Finally ended up solving it as follows , this one worked perfect.
self.navigationController.navigationBar.topItem.title = @"";
from this link Removing the title text of an iOS UIBarButtonItem
But if you navigate from previous view to next view you can see that the title of the previous view navigation bar vanishes when i put the above mentioned solution in viewDidDisappear of viewWillDisappear of previous view, which isn't an elegant solution in storyboard based UINavigationController scenario , in another situation i finally decided to use a bar button and set its image as per the native back button chevron, this gives better results.