Identification of Gene Markers in Aflatoxin-Resistant Maize Germplasm for Marker-Assisted Breeding

Abstract

Aflatoxins, the toxic and highly carcinogenic secondary metabolites of Aspergillus flavus, A. parasiticus are the most widely investigated of all mycotoxins due to their role in establishing the significance of mycotoxins in animal diseases, and to the regulation of their presence in food (Brown et al., 1998; Dorner et al., 1999). Aflatoxins pose serious health hazards to humans and domestic animals, because they frequently contaminate agricultural commodities (CAST, 1979; Diener et al., 1987). Presently, numerous countries have established or proposed regulations for controlling aflatoxins in food and feeds (Haumann, 1995); the US Food and Drug Administration (FDA) has limits of 20 ppb, total aflatoxins, on interstate commerce of food and feed, and 0.5 ppb of aflatoxin M1 on the sale of milk. However, many countries, especially in the developing world, experience contamination of domestic-grown commodities at alarmingly greater levels than does the U.S. Evidence of this was demonstrated in a study that revealed a strong association between exposure to aflatoxin and both stunting (a reflection of chronic malnutrition) and being underweight (a reflection of acute malnutrition) in West African children (Gong et al., 2002). Also, a 2004 outbreak of acute aflatoxicosis in Kenya, due to ingestion of contaminated maize, resulted in 125 deaths (Probst et al., 2007). Recognition of the need to control aflatoxin contamination of food and feed grains has elicited various approaches from researchers to eliminate this toxin from maize and other susceptible crops. The approach to enhance host resistance through conventional or molecular breeding gained renewed attention following the discovery of natural resistance to A. flavus infection and aflatoxin production in maize (Gardner et al., 1987; King & Scott, 1982; Widstrom et al., 1987; Scott & Zummo, 1988; Campbell & White, 1995; Brown et al., 1995, 1999). During the past two decades, maize genotypes with natural preharvest resistance to aflatoxin production have been identified through field screening (Scott & Zummo, 1988; Campbell & White, 1995; Warner et al., 1992). However, there is always a