More Citrus is produced on a world-wide basis than any other fruit crop. The genus includes a number of species grown for fruit and/or juice products, including sweet oranges (C. sinensis [L.] Osbeck), grapefruit (C. paradisi Macf.), mandarins (C. reticulata Blanco), lemons (C. limon [L.] Burm. f.), and limes (C. aurantifolia [Christm.] Swing.) (Hodgson, 1967). Other species, such as sour orange (C. aurantium L.), are primarily grown for use as rootstocks, to which scions are budded. Citrus species are diploid with a relatively low chromosome number (n=9) and a small genome (1c=0.62 pg) (Guerra, 1984). They are grown throughout tropical and subtropical regions of the world.