Pending solution

Fusarium head blight is one of the most important diseases that affect ears and grains of wheat crops in the world. Described in England in 1894, it continues as a global challenge. Also referred to as fusariosis, its main causal agent is the fungus Gibberella zeae (Schwein) Petch, the asexual form Fusarium graminearum Schwabe. In addition to F. graminearum, several species are associated with the disease in cereals, with F. culmorum, F. equiseti, F. avenaceum and F. nivale being the most reported.

In Brazil, Fusarium head blight causes damage and losses to wheat, barley and triticale crops in the three states of the southern region of Brazil (Paraná, Santa Catarina and Rio Grande do Sul), where 90% of wheat production is concentrated and 97% % barley. The characteristic symptoms of the disease are depigmented spikelets, whitish or straw in color, and the grains are flat, wrinkled, white-pinkish to light brown in color. The pathogen has a wide host range, such as alfalfa, rice, oats, rye, corn, clover, sorghum and several weeds.

The environment plays an important role in the development of Fusarium head blight, with the most favorable conditions being rainfall on two or three consecutive days and a temperature of 24oC to 30oC, a situation that frequently occurs after the heading of winter cereals in the southern region of Brazil. Brazil. The damage caused by the disease is directly influenced by the environmental conditions of the year and the cultivar, ranging from 14% to 60% according to reports on wheat in Brazil. From 1997 to 2009, epidemics were recorded in eight years: 1997, 1998, 2000, 2002, 2005, 2007, 2008 and 2009. In years with drier periods, FHB is not considered a problem.

The reduction in yield due to FHB is attributed to the abortion of flowers and the formation of grains with low weight and reduced density, which are largely discarded on the trail during harvest. Fusarium head blight also harms technological quality due to the reduction of starch, proteins, cellulose and hemicellulose.

However, the biggest problem is the accumulation of mycotoxins, one of the main contaminants in cereals. Mycotoxins are toxic secondary metabolites, produced by toxigenic fungi that infect and/or colonize grains and their by-products, especially cereals during the cultivation and/or storage period. Mycotoxins may also be present in asymptomatic grains, mainly due to late infections that occur in the final grain filling phase, if there is favorable weather conditions. Mycotoxins are chemically stable, tending to remain intact during the processing, storage and processing stages, including baking at high temperatures. They cause harm to the health of humans and animals, causing food rejection, interfering with hormonal systems, inhibiting protein synthesis, as well as affecting general immunity, favoring the appearance of chronic diseases.

Mycotoxins can also generate technological problems in bread production, as F. graminearum modifies the protease that acts on gluten, resulting in heavier and less voluminous bread. Seeds infected by the pathogen present inferior quality in relation to germination power and vigor. In barley, mycotoxins are directly related to the “gushing” effect in beer, which is mainly attributed to the genus Fusarium and mycotoxins. These can also cause technological problems in the quality of malt for brewing, due to the inhibition of enzyme synthesis or fermentation.

The main mycotoxins produced by Fusarium spp. in winter cereals these are trichothecenes, zearalenone (ZEA) and, less frequently, fumonisins. Among the most important trichothecenes, we can mention deoxynivalenol (DON), nivalenol (NIV), T2 toxin, HT2 toxin and diacetoxyscirpenol (DAS). The occurrence, type and concentration of mycotoxins depend on environmental conditions, mainly temperature and humidity, which vary with the year and the species of the pathogen. Deoxynivalenol is the mycotoxin most commonly found in wheat and barley grains.

In several countries there are laws regarding limits for mycotoxins in food. In Brazil, resolution RDC No. 7, of February 18, 2011, provides for the maximum tolerated limits (LMT) for some mycotoxins. The LMT for wheat and barley were established according to year, product, byproduct and food, for applications in 2011, 2012, 2014 and 2016. For application in 2014 and 2016, the LMT are presented in Tables 1 and 2, respectively.

How to manage

To date, there are no wheat, barley or triticale cultivars resistant to Fusarium head blight, nor efficient management to control the disease and eliminate mycotoxins. To minimize losses, the producer can adopt some measures, such as staggering sowing or sowing cultivars with different seeding cycles. The objective is to escape the disease epidemic in at least part of the crop, in periods with excessive rainfall. Chemical treatment is an aid in preventive control of the disease, but, to date, its efficiency is not adequate, as is crop rotation. The most efficient management strategy is the use of cultivars that present moderate resistance to FHB. Another practice is the application of fungicides guided by meteorological conditions (Alert System) and monitoring to determine the occurrence of mycotoxins, for the identification and segregation of batches with high levels of contamination.

Grains affected in the initial filling phase are lighter and are normally discarded in the harvesting process. Affected grains in the final stage of development are heavier and are harvested. In the processing stages, grains with FHB symptoms can be eliminated by cleaning with air, sieve and gravity table.

Therefore, in order to meet the requirements of legislation and guarantee the sale of safe and quality food, there is a need for integrated actions to monitor, manage and control mycotoxins at all stages of the production chain.

This article was published in issue 175 of Cultivar Grandes Culturas magazine. Click here to read the edition.