How to save selected item from dropdown list into text field

A lot of days I'm searching...

I have got a sharepoint list with 2 single line text field : Title and Level

I use visual studio to create an application page to replace de default form to add an item into this list because I want to have a dropdown list to put the value (not an id) of the Level field.

So I have a aspx page with like this :

 <tr>
            <td width="190px" valign="top" class="ms-formlabel">
                <H3 class="ms-standardheader">
                    <nobr>Titre : <span class="ms-formvalidation"> *</span></nobr>
                </H3>
            </td>
            <td class="ms-formbody" valign="top">
                <SharePoint:FormField runat="server" ID="FormField1" ControlMode="New" FieldName="Title" />
            </td>
        </tr>
        <tr>
            <td width="190px" valign="top" class="ms-formlabel">
                <h3 class="ms-standardheader">
                    <nobr>Level : <span class="ms-formvalidation"> *</span>
                                </nobr>
                </h3>
            </td>
            <td width="400px" valign="top" class="ms-formbody">

                 <SharePoint:DVDropDownList runat="server" ID="drop1" ControlMode="New" FieldName="Level">                 
                </SharePoint:DVDropDownList>

                <SharePoint:FieldDescription runat="server" ID="FieldDescription1"  ControlMode="New" />
            </td>
        </tr>

and the cs file with this to populate my dropdown list with values :

public partial class NewActiviteLevelForm : Microsoft.SharePoint.WebPartPages.WebPartPage
{

    string siteUrl = SPContext.Current.Web.Url;

    protected void Page_Load(object sender, EventArgs e)
    {
        if (!this.Page.IsPostBack)
        {
            using (SPSite site = new SPSite(SPContext.Current.Web.Url))
            {
                using (SPWeb web = site.OpenWeb())
                {
                    //SPList list = web.Lists["List_Level"];
                    SPList list = web.Lists.TryGetList("List_Level");

                    if (list != null)
                    {
                        drop1.DataSource = list.Items;
                        drop1.DataValueField = "Title";
                        drop1.DataTextField = "Title";
                        drop1.DataBind();
                    }
                    else
                    {
                        //erreur sur le nom de la liste

                    }

                }
            }
        }
    }

My problem is that when I click the save button the title field work fine but the selected value for Level is not saving.

How can I fix this?

Thanks for your help.