So in Josh's plant breeding web page he has links to two papers that show that corn hybrid vigor may be due to inconsistent sequences. In some cases the genes themselves are hemizygous. In others the retrotransposon insertions are different, affecting gene expression due to changes in upstream promoters. O what we don't know else is going on.
I have too much to do. I will explain later. Right now I have to write it up for Cotton inc. They pay the bills.