Caracterización fenotípica en aislados de varias razas de Plasmopara halstedii (mildiu del girasol) (Inglés)

Phenotypic variation (morphological and pathogenic characters), and genetic variability were studied in 50 isolates of seven Plasmopara halstedii (sunflower downy mildew) races 100, 300, 304, 314, 710, 704 and 714. There were significant morphological, aggressiveness, and genetic differences for pathogen isolates. However, there was no relationship between morphology of zoosporangia and sporangiophores and pathogenic and genetic characteristics for the races used in our study. Also, our results provided evidence that no relation between pathogenic traits and multilocus haplotypes may be established in P. halstedii. The hypothesis explaining the absence of relationships among phenotypic and genetic characteristics is discussed.Se ha estudiado la variación fenotípica (caracteres morfológicos y patógenos) y la variabilidad genética de 50 aislamientos de las razas 100, 300, 304, 314, 710, 704 y 714 de Plasmopara halstedii (mildiu del girasol). Se han encontrado diferencias significativas en la morfología, la agresividad y las variaciones genéticas para los aislados patógenos. Sin embargo, no se ha encontrado relación entre la morfología de los zoosporangios y esporangióforos, y las características patogénicas y genéticas entre las razas estudiadas. También nuestros resultados aportan evidencia de que no existe relación entre los patógenos estudiados y los haplotipos con múltiples loci resistentes en P. halstedii. Se comenta la hipótesis explicativa de la ausencia de relaciones entre las características fenotípicas y genotípicas

Silicon Root Irrigation Enhances Barley Resistance to Fusarium Head Blight

Silicon (Si) is recognized for its protective role in decreasing disease damage when absorbed by barley plants and has been proposed as a possible solution against Fusarium head blight, associated with devastating agronomic effects on overall yield and grain quality. However, root treatment of exogenous Si irrigating to enhance host resistance to Fusarium infection is unknown. For this purpose, a series of greenhouse experiments was conducted to examine the effects of Si irrigation at 1.7 mM to roots on pathogen development in barley heads. Two barley cultivars with contrasting FHB resistance (moderately resistant Arabi Aswad, AS, and moderately susceptible Arabi Abiad, AB) and infected with four Fusarium species with diverse pathogenicity were used. The quantification of the disease was through the determination of the disease incidence (DI, Type I resistance), disease severity (DS, Type II) and area under disease progress curve (AUDPC) calculated on the basis of DI and DS. Si absorption in barley enhanced the defense system in head tissues to pathogen invasion; FHB developed more severely on AS and AB plants grown without Si irrigation than on plants supplied with Si. Barley plants treated with exogenous Si irrigating were associated with a reduction of up to 19.3%, 19.8%, 18.7%, and 20.0%, respectively, in DI, DS and AUDPC calculated on the basis of DI and DS. Si contributed to the reduction of FHB in barley, especially for the moderately resistant cultivar; however, Si reduced the intensity of FHB in AB to a level comparable with AS. Importantly, Si treatment at 1.7 mM decreased disease damage FHB in previous bio-trials conducted on AS and AB under in vitro and field environments, showing that Si enhanced the expression of resistance to FHB infection in seedlings and adult barley plants. Taken together, the link of Si and host resistance provided a greater decrease in head blight in which both cultivars had augmented performances upon exogenous Si irrigating to roots; highlighting that Si is a potential safe and efficient policy to defend barley when invaded by Fusarium

Diversity in Plasmopara halstedii, the causal agent of sunflower downy mildew

Diversity of the level of morphological, pathogenic and genetic characteristics was studied in seven Plasrnopara halstedii (sunflower downy mildew) isolates of seven races namely 100, 300, 304, 314, 710, 704 and 714. All analyses were carried out by using five single zoosporangium isolates per pathogen isolate. Morphological analyses were performed on zoosporangia for P. halstedii single zoosporangium isolates. Aggressiveness criteria were analysed in one sunflower inbred line showing a high level of quantitative resistance. Genetic relationships were detected between the single zoosporangium isolates using 12 EST-derived as SNPs markers. Based on the aggressiveness reaction for the P. halstedii single zoosporangium isolates, there were significant intra and inter-race differences for all criteria studied. Isolates of races 100 and lac were less virulent and more aggressiveness than isolates of races 7xx. There was no relation between morphology of zoosporangia and pathogenic characteristics for 35 single zoosporangium isolates. There was no intra-race genetic variation, but five genetically-identified groups were detected among pathogen isolates of all races. No correlation was detected between EST genotypes on the one hand and both pathogenic traits and morphological characteristics on the other

Analyse du coût de virulence chez Plasmopara halstedii, l'agent du mildiou du tournesol

Diplôme : Dr. d'UniversitéAfin de mieux comprendre les interactions entre Plasmopara halstedii et le tournesol, nous nous sommes intéressés à la variabilité du pouvoir pathogène du parasite. Sur une population locale de P. halstedii obtenue sous des conditions naturelles renforcées d'infection et sous différentes pressions de sélection appliquées durant 5 années consécutives, nous avons analysé les liens existants entre l'apparition de nouvelles virulences et l'agressivité d'une part, la variabilité de l'agressivité de populations de la race 710 multipliées sous les différentes méthodes de gestion de gènes Pl, d'autre part. Deux méthodes ont été développées au cours de notre travail : -la première pour obtenir des isolats mono zoosporanges afin d'étudier la variabilité intra et inter pathotype ; -la deuxième pour mesurer l'agressivité

Components of quantitative resistance in barley plants to Fusarium head blight infection determined using three in vitro assays

Quantitative resistance in barley to four Fusarium head blight (FHB) species was investigated in vitro. Nine components involved in three assays (detached leaf, modified Petridish and seedling tests) were compared on two widely grown Syrian barley cultivars: Arabi Aswad (AS) and Arabi Abiad (AB). On AB, inoculation with FHB species resulted in a significantly shorter latent period and larger lesion length of detached leaf inoculation, more standardized area under disease progress curve (AUDPCstandard) of modified Petridish inoculation and a higher percentage of infected seedlings of pin-point inoculation than on AS. The latent period of AB was 14.89% less than AS, lesion length of AS was 6.01% less than AB, AUDPCstandard of AS was 17.07% less than AB and the percentage of infected seedlings of AS was 4.87% less than AB. Inoculation with FHB species resulted in no significant differences in the other five components measured: incubation period of detached leaf inoculation, germination rate reduction and coleoptile length reduction of modified Petridish inoculation, percentage of infected seedlings of foliar-spraying inoculation and lesion length of clip-dipping inoculation. AS was more resistant to in vitro FHB infection than AB. The latent period and AUDPCstandard recorded the highest values compared with the lowest values for lesion length and percentage of infected seedlings. It seems that measurement of the latent period and AUDPCstandard may be useful in identifying barley cultivars which are highly susceptible or resistant to FHB at early stages

Silicon control of bacterial and viral diseases in plants

Silicon plays an important role in providing tolerance to various abiotic stresses and augmenting plant resistance against diseases. However, there is a paucity of reports about the effect of silicon on bacterial and viral pathogens of plants. In general, the effect of silicon on plant resistance against bacterial diseases is considered to be due to either physical defense or increased biochemical defense. In this study, the interaction between silicon foliar or soil-treatments and reduced bacterial and viral severity was reviewed. The current review explains the agricultural importance of silicon in plants, refers to the control of bacterial pathogens in different crop plants by silicon application, and underlines the different mechanisms of silicon-enhanced resistance. A section about the effect of silicon in decreasing viral disease intensity was highlighted. By combining the data presented in this study, a better comprehension of the complex interaction between silicon foliar- or soil-applications and bacterial and viral plant diseases could be achieved

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

Interaction between sunflower plants and five isolates of Plasmopara halstedii on the level of pathogenicity

The interaction between sunflower plants showing a high level of quantitative resistance and five Plasmopara halstedii (the causal agent of downy mildew) isolates of several races were studied using five single zoosporangium isolates per pathogen isolate. Aggressiveness criteria were analyzed for 25 P. halstedii single zoosporangium isolates. Based on the reaction for the P. halstedii isolates to four sunflower hybrids H1-H4 varying only in their downy mildew resistance genes, there were differences in virulence spectrum in pathogen isolates. Analysis of five single zoosporangium isolates for P. halstedii isolates showed significant variability within pathogen isolate for all aggressiveness criteria but not for all pathogen isolates. The hypothesis explaining the interaction between P. halstedii and its host plant was discussed on the level of pathogenicity

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

Pathogenic, morphological and genetic variation was studied in 35 Plasmopara halstedii(sunflower downy mildew) isolates of different races. Virulence spectrum was analyzed in sunflower hybrids carrying effective Plgenes. Aggressiveness was analyzed in one sunflower inbred line showing a high level of quantitative resistance. There were differences in virulence spectrum for pathogen isolates. Index of aggressiveness was calculated for each isolate and two groups were revealed as more aggressive isolates of 100 and 3xx races, and less aggressive isolates of 7xx races. Significant morphological differences were found in zoosporangia and sporangiophores morphology. Genetic relationships were detected between the pathogen isolates using 12 EST-derived markers. Five multilocus genotypes (MLG) were identified among 35 P. halstedii isolates. Our results did not show a correlation between pathogen variation and both morphological and genetic characteristics

Aggressiveness in Plasmopara halstedii (sunflower downy mildew)

Aggressiveness was studied in seven Plasmopara halstedii (sunflower downy mildew) pathotypes: 100, 300, 304, 314, 704, 710 and 714. Aggressiveness criteria including percentage infection, latent period, sporulation density and reduction of hypocotyl length (dwarfing) were analysed in one sunflower inbred line showing a high level of quantitative resistance. Genetic relationships were detected between the seven pathotypes using 12 EST-derived markers. Pathotypes 100, 300, 304 and 314 were characterized with shorter latent period and higher sporulation density than pathotypes 710, 704 and 714. All pathotypes showed high percentage infection values and caused a large reduction in seedling size except for pathotype 314 involved in dwarfing. Pathotypes 714, 704 and 314 had an intermediary genetic position between the pathotypes 100 and 710. No correlation was detected between aggressiveness traits and EST genotypes