it’s working with a SetEnv PHP_ADMIN_VALUE alone in Directory, like this :
<Directory "/usr/local/www/appli">
SetEnv PHP_ADMIN_VALUE "open_basedir=/tmp:/users/:/users/home:/usr/local/www/appli;error_reporting=6143"
</Directory>
Alias /env_etu "/usr/local/www/appli/environ_etudiant/root"
<Directory "/usr/local/www/appli/environ_etudiant/root">
SSLRequireSSL
AllowOverride None
Require all granted
</Directory>
Probably a bug in apache ?