Utilization of the major corn (Zea mays) reserve materials (free saccharides,
starch,
triglycerides, and
zein) was monitored during
infection of detached kernels by Aspergillus flavus (A. flavus) over a 12-day period. Inoculated whole kernels were compared to noninoculated kernels. Concentrations of
sucrose and
raffinose in inoculated seed decreased to nearly zero at 6 days, whereas concentrations of these saccharides in noninoculated seed dropped at a considerably slower rate, and significant levels remained at the end of the incubation period.
Triglyceride concentrations remained unchanged in the noninoculated seed but dropped continuously after 2 days in the inoculated seed.
Starch and
zein concentrations did not change during the 12-day incubation period.
Aflatoxin B1 was first detected after 2 days and increased to about 20 microg/g (20,000 ppb) after 12 days. Very low
aflatoxin concentrations were detected in the noninoculated seed. Significant concentrations of
erythritol,
arabitol, and
mannitol were produced during
infection, with peak concentrations occurring at 8 days. Whole seed and germ tissue appeared to support good fungal growth and
aflatoxin production, whereas ground tissues and endosperm did not. A. flavus preferentially utilized saccharides as initial
carbon substrates followed by
triglycerides. When invading nonwounded corn kernels, the fungus selectively targets the germ tissue where these materials are localized in the highest concentrations.