Thoughts on newly planted Gem avocado.

Hi Everyone,

I have been growing avocados in San Diego for a while (10b). I have been successfully caring for a fuerte avo I planted 4 years ago (last pic). I planted this gem with a Tammy rootstock in February and it was doing great. We had a rain storm a couple of weeks ago and it held up fine, then one day I took a look and all of the leaves had started to dry out. Trying to figure out if this is root rot or underwatering or sun damage? It’s sitting on a 8” mound in full sun. Thanks for your help on this!