Sub-optimum nutrition of zinc is one of the prime concerns of citrus nutrition. Worldwide occurrence of Zn deficiency known by various names like, rosette, little leaf, frenching, mottle leaf etc. is basically characterized by interveinal chlorosis mayor may not be coupled with rosetting of leaves. Metabolically, zinc deficiency induces many morphological, cytological as well as anatomical changes. With the available information, etiology of Zn deficiency can now be precisely established with further support of leaf/soil analysis data. Zinc deficiency is also suggested to appear due to competition from P, Fe, Mn, Ca and upto some extent K besides soil properties on the Zn availability. Though, citrus decline is considered to be a syndrome of many contributory factors. But, a number of hypotheses have been postulated to establish the role of zinc nutrition is citrus decline carried out from time to time over the last 70 years. These include: dysfunction of water translocation, increased resistance to water transport in the xylem, altered disturbance and redistribution of Zn especially in bark suggesting horizontal movement of Zn instead of vertical movement, outer wood next to cambium with distinct seasonal cycles. However, the evidences of late suggested that citrus decline effect on abnormal zinc metabolism developed prior to the dysfunction of water translocation.
