barley and rye plants. Oat isolates showed an avirulence response on barley, rye and various genotypes of durum wheat and rye. Barley isolates were also pathogenic on bread wheat, triticale and barley and avirulent on durum wheat and rye. Although wild barley isolates were virulent on bread wheat, durum wheat, and triticale, they were avirulent on other hosts. Oat is a non-host for all leaf rust isolates, except for its own isolates. The findings indicate that in the absence of wheat, leaf rust populations are able to survive on other members of the Poaceae family.

Mapping Oat Crown Rust Resistance Gene Pc45 Confirms Association with PcKM.

Molecular mapping of crown rust resistance genes is important to effectively utilize these genes and improve breeding efficiency through marker-assisted selection. Pc45 is a major race-specific crown rust resistance gene initially identified in the wild hexaploid oat Avena sterilis in the early 1970s. This gene was transferred to cultivated oat (Avena sativa) and has been used as a differential for identification of crown rust races since 1974. Previous research identified an association between virulence to Pc45 and PcKM, a crown rust resistance gene in the varieties ‘Kame’ and ‘Morton’. This study was undertaken to reveal the relationship between Pc45 and PcKM. Pc45 was studied in the crosses ‘AC Morgan’/Pc45 and ‘Kasztan’/Pc45, where Pc45 is the differential line carrying Pc45. F2 progenies and F2:3 families of both populations were inoculated with the crown rust isolate CR258 (race NTGG) and single gene segregation ratios were observed. SNP markers for PcKM were tested on these populations and linkage maps were generated. In addition, 17 newly developed SNP markers identified from genotyping-by-sequencing (GBS) data were mapped in these two populations, plus another three populations segregating for Pc45 or PcKM. Pc45 and PcKM mapped to the same location of Mrg08 (chromosome 12D) of the oat chromosome-anchored consensus map. These results strongly suggest that Pc45 and PcKM are the same resistance gene, but allelism (i.e., functionally different alleles of the same gene) or tight linkage (i.e., two tightly linked genes) cannot be ruled out based on the present data.

Pathotypic variation of Phakopsora pachyrhizi isolates from Uruguay

Soybean rust, caused by Phakopsora pachyrhizi, is one of the most important foliar diseases threatening soybean production in Uruguay. Knowledge of pathogenic variation among Uruguayan rust populations is necessary to guide development of resistant soybean cultivars in national breeding programs. To assess pathogenic variation,12 P. pachyrhizi isolates were collected from fields across the country over a four-year period and were inoculated onto a set of 12 differential soybean genotypes. All Uruguayan rust isolates (URPs) were highly virulent on differential soybean plants carrying resistance genes Rpp1, Rpp3, and Rpp4. Conversely, all isolates showed resistant reactions on soybean differentials with Rpp1-b and on a line carrying the genes Rpp2, Rpp4, and a Rpp5 allele. The pathogenic variation of the URPs was compared to that of a collection of 157 P. pachyrhizi isolates from other Latin American countries and Japan. All URPs clustered together and with other fungal isolates from South America. Of the seven different pathotypes that were found, four shared identical virulence patterns with isolates from South America, and three were associated with unique virulence patterns, which mainly resulted from the reactions they caused on plants carrying Rpp3, Rpp4 and especially Rpp6. The results indicate that the URPs can overcome the resistance of a larger number of Rpp genes than P. pachyrhizi isolates from neighboring countries. The resistant genes Rpp1-b and Rpp5 proved to be effective against the pathogen and will be introgressed into local soybean lines.

Breeding Progress in Seedling Resistance against Various Races of Stripe and Leaf Rust in European Bread Wheat

Background: Stripe and leaf rust are major constraints of wheat production with substantial impacts on grain yield. Population dynamics of both pathogens and the emergence of new virulent races have resulted in relentless efforts related to wheat breeding to improve resistance during the last decades. Methods: To evaluate the breeding progress achieved with respect to race-specific resistance, a set of nine isolates of the two rust pathogens have been tested in seedling assays on a panel of 191 elite winter wheat cultivars representing wheat breeding in Europe between 1966 and 2013. Results: Significant differences in the resistance of wheat cultivars concerning both pathogens have been detected by means of two-way ANOVA. Isolates as well as genotype × isolate interaction had a significant effect for both pathogens. Breeding progress, resulting in an increased seedling resistance, has been achieved against all nine isolates over the past five decades. The slope of progress was steeper for leaf rust than for stripe rust isolates. Progress against the highly common leaf rust isolate “4171” and” the stripe rust isolate “Warrior(-)” was strongest. Conclusions: The study reveals that a steady increase in seedling resistance was achieved during the past five decades. An additive contribution of these isolate specific R genes after breakdown has been hypothesised.

ВИРУЛЕНТНОСТЬ ПОПУЛЯЦИЙ PUCCINIA TRITICINA ERIKSS. В НЕЧЕРНОЗЕМНОЙ ПОЛОСЕ РОССИИ

As a result of surveys of wheat crops in the Moscow region in 2009-2017 there were collected 27 wheat samples leaf rust infected. Isolates from single pustule were studied by the standard method. To study the frame of leaf rust population there was used a set of 42 Lr-lines monogenic of cv. Thatcher. For the period from 2009 to 2017 there were studied for virulence 120 isolates of P. triticina. Isolates differed significantly in virulence. By virulence formulas all leaf rust isolates were attributed to 103 phenotypes, differing by one or two or several genes. During all the years of testing the population of P. triticina was showed high virulence affecting from 30 to 34 Lr-lines of wheat. Annually in the population of P. triticina there were found out 18 virulence genes with a high frequency (average 78.0-98.9%): p1, p2c, p3a, p3b, p3ka, p10, p14a, p14b, p17, p18, p21, p27 + p31, p30, p32, p33, p39, p40, pB, and 7 genes were never met: p24, p29, p41, p42, p47, p51, p53. The genes p2a, p2b, p11, p15, p20, p23, p25, p26, p46 were constantly detected in the fungus population, but their frequency varied greatly over the years (on average, from 34.5 to 72.0%). As for the genes p9, p16, p19, p28, p36, p38, p44, p45, they there were not found every year in the population of P. triticina. Depending on the stability of the isogenic Lr-line of wheat, the type reactions to disease development were differed: from high susceptibility to immunity. By the number of virulent isolates of the fungus to wheat Lr-lines there were determined the degree of effectiveness of resistance genes. Lr-genes so as Lr24, Lr29, Lr41, Lr42, Lr47, Lr51, Lr53 were effective to leaf rust. They can be recommended for breeders as donors of resistance to leaf rust.

The genetic architecture of colonization resistance in Brachypodium distachyon to non-adapted stripe rust (Puccinia striiformis) isolates.

Multilayered defense responses ensure that plants are hosts to only a few adapted pathogens in the environment. The host range of a plant pathogen depends on its ability to fully overcome plant defense barriers, with failure at any single step sufficient to prevent life cycle completion of the pathogen. Puccinia striiformis, the causal agent of stripe rust (=yellow rust), is an agronomically important obligate biotrophic fungal pathogen of wheat and barley. It is generally unable to complete its life cycle on the non-adapted wild grass species Brachypodium distachyon, but natural variation exists for the degree of hyphal colonization by Puccinia striiformis. Using three B. distachyon mapping populations, we identified genetic loci conferring colonization resistance to wheat-adapted and barley-adapted isolates of P. striiformis. We observed a genetic architecture composed of two major effect QTLs (Yrr1 and Yrr3) restricting the colonization of P. striiformis. Isolate specificity was observed for Yrr1, whereas Yrr3 was effective against all tested P. striiformis isolates. Plant immune receptors of the nucleotide binding, leucine-rich repeat (NB-LRR) encoding gene family are present at the Yrr3 locus, whereas genes of this family were not identified at the Yrr1 locus. While it has been proposed that resistance to adapted and non-adapted pathogens are inherently different, the observation of (1) a simple genetic architecture of colonization resistance, (2) isolate specificity of major and minor effect QTLs, and (3) NB-LRR encoding genes at the Yrr3 locus suggest that factors associated with resistance to adapted pathogens are also critical for non-adapted pathogens.

Fine mapping Ruv2, a new rust resistance gene in cowpea (Vigna unguiculata), to a 193-kb region enriched with NBS-type genes.

A new rust resistance gene Ruv2 was fine-mapped in cowpea to a 193-kb region on chromosome 2, which harboured 23 predicted gene models enriched with NBS-type genes. ZN016 is a landrace vegetable cowpea highly resistant to rust. Two previous studies using mixed-spores inoculation suggested different modes of inheritance of rust resistance in ZN016. In this study, we initially developed a detached leaf assay with a purified single-rust isolate (Auv-LS). Using this approach, we assessed the inheritance of rust resistance in a recombinant inbred line (RIL) population and an F2 population, both derived from the cross of "ZN016" and the susceptible cultivar "Zhijiang282." A single dominant gene mode against Auv-LS was revealed in both populations. QTL mapping showed that this gene was coincident with the Ruv2 locus on LG7, one of the three resistance QTLs previously mapped based on mixed-spores inoculation data. Therefore, Ruv2 was considered as specifically against the rust isolate Auv-LS. Through an analysis of the RIL recombinants at Ruv2, we fine-mapped the gene to an ~ 0.45-cM interval between SNP markers 2_09656 and 2_00973, which corresponded to an ~ 193-kb region on chromosome 2 that harboured 23 predicted gene models enriched with NBS-type genes. Re-sequencing of the two parents revealed polymorphisms in four genes predictively to cause substantial protein structural changes, rendering them valuable candidate genes for future validation. Cross-species syntenic analysis indicated that Ruv2 may represent a novel rust resistance gene in food legumes. A cleaved amplified polymorphic sequences marker tightly linked to Ruv2 was developed to facilitate breeding. This work establishes a basis for map-based cloning of Ruv2 and breeding for rust resistance in cowpea and other legume crops.

Simultaneous Transfer of Leaf Rust and Powdery Mildew Resistance Genes from Hexaploid Triticale Cultivar Sorento into Bread Wheat.

Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici, and wheat leaf rust, caused by Puccinia triticina Eriks, are two important diseases that severely threaten wheat production. Sorento, a hexaploid triticale cultivar from Poland, shows high resistance to the wheat powdery mildew isolate E09 and the leaf rust isolate PHT in Beijing, China. To introduce resistance genes into common wheat, Sorento was crossed with wheat line Xuezao, which is susceptible to both diseases, and the F1 hybrids were then backcrossed with Xuezao as the recurrent male parent. By marker analysis, we demonstrate that the long arm of the 2R (2RL) chromosome confers resistance to both the leaf rust and powdery mildew isolates at adult-plant and seedling stages, while the long arm of 4R (4RL) confers resistance only to powdery mildew at both stages. The chromosomal composition of BC2F3 plants containing 2R or 2RL and 4R or 4RL in the form of substitution and translocation were confirmed by GISH (genomic in situ hybridization) and FISH (fluorescence in situ hybridization). Monosomic and disomic substitutions of a wheat chromosome with chromosome 2R or 4R, as well as one 4RS-4DL/4DS-4RL reciprocal translocation homozigote and one 2RL-1DL translocation hemizigote, were recovered. Such germplasms are of great value in wheat improvement.

Pathotypes of wheat leaf rust (Puccinia triticina Eriks.) and resistance of registered cultivars in the Czech Republic in 2012-2015

In 2012–2015 the virulence of the wheat leaf rust (Puccinia triticina Eriks.) population was studied on Thatcher near-isogenic lines with Lr1, Lr2a, Lr2b, Lr2c, Lr3a, Lr9, Lr10, Lr11, Lr13, Lr15, Lr17, Lr19, Lr21, Lr23, Lr24, Lr26 and Lr28. Samples of leaf rust were obtained from different parts of the Czech Republic. A total of 163 wheat leaf rust isolates were analysed. No virulence for the resistance gene Lr9 was found. Virulence for Lr19 was found only in one isolate in 2015. A lower frequency of virulence to Lr24, Lr2a, 2b, 2c and Lr28 was also observed. The presence of Lr10, Lr24, Lr26, Lr28 and Lr37 in registered cultivars was detected by polymerase chain reaction (PCR) molecular markers.

Genetic analysis of crown rust (Puccinia coronata f. sp. lolii) resistance in a perennial ryegrass (Lolium perenne) genotype

In order to study the inheritance of resistance to crown rust (Puccinia coronata f. sp. lolii) in perennial ryegrass (Lolium perenne), we crossed a resistant, diploid genotype (A6128/05) with a susceptible genotype of the cultivar Aurora to generate a F1 population. Individuals of the F1 population were screened for their response to three single-pustule isolates (SPI) of crown rust in a detached-leaf segment test under growth chamber conditions. Out of the F1 population, we selected two genotypes (I and II) based on the reaction to SPI of crown rust: genotype I was resistant to SPI A, D and F. Genotype II was resistant to SPI A, but susceptible to SPI D and F. Both genotypes were backcrossed with a second, susceptible Aurora genotype to generate two F2 populations. A resistant genotype out of each of the two F2 populations was used to generate a F3 population by backcrossing with a susceptible Aurora genotype. In the F2 and F3 populations, derived from a cross with the genotype I, a good fit to a segregation ratio of 1R:1S (resistant:susceptible) was observed for the three SPI A, D and F. The frequency of resistant and susceptible plants within the F2 and F3 populations, derived from the genotype II, resulted in a ratio of 1R:1S for SPI A. In contrast, the F2 and F3 progeny was susceptible to SPI D and F. These results provide evidence that at least two different dominant genes for crown rust resistance occur in the resistance donor A6128/05.

Genome-Wide Association Mapping of Crown Rust Resistance in Oat Elite Germplasm.

Oat crown rust, caused by f. sp. , is a major constraint to oat ( L.) production in many parts of the world. In this first comprehensive multienvironment genome-wide association map of oat crown rust, we used 2972 single-nucleotide polymorphisms (SNPs) genotyped on 631 oat lines for association mapping of quantitative trait loci (QTL). Seedling reaction to crown rust in these lines was assessed as infection type (IT) with each of 10 crown rust isolates. Adult plant reaction was assessed in the field in a total of 10 location-years as percentage severity (SV) and as infection reaction (IR) in a 0-to-1 scale. Overall, 29 SNPs on 12 linkage groups were predictive of crown rust reaction in at least one experiment at a genome-wide level of statistical significance. The QTL identified here include those in regions previously shown to be linked with seedling resistance genes , , , , , and and also with adult-plant resistance and adaptation-related QTL. In addition, QTL on linkage groups Mrg03, Mrg08, and Mrg23 were identified in regions not previously associated with crown rust resistance. Evaluation of marker genotypes in a set of crown rust differential lines supported as the identity of . The SNPs with rare alleles associated with lower disease scores may be suitable for use in marker-assisted selection of oat lines for crown rust resistance.

Molecular Cytogenetic Characterization of Novel Wheat-rye T1RS.1BL Translocation Lines with High Resistance to Diseases and Great Agronomic Traits.

Rye has been used worldwide as a source for the genetic improvement of wheat. In this study, two stable wheat-rye primary T1RS.1BL translocation lines were selected from the progeny of the crossing of the wheat cultivar Mianyang11-1 and a Chinese local rye variety, Weining. These two novel translocation lines were identified by molecular cytogenetic analysis. PCR results, multi-color fluorescence in situ hybridization (MC-FISH), and acid polyacrylamide gel electrophoresis (A-PAGE) indicated that both new translocation lines harbor a pair of T1RS.1BL translocation chromosomes, and have been named RT828-10 and RT828-11, respectively. The cytogenetic results also indicated that the pSc119.2 signals of 5AL were absent in both lines along with the pSc119.2 signals of 4AL of RT828-11. When inoculated with different stripe rust and powdery mildew isolates, both lines expressed high resistance to Puccinia striiformis f. sp. tritici and Blumeria graminis f. sp. tritici pathotypes, which are prevalent in China and are virulent on Yr9 and Pm8. The line RT828-11 also exhibited excellent agronomic traits in the field. The present study indicates that this rye variety may carry untapped variations that could potentially be used for wheat improvement.

High-resolution mapping of genes involved in plant stage-specific partial resistance of barley to leaf rust

Partial resistance quantitative trait loci (QTLs) Rphq11 and rphq16 against Puccinia hordei isolate 1.2.1 were previously mapped in seedlings of the mapping populations Steptoe/Morex and Oregon Wolfe Barleys, respectively. In this study, QTL mapping was performed at adult plant stage for the two mapping populations challenged with the same rust isolate. The results suggest that Rphq11 and rphq16 are effective only at seedling stage, and not at adult plant stage. The cloning of several genes responsible for partial resistance of barley to P. hordei will allow elucidation of the molecular basis of this type of plant defence. A map-based cloning approach requires to fine-map the QTL in a narrow genetic window. In this study, Rphq11 and rphq16 were fine-mapped using an approach aiming at speeding up the development of plant material and simplifying its evaluation. The plant materials for fine-mapping were identified from early plant materials developed to produce QTL-NILs. The material was first selected to carry the targeted QTL in heterozygous condition and susceptibility alleles at other resistance QTLs in homozygous condition. This strategy took four to five generations to obtain fixed QTL recombinants (i.e., homozygous resistant at the Rphq11 or rphq16 QTL alleles, homozygous susceptible at the non-targeted QTL alleles). In less than 2 years, Rphq11 was fine-mapped into a 0.2-cM genetic interval and a 1.4-cM genetic interval for rphq16. The strongest candidate gene for Rphq11 is a phospholipid hydroperoxide glutathione peroxidase. Thus far, no candidate gene was identified for rphq16.

Higher rust resistance and similar yield of oat landraces versus cultivars under high temperature and drought

Oat crop is not particularly well adapted to hot and dry weather, as shown by a 3-fold yield reduction in Mediterranean compared to Northern regions. As a consequence, there is a need to identify more resilient oats adapted to current Mediterranean and future climate conditions. Here, we studied the performance of oat landraces under Mediterranean conditions, including the resistance to their most devastating disease, the crown rust. One hundred forty-one genetically characterized Spanish landraces were evaluated over two crop seasons at four contrasting locations in Spain and Egypt. Genotype-environment interactions were studied using heritability-adjusted genotype plus genotype-environment biplot analyses. The impact of climate variables on agronomic traits and the adaptation of particular landraces to environmental factors were inferred from non-metric multivariate scaling and canonical correspondence analyses. Results show an average oat landrace grain yield of 1500 kg/ha, which is similar to the mean yield of commercial varieties. Nonetheless, commercial varieties had 20% higher harvest index than landraces, which is explained by the higher biomass of landraces. Moreover, oat landraces showed high levels of rust resistance with mean values of the area under the disease curve of 2.58, which is approximately 25% lower than that of commercial varieties. Furthermore, several landraces carried a broad spectrum type of resistance which is expected to be more durable and efficient against different rust isolates.