Fusarium-Befall bei Emmer und Nacktgerste

Abstract

The results of the thesis showed that emmer was highly susceptible to F. graminearum and F. culmorum infection and trichothecene accumulation, but naked barley had a relatively low susceptibility. Most of the fungal biomass and trichothecenes found in emmer and spring barley was located in the glume. Although naked barley does not possess this protective organ, it was in general less susceptible to Fusarium infection than emmer. The phenolic acid contents in the grains of both emmer and naked barley were influenced by Fusarium infection, leading to a significant reduction in the total content of ferulic acid as the predominant phenol in the grains. Comparing the two types of cereals, we found higher arabinoxylane contents in naked barley than in emmer and more arabinose providing a possible site for a phenol involved crosslinking between arabinoxylane backbone and other cell wall compositions. In addition, naked barley grains contained the flavonoid catechin which was significantly higher concentrated after artificial Fusarium infection in comparison to naturally infected samples. Catechin is lacking in emmer and this might be one of the reasons for the higher susceptibility of this species to the fungus.Emmer showed in addition to the basic findings in wheat, new cognitions on the degradation and changes of storage protein subunits by Fusarium infection. Therefore fungal treatment and nitrogen supply led to a species specific effect of the gliadin/glutenin ratio. Comparison of emmer and wheat showed that emmer gliadin proteins were more affected by nitrogen supply as in wheat, in contrast the wheat glutenin fraction changed in the same range as in emmer.Gliadin and glutenin digestion by Fusarium graminearum trypsin-like serine protease investigated in a model system showed a preference for the glutenin subunits in the degradation of gluten. Here the HMW-GS were the most effected fraction resulting from the higher lysine content in this fraction in comparison to LMW-GS. Isolated digestion of gliadin and glutenin by F. graminearum proteases confirmed former results, i.e. showed clearly a strong effect also on gliadin degradation. These digestion affected the yield and composition of proteins extracted according to the traditional solvent procedure (Osborne) because glutenin fragments were found in the gliadin extraction solution after digestion. In contrast to the effects visible in emmer naked barley, showed no characteristic changes in protein composition as a reaction to Fusarium infection. The influence of the growing location and nitrogen availability present characteristic changes in the synthesis of barley protein types in response to increased nitrogen. The increasing nitrogen supply resulted in a significantly positively affected C-hordeins, γ-hordeins and D-hordenins but a negatively influenced B-hordenin content. The proteome analysis of a selected emmer and naked barley cultivar showed in connection to Fusarium infection the significant change of specific proteins i.e. involved in defence strategies in late development stages of the grain. In both cultivars the infection leads to an up-regulation of serine protease inhibitors from the serpin group that can inhibit fungal protease and infection success. It also results in the up-regulation of pathogenesis related proteins that can interact with the fungus and inhibit hyphal growth and sporulation. A down regulation of proteins involved in molecular redox regulation in emmer indicated a time dependent management of specific defence mechanisms after fungal infection. Additionally an infection depending degradation of storage proteins is visible in both cultivars and underlines the degradation potential of Fusarium proteases. Nevertheless more studies about the influence of fungal infection for emmer and naked barley cultivars are necessary to enhance the knowledge about plant fungal interaction to clarify practice relevant changes beside extreme artificially infection conditions for grains in general.