ABSTRACT
Maize (Zea mays L) is one of the most important food crops in the world, but the productivity and safety of grain produced by this plant is seriously decreased by a multitude of fungal pathogens causing ear rots. Depending on the growing environment, maize grains can be infected by one or more ear rot fungi, which may decrease grain yield and quality. Many of them also produce secondary metabolites, known as mycotoxins, which can have serious detrimental effects on humans and animals that consume the infected grain. The most commonly occurring ear rot fungi include Aspergillus, Fusarium and Gibberella species, all of which produce one or more mycotoxins (Table 1) and occur over very large geographic regions. Many other fungal species that are not as widespread also infect maize and may produce mycotoxins in the ears (Table 1). Mycotoxin content in maize is highly regulated in many countries of the world, leading to more of an economic than a health problem, as infected grain is destroyed before it can enter the food stream. In some countries, however, regulatory infrastructure is unequal to the task of inspection and enforcement; therefore, much of the infected grain is consumed, often within the household of the farmer who produced it. Immediate symptoms of large doses of mycotoxins may include abdominal pain, vomiting and diarrhoea, and may even lead to death, while long-term exposure to sublethal doses of mycotoxins has been linked to liver and oesophageal cancers, neural tube defects in newborns, stunted growth during childhood and depressed or severely
Table 1 Causal organism and associated mycotoxins of the fungal rots known to affect maize ears
Ear rot Causal organism Associated mycotoxin Geographic spread
Commonly occurring ear rots:
Aspergillus ear rot Aspergillus flavus and A. parasiticus
aflatoxin Worldwide but more common in tropical areas
Gibberella ear rot Gibberella zeae (same organism that causes Fusarium head blight in wheat Fusarium graminearum), G. fujikuroi and G. moniliformis
deoxynivalenol (also known as DON or vomitoxin), zearalenone
Worldwide
Fusarium ear rot Fusarium verticillioides, F. moniliformis, F. proliferatum, F. sporotrichioides, F. subglutinans, F. avenaceum, F. cerealis, and F. poae
Fumonisin, deoxynivalenol, trichothecene, zearalenones; minor toxins include beauvericin, fusaproliferin, nivalenol, fusarenone-X, moniliformin, T-2 toxin, and diacetoxyscirpenol
Worldwide
Less commonly occurring ear rots:
Penicillium ear rot Penicillium oxalicum or P. roqueforti
PR toxin, roquefortin C, patulin, mycophenolic acid
Worldwide
Diplodia or Stenocarpella ear rot
Stenocarpella maydis no mycotoxins Tropical maize-growing countries and states
Cladosporium ear rot Cladosporium herbarum and C. cladosporoides
no mycotoxins Widespread but rare, usually occurring under cool and humid conditions
Nigrospora ear rot Nigrospora oryzae no mycotoxins Widespread but rare, usually occurring when plants are damaged
Trichoderma ear rot Trichoderma viride no mycotoxins Widespread but rare, usually occurring when plants are damaged
compromised immune systems, among others (Eaton and Groopman, 1993; Bennett and Klich, 2003; Williams et al., 2004).
