Abstract
Zymoseptoria tritici is a hemibiotrophic pathogen which causes Septoria leaf blotch in wheat. The pathogenesis of the disease consists of a biotrophic phase and a necrotrophic phase. The pathogen infects the host plant by suppressing its immune response in the first stage of infection. Hemibiotrophic pathogens of the genus Fusarium cause Fusarium head blight, and the necrotrophic Parastagonospora nodorum is responsible for Septoria nodorum blotch in wheat. Cell wall-degrading enzymes in plants promote infections by necrotrophic and hemibiotrophic pathogens, and trichothecenes, secondary fungal metabolites, facilitate infections caused by fungi of the genus Fusarium. There are no sources of complete resistance to the above pathogens in wheat. Defense mechanisms in wheat are controlled by many genes encoding resistance traits. In the wheat genome, the characteristic features of loci responsible for resistance to pathogenic infections indicate that at least several dozen genes encode resistance to pathogens. The molecular interactions between wheat and Z. tritici, P. nodorum and Fusarium spp. pathogens have been insufficiently investigated. Most studies focus on the mechanisms by which the hemibiotrophic Z. tritici suppresses immune responses in plants and the role of mycotoxins and effector proteins in infections caused by P. nodorum and Fusarium spp. fungi. Trichothecene glycosylation and effector proteins, which are involved in defense responses in wheat, have been described at the molecular level. Recent advances in molecular biology have produced interesting findings which should be further elucidated in studies of molecular interactions between wheat and fungal pathogens. The Clustered Regularly-Interspaced Short Palindromic Repeats/ CRISPR associated (CRISPR/Cas) system can be used to introduce targeted mutations into the wheat genome and confer resistance to selected fungal diseases. Host-induced gene silencing and spray-induced gene silencing are also useful tools for analyzing wheat–pathogens interactions which can be used to develop new strategies for controlling fungal diseases.
Highlights
Various species of the genus Triticum L., in particular the allohexaploid wheat species of the genus T. aestivum L., are among the major groups of domesticated crops [1]
Septoria leaf blotch caused by the Zymoseptoria tritici (Desm.) Quaedvlieg and Crous, a hemibiotrophic pathogen, is able to decrease wheat yields by up to 30–50% [5]
All winter wheat cultivars are susceptible to infections caused by Z. tritici which is increasingly resistant to quinone outside inhibitors (QoI) and demethylation inhibitors (DMI) [6]
Summary
Various species of the genus Triticum L., in particular the allohexaploid wheat species of the genus T. aestivum L., are among the major groups of domesticated crops [1]. The infection process of the described wheat pathogens is similar towards the end of tissue colonization and penetration because it relies mainly on the production of cell wall-degrading enzymes. According to Pöggeler and Wöstemeyer (2011) [55], in the process of wheat infection with P. nodorum, pathogenicity effectors and cell wall-degrading enzymes are released into extracellular space to induce necrosis and disorganization of the neighboring cells and to produce simple metabolites that are later carried to fungal cells by protein transporters. Z. tritici is characterized by low expression of genes that encode cutinase and degrade cutin in early stages of infection in wheat, which is consistent with the model depicting the role of stomata in plant infections [68]. Fusarium graminearum does not produce appressoria, but this fungus has been found to penetrate the adaxial surface and stomatal openings of glumes, lemma and palea [69]
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