Citrus Origin, Diffusion, and Economic Importance

Citrus are widely cultivated in more than 140 countries in the world, in tropical, subtropical and Mediterranean climates, in the “citrus belt” between approximately 40° N and 40° S latitude, but their natural distribution areas before domestication must be much smaller. The chapter briefly outlines the issues related to the exact identification of the geographical origin and spread of citrus fruits: these simple questions have bothered citrus breeders and taxonomists for centuries. Nevertheless, we have witnessed a tremendous progress in the past two decades since the introduction of molecular tools in citrus researches, and the release of the first citrus genome has made an unprecedented breakthrough in our understanding of citrus genetics, taxonomy and evolution. Currently, on the basis of genomic, phylogenetic, and biogeographic analyses, scientists from different part of the world agree and haven’t doubt that the main centers of origin for the citrus species are the tropical and subtropical regions of south-east Asia, the northeastern India in the Himalayan foothills, Yunnan province of south-west China, northern Myanmar, the Indochinese peninsula, and the Malaysian archipelago, from which Citrus began the spread into the other continents. The genus Citrus is the result of a long and complex domestication process and this, together with sexual compatibility between Citrus and related genera and the frequency of bud mutations, makes citrus taxonomy and phylogeny very complicated. The chapter focuses on the genetic origin of the main cultivated species such as sweet oranges, clementine, citron, pummelo, grapefruit and mandarins. Finally, the major citrus production areas and the main commercial citrus groups and producing countries are reported.