**2. Biological control: a powerful management strategy**

**Figure 1.** The life cycle of *A. flavus* is shown in a pistachio orchard. Infection of fruits with air-borne conidia occurs during Spring/Summer, while the fungus will survive by resistant structures named "sclerotia" during Autumn/Winter.

24 Aflatoxins - Recent Advances and Future Prospects

To ensure global safety on food and feed supplies, extensive researches have been carried out to effectively control and manage AF contamination of crops. The strategies for preventing AF contamination are generally divided into two categories including pre- and post-harvest con‐ trols (Kabak et al., 2006). Pre-harvest control strategies include appropriate field management practices (crop rotation, irrigation, soil cultivation, etc.), enhancing host resistance (transgenic or genetically modified crops), biological (application of antagonistic fungi and bacteria) and chemical control (fungicides, insecticides). Respect to biocontrol approaches, the rapid expan‐ sion in our knowledge about the role of microorganisms in inhibiting AF biosynthesis has en‐ abled us to utilize them as potential AF biocontrol agents (Holmes et al., 2008; Raaijmakers et al., 2002). A large number of plants, mushrooms, bacteria, microalgae, fungi and actinomy‐ cetes have now been screened for the ability to inhibit toxigenic fungal growth and/or AF pro‐ duction (Alinezhad et al., 2011, Bagheri-Gavkosh et al., 2009; Ongena & Jacques, 2007; Razzaghi-Abyaneh & Shams-Ghahfarokhi, 2011; Razzaghi-Abyaneh et al., 2005, 2007, 2008, 2009, 2010, 2011). Substantial efforts have been carried out in identifying organisms inhibitory to AF biosynthesis through co-culture with aflatoxigenic fungi with the aim of finding poten‐ tial biocontrol agents as well as novel inhibitory metabolites. The use of beneficial microorgan‐ isms is one of the most promising methods to the development of environmentally friendly alternatives to chemical pesticides in preventing the growth of aflatoxigenic fungi and subse‐ quent AF contamination of susceptible crops. Among beneficial microorganisms, antagonis‐ tic bacteria are in the first line of investigation because of a much greater diversity than that of any other organism and possessing valuable pharmaceutically active molecules (Ongena & Jacques, 2007; Stein, 2005). Recent advances in analytical methods and enormous expanding of natural products libraries, cloning, and genetic engineering have provided a unique opportu‐ nity for isolation and structural elucidation of novel bioactive antifungal compounds from bac‐ terial communities all over the world. It has been reported that, on average, two or three antibiotics derived from bacteria break into the market each year (Clark, 1996). Among an esti‐ mated number of 1.5 million bacterial species exists on our planet, only a little portion (less than 1%) has been identified yet of which a more little have tested for bioactive antifungal me‐ tabolites. Terrestrial bacteria are an interesting group of antagonistic microorganisms capable

Biological control is defined as i) a method of managing pests by using natural enemies ii) an ecological method designed by man to lower a pest or parasite population to acceptable subclinical densities or iii) to keep parasite populations at a non-harmful level using natural liv‐ ing antagonists (Baker, 1987). The history of biological control dates back to an outstanding successful story, the biocontrol of the cottony-cushion scale (*Icerya purchasi*) on *Citrus* plant in California (Debach & Rosen, 1991). Biological control agents act against plant pathogens through different modes of action. Antagonistic interactions that can lead to biological control include antibiosis, competition and hyperparasitism (Bloom et al., 2003; Bull et al., 2002; Cook, 1993; Hoitink & Boehm, 1999). Competition occurs when two or more microorganisms re‐ quire the same resources in excess of their supply. These resources can include space, nu‐ trients, and oxygen. In a biological control system, the more efficient competitor, i.e., the biological control agent out-competes the less efficient one, i.e., the pathogen. Antibiosis oc‐ curs when antibiotics or toxic metabolites produced by one microorganism have direct inhibi‐ tory effect on another. Hyperparasitism or predation results from biotrophic or necrotrophic interactions that lead to parasitism of the plant pathogen by the biological control agent. Some microorganisms, particularly those in soil, can reduce damage from diseases by promoting plant growth or by inducing host resistance against a myriad of pathogens. Nowadays, atoxi‐ genic *A. flavus* strains, biocompetitive bacteria and antagonistic yeasts has been effectively used to reduce AF contamination in field and laboratory conditions (Brown et al., 1991; Dorn‐ er et al., 1998, 1999; Hua et al., 1999; Palumbo et al., 2006). Commercial products from atoxigen‐ ic *A. flavus* under the names of AF36, AflaSafe and AflaGuard have been successfully used for biocontrol of aflatoxigenic fungi in maize, peanuts, cottonseed and pistachio fields in South‐ ern US, Northern Mexico, Nigeria and West Africa (Atehnkeng et al., 2008; Donner et al., 2010).
