Penetration and Development of Aspergillus flavus Link ex Fries in Corn Kernel.
Kasetsart University Chatuchak, Bangkok 10900
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The morphological characters of Aspergillus flavus Link ex Fries showed that the fungus produced 1-celled conidia measuring 2.5 –5 microns in diameter of globose and subglobose with definitely echinulate. Its conidiophores were thick walled, colourless, coarsely roughened, 480 –800 microns long and 10 –15 microns in diameter. Its vesicles were globose or subglobose, varying from 25 – 45 microns in diameter.
The investigations on penetration and development of A. flavus in corn kernel by scanning electron microscope (SEM) revealed that the fungus penetrated directly via tip cap of the corn kernel but indirectly through the intercellular space of the corn kernel surface. Conidia germinated within 8 hours after inoculation on the kernel surface. The germinated conidia penetrated through intercellular space of the kernel surface within 12 hrs before the hyphae continuously to grow and vaginate through both intercellular space and host tissue. The development of A. flavus from spore germination to conidial head formation occurred on both kernel surface and tip cap of the corn kernel within 24 hrs. The mycelia rampaged profusely throughout the parenchyma tissue of the tip cap within 36 hrs and occasionally found in embryo and endosperm. The position of the internal seed infection revealed that the fungus infection was commonly found in both the tip cap and pericarp. The prevalence of infection was found in decreasing levels in the tissue of the germ, floury endosperm and horny endosperm. Infection levels of A. flavus in four corn inbred lines at post harvest were 85% in Ki 3, 79% in Ki 28, 55% in Ki 27, and 51% in Ki 21. Mean infection rating scores resulting from dipping the corn kernel into the spore inoculum suspension of 107 spores/ml for inbred lines Ki 27, Ki 28, Ki 3, and Ki 21 were 2.425, 2.050, 1.350, and 1.075, respectively. The pericarp thickness of all four inbred lines ranged from 0.103 mm for the Ki 28 inbred line to the highest of 0.186 mm for the Ki 3 inbred line. However, the thickness of pericarp was also depending on the position of pericarp measurement.
Chanida