The Greek equivalent of PDO is POP (Prostatevmeni Onomasia Proelefsis). 33 located throughout Greece,7 20 per cent of total annual production. The individual PDOs lay down rules on grape growing and winemaking, such as yields and which varieties can be grown (PDO Naoussa is unusual in also having ageing requirements). With the notable exception of Muscat for sweet wines, PDO wines are usually restricted to native varieties.