Bumps on avocado leaf underside, discoloration

[swincher]

I’m in my first winter trying to grow some young avocados under lights, so forgive me if this is something obvious, but one of my 9+ trees (4 grafted named varieties, the rest seedlings under a year old) looks sick. This is the Choquette on Lula rootstock:

Does anyone know what this is and how to treat it? Thanks!

[swincher]

Here’s a better closeup of a leaf underside.