In chlorosis green areas become yellow by the destruction 
of chlorophyll.chlorosis occurs due to the deficiency of mg 
and iron.chlorosis occurs due to the deficiency of minerals.
    

In necrosis the tissue in thegreen areas dies due to the 
invasion of some diseased parasites.

Chlorosis is a yellowing of leaf tissue due to a lack of 
chlorophyll. Possible causes of chlorosis include poor 
drainage, damaged roots, compacted roots, high alkalinity, 
and nutrient deficiencies in the plant


Necrosis is death of body tissue. It occurs when there is 
not enough blood to the tissue, whether from injury, 
radiation, or chemicals. Necrosis is not reversible.

When substantial areas of tissue die due to a lack of blood 
supply, the condition is called gangrene.