Management of Fumonisins in Corn

the fungus Fusarium verticillioides, which causes rot in corn, is also responsible for the production of fumonisins, a group of toxic mycotoxins that are highly harmful to human and animal health. When they have a high content, they also result in the imposition of trade barriers that harm the producer's profitability. Its management requires correct measures adopted both in the field phase and in grain storage. 

 With 80 million tons produced in the 2012/13 harvest, Brazil stands out as the third largest corn producer in the world. Recently it became not only a supplier of this grain for domestic consumption, but also an exporting country, currently being the third largest exporter in the world, with more than 15 million tons exported. Currently, the requirements on the quality of products, not only intended for export, but also for domestic consumption, have become increasingly stringent, especially those focused on the sanitary quality of grains and mycotoxin levels.

Therefore, as it is a crop widely cultivated in Brazil, under different climatic conditions, the plants are subject to attack by a high number of pathogens that are responsible for ear rot, with consequent accumulation of mycotoxins. The fungus Fusarium verticillioides (Saccardo) Nirenberg is the pathogen most often associated with corn kernels, causing kernel and ear rots. F. verticillioides, in addition to being found with high frequency, is the species with the greatest potential for production of fumonisins, the most important group of mycotoxins for corn crops. Fumonisins are toxic to humans and are mainly linked to esophageal cancer. They are also toxic to animals, being mainly associated with pulmonary edema in pigs, encephalomalacia in horses, and generalized problems in birds.

Due to these problems, in recent years, government agencies have been monitoring the quality of batches of corn grains, especially regarding fumonisin levels. The Ministry of Agriculture and the National Health Surveillance Agency (Anvisa) established a tolerance limit of 2µgg^-1 for fumonisins in corn grains (Official Federal Gazette, 2011). This limit often creates barriers for the export and national trade of lots of corn grains, generating large losses for producers.

In view of the commercial barriers imposed by the agroindustry and government agencies, management strategies to reduce the levels of fumonisins have been studied over the years, being fundamental for obtaining corn grains with low levels of fumonisins.

Fumonisin management

The production and consequent accumulation of fumonisins in corn grains can occur both in the field and in stored grains. There are different types of management strategies for the different phases.

For the management of fumonisins in the field, the use of genetic resistance is considered the main methodology. The inheritance of genetic resistance to F. verticillioides has been studied over the years, using both visual symptoms and asymptomatic infections. However, most companies developing corn genotypes only use the discarding of genotypes that are highly susceptible due to visual symptoms as a selection methodology. This methodology presents a serious problem, as it is based on visual disease rates, which do not always reflect asymptomatic infections or fumonisin levels, ruling out possible resistance genes specific to the accumulation of fumonisins.

However, some reports of genotypes with acceptable levels of resistance, both to infection by F. verticillioides as well as the accumulation of fumonisins, can already be found in the literature.

Another methodology that can be used in the integrated management of fumonisins in corn is the adoption of transgenic genotypes, mainly Bt. Briefly, corn genotypes Bt are cultivars that received genes from a bacterium called Bacillus thuringiensis, and became capable of synthesizing a protein derived from these genes, known as CryIA. In order, the Cry protein is toxic to certain types of insects, especially those that use corn in their food. Such insects often open doors for the entry of F. verticillioides or provide a favorable environment for its development, thus causing an increase in fumonisin levels. Consequently, genotypes that are called Bt They are often resistant to infection and the accumulation of fumonisins. However, the use of corn genotypes is still the subject of much speculation. Bt in the management of fumonisins in corn, as, even with these genotypes, high levels of fumonisins in grains in conventional plantations are still detected in some cases. Basically, studies focused on the direct action of these genes on the colonization of F. verticillioides and accumulation of fumonisins in corn still need to be carried out.

The choice of planting density can also be adopted as a fumonisin control methodology. Recent studies report that fumonisin levels at a density of 65 thousand plants/ha can be doubled when a planting density of 85 thousand plants/ha is adopted, that is, when there is a density of plants.

Another important aspect to be addressed is the combat of Fumonisins in corn grains using chemical control. There are several reports in the literature on the effect of applying fungicides on the control of fumonisins in corn, however, these are studies that present inconclusive results. Last year, at Embrapa Milho e Sorgo, in Sete Lagoas, Minas Gerais, a series of three experiments were conducted using various fungicides to control burnt grains and fumonisins in corn. The results of this work were conclusive, indicating that the fungicides on the market applied via foliar treatment in a conventional manner, regardless of the number of applications, were not able to control the Fumonisin levels in the grains.

However, fumonisin levels can be influenced by environmental conditions, mainly by periods of summer during the grain filling phase and rain during the drying phase in the plant, which provides increases in the levels of this important mycotoxin. However, the correct management of irrigation, avoiding water stress, can also be used to reduce the risks of Fumonisin contamination. 

In harvesting, processing and storage

Many species of toxigenic fungi, such as F. verticillioides, which colonize grains, are well adapted to develop in substrates with low humidity. For this reason, delaying harvesting can result in increased contamination with fumonisins, especially when rain occurs after the grains mature. Although the kinetics of fumonisin production in corn is still the subject of studies, it has been reported that F. verticillioides can grow in grain until the water content reaches 18% to 20%. However, for good grain storage, it is widely accepted that the water content should not exceed 15%.

During harvest, it is important to correctly adjust combines to avoid excessive damage to the grains, which can predispose to infection during storage, as the highest levels of fumonisins are often associated with broken grains and those damaged by insects. In general, the reduction in fumonisin levels can reach 60% with the removal of damaged grains. Careful adjustment of the harvester or densimetric table can eliminate these contaminated grains, respectively, while still in the field or during processing, with minimal loss of healthy grains. However, healthy grains can carry high levels of fumonisins, so the removal of damaged grains can be a strategy to reduce the levels of fumonisins, however, it is not always as effective.

During storage, the development of toxigenic fungi, such as F. verticillioides, is influenced by water activity, substrate temperature, grain damage, aeration, fungal inoculum, interactions with other organisms and insects. However, the accumulation of fumonisins depends primarily on humidity control. However, if there is activity by insects, rodents or some other factor that causes changes in water content, the accumulation of fumonisins may occur.

Low-toxicity antifungal agents can be used to complement good tobacco management practices, but not as a substitute for other practices aimed at high-quality foods. Fungal growth and mycotoxin contamination of high-moisture grains can be prevented with propionic acid or mixtures of acetic and propionic acid. Liquid sprays are generally more effective than dry formulations of propionic acid, but dry formulations are easier to use.   

Fabrício Eustáquio Lanza, Postdoctoral fellow at the Federal University of Viçosa; Dagma Dionísia da Silva, Embrapa Corn and Sorgo Researchers; Rodrigo Véras da Costa, Embrapa Corn and Sorghum Researchers; Luciano Viana Cota, Embrapa Corn and Sorghum Researchers; Laércio Zambolim, Professor at the Federal University of Viçosa; Elaine Aparecida Guimarães, PhD student, Federal University of Lavras

Article published in issue 193 of Cultivar Grandes Culturas.