Wheat can present several diseases caused by phytopathogenic pathogens (fungi, bacteria and viruses). These diseases result from disturbances in the normal functioning of the crop, such as the functioning of cells, tissues and organs, and can therefore cause significant damage not only to the production of the cereal, but also to the economic return to the farmer. Given the upward trend in wheat prices, the financial impacts could be considerable.
In this context, understanding the diseases that affect wheat, such as wheat mosaic, blast, powdery mildew and Fusarium head blight, is essential for farmers, as well as developing skills to detect them early and implement appropriate management strategies. Technical knowledge combined with the adoption of sustainable agricultural practices is essential to mitigate risks and ensure healthy and profitable production.
Main diseases that make up the complex:
Common wheat mosaic
Common wheat mosaic is caused by Soil-borne wheat mosaic virus (SBWMV), which is transmitted by Polymyxa graminis. The microorganism resides in the soil and is an obligatory parasite of plant roots, and its appearance is favored in conditions of high humidity and in cold regions. The long persistence of the vector in the soil, which can exceed five years, and the diversity of host plants make control of this virus challenging, predominantly requiring approaches based on genetic resistance.
The typical symptoms of the virus are the alternation of areas of the leaf and stem with discoloration in well-defined bands or in an alternating fashion. These bands may be more whitish, yellowish or even progress to rapid necrosis.
blast
Pyricularia grisea is a fungus that causes the disease known as blast in wheat plants, reflected in visible symptoms on leaves, stems and ears. Although uncommon, symptoms may be present before flowering begins, being identified by elliptical lesions on the leaves that vary from white to light brown, with edges that can vary from dark gray to reddish brown.
Infection of the ears may result in white areas starting from the point of infection on the rachis. Infection in the rachis interferes with the translocation of nutrients to the upper parts of the cob, resulting in small, wrinkled, deformed and low-weight kernels.
The disease can be favored by a combination of conditions such as temperatures between 24ºC and 28ºC, high humidity and constant periods of rain.
Powdery mildew
Powdery mildew, caused by the fungus Blumeria graminis f. sp. tritici, is a foliar disease in wheat, which causes a reduction in ears and their size, causing a significant loss in crop yield.
Its pathogen is a biotroph that remains in the off-season on volunteer plants and wheat crop residues, being spread by the wind. Its symptomatology on the leaf is its yellowish and whitish tissues, which can be severely attacked, causing its abscission. High relative air humidity, mild temperatures and periods without rainfall are favorable for the development of the disease.
Gibberella
Caused by the fungus Fusarium graminearum, Fusarium head blight is influenced by favorable environmental conditions, such as temperatures between 20ºC and 25ºC, with frequent rains, especially in El Niño conditions. Its symptoms are analyzed in the spikelets, which deviate from the direction of the spikelets that are not affected.
The affected spikelets are whitish in color, like straw, and the peduncle may turn brown in severe cases. These promote the production of flat, wrinkled grains, with a pinkish-white to light brown color, affecting their size and crop yield.
Integrated disease management strategies
To increase productivity and improve production quality, good management is extremely important, and starts with an accurate diagnosis. The diagnosis can be visual, based on symptoms or based on more specific analyzes carried out in the laboratory. Therefore, the technologies and solutions we have available in management are strategies that the producer can adopt in the field to achieve a good result.
Excellent disease management depends on several factors, in this sense, the combination of management serves to prevent, control and manage diseases that affect the crop from pre-planting to post-harvest. Among them, there are some that are more efficient, such as the use of crop rotation, which consists of alternating crops planted in the same area at the same time of year, as a way of reducing the incidence of crop-specific pathogens. Another is off-season management, which provides opportunities to manage the soil, controlling volunteer plants that can be alternative hosts for pathogens and a source of inoculum for some pathogens.
Furthermore, there are preventive methods, such as choosing a resistant cultivar, which is the selection of a cultivar aiming at the greatest set of resistance to different types of diseases. Seed treatment is also one of the alternatives recommended for controlling some fungal diseases. Furthermore, maintaining balance in nitrogen fertilization is one of the factors that can help with crop health, strengthening plant resistance. There are also chemical methods, such as the use of fungicides, such as triazoles and strobilurins, which will contribute to the efficiency of managing these diseases.
Text written by Bianca Carolina Bariquelo and Berno Alexis, members of AGR Jr. Consultoria Agronômica, Junior Company of the Agronomy Course at UFSM Campus Frederico Westphalen, under the guidance of professor Dr. Gizelli Moiano de Paula.
References:
BRUNETTO, E. et al. Two-component cultivar mixture in the management of multiple wheat diseases. Available in: Brazilian Journal of Agricultural Sciences, Number V.12, n.3, p.269-276, 2017. Accessed on: 02/06/2024.
EMBRAPA. Time to watch for powdery mildew in wheat. Available at: . Accessed on: May 27th. 2024.
EMBRAPA. Blasone - Embrapa Portal. Available at: . Accessed on: May 27th. 2024.
EMBRAPA. Diseases - Embrapa Portal. Available at: . Accessed on: May 27th. 2024.
EMBRAPA. Giberela - Embrapa Portal. Available at: . Accessed on: May 27th. 2024.
LAU, D. et al. Common wheat mosaic - Embrapa Portal. Available at: . Accessed on: May 27th. 2024.
LAU, D. et al. Main wheat diseases in southern Brazil: diagnosis and management. - Embrapa Portal. ComTec-375-Online-2021. Available at: . Accessed on: May 27th. 2024.
PONGELUPPI, T. BASF. Wheat: susceptibility of cultivars to diseases. Genetic resistance is one of the pillars of integrated disease management in wheat. Available at: https://agriculture.basf.com/br/pt/conteudos/cultivos-e-sementes/trigo/suscetabilidade-de-cultivares-as-doencas-na-cultura-do-trigo.html. Accessed on: 05/27/2024.
