SAML and IBMi/AS400 and SSO

Hello, a couple of questions here.

1) We want to enable SSO for our users so that, once they authenticate through the FA that they are not prompted again for a user/pass to other resources.  I have LDAP setp-up on the FortiAuthenticator(FA) and the FG is acting as a radius client, this is all working.  What I want to do is extend SSO to the IBMi.  Do I have to use SAML for this?  The IBMi supports RADIUS and LDAP, wondering if these authentication methods can be passed to it via the FA so SSO works.  Seems the only way that SSO would work in this environment is with SAML?