Sunflower Downy Mildew Research Articles

Advances in sunflower downy mildew research

This review summarises the progress in research on sunflower downy mildew as reported in publications of the past 10 to 15 years, the period since the last comprehensive review on Plasmopara halstedii. Particular attention is paid to subjects that showed much progress and may be of particular interest to sunflower pathologists, mycologists or molecular biologists. Accordingly, single sections are devoted to the problems of taxonomic and phylogenetic aspects, host specificity, the host—pathogen interaction including resistance phenomena, as well as epidemiology and disease management. Reflecting the progress achieved in some fields and illuminating the deficits in others should stimulate the reader's interest in this very significant pathosystem.

Studies on pathogenicity in <i>Plasmopara halstedii</i> (sunflower downy mildew)

Studies on morphological and genetic variabilities as well as alterations in pathogenicity were carried out in Plasmopara halstedii (sunflower downy mildew) isolates of several races. Aggressiveness was analyzed in one sunflower inbred line showing a high level of quantitative resistance. Viability analyses were performed on oval and spheric zoosporangia. Genetic relationships were detected between the pathogen isolates using 12 EST-derived markers. There were significant differences between pathogen isolates for aggressiveness criteria. Based on virulence and aggressiveness reaction for P. halstedii to D3 line of sunflower, there were two groups as more aggressive and less virulent isolates of 100 and 3xx races, and less aggressive and more virulent isolates of 7xx races. The oval zoosporangia for more aggressive isolates of races 100 and 3xx produced more zoospores than the oval ones for less aggressive isolates of races 7xx. The isolates of races 714, 704 and 314 had an intermediary genetic position between the two isolates of races 100 and 710. It is concluded that the relationship between aggressiveness and oval zoosporangia viability may be established in P. halstedii. No correlation was detected between pathogenicity traits and EST genotypes.Key words: aggressiveness; D3 line of sunflower; EST-derived markers; oval zoosporangia; spheric zoosporangia; virulenceDOI: 10.3126/ijls.v4i0.3481International Journal of Life Sciences Vol.4 2010 pp.48-59

Retracted: Trade-off between Virulence and Aggressiveness in Plasmopara halstedii (Sunflower Downy Mildew)

Journal of PhytopathologyVolume 159, Issue 9 p. i-iii Retracted: Trade-off between Virulence and Aggressiveness in Plasmopara halstedii (Sunflower Downy Mildew) Correction(s) for this article Retraction Volume 159Issue 9Journal of Phytopathology pages: 648-648 First Published online: August 3, 2011 Nachaat Sakr, Nachaat Sakr Author’s address: INRA-UBP, 234 Avenue du Brézet, 63100 Clermont-Ferrand, France (correspondence to N. Sakr. E-mail: nsakr@clermont.inra.fr; snachaat@hotmail.com)Search for more papers by this author Nachaat Sakr, Nachaat Sakr Author’s address: INRA-UBP, 234 Avenue du Brézet, 63100 Clermont-Ferrand, France (correspondence to N. Sakr. E-mail: nsakr@clermont.inra.fr; snachaat@hotmail.com)Search for more papers by this author First published: 09 August 2011 https://doi.org/10.1111/j.1439-0434.2010.01733.xRead the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Volume159, Issue9September 2011Pages i-iii RelatedInformation

Relative efficacy of strobilurin formulations in the control of downy mildew of sunflower

The efficacy of three commercial formulations of strobilurins, viz., trifloxystrobin, kresoxim-methyl, and azoxystrobin was evaluated against sunflower downy mildew disease caused by Plasmopara halstedii under laboratory, greenhouse, and field conditions. Complete inhibition of sporangial sporulation, zoospore release, and motility was observed with 2 μg ml−1 in trifloxystrobin, and 5 μg ml−1 for azoxystrobin and kresoxim-methyl. Seed treatment with different concentrations of strobilurins enhanced seed germination and seedling vigor of sunflower to varying degrees compared to control. Highest seed germination was recorded at 10 μg ml−1 in kresoxim-methyl, and maximum seedling vigor was noticed with trifloxystrobin at 30 μg ml−1. The effect of strobilurins was tested as seed treatment, foliar application, and seed treatment followed by foliar application. Under greenhouse conditions none of the concentrations used, either as seed treatment and foliar application, were phytotoxic. For the three strobilurins, the seed treatment along with foliar application enhanced the protection of the plants as compared to only the treatment of seeds. Foliar spray treatments alone provided an intermediate control of the disease. Trifloxystrobin showed a better effect than kresoxim-methyl and azoxystrobin. Disease curative activity of trifloxystrobin was higher compared to kresoxim-methyl and azoxystrobin. Tested fungicides when applied on adaxial leaf surface showed partial translaminar activity, and disease inhibition was marginal. Loss of trifloxystrobin and azoxystrobin activity over time was low, indicating stable rainfastness residual activity. A trend in protection against downy mildew disease similar to greenhouse results was evident in the field trials. This is the first report of strobilurins exhibiting high activity against P. halstedii and is a promising fungicide for controlling sunflower downy mildew disease by seed treatment and foliar spray.

Can We Enhance Durable Resistance Against Plasmopara Halstedii (Sunflower Downy Mildew)?

Can We Enhance Durable Resistance AgainstPlasmopara Halstedii(Sunflower Downy Mildew)?Sunflower downy mildew caused byPlasmopara halstediiis one of the most potentially important diseases. So far, a complete, major gene resistance (Pl) has been used successfully, but with the appearance of eight races in France since 2000, research on more durable resistance was undertaken. In this study, we present new results concerning the evolution of pathogenicity ofP. halstediiunder conditions of re-enforced infection and differentPlgene selection pressures. Moreover, we imagine the evolution of virulence and aggressiveness ofP. halstediiunder a mixture model of sunflower inbred lines carrying the two types of resistance which may enhance durable resistance against it. Examples of host-parasite interactions including the influence of plant mixture models against pathogens are equally presented to understand how the pathogen develops its pathogenicicity.

A Plant Mixture Model Against Plasmopara Halstedii (Sunflower Downy Mildew)

Sunflower downy mildew caused by Plasmopara halstedii is one of the most potentially important diseases. So far, a complete, major gene resistance (Pl) has been used successfully. But, with the appearance of eight races in France since 2000, research on more durable resistance was undertaken. In this study, we presented new results concerning the evolution of pathogenicity in P. halstedii under conditions of re-enforced infection and different Pl gene selection pressure. Moreover, we studied the evolution of virulence and aggressiveness of P. halstedii under a mixture model of sunflower inbred lines carrying the two types of resistance (qualitative and quantitative). This sunflower model may enhance durable resistance against P. halstedii.

Development of sunflower genotypes resistant to downy mildew

Sunflower is attacked by more than 40 different diseases of which only a certain number causes serious reduction of seed yield. One of the most damaging diseases is downy mildew, which is caused by the fungus Plasmopara halstedii (Farl.) Berl. et de Toni (syn. Plasmopara helianthi Novot.). Sunflower downy mildew has great economic importance in all countries where sunflower is grown. When the meteorological conditions during the vegetation period of sunflower become favourable for disease development, the damages produce considerable reducing of the seed yield and the oil content.

Variation in aggressiveness of Plasmopara halstedii (sunflower downy mildew)

Variability in aggressiveness was studied in seven Plasmopara halstedii (sunflower downy mildew) parental isolates of races 100, 300, 304, 314, 704, 710 and 714 using five single zoosporangium isolates per parental isolate. Aggressiveness criteria, including latent period and sporulation density, were analysed in one sunflower inbred line showing a high level of quantitative resistance. Analysis of five single zoosporangium isolates of each parental isolate showed variability within parental isolate for the two aggressiveness criteria, but not for all parental isolates. The parental isolates of races 100, 300, 304 and 314 had a shorter latent period and greater sporulation density than the parental isolates of races 710, 704 and 714. Consequently, parental isolates of races 100, 300, 304 and 314 were significantly more aggressive than the parental isolates of races 710, 704 and 714.

Components of Quantitative Resistance to Downy Mildew (Plasmopara Halstedii) in Sunflower (Helianthus Annuus)

Components of Quantitative Resistance to Downy Mildew (Plasmopara Halstedii) in Sunflower (Helianthus Annuus)Components of quantitative resistance in sunflower (Helianthus annuus) toPlasmopara halstedii, the pathogen causing downy mildew, were investigated. Percentage infection, latent period, sporulation density and reduction of hypocotyl length were compared on two sunflower lines showing different levels of quantitative resistance in the field infected with differentP. halstediistrains of races 100, 300, 710 and 714 in controlled conditions. The inbred line BT, rather susceptible in the field, showed a higher percentage infection, a higher sporulation density, a shorter latent period and less reduced hypocotyl length than inbred line FU, which showed a greater resistance in the field. The very good resistance of inbred line FU observed in the field was confirmed by the measurements of quantitative resistance criteria described in this study. Percentage infection of FU was 1.4% less than BT, latent period of BT was 12.4% less than FU, sporulation density of FU was 22.3% less than BT and reduced hypocotyl length of BT was 15.3% less than FU. It seems that the criteria such as latent period, sporulation density and reduction of hypocotyl length may be used to measure quantitative resistance in sunflower toP. halstedii.

Inheritance and molecular mapping of a downy mildew resistance gene, Pl 13 in cultivated sunflower (Helianthus annuus L.)

The inheritance of resistance to sunflower downy mildew (SDM) derived from HA-R5 conferring resistance to nine races of the pathogen has been determined and the new source has been designated as Pl ( 13 ) . The F(2) individuals and F(3) families of the cross HA-R5 (resistant) x HA 821 (susceptible) were screened against the four predominant SDM races 300, 700, 730, and 770 in separate tests which indicated dominant control by a single locus or a cluster of tightly linked genes. Bulked segregant analysis (BSA) was carried out on 116 F(2) individuals with 500 SSR primer pairs that resulted in the identification of 10 SSR markers of linkage groups 1 (9 markers) and 10 (1 marker) of the genetic map (Tang et al. in Theor Appl Genet 105:1124-1136, 2002) that distinguished the bulks. Of these, the SSR marker ORS 1008 of linkage group 10 was tightly linked (0.9 cM) to the Pl (13) gene. Genotyping the F(2) population and linkage analysis with 20 polymorphic primer pairs located on linkage group 10 failed to show linkage of the markers with downy mildew resistance and the ORS 1008 marker. Nevertheless, validation of polymorphic SSR markers of linkage group 1 along with six RFLP-based STS markers of linkage group 12 of the RFLP map of Jan et al. (Theor Appl Genet 96:15-22, 1998) corresponding to linkage group 1 of the SSR map, mapped seven SSR markers (ORS 965-1, ORS 965-2, ORS 959, ORS 371, ORS 716, and ORS 605) including ORS 1008 and one STS marker (STS10D6) to linkage group 1 covering a genetic distance of 65.0 cM. The Pl (13) gene, as a different source with its location on linkage group 1, was flanked by ORS 1008 on one side at a distance of 0.9 cM and ORS 965-1 on another side at a distance of 5.8 cM. These closely linked markers to the Pl (13) gene provide a valuable basis for marker-assisted selection in sunflower breeding programs.

Resistance to downy mildew in sunflower induced by chemical activators

Downy mildew of sunflower (Plasmopara halstedii) can be effectively controlled by either genetic resistance or chemical pesticides but the development of new pathogen genotypes may lead to a re-emergence of the disease. The aim of the present work was to determine whether chemical inducers of disease resistance such as dichloroisonicotinic acid (INA) and β-aminobutyric acid (BABA) induce resistance to downy mildew in susceptible sunflowers, and affect resistant responses in mildew-inoculated resistant sunflower lines. Treatments of 3-day-old seedlings with one of these chemicals significantly reduced downy mildew disease symptoms (sporulation, stunting) in susceptible plants, and inhibited systemic mycelial growth of the pathogen. Furthermore, host cellular responses, like necrosis and secondary cell division became evident at infection sites. These effects are similar to those found in previous studies with benzothiadiazole, and closely resemble defense responses in sunflower plants carrying P. halstedii...

Epidemic outbreaks of downy mildew caused by Plasmopara halstedii on sunflower in Thrace, part of the Marmara region of Turkey

Downy mildew of sunflower (Helianthus annuus) caused by the pathogen Plasmopara halstedii is a potentially devastating disease in Europe and the USA (Miller & Gulya, 1987). During the spring of 2007 and 2008, a serious outbreak of downy mildew caused by P. halstedii at the V4 (four true leaves) stage of development was observed on sunflower plants grown in commercial fields in Thrace, part of Marmara, the main producing area in Turkey. It is thought that low temperature and extensive spring rains encouraged the disease, resulting in approximately 85% yield loss and lower quality of sunflower production in some areas. Plants carrying systemic downy mildew infection were stunted and leaves showed characteristic green and chlorotic mottling along the main veins and over the lamella. Under moist conditions, a white downy growth composed of sporangiospores and sporangia of the fungus appeared on the leaf surface corresponding to chlorotic areas above. Microscopic observations revealed the monopodial branching of sporangiospores at nearly right angles, with five or six terminal branches 6–10 µm long and bearing single elliptic, papillate zoosporangia, 15–25 × 12–16 µm. Sporangiophores were 270–450 µm. These morphological characteristics were typical of P. halstedii, as described by Hall (1989). Plasmopara halstedii is listed as an A1 quarantine pest by IAPSC, but not by any other regional plant protection organization. However, Australia treats it as a major quarantine pest. EPPO is currently examining its quarantine status. In the EPPO region, it is potentially dangerous everywhere that sunflower is grown, except where high soil temperature (above 25°C) and/or drought are limiting factors. If control measures are lacking and conditions are favourable, downy mildew can be devastating to sunflower. Plasmopara halstedii was recorded by Karel (1958) in a single crop near Adapazarı, but the events of 2007 and 2008 signal epidemic spread of downy mildew and economic losses to sunflower crops.

Transition of secondary to systemic infection of sunflower with Plasmopara halstedii – An underestimated factor in the epidemiology of the pathogen

Plasmopara halstedii, the downy mildew pathogen of sunflower causes significant economic loss world-wide, mostly through soilborne systemic infection of seedlings. Natural infection of sunflower with P. halstedii was monitored in a sunflower field cultivated for ornamental purpose in soil where no sunflower had been grown before. Local and systemic infections were observed in plants of different developmental stages which were sown in five consecutive field plots between Apr. and Jul. The airborne origin of the infection by zoosporangia was concluded from field history, pathogenic symptoms, time course of infection and microscopic investigation of mycelium distribution in stems. A high potential for transition from local to systemic infection was found, at least in ornamental sunflower cultivation under the typical weather conditions in Central Europe. This questions the paradigm that economically and epidemiologically relevant sunflower downy mildew incidences are only derived from subterranean infections. Airborne secondary infections, as they may occur in all developmental stages and on all organs of the host plant, are responsible for late systemic infection and can play a key role in the production of contaminated seeds carrying the pathogen into the next season.

A Method to Measure Aggressiveness of Plasmopara halstedii (Sunflower Downy Mildew)

AbstractFor the first time, a method was used to measure aggressiveness of two Plasmopara halstedii races (100 and 710), the parasite causing sunflower downy mildew. Two sunflower lines showing different levels of quantitative resistance were used to measure two aggressiveness criteria: latent period and sporulation density. A strain of race 100 had a shorter latent period and greater sporulation density than a strain of race 710. The sunflower inbred line BT, rather susceptible in the field, presented a greater sporulation density and a shorter latent period than another inbred line FU, which shows greater resistance in the field. These results indicated that race 100 was more aggressive than race 710. The behaviour in the field of the two inbred lines was confirmed in the laboratory observations.

Pathogenic and morphological variability of Plasmopara halstedii, the causal agent of downy mildew in sunflower

SUMMARY Isolates of P. halstedii collected from different parts of Karnataka, Maharashtra and Andhra Pradesh belong to a single race, i.e ., race 100. Based on virulence pattern, they can be grouped into five different groups, A, B, C, D and E. Bangalore isolate was most virulent and Bidar isolate was least virulent. Morphological variations existed among the isolates with regard to the size of sporangiophores and sporangia. Sporangiophores were longer Dharwad isolate and sporangia were larger in Mysore and Latur isolates. RESUMEN Las aislaciones de P. halstedii provenientes de diferentes partes de Karnataka, Maharashtra y Andhra Pradesh pertenecen a una sola raza (raza 100). Sobre la base de patrones de virulencia, éstas pueden ser agrupadas en cinco diferentes grupos denominados A, B, C, D y E. El aislamiento de Bangalore fue el más virulento mientras que el de Bidar fue el de menor virulencia. Se observaron variaciones morfológicas entre aislamientos en relación al tamaño de los esporangióforos y los esporangios. El aislamiento de Dharward presentó los esporangióforos más largos mientras que los aislamientos de Mysore y Latur presentaron los esporangios más grandes. RÉSUMÉ Des isolats de P. halstedii collectés dans différentes parcelles de Karnataka, Maharashtra et Andhra Pradesh appartiennent à une seule race, à savoir la race 100. La quantification de l’agressivité a conduit à l’identification de 5 groupes (A à E): l’isolat de Bangalore a été le plus agressif, et celui de Bidar le moins agressif. Des variations de longueur des sporangiophores et des sporanges ont été notées: la longueur des sporangiophores de l’isolat de Dharwad était la plus importante, tandis que les tailles des sporanges des isolats de Mysore et Latur étaient les plus importantes.

Plasmopara halstedii

<i>Plasmopara halstedii</i>

Different pathotypes of the sunflower downy mildew pathogen Plasmopara halstedii all contain isometric virions†

Eight pathotypes of Plasmopara halstedii were screened to investigate the occurrence of virions and the potential viral influence on the pathogenicity of the sunflower downy mildew pathogen. In 23 of 26 P. halstedii isolates derived from eight countries in Europe, North America and South America, virions were detected by transmission electron microscopy. By contrast, there were no ultrastructural indications of virus-like particles in eight other related Oomycetes. The virions of representative P. halstedii isolates were morphologically and biochemically characterized and compared among each other. Regardless of their host's pathotypes, the geographical origin of the isolate and the sensitivity towards the fungicide metalaxyl, the viral characters obtained were uniform. The virions were isometric and measured approximately 37 nm in diameter. One polypeptide of c. 36 kDa and two segments of single-stranded RNA (3.0 and 1.6 kb) were detected. Both viral RNA segments were detected by capillary electrophoresis in the three remaining P. halstedii isolates where virions were undetectable by transmission electron microscopy. Virus-specific primers for the 1.6 kb-segment were synthesized and used to determine and compare a partial sequence of the viral coat protein among virions of different P. halstedii pathotypes. In all tested isolates, fragments of 0.7 kb were amplified which were directly sequenced. Sequence variation was insignificant. As both less aggressive and more aggressive P. halstedii isolates contained virions, the presence or absence of virions could not explain the diverse aggressiveness of the downy mildew pathogen towards sunflower. Moreover, the results indicated that pathogenicity of P. halstedii was not related to variation in morphological or biochemical characters of the virions.

Variation in form and size of Plasmopara halstedii (sunflower downy mildew) zoosporangia

Zoosporangia form and size were studied on a collection of 94 strains of Plasmopara halstedii (sunflower downy mildew). Both oval and round forms were present in all strains analysed. The proportion of two forms varied significantly according to strain and plant age but more especially to host plant genotype. Whatever the strain or host genotype, oval zoosporangia were larger than round ones, but there was no relation between the proportion of the oval form and mean zoosporangia size. There was no relation between zoosporangia form or size and race virulence profiles or aggressiveness criteria, with the possible exception of zoosporangia size and sporulation density. It is concluded that, for this obligate parasite, although form and size of zoosporangia depend on pathogen strain, these characters also vary according to growth conditions of Plasmopara halstedii, in particular to the genotype of the plant host.

Inheritance of quantitative resistance to downy mildew (Plasmopara halstedii) in sunflower (Helianthus annuus L.)

Quantitative resistance to sunflower downy mildew was studied on inbred lines and hybrids not carrying efficient major gene resistance, in field trials in one to four sites over 3 years. Hybrids from factorial crosses showed that inheritance is under additive control and comparison with reactions of parental inbred lines gave narrow sense heritabilities of 27-57%. Analysis of a polymorphic recombinant inbred line population without efficient major gene resistance indicated that two highly significant Quantitative Trait Loci (QTL) explained 42% of variation in field reaction to downy mildew. These QTL were mapped on linkage groups 8 and 10, and do not appear related to any of the known major resistance gene clusters. Possible bases of this type of resistance and its use in breeding are discussed.

Quantitative resistance to downy mildew (Plasmopara halstedii) in sunflower (Helianthus annuus)

Downy mildew of sunflower, caused by the Oomycete, Plasmopara halstedii is at present controlled by major resistance genes. However, the pathogen has shown a considerable capacity for changes in virulence and these resistance genes are overcome only a few years after they have been introduced into new sunflower varieties. This paper presents research for quantitative, non-race-specific resistance independent of major genes. The reaction of cultivated sunflower genotypes to field attack by downy mildew was studied over 4 years in several environments and in the presence of the two most common races in France: 703 and 710. An experimental protocol with pre-emergence irrigation was developed, making it possible to observe downy mildew reaction whatever the weather conditions. Significant levels of partial resistance were observed in about 50 inbred sunflower lines among the 800 observed. These results suggest that it should be possible to select for non-race-specific downy mildew resistance and to include it in modern varieties. However, since this non-specific resistance is partial, it may be necessary to combine it with major gene resistance. Possible strategies are discussed to obtain durable resistance to downy mildew.