inheritance main-menu into menu-strip?

That is a menu item inside the Windows Form. And like all other objects, there are some properties attached to the objects. Similarly you can call different methods and function to change the properties of the object inside your Windows Forms application.

For example the following example,

// create a new instance, 
MenuItem item = new MenuItem();
// radio check it..
item.RadioCheck = true;

..this will do the job for you.

http://msdn.microsoft.com/en-us/library/system.windows.forms.menuitem.radiocheck(v=vs.110).aspx[^]

As you've stated that you wanted to know, how to add the property to the control. Here is a basic code to do the thing you're asking,

// suppose you're having a control with name menuItem, then you will do this
menuItem.RadioCheck = true; 

..the thing is that you call the control using its name and then you work with the property it has. In the above code, I have selected the control and modified its RadioCheck property and set it to true.