1,721,045 research outputs found
Race spectra of Leptosphaeria maculans, the causal agent of blackleg disease of oilseed rape, in different geographic regions in northern Germany
No full textThe fungal pathogen Leptosphaeria maculans (LM), causing blackleg in oilseed rape (OSR), develops gene-for-gene interactions with OSR cultivars. Thus, virulent races can cause severe OSR yield losses in genotypes that depend only on the major resistance genes. LM race spectra were determined using 644 isolates collected from four OSR growing areas in northern Germany in autumn 2011 and 2012. Avirulence alleles (AvrLm) and race spectra of the isolates was identified with OSR cultivars harbouring the major genes Rlm1, Rlm2, Rlm3, Rlm4, Rlm7, and Rlm9. Thirteen LM races were determined, whereby 85 % of the collected isolates belonged to race AvrLm(5)-(6)-7-(8) (virulent to Rlm1-4 and Rlm9) and 10 % belonged to race AvrLm1-(5)-(6)-7-(8) (virulent to Rlm2-4 and Rlm9). Only six of 644 isolates (0.9 %) showed virulence to Rlm7. Using tester isolates that identify Rlm7, we showed that Rlm7 was absent in the most sown cultivars in northern Germany, explaining the low frequency of isolates being virulent to Rlm7. However, blackleg disease incidence (DI) increased significantly in the cultivar Exocet (harbouring Rlm7) between 2011/12 and 2012/13, whereas DI was the same in a susceptible control cultivar across all sampled regions and years. Our results show that Rlm7 is the only known major resistance gene in German OSR cultivars that is still effective against LM, but increasing deployment in commercial cultivars may foster resistance breakdown in the future
Entwicklung und Erprobung von DNA-Sonden und Anwendung der Polymerase-Kettenreaktion zur Differenzierung und zum Nachweis der getreidepathogenen Pilze Fusarium culmorum (WG Sm.) Sacc., Fusarium graminearum Schwabe und Fusarium avenaceum (Fr.) Sacc. im pflanzlichen Gewebe
No full textLignin composition and timing of cell wall lignification are involved in Brassica napus resistance to Sclerotinia sclerotiorum stem rot
No full textSclerotinia stem rot (SSR) is an economically and globally significant disease in oilseed rape (Brassica napus L.) caused by the necrotrophic ascomycete Sclerotinia sclerotiorum. This study explored the role of cell wall reinforcement by lignin as a relevant factor for effective plant defence against attack of this pathogen. Expression of key genes in the phenylpropanoid pathway and the induced synthesis of lignin in infected stem tissues were investigated in a study comparing a susceptible (Loras) and a moderately resistant cultivar (Zhongyou 821, ZY821). Data revealed an earlier and more rapid defence activation in ZY821 through up-regulation of transcript levels of genes related to key steps in the phenylpropanoid pathway associated with enhanced lignin deposition in the resistant B. napus genotype. Expression level of BnCAD5, encoding a cinnamyl alcohol dehydrogenase, responsible for conversion of monolignol to lignin, was more rapidly up-regulated in ZY821 than Loras. The similar expression pattern of BnCAD5 and the gene BnF5H, encoding for the ferulate-5-hydroxylase which catalyses the synthesis of syringyl (S) lignin precursors, suggests that BnCAD5 is involved in the S lignin formation. Histological observations confirmed these results, showing an earlier increase of S lignin deposition in the infected resistant genotype. Deposition of guaiacyl (G) lignin was detected in both genotypes and is thus considered a component of basal, cultivar-independent defence response of B. napus to stem rot. The results indicate the importance of cell wall modification for quantitative stem rot resistance by responses in the phenylpropanoid metabolism generating distinct lignin types on different temporal scales
Distribution of Leptosphaeria maculans pathogenicity groups in Germany-Review of the results 1986-1999
No full textDevelopment of fungicide resistance of wheat and barley pathogens against strobilurins: A methodological approach
No full textA methodological approach was conducted to investigate how fast isolates of a "one-race-population" adapt to an ingredient with fungicidal activity. A major objective was to maintain a continuous selection pressure on the fungal populations. Different concentrations of strobilurin azoxystrobin (Amistar(R)) were applied on wheat and barley cotyledons to ensure selection pressure. The fungi reproduced on fungicide-treated leaves in order to display a "worst-case-scenario". Wheat powdery mildew (Blumeria graminis f. sp. tritici) adapted rapidly to higher concentrations of the fungicide. Already the fifth generation of the fungus was able to grow and reproduce on leaves containing high concentrations of azoxystrobin (0.5x of the recommended dosage in the field). Two replicates led to the same results. Although rapidity of the adaptation was remarkable, the adapted isolates apparently lost their fitness. In contrast, Blumeria graminis f. sp. hordei was significantly more susceptible to azoxystrobin. The dosage of the fungicide was reduced by the factor of 10 to 40. The lowest concentration of Amistar(R) efficient against wheat powdery mildew was equal to the highest tolerable concentration applicable for barley powdery mildew. Even when the fungus could adapt to these low concentrations, a change to resistance is not likely, because in the field, 0.1 x of the recommended dosage will normally not be used. The third fungus investigated, glume blotch of wheat (Septoria nodorum) was tested ad planta and in vitro. Ad planta, the fourth and fifth generation of the fungus seemed to be less susceptible against the active ingredient azoxystrobin, but in vitro no such effects were observed. The methods used in these studies seem to offer an easy and fast tool to estimate the risk of adaptation and to compare sensitivity levels of different fungal species. The experiments showed significant differences in fungicide susceptibility between the two powdery mildews. We presume that disruptive as well as adaptive resistance mechanisms occur in both pathogens and that the two resistance mechanisms are correlated. Fungi possessing high affinity to both are more assertive than other fungi. A disadvantage is that these artificial circumstances do not exactly reflect the situation in the field because sexual reproduction is not considered. Nevertheless, the risk of a continuous selection pressure caused by a single-site-inhibiting fungicide was obvious in these experiments
Development of fungicide resistance of wheat and barley pathogens against strobilurins: A methodological approach
No full textA methodological approach was conducted to investigate how fast isolates of a "one-race-population" adapt to an ingredient with fungicidal activity. A major objective was to maintain a continuous selection pressure on the fungal populations. Different concentrations of strobilurin azoxystrobin (Amistar(R)) were applied on wheat and barley cotyledons to ensure selection pressure. The fungi reproduced on fungicide-treated leaves in order to display a "worst-case-scenario". Wheat powdery mildew (Blumeria graminis f. sp. tritici) adapted rapidly to higher concentrations of the fungicide. Already the fifth generation of the fungus was able to grow and reproduce on leaves containing high concentrations of azoxystrobin (0.5x of the recommended dosage in the field). Two replicates led to the same results. Although rapidity of the adaptation was remarkable, the adapted isolates apparently lost their fitness. In contrast, Blumeria graminis f. sp. hordei was significantly more susceptible to azoxystrobin. The dosage of the fungicide was reduced by the factor of 10 to 40. The lowest concentration of Amistar(R) efficient against wheat powdery mildew was equal to the highest tolerable concentration applicable for barley powdery mildew. Even when the fungus could adapt to these low concentrations, a change to resistance is not likely, because in the field, 0.1 x of the recommended dosage will normally not be used. The third fungus investigated, glume blotch of wheat (Septoria nodorum) was tested ad planta and in vitro. Ad planta, the fourth and fifth generation of the fungus seemed to be less susceptible against the active ingredient azoxystrobin, but in vitro no such effects were observed. The methods used in these studies seem to offer an easy and fast tool to estimate the risk of adaptation and to compare sensitivity levels of different fungal species. The experiments showed significant differences in fungicide susceptibility between the two powdery mildews. We presume that disruptive as well as adaptive resistance mechanisms occur in both pathogens and that the two resistance mechanisms are correlated. Fungi possessing high affinity to both are more assertive than other fungi. A disadvantage is that these artificial circumstances do not exactly reflect the situation in the field because sexual reproduction is not considered. Nevertheless, the risk of a continuous selection pressure caused by a single-site-inhibiting fungicide was obvious in these experiments
Wheat Blast and Fusarium Head Blight Display Contrasting Interaction Patterns on Ears of Wheat Genotypes Differing in Resistance
No full textThe interaction of wheat with two ear pathogens, Magnaporthe wheat blast (MWB) and Fusarium graminearum (Fusarium head blight, FHB), was studied on the phenotypic, histological, and gene expression level. Most of the 27 wheat cultivars inoculated with MWB and F. graminearum displayed inverse disease responses to blast and FHB infection. Two cultivars, Milan and Sumai 3, were selected expressing converse disease phenotypes to blast (Milan, R)/(Sumai 3, S) and FHB (Milan, S)/(Sumai 3, R). Confocal laser scanning microscopy revealed early (12 h postinoculation) colonization of the spikelets by MWB similarly on both cultivars, while F. graminearum infected anthers of the susceptible cultivar earlier. Both pathogens grew much faster in the rachilla of susceptible than resistant cultivars, indicating that resistance is mainly expressed in this part connecting the spikelet with the rachis. In general, O-2(-) and H2O2 levels were unrelated to disease expression in the four studied interactions. The differential disease phenotypes, fungal spread in the rachis, and colonization patterns in the spikelets were confirmed by distinct gene expression patterns. Among the eight genes analyzed, seven were more strongly induced by FHB than by blast. Genes for chitinase (Chi2), beta-1,3-glucanase (PR2), a plant defensin homolog (PRP1), and peroxidase (Pox2) were strongly upregulated in Milan in response to both pathogens, while PR2 and PR5 (thaumatin-like protein) were transiently triggered by MWB on both cultivars. Upregulation of cinnamoyl-CoA reductase (CCR), cytochrome P450 (CYP709C1), and UDP-glycosyl transferase (UGT) were more prominent in ears infected with F. graminearum, while upregulation of UGT was higher in Sumai 3 when infected with either pathogen. Cultivar resistance to FHB was reflected by clearly higher expression levels of UGT and CYP709C1 in Sumai 3. The differential responses of wheat to the two ear pathogens demonstrated in this study makes it unlikely that common resistance genes exist for control of FHB and blast, suggesting the need to stack many genes associated with resistance in breeding programs for multiple resistance
Long-term survival of Sclerotinia sclerotiorum sclerotia and Verticillium longisporum microsclerotia in soil and the effects of soil depth, soil temperature, and a biocontrol agent
No full textInduced resistance to Verticillium longisporum in Brassica napus by beta-aminobutyric acid
No full textA preinoculative soil drench application of 0 center dot 5mm -aminobutyric acid (BABA) significantly inhibited colonization of oilseed rape (Brassica napus, susceptible cultivar Falcon) by Verticillium longisporum and also prevented plant stunting caused by the pathogen. To better understand the defence responses induced by BABA, the presence of occlusions in the plant hypocotyl, levels of salicylic acid (SA) and hydrogen peroxide (H2O2), phenylalanine ammonia lyase (PAL) activity and expression of PR-1 and PDF1.2 genes were examined. Transverse sections through the hypocotyl region of BABA-treated plants showed clear vessels surrounded by phenol-storing cells, in contrast to numerous obstructed vessels in water-treated plants, in response to the pathogen. A significant increase in SA levels was observed in the hypocotyls of both water- and BABA-treated plants in response to the pathogen; however, SA levels were unrelated to disease resistance. The level of H2O2 decreased in both treatments in response to the pathogen. A significant increase in PAL activity was observed in hypocotyl tissues of BABA-treated plants. The expression patterns of PR-1 and PDF1.2 were similar in the two treatments in response to the pathogen, indicating no involvement of these genes in resistance. The results indicate a similar organ specificity of the plant hypocotyl for chemically induced internal resistance as for genotype-related resistance, two phenomena which, however, are based on contrasting cytological responses in the vascular tissues. Nonetheless, evidence is provided that the activity of the phenylpropanoid pathway plays a crucial role in both types of resistance.Gottingen International; University of Gottingen in Gottinge
Entwicklung und Erprobung von DNA-Sonden und Anwendung der Polymerase-Kettenreaktion zur Differenzierung und zum Nachweis der getreidepathogenen Pilze Fusarium culmorum (WG Sm.) Sacc., Fusarium graminearum Schwabe und Fusarium avenaceum (Fr.) Sacc. im pflanzlichen Gewebe
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