Why have some crop species experienced a larger reduction in genetic diversity than others?

[Dean22April]

I've come across the trend that almost all crops lost genetic diversity during domestication as a result of selection. But some species seem to have lost more than others. For example maize retains around 83% of its diversity but rice retains only around 10-20%, yet they likely both suffered similar selection pressures. Is there any reason why there would be such variation in genetic diversity loss?

 

I know perennials have retained more diversity than annuals because they've experienced fewer bottlenecks, having only recently been domesticated. But why would maize and rice, both domesticated at similar times and with similar selection pressures, have such variation?

[Moontanman]

Maize "corn" is grown in many varieties, some very different from each other and used in several different ways. Many of these varieties of "corn" are highly localized, and grown in what amounts to extreme isolation. From a variety of popcorn that has many mini ears on each plant to huge ears that are used to make a variety of local dishes in places like Peru. There are 6 basic types of corn and many varieties of each. My own grandfather developed his own strain of sweet corn that he grew much of his life. It was small ears that were so full of sugar the seeds often burst open with sugar crystals when it was dried. 

I am not that familiar with rice or wheat but google is your friend... 

Edited March 17, 2018 by Moontanman