Aspergillus silk infection

It is ideal when freshly emerged silks are exposed to corn pollen for more than just assuring a full set of kernels on the developing ear.  Growth of the pollen down the silk channel is followed by rapid dehydration of the silk, inhibiting or at least reducing the infection of the silk by fungi such as Aspergillus species (A. flavus and A parisiticus).  Drought stress tends to delay elongation of silk but have little effect on pollen production, resulting in silks emerging from the ear after most pollen has been distributed.  Excellent soil moisture conditions can cause silk emergence before tassels have produced viable pollen for distribution.  Rain during silk and pollen emergence can inhibit pollen distribution and viability.
 
Even pollinated silks are vulnerable to infection by fungi, at least for a short time before the complete ‘browning’ of the silk.  Completely yellow silks and very brown silks appear to be more resistant to the invasion of fungi.  It seems probable that the new bright yellow silks have resistance factors that are reduced as the silk deteriorates.  Perhaps the brown silks are too dry for fungal growth.  Those conditions between these stages are most easily invaded by Aspergillus species according to this report: (Phytopathology 74:1284-1289).  It was also shown that the fungus reached the ovule within 8 days, depending upon environment, after applying the fungus to the silk.  After reaching the ear, the fungus spreads to other deteriorating silk and eventually to the kernel surfaces.  Without physical injury to the developing kernels, such as from insect feeding, the fungus remains on the pericarp surfaces.  However, as the kernels mature, then it does start infecting endosperm tissue as well.
 
Resistance to Aspergillus species is believed to involve many common corn fungal resistance genes.  Part of the interaction in the kernel involves the starch synthesis.  The fungus thrives best on glucose as an energy source but there is some resistance metabolism that could be interfering with the synthesis of starch from glucose molecules.  Regardless of the cause of the interactions, Aspergillus infected kernels have less hard starch.  Review of resistance studies of Aspergillus flavus in corn can be found at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4117183/