I found an article at blogs.microsoft.com that may help you
Click here to see the article
In order to instruct SharePoint to query those trusted domain or forests we need to configure access to them by using the Stsadm command-line tool and selecting an account to use when accessing each forest or domain. Those credentials must be from the forest/domain to be queried or from a trusted domain, as long as it is allowed to authenticate and is not denied to logon remotely.
You can use a different account for each target domain or forest, or the same account for all domains and forests.
On every front-end Web server on a farm, at a command prompt, type the following command, and then press ENTER:
STSADM.exe -o setapppassword -password key
Note: The account and password used to access each domain or forest is stored on each front-end Web server in the farm . This key is an encryption string that is used to encrypt the password for the account that is used to access the forest or domain . This encryption string must be the same for all servers in the farm, and unique for each server farm in a deployment with multiple farms.
On a front-end Web server, at a command prompt, type the following command, and then press ENTER
STSADM.exe -o setproperty-propertyname peoplepicker-searchadforests -propertyvalue <Valid list of forests or domains> -url <URL of the Web application>
Note : You have to provide a valid list of forest/domains to be queried as well as the credentials to do so, this can be specified as below .
You can add multiple forests and or domains by listing multiple domains or forests in the format Forest/Domain:DnsName,LoginName,Password separated by semicolons. For e.g.
STSADM.exe -o setproperty-propertyname peoplepicker-searchadforests -propertyvalue "forest:Contoso.com,Contoso\User1,PasswordofUser1; domain:Fabrikam.com,Fabrikam\User2,PasswordofUser2" -url http://webapp
Note : You can omit the username and password if the application pool identity already has access to Target domain or forest, this would be the case where application pool identity is from the Trusted forest or domain itself .