Meaning of Disease
Plants are the only higher organisms that can convert the energy of sunlight into stored, usable chemical energy in carbohydrates, proteins and fats. All animals including humans depends on these plant substances for survival.
Plants whether cultivated or wild grow and produce well as long as the soil provides them with sufficient nutrients, moisture sufficient light and temperature within a normal range.
Plants however also gets sick, grow and exhibit various types of symptoms and sometimes whole plant die. It is not known whether diseased plant feel pain or discomfort. If a plant is looking different from its community then it is equal to be diseases one. Any biotic or abiotic agents which induce the disease in plant is referred as the cause of diseases.
The causative agents of disease in plants are pathogenic such as fungi, bacteria, viruses, protozoa and nematodes and environmental conditions such as lack or excess of nutrients, moisture, light, etc to presence of toxic chemicals in Air or soil.
Disease in plants has been known since ancient time.
Definition of Disease:
Disease is defined as a disturbance in the rhythmical equilibrium in the activities of host in respect of structure or physiology or both, leading to the death of a part or entire host, or reduces the economic value of the products.
Disease is a complex phenomenon; it is an interaction between the host, the pathogen and the environment.
Disease is malfunctioning process caused by continuous irritation, which results in some suffering producing symptoms.
The plant disease is, therefore , a structural abnormality or physiological disorder or both due to an organism or unfavorable conditions that may affect the plant or its parts or products or may reduce their economic value.