Data Controls :: How To Edit GridView Row Using RadioButton

I am using an grid in which inside the item template(the first one in which radio button is there). i use link button instead of radiobutton ,when i click on it iam able to edit as the textbox appears, but if i use the radio button,that editing option is not coming;

aspx:

<div id="banner" style="background-color: #00FFFF">
</div>
<div id="loginblock">
<table> <tr>
<td>UserName:</td>
<td>
<asp:TextBox ID="username" runat="server" onBlur="txtvalidation();" AutoPostBack="true"></asp:TextBox>

[Code] ....

CS:
protected void selectrd_CheckedChanged(object sender, GridViewEditEventArgs e) {
grd.SelectedIndex = e.NewEditIndex;
ldgrid();
}

Here if we remove the radiobutton and insert link button, onclick of the link button we can edit the values, how to do the same operation with the radio button.