Fungal Infection and Disease Progression: Fusarium spp. Enzymes Associated with Pathogenesis and Loss of Commercial Value of Wheat Grains

Abstract

Fusarium Head Blight (FHB) one of the most devasting diseases on small-grain cereals has caused severe epidemics worldwide, altering yield and quality parameters of the grains, as their weight, carbohydrate and protein composition and contamination with fungal toxins. The aggressiveness of Fusarium spp. utilizes different mechanisms, such as the production and release of extracellular plant-cell-wall-degrading enzymes so crucial in the processes of fungal colonization and disease establishment. A reduced secretion of enzymes might retard both the growth of the fungus on the host surface and the overall infection process, thus giving the host more time for a defensive response. Once infection is established, mycotoxins are released, which interfere with the metabolism of the host. Among the early extracellular enzymes secreted by fungal pathogens during infection, the pectic enzymes are often required for full virulence because the hydrolytic activity softens the cell walls, thus enabling the success of further infection steps and the spread of the mycelium into the inner tissues of the plant. Another group of enzymes relevant are the proteases, which degrade the storage proteins and thus have the greatest influence on quality of the grains. The nature and concentration of the proteins in wheat are some of the main determinants of its commercial value. Different techniques and methodologies are used in laboratories and in industry to analyze the protein content of wheat flours, since the result obtained enables a classification with respect to their quality and a categorization in terms of their end use.