Zinc Nutrition, a Global Concern for Sustainable Citrus Production

ABSTRACT

Sub-optimum nutrition of zinc is globally one of the prime concerns of targeting sustainability in citrus production. Metabolically, Zn-deficiency induces many morphological, cytological and anatomical changes that lead to low flowering intensity and fruit set in addition to affecting the quality of citrus produced on sustained basis. Global occurrence of Zn-deficiency known by various names like rosette, little leaf, frenching, mottle leaf, etc., is basically characterized by interveinal chlorosis which may or may not be coupled with rosetting or smalling of leaves. Zinc deficiency is also suggested to appear due to competition from P, Fe, Mn, Ca and up to some extent K, besides a number of soil properties influencing the Zn-availability. Etiology of Zn-deficiency can now be precisely established using a variety of soil-plant diagnostics including the use of biochemical markers like peroxidase, carbonic anhydrase and nitrate reductase for more accurate diagnosis compared to leaf/soil analysis. Citrus decline is, though, considered to be a syndrome of many contributory factors. But, a number of postulated hypotheses have established a definite role of zinc nutrition, a causal factor to citrus decline/blight. 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 instead of vertical movement of Zn in the outer wood next to cambium with distinct seasonal cycles of accumulation pattern. However, recent evidences suggest that abnormal zinc metabolism develop before the real dysfunction of water translocation becomes apparent.

KEYWORDS:

• Zinc nutrition
• deficiency
• diagnostics
• citrus decline
• Zn-metabolism