Fusarium head blight control in wheat

Productivity reducer and responsible for production of mycotoxins harmful to human health, Fusarium head blight is an aggressive fungal disease in wheat cultivation. Its efficient control involves adopting strategies in set, such as crop rotation, use of cultivars with partial resistance and application of fungicides preventively or at the beginning of the infestation.

A Fusarium head blight is a fungal disease whose causal agent is Gibberella zeae (Schw.) Petch (anamorph – Fusarium graminearum Schwabe.). During its life cycle, the fungus presents a saprophytic phase and another parasitic. It survives in cultural remains until, under climatic conditions favorable conditions and from the beginning of the wheat crop, the beginning of parasitic phase. That way, G. Zeae is the main pathogen of ear of culture. This disease appears regularly in wheat crops, with losses in national productivity being reported above 13%. In other countries, like China and Japan, these values ​​exceed 50%. In addition to losses in productivity, its etiological agent is responsible for producing several mycotoxins. It stands out deoxynivalenol (DON). This toxin, once present in cereal grains, used in food, human and animal (monogastric), can cause serious problems to health, as it is highly toxic and supports high temperatures when the grain is subjected to processing. In this scenario and for food security, the inspection to control this mycotoxin is already carried out in Brazil, with specific legislation that determines the maximum limits allowed for grains of wheat and its by-products. Therefore, controlling the occurrence in culture and presence in the grains produced is extremely important.

O The causal agent of FHB can survive on living host plants, such as barley and triticale, which causes losses similar to those occurring in wheat. However, the main primary source of inoculum for G. zeae under field conditions are cultural residues, having the corn straw the greatest capacity for colonization by the fungus in the saprophytic. To infect new plants, the fungus present in living tissue or crop residues need to produce sexual structures (perithecia), which produce ascospores, these structures being responsible for the dissemination of illness. Conidial infection can also occur in FHB, however, only at short distances.

A Fusarium head blight presents infection during the flowering phase of wheat, with the anthers being the main entrance door. Under favorable environmental conditions, high humidity and temperature, the fungus begins the infection close to the anthers retained in the spikelet, branching until reaching other parts of the spikelet, such as the grain development. Next, the nearest spikelets are infected, and Contamination of the entire ear has been reported in severe cases. The infection also can occur in the stalk, immediately below the ear, causing symptoms such as early maturation of the spikelets or the entire ear.

To the Infected spikelets lose their chlorophyll and become whitish or white in color. palea. Furthermore, the edges become ‘goose bumps’. In conditions of high humidity and heat, the formation of macroconidia occurs, thus making the pink spikelets, especially at the base and edges of the glumes. Infected grains have smaller volume and mass, with a dull and discolored. As the disease progresses, the entire spikelet becomes whitish color. High humidity level after flowering tends to increase the number of gibberellated grains, accumulation of DON and in case of severe epidemics the absence of grain on the cob is regularly observed.

A Fusarium head blight can also be spread by infected seeds, causing death of seedlings, which are characterized by having moist cortical rot of color reddish brown to light brown. Seedling infection, in addition to being a result the use of infected seeds, may occur due to the presence of straw or plant material colonized by the fungus in the crop. In this context, control cultural of G. zeae from Crop rotation becomes an important component in crop management, avoiding early infections and severe epidemics. Species such as soybeans, sunflower and canola are examples of crops that can be used in rotation for Fusarium head blight control. However, the required rotation period varies depending on according to the rate of decomposition of infected waste.

O Chemical control of Fusarium head blight, using fungicides, is effective, counting currently with 52 commercial products registered for wheat cultivation in Brazil, with Triazoles and benzimidazoles being the most frequent chemical groups. While the associated formulations of strobilurin + triazole or strobilurin + metconazole, has been shown to be more efficient for the management of G. zeae. However, chemical control and the efficiency of fungicides is linked to their use in the initial phase of fungus infestation. In this way, applications at the beginning of the reproductive phase of the wheat and with exposed anthers are the most effective, as well as in periods when precede long periods of leaf wetness and high temperatures.

A use of wheat cultivars with moderate genetic resistance to FHB has been shown to be an important tool in the management of this disease. Nonetheless, There are no cultivars available on the market with complete resistance to this fungus, soon, under conditions favorable to the development of the causal agent, the use of recommended fungicides is necessary. Therefore, for efficient control of Fusarium head blight in the crop of wheat, joint strategies must be used, combining the rotation of crops, the use of cultivars with partial resistance and the application of fungicides preventively or at the beginning of the fungus infestation. Per Finally, monitoring weather conditions and even scheduling sowing must be observed by the producer, in order to favor the crop in relation to Fusarium head blight, maintaining the production and quality of the wheat produced.

The Wheat

Cereals constitute the group of cultivated species with the greatest agricultural importance worldwide. In addition to representing the basis of the diet human food in many countries, its cultivation played a crucial role in the beginning of agriculture and, consequently, the formation and organization of Actual society. Among these species, hexaploid wheat (Triticum aestivum L.) was one of the first plant species to be domesticated by man. Currently, he exercises important economic function supporting various industrial branches and, in addition to that, it is an alternative in crop succession for systems of cultivation in southern Brazil, where monoculture with soybeans is predominant.

World wheat production in 2016, according to data from United State Ministry of Agriculture, was 735.229 thousand tons. O Brazil represents less than 1% of world production, with its production concentrated in the center-south of the country. In this region, between the months of September and November, excessive periods of plant wetness occur frequently, together with average temperatures above 15ºC, generating a microclimate favorable for the development of fungal diseases. This scenario coincides with the reproductive period of wheat, the stage of greatest sensitivity of the crop, making diseases the main health factor limiting culture in the region.

Article published in issue 226 of Cultivar Grandes Culturas, March, 2018.