Résumé
`Carvalhais' mandarin is a well-known Portuguese mandarin used in several
Citrus breeding programmes throughout the world. The first step in the implementation of a breeding programme of this variety was to screen for its natural genetic variability. A significant number of adult trees and young seedlings were submitted to isozyme analysis. For better interpretation of the isozyme patterns of `Carvalhais', several plants resulting from crosses between this Portuguese mandarin cultivar and the monoembryonic mandarin cultivar Clementine MA3 SRA 649, were also analysed. All the analysed trees of `Carvalhais' showed similar monomorphic patterns for each isozyme system, indicating that this mandarin cultivar originated as a single initial clone. Young seedlings exhibited monomorphic isozyme patterns identical to the adult plants revealing a high level of apomixis in this cultivar.