respectively. In the var. AM the growth rise the 29th and 21st sections at the same time. The NO was measured using DAF-2DA that is a cell permeable molecule that does not fluoresce until it reacts with NO. This allowed us to monitor relative intracellular NO content using fluorescence and confocal microscopy. Our results confirm the presence of NO in the interaction Capsicum annuum-Phytophthora capsici. The intensity of signal is always higher in the SCM tissues than in AM. The highest intensity was detected in the following four sections after necrosis zone, 3 days after inoculation in var. SCM, that corresponded to the fungal invasion zone. The control tissues also showed NO production, but again the response of SCM was more intense than in AM. These results suggested that NO is implicated in the defence reaction against the fungus and also in the reaction against wounding. Finally we detected the NADPH-diaforase domain, a marker of nitric oxide synthase (NOS) enzyme by histochemical staining. The NO production in pepper would be associated with the presence in chloroplasts of this enzyme. This is the first time that a signal system of the pathogenic infection, in which NO is implicated, has been reported in pepper plants.
Genotype-dependent accumulation of Triticum aestivum transcripts in response to deoxynivalenol
Khairul Ansari, Damian Egan and Fiona Doohan
Molecular Plant Microbe Interactions Group, Department of Environmental Resource Management, Agriculture and Food Science Building, University College Dublin, Belfield, Dublin 4, Ireland
Deoxynivalenol (DON) is a trichothecene mycotoxin produced by cereal-pathogenic Fusaria and evidence suggests that it acts as a phytotoxic disease virulence factor aiding host pathogenesis. The effect of DON (20 ppm) on gene expression in roots of Fusarium head blight (FHB) disease resistant (Frontana and CM 82036) and susceptible (Remus and Riband) wheat (Triticum aestivum) cultivars was determined (24-h post-treatment). Despite inhibition of protein synthesis being the mode of action of this toxin, at least 70 transcripts were overexpressed in the wheat roots of different cultivars in response to DON. We assessed the effect, over time, of DON and Fusarium avenaceum culture filtrate on the production of specific transcripts including translation elongation factor 1 (EF-1), adenosine kinase (ADK), retrotransposon-like homologs and genes of unknown function. We describe the genotype and treatment-specificity of transcript accumulation over time and consider the potential implications on the host cell response to trichothecenes and trichothecene-producing Fusaria.
Potential of bacteria to control Septoria leaf blotch of wheat
S. Kildea, M.R. Khan, J. Tuohy and F. Doohan
Molecular Plant Microbe Interactions Group, Department of Environmental Resource Management, Faculty of Agriculture, University College Dublin, Belfield, Dublin 4, Ireland
At present fungicides are the principle mechanism relied upon to control Septoria leaf blotch disease of wheat caused by the fungal pathogen Mycosphaerella graminicola. But, due to emerging M. graminicola resistance and decreasing sensitivities towards fungicides the demand for alternative control mechanisms has increased. This study examined the potential role of bacteria (isolated from cereal leaves and agricultural soils throughout Ireland) as biological control agents of Septoria leaf blotch. Of 150 bacterial isolates, three (unidentified isolates MKB21 and MKB91, and Bacillus megaterium strain MKB135) caused inhibition (64%) of Septoria leaf blotch on seedlings of the wheat cv. Equinox, under controlled environmental conditions (bacteria applied two days post fungal inoculation). The ability of these isolates to control Septoria leaf blotch in adult plants (cv. Raffles) under field conditions was then determined. When applied two days post fungal inoculation, B. megaterium strain MKB135 and isolate MKB91 significantly reduced disease by 72% and 29% respectively (P 0.05); isolate MKB21 did not significantly affect disease levels (P> 0.05).
Analysis of intra- and inter-species genetic evolution of European wheat-pathogenic Fusarium fungi
Josephine M. Brennan*, Damian Egan and Fiona M. Doohan
Department of Environmental Resource Management, Agriculture and Food Science Building, University College Dublin, Belfield, Dublin 4, Ireland
Fusarium head blight (FHB) is an important disease of wheat, barley and maize world-wide. Fusarium fungi exhibit an extraordinary degree of biodiversity with respect to morphological, physiological and ecological characteristics. This study used AFLP analysis to examine the inter- and intra-species genetic diversity of 80 Fusarium wheat-pathogenic isolates representing five species (F. avenaceum, F. culmorum, F. graminearum, F. poae and M. nivale) and originating from Ireland, the UK, Hungary and Italy. Nine other F. graminearum isolates representing the different geographic lineages and isolates of seven other Fusarium species were included in this study. Isolates were identified morphologically and by species-specific PCR analysis. At the intra-species level, UPGMA cluster analysis of AFLP data revealed that the F. poae isolates showed the highest level of genetic similarity, closely followed by the F. culmorum isolates. The most genetically diverse species was F. avenaceum. Principal coordinate analysis of AFLP data generally confirmed the same cluster profile as did the dendrograms. The present study also found a relationship between genetic diversity and country of origin of the isolates within certain species; no relationship was found between genetic diversity and growth or pathogenicity of the isolates.