Question

Necrosis in crops is due to the deficiency of
A. Ca, K, Cu and Mg.
B. N, K, S and Mo.
C. N, S, Fe and Zn.
D. Mg, S, Mn and Ca.

Answer 1

Hint: Plants require various mineral elements for their normal growth, development and metabolism. They fulfil their mineral requirement usually from the soil. That means all the essential elements must be present in the soil where a plant grows. If a particular element or a group of elements become limited in the soil, plant growth would be retarded.

Complete Answer:
- The concentration of the essential element below which plant growth is retarded is termed as critical concentration. The element is said to be deficient when present below the critical concentration.
- Since each element has one or more specific structural or functional role in plants, plants show certain morphological changes in the limitation of any particular element. These externally visible morphological changes which are produced due to absence or deficiency of essential mineral elements, are called deficiency symptoms, they are also called hunger signs.
- The deficiency symptoms vary from element to element and they disappear when the deficient mineral nutrient is provided to the plant. However, if deprivation continues it may eventually lead to the death of the plant.

- Ca, K, Cu and Mg: The deficiency of these elements leads to necrosis. Necrosis is defined as the death of tissue and particularly that of the leaf tissue.
- N, K, S and Mo: The deficiency of these elements leads to inhibition that is a stoppage of the cell division. Their deficiency symptoms are first visible in the older tissue.
- N, S, Fe and Zn: The deficiency of these elements leads to chlorosis. Chlorosis is defined as loss of chlorophyll that leads to yellowing of the leaves.
- Mg, S, Mn and Ca: The deficiency of these elements leads to the condition that flowers occur late. The late flowering is responsible for the late growth of the fruit.

Hence the correct answer is option A.

Note: The parts of the plants that show the deficiency symptoms also depend on the mobility of the element in the plant. For elements that are actively mobilised within the plants and exported to young developing tissues, the deficiency symptoms tend to appear first in the older tissues. For example, the deficiency symptoms of N, K and Mg are visible first in the senescent (older) leaves. In the older leaves, biomolecules containing those elements are broken down, thereby making these elements available for mobilising to younger leaves.