rivates [6,7], and even chocolates [8]. In order to find a solution for this problem, some organizations and institutions have purposed prevention strategies in order to reduce the risks given by this public problem especially in low-income countries, but those strategies are not enough to give a real solution to this worldwide daily problem. 2. The global problem of AF in crops and food The prevalence of AF in crops and livestock is a serious problem in many parts of the world, undermining public health and development efforts. AF are highly toxic, cancer causing fungal metabolites known to cause immune-system suppression, growth retardation, liver disease, and death in both humans and domestic animals. According to the United Nations Food and Agriculture Organization (FAO), 25% of world food crops are affected, and countries that are situated between 40ºN and 40ºS are most at risk. Over 4.5 billion people in developing countries are at risk of chronic AF exposure [9]. Unless AF levels in crops and livestock are effectively managed, international development efforts to achieve greater agricultural development, food security and improve health will be undermined. AF are very stable and persistent, so they are difficult to remove. Due to they are contained in many crops that are consumed by animals, AF have turned into a serious animal problem too. The most susceptible animals are rabbits, turkeys, chickens, pigs, cows and goats [10]. AF can be transmitted from animals to human food (by eggs, meat and dairy) with the consequent risk to human health. Even non-mouldy foods or raw materials may contain AF. Spores can be transferred by insects (especially flies, wasps and bees) or by birds to foods where the spores germinate, produce mycelium, and AF are excreted. Seeds can contain AF by infection of the egg-cells of the flowering plants. The spores of A. flavus and A. parasiticus can germinate on the stigma surfaces of plants, then the germ tube penetrates to the developing embryo mimicking pollen germ tubes. The mycelium can establish an endotrophic relationship which is not harmful for the healthy plant. However, if the plant is under drought stress, then significant levels of AF may be produced in the plant tissue during growth in the field. Under these circumstances food commodities may already be contaminated at harvest and, although the concentrations are never as high as those formed in stored commodities, they can be economically significant [11, 12].
El maíz (Zea mays L.) es un cultivo importante en México, que es a menudo afectado por la presencia de hongos patógenos. El objetivo de este estudio fue determinar el efecto protector del quitosán en plántulas de maíz sometidas a estrés biótico. El experimento se llevó a cabo en la Facultad de Estudios Superiores Cuautitlán, UNAM, durante 2008. Para cumplir el objetivo, después de algunas pruebas de calidad, tres grupos de semillas fueron sometidos por separado a los ataques de Aspergillus flavus y Fusarium moniliforme. Un primer grupo fue considerado como testigo positivo, otro fue recubierto con solución de quitosán y un último grupo fue dañado mecánicamente antes de la aplicación del biopolímero. Durante cinco semanas, el crecimiento de las plántulas se evaluó midiendo la longitud total, longitud de las hojas, de los tallos y el grosor de estos. No hubo incremento significativo en el tamaño de las plántulas, provenientes de semillas recubiertas con quitosán al compararse con el resto de los grupos; sin embargo, la ausencia de enfermedades en las plántulas tratadas con el biopolímero fue evidente. En la quinta semana de crecimiento, las estructuras foliares de las plántulas se sembraron en agar PDA, para determinar la presencia de los hongos estresantes. Se encontró que las hojas provenientes de las semillas tratadas con quitosán, desarrollaron carga fúngica nula, lo que sugiere que el quitosán actúa como un activador de mecanismos de defensa en plántulas de maíz, impidiendo la infección por los hongos patógenos utilizados.
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