Seed Health Management for Better Productivity - Govind Ballabh ...

(Seed Health Management for Better Productivity)agriculture.Aflatoxin in MaizeS.C. SaxenaDepartment of Plant Pathology, G.B.P.U.A.&T., Pantnagar-263145 (Uttarakhand)Fungal contamination of agricultural crops has plagued farmers since the beginning ofAflatoxin DiscoveryThe current epoch of fungal research in food/feed safety emerged as a result of anoutbreak of disease in turkeys in England in 1960. Fortunately, the English penchant for thoroughand detailed explanations initiated a search for the causative agent of the disease; this effort wasthe beginning of a new area of agricultural research that has been labeled mycotoxicology. Initialhistological examination of tissues from the diseased birds demonstrated an acute hepaticnecrosis associated with bile-duct proliferation. Examination of bird rations showed that a commonfactor in disease outbreaks was the use of a Brazilian peanut meal. Subsequent tests showed thecommon occurrence of fungal isolates associated with the Aspergillus flavus group. Two closelyrelated species, A. flavus and A. parasiticus, have since been identified as the toxin-producingspecies.Four closely related compounds were characterized and were generically named aflatoxinsB 1 and B 2 G 1 and G 2 (B= blue fluorescence; G= green fluorescence). A. flavus to produceexclusively B 1 and B 2 , whereas A. parasiticus exhibited the capacity to produce all four toxins.Plant Pathology/mycotoxicologyTo explain the differences between parasites and saprophytes broadly grouped into twobiotrophy or parasitism (deriving nutrients living material and necrotrophy or saprotrophy (derivingnutrient from non living material). Obligate saprotrophy and obligate or facultative necrotrophy.Numerous mycotoxin-producing fungi can be saprophytic, but they also occur in living tissues andare difined as facultative necrotrophs, i.e., species that are usually saprotrophic, but which canalso function as parasites.Aflatoxin in Postharvest Maize Storage fungiThe development of storage fungi in a post harvest commodity is determined by a numberof factors, such as availability of inoculum, physical integrity of seed, moisture, temperature,aeration and nature of the substrate. Among the variables, moisture is clearly a dominant factor.Storage fungi, principally Aspergillus and Pencillium spp. are commonly found in maize stores at13 to 18% moisture. The A. glaucus group predominates at 13 to 15% moisture, but above 15%other microbes appear, including the toxin-producing species A. flavus, A. ochraceus and A.versicolor. It has been reported that A. flavus did not invade starchy grains below 17.5% moisture.In response to observations relating moisture levels to fungal growth, the US Department ofAgriculture (USDA) assumed a very conservative position, describing drying techniques for control- 133 -