**2. Stress**

Stress, in general, refers to any deviation from the normal condition of a character or phenomena. In biology, stress mostly exerts adverse impact on individual or group or mass. In agriculture, negative impact of stress is seen on crop growth, development, productivity and quality. Stress induces various responses inside the plant such as change in gene expression, change in cell metabolic activities, and changes in plant's physiological and biochemical activities and thus, affects its growth rate, productivity and quality. In environment, stress is of two types: biotic stress and abiotic stress (**Figure 1**). Biotic stress arises due to interaction between living organisms, while abiotic stress is a result of interaction between organisms with non-living environmental properties. In reality, both these two stresses are linked to each other.

### **2.1 Biotic stress**

Biotic stress arises when living organisms such as weeds, insects, diseases (caused from bacteria, fungi, virus etc.) exert stresses on plant and thereby, hampers its growth and development. The kinds of biotic stress on plant depend on edaphic and climatic conditions. However, yield loss is a common occurrence due to this stress.
