Ember component cannot use access controller property via "needs"

I'm trying to change a controller's property from a component as follows(JSBIN example http://jsbin.com/gevuhu):

App.CategoryManagerController = Ember.Controller.extend({
  selectedCategory: null,
});

App.BlogPostComponent = Ember.Component.extend({
    needs: ['categoryManager'],
    selectedCategory: Ember.computed.alias('controllers.categoryManager.selectedCategory'),
    actions:{
        selectedCategory: function (){
            this.set('selectedCategory',1);
        }
    }
});

but getting the error Property set failed: object in path "controllers.categoryManager" could not be found or was destroyed.

Is it that we cannot use "needs" in components ?