In agricultute, problems of drought, salinity and alkalinity are of major concern among environmental stresses. Drought refers to the condition of soil moisture deficiency or water scarcity. Soil drought is more common in the arid and semi-arid tropics and in the areas of steep slope. Thus desert areas are more prone to drought conditions.

The ability of crop plants to grow, develop and reproduce normally under moisture deficit conditions is referred to as drought resistance. In other words, drought resistance refers to survival of plants under water deficit or scarcity conditions without injury. Improvement in the drought tolerance ability of a plant is known as drought hardening. Main features of drought are given below:

1. Drought is characterized with soil moisture deficit or low soil moisture.

2. Arid and semi-arid areas are more prone to drought than humid zones. About 36% of the land area constitute arid and semi-arid zones.

3. Drought leads to reduction in both yield and quality of economic product in crop plants. It has adverse effects on plant growth and development.

4. Drought damages chloroplasts and lowers output of the photosynthetic apparatus.

5. There is an increase in proline level in the leaves of plants which are subjected to drought, Proline level can be used as an indicator of water stress, but not as a measure of drought resistance.

6. The occurrence of drought depends on the amount and distribution pattern of rainfall. If the rainfall is adequate and well distributed over the crop season, there are less chance of drought. On the other hand, when rainfall is erratic there are more chances of drought. Soil type and topography also affect drought.

7. Drought resistance is a genetically controlled physiological property of plant species. Resistance to drought is associated with various morphological and physiological features of the plant.

8. Xerophytic plants are more resistant to drought than mesophytes.

9. There is an increase in abscisic acid content in leaves of barley, and in ethylene level, in cotton and wheat under drought conditions.