I just find this error when I retrieve all my records on twig page from the database through doctrine

here is my twig code :

    {% extends "gestionConferenceApplicationBundle::layout.html.twig" %}
{% block title "Hello " ~ name %}
{% block content %}
je suis un debutant
<table border=2 >
    <th>Numéro</th>
    <th>Titre</th>
    <th>Ville</th>
    <th>Lieu</th>
    <th>Date de début</th>
    <th>Date de fin</th>

    {% for item in conferences %}
    <tr>
        <td>{{ item.id }}</td>
        <td>{{ item.titre }}</td>
        <td>{{ item.ville }}</td>
        <td>{{ item.lieu }}</td>*
        <td>{{ item.dateDebut }}</td>
        <td>{{ item.dateFin }}</td>        
    </tr>     
     {% endfor %}
</table>
{% endblock %}

the error in the date :

here it is :

An exception has been thrown during the rendering of a template ("Catchable Fatal Error: Object of class DateTime could not be converted to string in C:\wamp\www\Symfony\app\cache\dev\twig\3c\dd\40a703549de9b8769fa40b82230e.php line 72") in gestionConferenceApplicationBundle:acceuil:acceuil.html.twig at line 19.

do you have any idea how to convert this date or any other things

in the MySql I have dateTime field and in doctrine I have :

/**
 * @var \DateTime $dateDebut
 *
 * @ORM\Column(name="date_debut", type="datetime", nullable=false)
 */
private $dateDebut;