Efeito dos Compostos de Zinco sobre Fusarium verticillioides com relação ao Crescimento das Colônias, Alterações nas Hifas,
Conídios e Produção de Fumonisinas
ARTIGO PUBLICADO: Savi, Geovana Dagostim, Bortoluzzi, A.J., Vitorino, V., Scussel, V.M., Effect of Zinc Compounds on Fusarium verticillioides Growth, Hyphae Alterations, Conidia, and Fumonisin Production. Journal of the Science of Food and Agriculture 93, 3395-3402, 2013. DOI: 10.1002/jsfa.6271
Effect of zinc compounds on Fusarium verticillioides growth, hyphae alterations, conidia, and fumonisin production
Geovana D Savi,a Vinícius Vitorino,a Adailton J Bortoluzzib and Vildes M Scussela
a
Laboratory of Mycotoxicology and Food Contaminants, Food Science and Technology Department, Center of Agricultural Sciences, Federal University of Santa Catarina, P.O. Box 476, 88034-001, Florianopolis, Santa Catarina, Brazil
b
Chemistry Department, Federal University of Santa Catarina, P.O. Box 476, 88034-001, Florianopolis, Santa Catarina, Brazil
Abstract
BACKGROUND: Several strategies are used to eliminate toxigenic fungi that produce fumonisinsin grains. Fusarium verticillioides can be controlled by the application of synthetic fungicides in the field or during storage. However, there may also be residuals, which may remain in the foods. Inorganic compounds such as zinc are cheap, stable and could present strong antifungal activity. Some Zn compounds can be utilized as dietary supplements and are authorized for the fortification of foods. Knowing the advantages and that low concentrations of Zn can have antimicrobial activity, our objective was to evaluate the effects of Zn compounds on the growth of F. verticillioides and the production of fumonisin and conidia. In addition, we aimed to verify that Zn compounds cause morphological alterations of the hyphae, mortality and production of reactive oxygen species.
RESULTS: Zn compounds efficiently reduced fungal growth and fumonisin production. Treatment using zinc perchlorate gave the best results. All treatments inhibited conidia production and caused morphological alterations of the hyphae. It was possible to observe cell death and production of reactive oxygen species.
CONCLUSION: Zn compounds have advantages compared to other antifungal compounds. In particular, they are non-toxic for the organism in appropriate amounts. They could be studied further as potential fungicides in agriculture.
Keywords: zinc compounds; Fusarium verticillioides; growth;
INTRODUCTION
Fusarium verticillioides is a widely distributed pathogen and is
reported as a species that infects all stages of plant development, having the ability to infect and cause tissue destruction in important crops (corn and wheat mainly). However, its scope is not limited to the crops on the field, as mycotoxins may be produced under storage conditions, although on a small scale, if under optimal conditions (e.g. high moisture content).1
The main toxins produced are the fumonisins (FBs), which are
associated with several mycotoxicoses, including equine
leukoencephalomalacia,2,3 swine pulmonary edema4,5 and experimental rats kidney and liver cancers.6,7 Among the FBs, FB1, FB2 and FB3 are the main grain contaminants detected. Generally, FB1 makes up 70% of the total FBs produced, followed of FB2 and FB3.
8
The International Agency for Research on Cancer has classified FB1 as a possible carcinogen to humans.9
The production of FBs in agricultural commodities depends upon several factors, such as the geographical region, season, and the environmental conditions under which the crops are grown. Tropical and subtropical regions are the most favorable for the development of field fungi on cereals and the production of these toxins.10 Although cereals are important as substrates, moisture level and temperature are the critical abiotic factors regulating the growth of F. verticillioides and the production of FBs.11 The presence of FBs has been reported in several foods worldwide, especially grains.12–17
Several strategies have been applied to eliminate toxigenic fungi FB producers in grains. Fusarium can be controlled by applying synthetic fungicides in the field. However, that treatment can be problematic due to the compounds toxicity on mammals and because their residues may remain in the foods.18 Indeed, fungicide treatment post-harvest, including during grain storage can lead to serious health hazards for consumers.19 Furthermore, the use of fungicides as chemical methods can develop resistance in the fungi.20
Therefore, the development of new antifungal agents that can assist in the current control strategies is essential. Inorganic compounds such as zinc (Zn) are stable, have been reported to be strong antimicrobial agents, apart from being less toxic, stable and cheaper than other products.21 The most common inorganic zinc compounds are zinc sulfate (ZnSO4), zinc perchlorate [Zn(ClO4)2] and zinc oxide (ZnO). In recent years ZnO in nanoscale particle size (NPs) also has received
special attention due to the special physical and chemical properties of the nanoparticles.22–24 Some studies have reported the utilization of these compounds for antibacterial activity.25–29 There are, however, only a few studies reporting their action against filamentous fungi30–32 and no studies on the effects of these compounds either against F. verticillioides or on its toxigenicity.
It is important to emphasize that several zinc compounds have been utilized in dietary supplements for human consumption under different forms (zinc acetate/ chloride /citrate/ gluconate/ lactate/ oxide /carbonate / sulfate) which are considered as Generally Recognized as Safe (GRAS) and authorized also in human foods fortification by several international official boards33,34 including approval by the European Commission (EC 2002). They are taken as supplements for their health benefits as zinc plays role in multiple enzyme systems related to the metabolism of protein, carbohydrates, fat and alcohol.35
Considering that (1) zinc compounds have advantages regarding effectiveness, safety and stability on anti-bacteria activity at low Zn concentrations; (2) lack of information of these compounds (including at NPs sizes) anti-fungal properties either for toxigenic species of Fusarium and FBs formation; and (3) the need for effective control and prevention methods against toxigenic F. verticilioides for application to field crops, this work reports an evaluation of the effects of three different zinc compounds (including ZnO at NPs size) on toxigenic F. verticillioides regarding: anti-fungi (colony growth inhibition) and possible anti-toxin (reduction of FBs) properties apart from conidia production and hyphae alterations (cell mortality and formation of reactive oxygen species) by using scanning electron microscopy (SEM), light microscopy (LM) and confocal optical microscopy (COM), respectively.