Plant Diseases are caused by Bacteria, Fungi , Virus and Other sources Disease can affect the yields through reduction of photosynthetic area in early stages and late infestations around booting stage. Disease causes reduction on photosynthate flow in the plant (equivalent to blocking of pipes) Disease Symptoms A disease symptom in a plant is expressed in the form of a distinct localized structural change on the host tissue. The changes are cytological, histological & morphological in nature. The following symptoms are important for our discussion. Discoloration Change in color of whole plant or parts and the intensity of Discoloration depends on intensity of disease. EX: Yellowing, browning, blackening, silvering and chlorosis. These symptoms are usually more in shoots, buds, and fruits, less in stem and roots. Spots and short holes Spots vary in size and color and margin of spots also vary in pattern and color. Margins may be circular and irregular spots may be isolated and coalesce after development. Spots generally occur in leaves but sometimes also on stems, leaf sheath, petioles, calyx and fruits. The spots on the leaves produce a hole due to death and drying of tissue and finally fall off resulting in a shot hole. Scorch Sometimes it misleads to toxic effects of foliar sprays of pesticides resulting in death of tissue. Factors Influencing Disease Symptoms Host parasite relation The intensity of the disease depends upon the susceptibility /Resistance of the host to the pathogen. Environmental factors Can be grouped as Soil borne, Seed borne and Air borne Soil borne Soil pH, Structure, Texture Moisture, Organic matter, fertility, cultural operations, Irrigation. Seed borne Seed Moisture, storage environment Air borne Temperature, RH, and Rainfall Wind.

Top