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Q.
What causes khaira disease of rice?
NTA AbhyasNTA Abhyas 2020
Solution:
Zinc occurs in the soil in the form of complex compounds like magnetite, biotite, and hornblende. When weathering of these minerals takes place, zinc is liberated in bivalent Zn2+ form. An increase in soil pH decreases the availability of zinc. The bivalent form of zinc (Zn++) is exchangeable and is readily available in the soil. Plants require this mineral in very minute quantity and its higher concentrations are highly toxic. Functions :
It is required for the synthesis of tryptophan which is a precursor of indole acetic acid-an auxin.
It is a constituent of enzymes like carbonic anhydrase, hexokinase, alcohol dehydrogenase, lactic dehydrogenase, and carboxy peptidase.
It is required for the metabolism of phosphorus and carbohydrates.
Zinc also appears to play an important role in protein synthesis because in its absence there is a substantial increase in soluble nitrogenous compounds.
Deficiency symptoms:
Early symptoms include inter veinal chlorosis of the older leaves, starting at the tips and the margins.
Growth becomes stunted due to the formation of smaller leaves and shortened internodes.
Reduced stem growth because of less synthesis of auxin.
The leaves become twisted and sickle-shaped, also get clustered to form rosettes - the 'little leaf disease'.
In maize, zinc deficiency produces 'white bud disease'.
Its deficiency causes khaira disease of rice and a mottled leaf of apple, Citrus, and walnut.