By Arooba Tariq M.Sc(Hons) PBG

Stress: ‘Stress’ in plants can be defined as any external factor that negatively influences plant growth, productivity, reproductive capacity or survival.

It divided into two main categories:  Abiotic or environmental stress factors.  Biotic or biological stress factors.

Biotic or biological stress Biotic stress would include such living disturbances as fungi or harmful insects, e.g., Animal stress, insect stress, fungi stress, etc. Fungi by rotting of heart wood, animals by breaking and grazing, insects by eating skeleton or leaves, etc.

Animal Stress by grazing

Insect stress by eating leaves

Fungi stress by rotting

A biotic or environmental stress A biotic stress is defined as the negative impact of non-living factors on the living organisms in a specific environment.

A biotic stress factors or stressors are naturally occurring factors such as intense sunlight or wind that may cause harm to the plants and animals in the area affected.

Stresses can be studied classifying into the following different kinds:  Drought stress.  Water stress.  Salt stress.  Heat stress.  Wind stress.  Nutrient stress.

Drought stress: It occurs when the available water in the soil is reduced and atmospheric conditions cause continuous loss of water by transpiration or evaporation. Drought stress is seen in almost all plants but its extent varies from species to species and even within species

Drought stress

Water stress: Water stress may result in the arrest of photosynthesis, disturbance of metabolism and finally the death of plant. Water stress inhibits cell enlargement more than cell division. It reduces plant growth by affecting various physiological and biochemical processes.

Water stress

Salt stress: It includes wild plants that thrive in the saline environments along the sea shore and saline deserts. These plants, called halophytes, have distinct physiological and anatomical adaptations to counter the hazards of water deficit. Salinity can affect any process in the plant's life cycle.

Salt stress

Heat stress: Heat stress often is defined as where temperatures are hot enough for sufficient time that they cause irreversible damage to plant function or development. In addition, high temperatures can increase the rate of reproductive development, which shortens the time for photosynthesis to contribute to fruit or seed production.

Heat stress

Wind stress: Wind stress is visual stress incurred by wind causes damage to seedlings, breaking branches and even uprooting the whole plants.

Wind stress

Nutrient stress: Nutrient stress is one of the major stressor causing dying back in plants. It causes due to the shortage of nutrients in soil such as nitrogen, phosphorus, iron, etc.

Nutrient stress

Difference between biotic and abiotic stress: Abiotic damage often occurs on many plant species. Drought stress will likely cause damage on several types of plants in a yard or garden. In contrast, Biotic disease problems are more limited to a certain species. The fungi that cause tomato leaf blight do not cause damage on sweet corn.

Abiotic damage does not spread from plant to plant over time. Biotic diseases can spread throughout one plant and also may spread to neighboring plants of the same species. Wind-blown rain is a common way for disease agents to spread from plant to plant.

Biotic diseases sometimes show physical evidence (signs) of the pathogen. Abiotic diseases do not show the presence of disease signs.