Fungal contamination and selected mycotoxins in pre- and post-harvest maize in Honduras.

Sixty nine samples of maize were collected from pre-harvest standing crops and on-farm storage facilities from 52 smallholder farms located within 4 regions of Honduras during October 1992 and November 1993. Samples were visually assessed for insect damage and fungal spoilage, and the mycoflora quantified on artificial media. The major components of the ear rot complex were: Fusarium moniliforme, F. moniliforme var. subglutinans, Penicillium species, Stenocarpella maydis, S. macrospora and Acremonium spp. Representative samples were also assayed for mycotoxin content. Fumonisin B1 was detected in all 24 samples tested at levels of between 68-6,555 (micrograms/kg), and aflatoxin was detected in 2 samples heavily contaminated with Aspergillus flavus. Moniliformin and tenuazonic acid were not detected in the samples tested. The implications of these findings for human and livestock health risk are discussed, together with possible strategies for controlling these pathogens.

Development of monoclonal-antibody-ELISA and -DIP-STICK immunoassays for Penicillium islandicum in rice grains.

Monoclonal antibodies (mAbs) were raised against Penicillium islandicum, a fungus commonly isolated from stored rice grains in South-East Asia. Mice were immunized by a direct, simple method; fresh cell-free surface washings from a solid agar slant culture were injected directly into the peritoneum without prior concentration. Hybridoma supernatants were screened by ELISA. Most of the mAbs raised cross-reacted with other storage fungi and/or uninfected rice grains but there were species-specific. One of these, PI01, was used to develop ELISA and DIP-STICK assays for the detection of P. islandicum in individual grains. All inoculated grains and approximately 90% of grains in natural infected samples from Indonesia tested positively, by ELISA, for P. islandicum. This result and those obtained for discoloured grains from both Indonesia and the Philippines, 32% and 14% respectively, are higher than those obtained by direct plating of surface-sterilized grains. Heat and periodate treatment of the PI01 antigen and binding on Western blots indicate that it is a glycoprotein of Mr greater than 90,000. Hyphae of all ages stained uniformly by immunofluorescence using the PI01 antibody but mature conidia stained only weakly.

Development of monoclonal-antibody-ELISA, -DOT-BLOT and -DIP-STICK immunoassays for Humicola lanuginosa in rice.

Monoclonal antibodies (MAbs) were raised against Humicola lanuginosa, a thermophilic, saprophytic fungus that is commonly isolated from freshly harvested rice grains in Indonesia. Mice were immunized by direct injection into the peritoneum, without prior concentration, of fresh cell-free surface washings from a solid agar slant culture. Hybridoma supernatants were screened by ELISA using wells coated with a dilution of the immunogen. From one fusion 403 hybridoma clones were obtained yielding 52 cell lines secreting antibodies positive for H. lanuginosa. Twelve cell lines were re-cloned, grown in bulk and tested against other storage fungi. Most of the MAbs raised were IgM antibodies that cross-reacted with several of the storage fungi and/or uninfected rice grains. However, the IgM antibody EC6 did not recognize antigens from rice grains and cross-reacted strongly with only one other test fungus, Penicillium variabile, and partially with two others. This MAb was used to develop a highly sensitive DIP-STICK immunoassay to detect the fungus in infected grains. These assays are simple to perform, require no equipment and are suitable for field use by untrained workers.