Like many fruit trees species, citrus trees blossom with high profusion and thereafter exhibit massive fruitlet abscission. Current evidence indicates that this process is under hormonal and metabolic regulation (Gillaspy et al. 1993). In citrus, it has been suggested that after hormonal activation of initial fruit growth subsequent development is mostly supported by nutrient supply (Talon et al. 1997). Thus, once mineral and water requirements are satisfied, competition for photoassimilates is thought to be responsible for fruit drop (Moss et al. 1972; Powell and Krezdorn 1977; Goldschmidt and Koch 1996).
Citrus is the main fruit tree crop in the world and therefore has a tremendous economical, social and cultural impact in our society. In recent years, our knowledge on plant reproductive biology has increased considerably mostly because of the work developed in model plants. However, the information generated in these species cannot always be applied to citrus, predominantly because citrus is a perennial tree crop that exhibits a very peculiar and unusual reproductive biology.