Plasmopara Halstedii Research Articles

Use of SNP markers by KASP assay for MAS studies in sunflower againstPlasmopara halstedii

Downy mildew is a fungal disease caused by Plasmopara halstedii and leads to loss of yield up to 100% in sunflower. Disease control is performed mostly through chemical seed treatment and breeding. Due to the time consuming nature of conventional breeding, it is supported by biotechnological approaches. Marker-assisted selection (MAS) is a strategic approach in molecular breeding using molecular markers. Single nucleotide polymorphisms (SNPs) such as insertions, deletions, and base-pair substitutions are more advantageous than other molecular markers. The abundance and biallelic nature of SNPs in a genome provide flexibility in the choosing of SNPs at the desired loci. Competitive allele-specific PCR (KASP) is a genotyping technology for screening of trait-specific SNP markers. In this study, SNP markers (NSA002867, NSA006138; NS52, NSA000354; NSA002220, NSA002251) linked with the downy mildew resistance genes Plarg, Pl13, and Pl8, respectively, were analyzed via KASP in three parental crosses (RHA-419 x Colombi, RHA-419 x P64LC53, RHA-419 x Oliva) for Plarg, one parental cross (HA-R5 x P64LC53) for Pl13, one parental cross (P64LC53 x HA-89) for Pl8, and 140 F2 individuals. According to the allelic discrimination results, NSA002867 and NSA006138 markers were discriminative in all crosses for Plarg, NSA000354 marker was discriminative for Pl13, and NSA002220 and NSA002251 markers were discriminative for Pl8. This study has revealed the potential use of SNP markers in combination with KASP assay for MAS studies, particularly downy mildew resistance in sunflower.

Breeding of sunflower lines for resistance downy mildew in the setting of changing pathogenic races

The aim and tasks of the study . The main objective of this study was to select starting material resistant to downy mildew pathogen for use in breeding programs. Phytosanitary monitoring of crop conditions for pathogen and races was concurrently performed. Materials and methods. Resistance of sunflower lines – pollen fertility restorers to downy mildew pathogen was evaluated in the phase of calathidium formation. Resistance of sunflower accessions to disease was determined by the prevalence of disease. In winter, resistance of accessions to pathogen was evaluated by a rapid method. Plasmopara helianthi races were identified with a triplet set of lines-differentiators. In addition to resistance, we determined ripeness group, plant height and branching type. Variance and correlation analyses were used for statistical processing of experimental data. Results and discussion . Maximum and average values of the disease prevalence fluctuated in the Eastern Forest-Steppe of Ukraine in 2007-2016 (at the maximum 17.5-100% of plants were affected). During half of the study years, the damage level was 1.4-3.3%. High prevalence (11.3-30.7%) was recorded during 3 years (2010, 2014 and 2016.) with excessive precipitation related to the multiyear average (by 14.0-42.4 mm). This is confirmed by close relationship between the average (r = 0.93) and maximum (r = 0.74) values of the disease prevalence and the precipitation amount. Negative correlation was found between these parameters and the average monthly temperature (r = -0.55). Race 330 was the most common until 2006. Since 2010, race 730 has taken a dominant position. In the setting of a prolonged excessively wet spring of 2016, race 732 was identified by response of lines -differentiators to pathogen. The spread pattern of race 730 predicts a probable spread of race 732 for 2017, provided favorable the for pathogen development conditions. Comparing the results of evaluation of sunflower breeding accessions for resistance to downy mildew pathogen in laboratory and field conditions, we identified 33 lines with resistance to 3 races of pathogen - 330, 730 and 732. Most of these sunflower lines - pollen fertility restorers (23) are mid-early; four lines are short-season; and six are early-ripening. They are characterized by various types of branching and plant height. Conclusions. The efficacy of combination of assessment of starting material for resistance to downy mildew in the field conditions in years with wide prevalence and large-scale affection of plants with continuous annual evaluation of breeding material for virulent races in winter in the laboratory conditions was proved. We selected 33 sunflower lines-pollen fertility restorers belonging to different groups of ripeness, which are resistant to 3 races (330, 730 and 732) of downy mildew pathogen and are a basis for new resistant hybrids.

RXLR and CRN Effectors from the Sunflower Downy Mildew Pathogen Plasmopara halstedii Induce Hypersensitive-Like Responses in Resistant Sunflower Lines.

Plasmopara halstedii is an obligate biotrophic oomycete causing downy mildew disease on sunflower, Helianthus annuus, an economically important oil crop. Severe symptoms of the disease (e.g., plant dwarfism, leaf bleaching, sporulation and production of infertile flower) strongly impair seed yield. Pl resistance genes conferring resistance to specific P. halstedii pathotypes were located on sunflower genetic map but yet not cloned. They are present in cultivated lines to protect them against downy mildew disease. Among the 16 different P. halstedii pathotypes recorded in France, pathotype 710 is frequently found, and therefore continuously controlled in sunflower by different Pl genes. High-throughput sequencing of cDNA from P. halstedii led us to identify potential effectors with the characteristic RXLR or CRN motifs described in other oomycetes. Expression of six P. halstedii putative effectors, five RXLR and one CRN, was analyzed by qRT-PCR in pathogen spores and in the pathogen infecting sunflower leaves and selected for functional analyses. We developed a new method for transient expression in sunflower plant leaves and showed for the first time subcellular localization of P. halstedii effectors fused to a fluorescent protein in sunflower leaf cells. Overexpression of the CRN and of 3 RXLR effectors induced hypersensitive-like cell death reactions in some sunflower near-isogenic lines resistant to pathotype 710 and not in susceptible corresponding lines, suggesting they could be involved in Pl loci-mediated resistances.

Asexual Recombinants of Plasmopara halstedii Pathotypes from Dual Infection of Sunflower.

Genetically homogenous strains of Plasmopara halstedii differing in host specificity and fungicide tolerance were used to test the hypothesis that asexual genetic recombination occurs and may account for the high genotype diversity of this homothallic reproducing oomycete, which causes downy mildew in sunflower. Dual inoculation of sunflower seedlings with single zoospore strains of complementary infection characteristics caused sporulation under conditions where inoculation with each strain alone failed to infect. PCR-based investigation with strain-specific primers proved the presence of genetic traits from both progenitors in single sporangia collected from sporangiophores of such infections. Sister zoospores released from these sporangia revealed the genotype of the one or the other parental strain thus indicating heterokaryology of sporangia. Moreover, some zoospores showed amplification products of both parents, which suggests that the generally mononucleic spores derived from genetic recombination. The possibility of parasexual genetic exchange in the host-independent stage of infection and the evolutionary consequences are discussed.

Discovery and introgression of the wild sunflower-derived novel downy mildew resistance gene Pl 19 in confection sunflower (Helianthus annuus L.).

A new downy mildew resistance gene, Pl 19 , was identified from wild Helianthus annuus accession PI 435414, introduced to confection sunflower, and genetically mapped to linkage group 4 of the sunflower genome. Wild Helianthus annuus accession PI 435414 exhibited resistance to downy mildew, which is one of the most destructive diseases to sunflower production globally. Evaluation of the 140 BC1F2:3 families derived from the cross of CMS CONFSCLB1 and PI 435414 against Plasmopara halstedii race 734 revealed that a single dominant gene controls downy mildew resistance in the population. Bulked segregant analysis conducted in the BC1F2 population with 860 simple sequence repeat (SSR) markers indicated that the resistance derived from wild H. annuus was associated with SSR markers located on linkage group (LG) 4 of the sunflower genome. To map and tag this resistance locus, designated Pl 19 , 140 BC1F2 individuals were used to construct a linkage map of the gene region. Two SSR markers, ORS963 and HT298, were linked to Pl 19 within a distance of 4.7cM. After screening 27 additional single nucleotide polymorphism (SNP) markers previously mapped to this region, two flanking SNP markers, NSA_003564 and NSA_006089, were identified as surrounding the Pl 19 gene at a distance of 0.6cM from each side. Genetic analysis indicated that Pl 19 is different from Pl 17 , which had previously been mapped to LG4, but is closely linked to Pl 17 . This new gene is highly effective against the most predominant and virulent races of P. halstedii currently identified in North America and is the first downy mildew resistance gene that has been transferred to confection sunflower. The selected resistant germplasm derived from homozygous BC2F3 progeny provides a novel gene for use in confection sunflower breeding programs.

Methodology of virulence screening and race characterization of Plasmopara halstedii, and resistance evaluation in sunflower – a review

Sunflower downy mildew is a disease of high global economic impact as well as a causal agent that is extremely difficult to eradicate. During the past decades, several approaches for the determination of Plasmopara halstedii (Ph) races have been used worldwide and are discussed in this review. Procedures of isolation, cultivation and maintenance of Ph isolates, as well as the screening of sunflower for resistance, are also critically reviewed. The predominant, globally used resistance screening protocol is a ‘whole seedling immersion’ inoculation. ‘Soil drench’ inoculation allows more precise control of the number of Ph zoosporangia applied to a single sunflower seedling. A detached leaf assay has been described, but it has been used mainly for Ph subcultivation and fungicide tests. For race determination, a differential set consisting of nine sunflower genotypes has been used since 1988, coupled with a numerical triplet code for virulence phenotyping of Ph. The increasing variability in global Ph populations has demonstrated the inadequacy of the current set of differentials, and several researchers have proposed additional public lines as new differentials. Furthermore, bulk isolates may show different results in repeated tests, as Ph may contain genetically distinct zoospores within a single zoosporangium. For precise race determination, single zoosporangia or single zoospore isolates are advisable. However, due to low success of isolation, approximately 1–2%, this method cannot be applied in routine Ph race screening. Methods surveyed in this review have a broad spectrum of applications, including taxonomic studies.

Changes in the Racial Structure of Plasmopara halstedii (Farl.) Berl. et de Toni Population in the South of the Russian Federation

AbstractThe population of oomycete Plasmopara halstedii (Farl.) Berl. et de Toni (sunflower downy mildew pathogen) has been monitored in Krasnodar and Rostov regions and the Republic of Adygea for more than 15 years. Prior to the beginning of the 2000s there were races 100, 300, 310 and 330 in the regions. In the period from 2004 to 2007 races 100, 300, 310 and 700 were recorded sporadically. The race 330 was the most common; in a number of agrocoenoses it was 100 % of samples. In some fields races 710 and 730 prevailed. In 2008–2011 only races 330, 710 and 730 were found; the race 330 have been still prevailed and was also found on Ambrosia artemisiifolia L. Since 2012, in the majority of fields races 710 and 730 prevailed, and the race 330 wasn’t allocated in many of them; for the first time in Russia pathotype 334, that able to overcome Pl6, was found in Krasnodar region. In the period of 2013–2015 increased distribution of the race 334 in the Krasnodar region and the Republic of Adygea was observed. At the same time, in 2014 in one field in the Rostov region only races 310 and 330 (prevailed) were identified. The virulence of the pathogen population is closely connected with the cultivated assortment of sunflower. Further spread and accumulation of P. halstedii race 334 and the emergence of new pathogen pathotypes in the said regions are predicted.

Evolution of Two Components of Pathogenicity in Plasmopara halstedii (Downy Mildew) under Sunflower Qualitative Resistance Selection Pressure

Evolution of pathogenicity, morphological, and genetic traits were analyzed in a local Plasmopara halstedii (downy mildew) population (including two parental and five progeny isolates) multiplied under sunflower qualitative resistance selection pressure for five years. The two components of pathogenicity developed in response to Pl resistance genes selection pressure. The emergence of new virulence in P. halstedii progeny isolates carrying several levels of aggressiveness was an important consequence of selection pressure. However, appearance of new virulence did get along with evolution of aggressiveness in progeny isolates as compared with parental ones. For progeny P. halstedii isolates, an increase in pathogen virulence had direct consequences on its aggressiveness. There was no influence of selection pressure on morphological traits, but an effect was observed on evolution of genetic architecture. However, arrangement of genetic traits did get along with evolution of pathogenicity. It is clear that qualitative resistance selection pressure plays an important role in the evolution of sunflower downy mildew population.

Induction of Resistance with Benzothiadiazole in Sunflower: a Comparison of Biotrophic vs. Necrotrophic Pathosystems

In the present work we aimed at comparing the effect of benzothiadiazole (BTH) treatment on defence reactions of sunflower plants to downy mildew and white rot diseases. BTH treatment resulted in reduced disease symptoms in biotrophic and in the early stage of the necrotrophic interactions. To get a better insight into the effect of BTH, changes in the activities of polyphenol oxidase and peroxidase enzymes, as well as the expression of the host response-associated sunflower genes were examined in the plants. Inoculation with Plasmopara halstedii enhanced the polyphenol oxidase and peroxidase enzyme activities, while inoculation with Sclerotinia sclerotiorum did it only at 4 dpi. However, most importantly, in each case extracts from BTH pretreated and inoculated plants showed the highest polyphenol oxidase and peroxidase enzyme activities. Similarly, the accumulation of GST and PDF transcripts was detected following inoculations with both biotrophic and necrotrophic pathogens, and again, BTH pre-treatment enhanced GST and defensine gene activities in the inoculated plants. We suggest that induction of enzyme activities, as well as of the elevated expression of GST, PDF and PR5 genes by BTH pre-treatment may be a significant part of the induced resistance of sunflower to downy mildew and white rot (white mold).

First Report of Plasmopara halstedii New Races 705 and 715 on sunflower from the Czech Republic - Short Communication

First Report of Plasmopara halstedii New Races 705 and 715 on sunflower from the Czech Republic - Short Communication

Registration of an Oilseed Sunflower Germplasm HA‐DM1 Resistant to Sunflower Downy Mildew

HA‐DM1 (Reg. No. GP‐335, PI 674793) sunflower (Helianthus annuus L.) germplasm was developed and released cooperatively by the USDA‐ARS, Sunflower and Plant Biology Research Unit and the North Dakota Agricultural Experiment Station in 2015. HA‐DM1 is a BC2F4–derived oilseed maintainer line from the cross HA 89*2/NMS HA 89/Helianthus argophyllus PI 494573, selected for resistance to downy mildew (DM) [caused by Plasmopara halstedii (Farl.) Berl. et de Toni], a destructive disease in sunflower. The DM resistance in HA‐DM1 originated from wild H. argophyllus accession PI 494573 and is conditioned by a single dominant gene designated Pl18. Pl18 has been mapped to linkage group 2 of the sunflower genome and is independent of all known identified DM resistance genes in sunflower. HA‐DM1 has resistance to all P. halstedii races identified in the United States to date, providing a potential new source for resistance to emerging virulent races of P. halstedii in sunflower in North America and around the world.

Effector Polymorphisms of the Sunflower Downy Mildew Pathogen Plasmopara halstedii and Their Use to Identify Pathotypes from Field Isolates.

The obligate biotroph oomycete Plasmopara halstedii causes downy mildew on sunflower crop, Helianthus annuus. The breakdown of several Pl resistance genes used in sunflower hybrids over the last 25 years came along with the appearance of new Pl. halstedii isolates showing modified virulence profiles. In oomycetes, two classes of effector proteins, key players of pathogen virulence, are translocated into the host: RXLR and CRN effectors. We identified 54 putative CRN or RXLR effector genes from transcriptomic data and analyzed their genetic diversity in seven Pl. halstedii pathotypes representative of the species variability. Pl. halstedii effector genes were on average more polymorphic at both the nucleic and protein levels than random non-effector genes, suggesting a potential adaptive dynamics of pathogen virulence over the last 25 years. Twenty-two KASP (Competitive Allele Specific PCR) markers designed on polymorphic effector genes were genotyped on 35 isolates belonging to 14 Pl. halstedii pathotypes. Polymorphism analysis based on eight KASP markers aims at proposing a determination key suitable to classify the eight multi-isolate pathotypes into six groups. This is the first report of a molecular marker set able to discriminate Pl. halstedii pathotypes based on the polymorphism of pathogenicity effectors. Compared to phenotypic tests handling living spores used until now to discriminate Pl. halstedii pathotypes, this set of molecular markers constitutes a first step in faster pathotype diagnosis of Pl. halstedii isolates. Hence, emerging sunflower downy mildew isolates could be more rapidly characterized and thus, assessment of plant resistance breakdown under field conditions should be improved.

Sunflower polygalacturonase-inhibiting proteins (HaPGIP) are genetically conserved in cultivated sunflower (Helianthus annuus L.) but diverse in wild species

Cultivation of sunflower is often associated with substantial pathogen-related yield losses. Natural defense mechanisms of plants might be improved by advantageous combination of genes encoding proteins that suppress important pathogenicity factors. Endopolygalacturonases (endoPGs) as cell-wall-degrading enzymes contribute to the virulence of fungi, bacterial pathogens, and oomycetes. However, plants have evolved families of polygalacturonase-inhibiting proteins (PGIPs) that specifically recognize and inactivate these polygalacturonases (PGs). Here, we describe the identification of four sunflower pgip genes. The genes were cloned, genetically mapped, in silico characterized, and subjected to expression analyses in response to pathogen infection. Three Helianthus annuus pgip genes (Hapgip2–4) are located on linkage group (LG) 10 and phylogenetically closely related to other dicot pgips. In contrast, Hapgip1 was mapped on LG1 and formed a separate Asteraceae branch, suggesting that HaPGIPs may represent structurally and functionally distinct proteins. All HaPGIPs displayed characteristic sequence structures such as the tandem repetition of leucine-rich domains. WRKY transcription factor-binding sites identified through in silico promoter analyses differed between Hapgips in number and architecture. A comprehensive diversity analysis indicated that HaPGIP1–HaPGIP4 are rather conserved in current breeding material but genetically diverse in wild species. Based on homologous positions determined as amino acids with known influence on PvPGIP–PG interaction, non-synonymous substitutions in HaPGIPs were identified in H. maximiliani, H. ciliaris, H. paradoxus, H. tuberosis, and H. petiolaris. Furthermore, relative real-time quantitative PCR analyses revealed enhanced Hapgip1–Hapgip4 expression upon Botrytis cinerea inoculation and an increased expression level of Hapgip3 in response to the oomycete Plasmopara halstedii.

Genetics and mapping of a novel downy mildew resistance gene, Pl(18), introgressed from wild Helianthus argophyllus into cultivated sunflower (Helianthus annuus L.).

A novel downy mildew resistance gene, Pl(18), was introgressed from wild Helianthus argophyllus into cultivated sunflower and genetically mapped to linkage group 2 of the sunflower genome. The new germplasm, HA-DM1, carrying Pl(18) has been released to the public. Sunflower downy mildew (DM) is considered to be the most destructive foliar disease that has spread to every major sunflower-growing country of the world, except Australia. A new dominant downy mildew resistance gene (Pl 18) transferred from wild Helianthus argophyllus (PI 494573) into cultivated sunflower was mapped to linkage group (LG) 2 of the sunflower genome using bulked segregant analysis with 869 simple sequence repeat (SSR) markers. Phenotyping 142 BC1F2:3 families derived from the cross of HA 89 and H. argophyllus confirmed the single gene inheritance of resistance. Since no other Pl gene has been mapped to LG2, this gene was novel and designated as Pl (18). SSR markers CRT214 and ORS203 flanked Pl(18) at a genetic distance of 1.1 and 0.4 cM, respectively. Forty-six single nucleotide polymorphism (SNP) markers that cover the Pl(18) region were surveyed for saturation mapping of the region. Six co-segregating SNP markers were 1.2 cM distal to Pl(18), and another four co-segregating SNP markers were 0.9 cM proximal to Pl(18). The new BC2F4-derived germplasm, HA-DM1, carrying Pl(18) has been released to the public. This new line is highly resistant to all Plasmopara halstedii races identified in the USA providing breeders with an effective new source of resistance against downy mildew in sunflower. The molecular markers that were developed will be especially useful in marker-assisted selection and pyramiding of Pl resistance genes because of their close proximity to the gene and the availability of high-throughput SNP detection assays.

Can Pl Resistance Gene in Sunflower Line D4 be Used to Differentiate the Pathogenicity in Four Plasmopara halstedii (Sunflower Downy Mildew) Races 304, 314, 704 and 714?

In order to clarify the role of PlPMI3 resistance gene in sunflower differential lines D4 for differentiation the pathogenicity in Plasmopara halstedii (sunflower downy mildew), analyses were carried out in two groups including four pathotypes which overcome and do not overcome PlPMI3 (Pl gene has still not been mapped) resistance gene. Based on the reaction for the P. halstedii isolates to sunflower hybrids varying only in Pl resistance genes, there were no virulence differences for the two groups. Index of aggressiveness was calculated for pathogen isolates and revealed the presence of significant differences between isolates of races 304 and 314; however, there were no aggressiveness differences for 7xx races. Regarding the life-history trait and the genetic architecture of the pathogen: there were morphological and genetic variations for the four P. halstedii isolates without a correlation with pathogenic diversity. The importance of the PlPMI3 resistance gene to differentiate the pathogenicity in sunflower downy mildew was discussed.

Comparative analysis of expressed CRN and RXLR effectors from two Plasmopara species causing grapevine and sunflower downy mildew

Plasmopara halstedii and Plasmopara viticola are the causative agents of downy mildew of two economically important crops, sunflower and grapevine, respectively. These phylogenetically related oomycetes are obligate biotrophs belonging to Peronosporales but have different pathological profiles. Despite the economic importance of diseases caused by both Plasmopara, genomic resources are very limited and their effector repertoire is unknown. In this study parallel transcriptome sequencing of P. halstedii and P. viticola was performed, and a Plasmopara species cDNA database (PlasmoparaSp) released containing 46 000 clusters. In oomycetes, two classes of effectors are translocated into the host cytoplasm, the RXLRs and the CRNs. The PlasmoparaSp database was screened in order to identify the repertoire of expressed effectors used by both Plasmopara species; about 50 putative RXLR and 60 CRN were identified for each. These effectors were compared within both species and with seven publicly available oomycete species representative of Peronosporales and Albuginales. Sequence analyses revealed the presence of 55 RXLR families, 12 of them shared by both Plasmopara, and 19 showing amino acid conservation with predicted peptides from at least one oomycete species. Analyses of Plasmopara spp. CRN C‐terminal variable regions revealed sequence conservation inside Plasmopara spp. and across oomycetes, with the exception of Hyaloperonospora arabidopsidis. Finally, the analyses confirmed the presence of eight CRN C‐terminal domains described in Phytophthora infestans and identified CRN effectors showing similarity to serine proteases. Species‐specific effectors were identified that may be involved in host specificity, as well as effectors conserved among oomycetes that might play important roles in the pathogen biology.

Genome analyses of the sunflower pathogen Plasmopara halstedii provide insights into effector evolution in downy mildews and Phytophthora.

BackgroundDowny mildews are the most speciose group of oomycetes and affect crops of great economic importance. So far, there is only a single deeply-sequenced downy mildew genome available, from Hyaloperonospora arabidopsidis. Further genomic resources for downy mildews are required to study their evolution, including pathogenicity effector proteins, such as RxLR effectors. Plasmopara halstedii is a devastating pathogen of sunflower and a potential pathosystem model to study downy mildews, as several Avr-genes and R-genes have been predicted and unlike Arabidopsis downy mildew, large quantities of almost contamination-free material can be obtained easily.ResultsHere a high-quality draft genome of Plasmopara halstedii is reported and analysed with respect to various aspects, including genome organisation, secondary metabolism, effector proteins and comparative genomics with other sequenced oomycetes. Interestingly, the present analyses revealed further variation of the RxLR motif, suggesting an important role of the conservation of the dEER-motif. Orthology analyses revealed the conservation of 28 RxLR-like core effectors among Phytophthora species. Only six putative RxLR-like effectors were shared by the two sequenced downy mildews, highlighting the fast and largely independent evolution of two of the three major downy mildew lineages. This is seemingly supported by phylogenomic results, in which downy mildews did not appear to be monophyletic.ConclusionsThe genome resource will be useful for developing markers for monitoring the pathogen population and might provide the basis for new approaches to fight Phytophthora and downy mildew pathogens by targeting core pathogenicity effectors.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1904-7) contains supplementary material, which is available to authorized users.

Pathogenic mycobiota of the weeds Bidens pilosa and Bidens subalternans

Bidens pilosa and B. subalternans are highly noxious herbaceous neotropical asteraceous weeds. A survey of fungal pathogens associated with these two species was undertaken in Brazil, aimed at finding natural enemies in order to establish the potential for introducing novel specific pathogens from other regions of the world, as classical biological control agents. Ten fungal species were found associated with both B. pilosa and B. subalternans, namely: Cercospora bidentis, C. maculicola, Entyloma bidentis, E. compositarum, E. guaraniticum, Neoerysiphe cumminsiana, Plasmopara halstedii, Podosphaera xanthii, Uromyces bidentis, and U. bidenticola. Three other species were found solely associated only with B. subalternans: Colletotrichum bidentis, Pseudocercosporella bidentis and Sphaceloma bidentis. Pseudocercosporella bidentis is described herein as new to science.

Recent Changes in the Pathogenic Variability of Plasmopara Halstedii (Sunflower Downy Mildew) Populations from Different Continents

AbstractThe obligate biotrophic Oomycete, Plasmopara halstedii, causal agent of sunflower downy mildew, is capable of producing new pathogenic races over time. Although changes in the P. halstedii race composition were reviewed for the first time in 2007, since then the pathogen has continued to change its virulence character dramatically. There was a need, therefore, to update information on pathogenic diversity of P. halstedii by making accounts of the temporal and spacial changes in the pathogen populations in North and South America and Europe. This paper, based on current publications and personal communications, attempts to present an accurate overview of races in Europe and Americas for the last 7 years.

Emergence of new virulence in Plasmopara halstedii (sunflower downy mildew)

The fast evolution of Plasmopara halstedii (downy mildew) remains a major risk for sunflower crop, as new races of the pathogen are bypassing the resistance of sunflower hybrids. In order to understand the processes which led a new virulence to appear in a local P. halstedii population, the genetic relationships were studied using 12 EST (Expressed Sequence Tag)-derived markers between five progeny isolates of races 300, 304, 314, 704 and 714 and two parental ones of races 100 and 710. All genetic analyses were carried out using five single zoosporangium isolates per P. halstedii isolate. There was no intra-isolate genetic variation among the seven pathogen isolates and five multilocus genotypes (MLG) were identified among the 35 P. halstedii single zoosporangium isolates. The single zoosporangium isolates of races 314, 704 and 714 had an intermediary genetic position between the single zoosporangium isolates of two parental isolates. The single zoosporangium isolates of three isolates of races 100, 300 and 304 were localized in the same genetic clade. Two genetic mechanisms could explain the emergence of new virulence in P. halstedii as a recombination between races and mutations in a clonal lineage.