Disease
The ascomycete fungus Mycosphaerella graminicola causes septoria tritici blotch, a foliar disease of wheat that poses a significant threat to global food production. It is the primary foliar disease of winter wheat in most western European countries.
It occasionally infects other grasses including barley. It is found in all wheat growing areas of the world and is the major disease of wheat in the UK.
Losses to septoria tritici blotch can reduce yields of wheat by 30 to 50% with a huge economic impact; global expenditures for fungicides to manage septoria tritici blotch total hundreds of millions of dollars each year. This fungus is difficult to control because populations contain extremely high levels of genetic variability and it has very unusual biology for a pathogen. Mycosphaerella graminicola has an active sexual cycle under natural conditions, which is an important driver of septoria tritici blotch epidemics and results in high genetic diversity of populations in the field.
Control of the pathogen (antifungal medication) now relies on the application of azole fungicides which are demethylase inhibitors that inhibit lanosterol 14 alpha-demethylase (CYP51) activity.
Mycosphaerella graminicola has resistance to multiple fungicides, because it has number of substitutions of CYP51. CYP51 substitutions include Y137F which confers resistance to triadimenol, I381V which confers resistance to tebuconazole and V136A that confers resistance to prochloraz.
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Typical infection caused by Mycosphaerella graminicola of the primary leaf of a resistant cultivar. Note the low fungal density in the apoplast (arrow) and the response of the mesophyll cells (arrow head), particularly the chloroplasts, to the presence of intercellular hyphae.
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(upper image) Typical symptoms of Mycosphaerella graminicola on a primary seedling leaf of a highly susceptible wheat cultivar. (lower image) Typical response to Mycosphaerella graminicola on a primary leaf of a highly resistant wheat cultivar.
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Symptoms of Mycosphaerella graminicola on a naturally infected adult plant flag leaf of wheat.
Read more about this topic: Mycosphaerella Graminicola
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