Citrus Genetics and Breeding

Abstract

Citrus is one of the most important fruit crops worldwide. It is grown in more than 130 countries, mainly in tropical and subtropical areas. Sweet orange represents about 60% of total citrus production, being marketed as fresh fruit or as processed juice. Mandarins represent about 21% of total citrus fruit production and are intended for the fresh market. Conventional breeding in citrus by hybridization is hampered by its complex genetics and reproductive biology (apomixis, partial pollen and/or ovule sterility, cross- and self-incompatibility and high heterozigosity). In addition, citrus have a long juvenile period and usually take several years for hybrids to set fruit. Despite these limitations, many citrus breeding programs exploiting both diploidy and polyploidy as well as mutation breeding exist worldwide. From them, very important advances in releasing new varieties adapted to new market demands, as well as achievements in gaining knowledge of citrus genetics and genomics. The development of molecular markers, the availability of a reference genetic map, the advances in biotechnological tools and the complete genome sequence of several citrus species allow the acceleration of key studies such as germplasm characterization, marker-assisted selection, gene function discovery and variety improvement.