Fusarium graminearum

Fusarium graminearum is a highly pathogenic ascomycete fungus, belonging to the Fusarium graminearum species complex (FGSC), which groups genetically close species, such as F. asiaticum e F. meridionale.

This pathogen stands out for causing severe diseases in crops of global economic importance, especially wheat and corn, compromising grain productivity and quality.

Its relevance in Brazilian and global agriculture is amplified by the production of mycotoxins, such as deoxynivalenol (DON), which affect human and animal health and reduce the commercial value of agricultural products.

Biology and life cycle

F. graminearum presents a complex life cycle, with sexual and asexual phases.

In the sexual phase, the fungus forms structures called perithecia, which produce ascospores, which are disseminated through the air to the spikes of the host plants. Infection occurs mainly during flowering, when the spores germinate in conditions of high humidity and moderate temperature (26–28°C).

In the asexual phase, the pathogen generates conidia, which contribute to the secondary spread of the disease.

It is a hemibiotrophic fungus: it begins the infection by feeding on living tissue (biotrophic phase) and then becomes necrotrophic, degrading dead tissue to complete its cycle.

Its ability to survive in crop residues and in the soil for prolonged periods, combined with transmission via seeds, facilitates its persistence in agroecosystems.

Diseases caused and symptoms

The main diseases associated with F. graminearum include:

• Wheat head blight (Fusarium Head Blight - FHB): characterized by premature bleaching of spikelets, depigmentation, whitish or straw-like coloration, and darkening of glumes. This disease reduces productivity and contaminates grains with mycotoxins, compromising food safety.

• Corn ear rot: It manifests itself through changes in the color of the grains (from slight darkening to intense brown), lesions on the stalk and ear, as well as a reduction in seed viability.

• Stem and root rot: affects the vascular system of plants, causing necrosis, weakening of the stem and drooping, especially in conditions of high humidity and temperatures between 28–30°C.

• Wilting in seedlings: originating from contaminated seeds, leads to the premature death of young plants due to stem and root rot.

Favorable environmental conditions

The proliferation of F. graminearum depends on specific weather conditions.

Temperatures between 15–29°C and high humidity are ideal for germination and infection.

Frequent rainfall during crop flowering creates microenvironments conducive to the release of spores and the penetration of the fungus into plant tissues.

Integrated control and management strategies

Combating F. graminearum requires multifaceted approaches, as the isolated use of fungicides or other practices is rarely sufficient. Key strategies include:

• Application of fungicides and biostimulants: triazole and strobilurin fungicides, applied at critical times (such as flowering), reduce infection. In addition, potassium and manganese phosphites (0,2–1 mL/L) inhibit pathogen growth.

• Resistant cultivars: selection of genotypes with genetic resistance reduces disease severity and mycotoxin accumulation. However, it is important to note that there are currently no wheat or corn cultivars that are completely resistant to F. graminearum in Brazil. Although there are genotypes with different levels of susceptibility, the development of more resistant varieties continues to be a research objective.

• Management of crop residues: incorporation or removal of infected residues minimizes the primary source of inoculum.

• Monitoring and early detection: laboratory methods, such as semi-selective methods, allow the pathogen to be identified in seeds before planting, enabling preventive decisions.

• Cultural practices: weed control, soil moisture management and adequate spacing between plants reduce the microclimate favorable to the fungus.

• Crop rotation: alternating susceptible crops (such as wheat and corn) with non-host species interrupts the pathogen's cycle, reducing its survival in the soil and in crop residues.

• Seed treatment: fungicides based on difenoconazole, triadimenol and fludioxonil show 61–100% efficiency in controlling the fungus in seeds.

See here the list of pesticides registered for the control of Fusarium graminearum