That newly create account will be under 'default' rate group and rates will be applied accordingly.
Customer portal wont need/have rate group information, its for admin/reseller's use.

but as you can see in the picture i have set default rate group for new accounts.

so probably the client must have some rates in his account.
correct?

in admin panel i can't see the rates for the new account it's empty.

Yeah, then new account(client/customer) will have the rates which are assigned to 'default' rate group.

Correct, that's what i thought. But in my installation i can't see rate group when a client signed up!

[~pscomgr] You mean in customer portal?
You will see it in admin portal and can change it also.
From customer portal you wont see it, it just applied to that customer. In customer portal they just see 'My Rates' as per the rate group assign to them.