Introduction

A disease is an abnormal condition that injures the plant or causes it to function improperly. Diseases are readily recognized by their symptoms - associated visible changes in the plant. The organisms that cause diseases are known as pathogens. Many species of bacteria, fungus, nematode, virus and mycoplasma-like organisms cause diseases in rice. Disorders or abnormalities may also cause by abiotic factors such as low or high temperature beyond the limits for normal growth of rice, deficiency or excess of nutrients in the soil and water, pH and other soil conditions which affect the availability and uptake of nutrients, toxic substances such as H2S produced in soil, water stress and reduced light. In broad sense such disorders and abnormalities refer as physiological diseases. However, here we will cover only the common diseases of rice those cause by pathogen. Before attempting diagnosis of rice diseases it is important to understand some frequently used terms.