IARC MONOGRAPHS ON THE EVALUATION OF CARCINOGENIC ...

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IARC MONOGRAPHS VOLUME 82
aflatoxin formation in peanuts (Pettit et al., 1971; Cole et al., 1982). However, peanuts
throughout the world are recognized as a drought-resistant crop and are mostly grown
under dry culture, with irrigation reserved for more moisture-sensitive crops such as rice
or vegetables. In many areas where peanuts are grown, irrigation is not an option. Under
these circumstances, reduction in drought stress by good agricultural practices can be a
beneficial approach. For example, weed control and wider spacing between peanut rows
can both assist in reducing drought stress (Rachaputi, 1999). Rapid drying of peanuts
using mechanical dryers as soon as possible after pulling has a major effect in reducing
the levels of aflatoxins in peanuts.
For maize also, irrigation and improved farm management practices have a beneficial
effect on aflatoxin formation (Payne et al., 1986). Resistant breeding stocks have been
identified (Widstrom et al., 1987; Campbell & White, 1995) and resistant maize genotypes,
dependent on kernel pericarp wax (Guo et al., 1995; Brown et al., 1999) or kernel
proteins (Huang et al., 1997) have been developed recently. As maize is usually dried in
the field, rapid drying techniques are not commonly practised, but should be in tropical
countries.
Cottonseed is a by-product of cotton production, so field drying is normal. Breeding
of cotton without nectaries has been proposed as one means of limiting A. flavus access
to cotton bolls (Klich & Chmielewski, 1985).
Genetic engineering may offer novel ways of limiting pre-harvest contamination by
mycotoxins, provided attention is paid to questions of importance specifically to developing
countries (Wambugu, 1999). Genetic approaches to aflatoxin control include engineering
of genes in Aspergillus species to influence the ability of the fungus to colonize
the host plant. An alternative approach is to select or engineer varieties of cereal grains
and oilseeds resistant to fungal infection or aflatoxin biosynthesis by the fungus once
infection occurs.
(b) Control of aflatoxin formation in other crops before and after
harvest
Entry of A. flavus into pistachio nuts depends on the time of splitting of hulls. Nuts
in which hull splitting occurs early are much more susceptible to A. flavus invasion on
the tree (Doster & Michailides, 1995). It is known that some cultivars are more prone to
early splitting than others, and this is especially important where nuts are harvested from
the ground, after contact with the soil.
In tree nut crops, various techniques, including timing of harvesting, are used to keep
aflatoxin formation to a minimum.
Figs are sometimes infected by A. flavus, both because of their unique structure developed
for insect fertilization and also because figs are harvested from the ground in some
countries. Immature figs are not colonized by A. flavus, but once they are ripe infection
occurs readily and fungal growth continues during drying (Buchanan et al., 1975; Le
Bars, 1990). The proportion of figs infected is only about 1% (Steiner et al., 1988).