Genetics and environmental and nutritional factors greatly affect the formation of mycotoxins. Depending on the susceptibility of the crop, geographic and seasonal factors, as well as cultivation, harvesting, storage, and transportation practices, mycotoxins are found worldwide (D'Mello and MacDonald 1997). In the field, weather conditions, plant stress, invertebrate vectors, species and spore load of infective fungi, variations within plant and fungal species, and microbial competition all significantly affect myco-toxin production. Physical factors such as time of exposure, temperature during exposure, humidity, and extent of insect or other damage to the commodity prior to exposure determine mycotoxin contamination in the field or during storage. Chemical factors including the nutritional status of the crops or chemicals (such as fungicides) used in crop management could affect fungal populations, and consequently toxin production. The temperature and relative humidity range for optimal mycotoxin production may differ from that supporting fungal growth. In general, mycotoxins are optimally produced at 24-28°C, but some toxins such as T-2 toxin is maximally produced at 15°C. Contamination during crop storage may be affected by changes in temperature and water activity, that allow ecological succession of different fungi as water activity and temperature of stored grain changes. During storage and transportation, water activity (aw), temperature, crop damage, time, blending with moldy components, and a number of physical and chemical factors, such as aeration (O2, CO2 levels), types of grains, pH, and presence or absence of specific nutrients and inhibitors are important.
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