Aflatoxin in corn: Modes of penetration and development in corn kernel of Aspergillus flavus
1993
Prachoom Jutawantana | Udom Pupipat | Chanida Yaeram (Kasetsart Univ., Bangkok (Thailand). National Corn and Sorghum Research Center)
Aflatoxin contamination in corn caused by Aspergillus flavus, is one of the most major constraint in grain quality. The fungus produced 1-celled conidia measuring 2.5-5 in diameter of globose to subglobose with definitely echinulate. Its conidiophores were thick walled, colorless, coarsely roughened, measured mostly 480-800 long and 10-15 in diameter. Its vesicles were globose or subglobose, varying from 25-45 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 the tip cap of the corn kernel but indirectly through the intercellular space of the kernel surface. Conidia germinated by germtube within 8 hrs 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 intracellular in 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 within 24 hrs. The mycelia rampaged profusedly throughout the parenchymatous tissue of the tip cap within 36 hrs and occasionally found in the embryo and the endosperm. The position of the internal seed infection revealed that the fungus infection was commonly found both in the tip cap and the pericarp. The prevalence of infection was found next in decreasing levels in the tissue of the germ, floury endosperm and horny endosperm. Infection of A. flavus in four corn inbred lines at postharvest showed that kernel infection gave a maximum infection with Ki3 at 85 percent, Ki28 at 79 percent, Ki27 at 55 percent and Ki21 at 51 percent. In the meantime, the means of infection rating scores resulting from dipping the corn kernel into the spore inoculum of 10*[7) spores/ml for inbred lines Ki27, Ki28, Ki3 and Ki21 were 2.425, 2.050, 1.350 and 1.075 respectively.
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