Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 3, 1997
Publication Date: N/A
Interpretive Summary: The fungus Aspergillus flavus and a toxin, aflatoxin, which is produced by the fungus are major concerns of corn growers in the Southeast and occasionally a major problem for growers in the Midwest. Aflatoxin is one of the most potent cancer causing agents found in nature. When and how the fungus enters corn kernels is not clearly defined. Information on the timing of infection by the fungus and aflatoxin production is needed to help researchers determine when to harvest corn to select resistant genotypes. Studies were conducted in the field for two years to monitor kernel infection by the fungus and aflatoxin production in the kernels. Ears that had been inoculated with the fungus were harvested at 35, 42, 49, 56, and 63 days after midsilk (when half of the ears on a row had silk showing). Differences in aflatoxin levels were between resistance and susceptible hybrids were observed on the first harvest date. Kernel infection by the fungus was not different between resistant and susceptible hybrids until the second harvest date. Kernel infection was highest on the third harvest date and aflatoxin was highest at the last harvest date. The greatest differences between resistant and susceptible hybrids for aflatoxin production were observed at the last harvest date (63 days after midsilk). Since aflatoxin levels are a better indication of resistance than kernel infection, ears should be harvested near 63 days after midsilk to determine which corn is the most resistant.
Technical Abstract: Field studies were conducted for two years in Mississippi to monitor maize kernel infection and aflatoxin accumulation caused by Aspergillus flavus at various times during the growing season. Hybrids resistant and susceptible to A. flavus were compared to determine cumulative differences in infection and aflatoxin levels. The resistant hybrids were Mo18W X Mp313E, Mp420 X Tx601, and SC54 X SC76; susceptible hybrids were GA209 X Mp339, Mp307 X Mp428, and Mp68:616 X SC212M. The top ear of each plant was inoculated with a suspension containing A. flavus conidia at 7 days after midsilk using the side needle technique. Inoculated ears were harvested 35, 42, 49, 56, and 63 days after midsilk to determine kernel infection by A. flavus and aflatoxin contamination. Differences in aflatoxin levels between resistant and susceptible hybrids were observed on the first harvest date. Aflatoxin levels ranged from 26 ng/g for Mp420 X Tx601 to 97 ng/g for GA209 X Mp339. Significant differences between resistant and susceptible hybrids for kernel infection were not observed until 42 days after midsilk. Differences between resistant and susceptible hybrids occurred for kernel infection and aflatoxin levels at 49, 56, and 63 days after midsilk. Kernel infection (8.1% for GA209 X Mp339) was highest at 49 days after midsilk, and aflatoxin levels (510 ng/g for Mp307 X Mp428) were highest at 63 days after midsilk. Maximum differences between resistant and susceptible hybrids for aflatoxin levels were observed at 63 days after midsilk. Two of the resistant hybrids, Mo18W X Mp313E and Mp420 X Tx601, had significantly less aflatoxin than the three susceptible hybrids at 63 days after midsilk.