C

Pre- and Postharvest

Aflatoxin Management

Figure 1. Schematic representation of ICRISAT's integrated management strategy for pre-and postharvest management of aflatoxins in peanut.

Aflatoxins, especially aflatoxin Bi produced by A. flavus in peanut seeds, are potent carcinogens and immunosuppressive agents that are directly responsible for various human and animal diseases, and result in economic losses due to the lower market potential of contaminated peanut products (Reed and Kasali, 1989; Waliyar et al, 2003b; Williams et al, 2004). In West Africa, many individuals are not only malnourished but also chronically exposed to high levels of aflatoxins in their daily diet (Gong et al., 2002; Williams et al, 2004). Due to concerns over aflatoxin contamination, African exports of peanut have declined by 19% during the last three decades, even though peanut utilization for food in West Africa has increased by 209% during the same period of time (Freeeman et al., 1999; Reveredo and Fletcher, 2002). Due to insufficient infrastructure for aflatoxin monitoring and a lack of awareness of the problem amongst farmers and the general populace, human and domesticated animal populations are at risk of health problems due to the consumption of aflatoxin-contaminated peanuts.

Although several Aspergillus spp. can produce aflatoxins, A. flavus is the most aggressive and most commonly occurring species on peanut. This fungus is saprophytic and survives in the soil as mycelium, conidia and sclerotia. It may infect peanut at the preharvest stages through the pegs that have penetrated into the soil. End of the season drought stress fa vors further fungal invasion and aflatoxin production in the seeds (Mehan et al., 19916; Cole et al., 1995). In Sub-Saharan Africa, peanuts are grown as a rainfed crop, under subsistence farming conditions in poor soils, and end-of-season drought is common. These conditions are highly conducive to A. flavus infestation and toxin production. Prevention of fungal contamination under such conditions is a complex task and requires a series of strategies to reduce infection incidence and the proliferation of the fungi both preharvest, and postharvest. ICRI-SAT and its partners have promulgated an integrated research program to mitigate aflatoxin contamination through the development of genetic resistance, and cultural and biological controls. In this chapter we describe briefly the ICRISAT research on integrated approaches for pre- and postharvest management of aflatoxin contamination in peanut (Fig. 1).

Prevention and control strategies

Aflatoxin prevention strategies can be divided into primary and secondary categories (Table 1; Semple et al., 1989). The primary prevention strategies include measures to stop fungal infestation and aflatoxin production, whereas secondary strategies focus on eliminating or limiting the spread of the fungal contaminant (Table 1). Field contamination is considered a significant source of inoculum in peanuts, thus efforts have focused on preharvest management through integrated approaches for controlling critical factors known to increase fungal infection and aflatoxin production (Cole et al., 1989; Mehan et al., 1991a). These practices include growing resistant cultivars, avoiding end-of-season drought stress, reducing inoculum sources, and avoiding pod damage through timely harvest and postharvest handling (Fig. 1). This research has been facilitated by sick plots containing highly aggressive, toxigenic strains of A. flavus that can be used to screen large amounts of germplasm (Waliyar et al., 1994), and an inexpensive ELISA for quantitative estimation of aflatoxin concentration in peanut kernels (Ramakrishna and Mehan, 1993; Devi et al., 1999).

Cultivar resistance through conventional and non-conventional approaches

There have been several efforts to breed resistant peanut cultivars for reduced aflatoxin contamination (Cole et al., 1995). Earlier research on genetic improvement at ICRISAT focused on in vitro seed colonization by A. flavus, as it was then thought to be a priority postharvest problem (Mehan et al., 1987). Subsequent field studies found that preharvest contamination by the fungi also occurs frequently and efforts were broadened to include breeding high-yielding varieties with resistance to seed infection and aflatoxin production (Mehan et al., 1988, 1991a,b). These efforts identified some A. favus-resistant germplasm sources and breeding lines, but the level of resistance in them was not sufficient to protect the crop from aflatoxin contamination under all conditions (Pettit, 1986; Waliyar et al., 1994). These efforts have resulted in the identification of over 30 resistant/tolerant germplasm accessions (Pettit, 1986; Waliyar et al., 1994; Upadhyaya et al, 2002, 2004). Some of these genotypes, including 55-437, Tamnut 74, PI 365553 (resistant to seed infection); PI 337394 F, PI 337409, UF 71513, Ah 7223, J 11, U 4-47-7, Var 27, Faizpur and Monir 240-30 (resistant to in vitro seed colonization), and U 4-7-5 and VRR 245 (resistant to aflatoxin production) were used to develop elite aflatoxin resistant varieties, e.g., ICGV # 88145, 89104, 91278, 91283 and 91284, which have been released as improved germplasm. Three lines, ICGV 87084, 87094 and

Table 1. Methods for minimizing pre- and postharvest aflatoxin contamination in peanuts.

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