The number of fungal species that can be found colonizing stored grain is very wide. These represent a high number of genera and include psychrotolerant, mesophilic, thermophilic, xerophilic, and hydrophilic species (Hill and Lacey 1983; Lacey et al. 1980; Magan and Lacey 1984a,b,c). The most characteristic of these are species belonging to the genus Aspergillus and Penicillium. In addition, it is possible to find species of Eurotium, Fusarium, Rhizopus, and thermophilics like Talaromyces thermophilus, Rhizomucor pusillus, and Thermomyces lanuginosus (Figure 2). All these species are widespread in their occurrence throughout the world and they cover almost the whole range of environmental conditions likely to be found in stored grain.
The aw and temperature are very important factors that determine the mycoflora present in stored grains. The fungi present in the field such as Alternaria species that need high levels of aw to grow, decrease in importance when the grain is stored and subjected to processing practices directed to decrease the water activity. On the other hand, genera such as Aspergillus, Penicillium, and Eurotium that have a low importance in the field, become very important during the storage of the grains. Another factor that determines the mycoflora in grain is the oxygen concentration, because the fungi are generally very sensitive to low oxygen concentrations. Under these conditions Magan and Lacey (1984) reported that Fusarium culmorum, P. roqueforti, and A. candidus were the most tolerant, which is consistent with the fungal community found on cereals under airtight storage.
Both climatic conditions and geographical location can explain the differences found in the mycoflora of different grains in the field. During storage, however, the mycoflora is very similar for all grains (Pelhate 1988). Many of the species found on maize, sorghum, rice, and other cereals in tropical climates are the same as those found in temperate regions except for a small number of additional species and, perhaps, a greater frequency of Aspergillus and fewer or different Penicillium spp.
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