Classification of plant disease: Plant diseases are classed as infectious or noninfectious based on the principal causative agent. Pathogenic organisms that cause plant illnesses include fungi, bacteria, viruses, viroid, nematodes, and parasitic flowering plants.

What is a plant disease?

A plant disease is an abnormality that disrupts or changes a plant’s vital functioning. Wild and domesticated plants equally are susceptible to illness. Although each species has its own unique diseases, they are rare.

Importance

Globally, enormous losses of the crops are caused by plant diseases. The loss can occur from the time of seed sowing in the field to harvesting and storage. Important historical evidence of plant disease epidemics is the Irish Famine due to late blight of potato (Ireland, 1845), the Bengal famine due to brown spots of rice (India, 1942), and Coffee rust (Sri Lanka, 1967). Such epidemics had left an effect on the economy of the affected countries. 

Classification of Plant Disease

Plant diseases must be grouped in an orderly fashion To facilitate the study. Plant diseases can be grouped in various ways based on the symptoms or signs (rust, smut, blight, etc.), nature of infection (systemic or localized), habitat of the pathogens, mode of perpetuation and spread (soil-, seed- and air-borne, etc.), affected parts of the host (aerial, root disease, etc.), types of the plants (cereals, pulses, oilseed, ornamental, vegetable, forest diseases, etc.).

The most useful classification has been made based on the type of pathogens that cause plant diseases. This type of classification indicates the cause of the disease and the knowledge and information that suggest the probable development and spread of the disease and their possible control measures. The classification is as follows: 

1. Infectious plant diseases: 

• Disease caused by parasitic organisms: The organisms, including inanimate or biotic causes, can incite diseases in plants. 
• Diseases are caused by viruses and viroids. 

2. Non-infectious or non-parasitic or physiological diseases: The factors, including inanimate or abiotic causes, can incite such diseases in plants under suitable environmental conditions.