Thank you Stefan. 

I am able to login Broker server using ssh userid and password   from below command.  

--broker-url=ssh://192.168.0.19:/usr/bin/x2gobroker

 Now I want to login broker server  through ssh .pem key,  how to do that ?   I am using x2go client in Windows 7.

If I share user id and password of broker server to anyone, he can login through Putty or any Terminal  via " ssh 192.168.0.19 "  as well as through x2go client.  It seems risky .

How to secure it  ? 

Is there a way to disable putty or terminal access of ssh and allow only  through x2go client.