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Plant diseases are diseases in plants caused by pathogens (infectious organisms) and environmental conditions (physiological factors). [1] Organisms that cause infectious disease include fungi , oomycetes , bacteria , viruses , viroids , virus -like organisms, phytoplasmas , protozoa , nematodes and parasitic plants . [ 2 ]
Plant disease triangle. Epidemiology is the study of factors affecting the outbreak and spread of infectious diseases. [10] A disease triangle describes the basic factors required for plant diseases. These are the host plant, the pathogen, and the environment. Any one of these can be modified to control a disease. [11]
The discovery of plant viruses causing disease is often accredited to A. Mayer (1886) working in the Netherlands demonstrated that the sap of mosaic obtained from tobacco leaves developed mosaic symptom when injected in healthy plants. However the infection of the sap was destroyed when it was boiled. He thought that the causal agent was bacteria.
Once a plant is infected, the bacteria spread through the xylem vessels from the area of infection to the main stem, and the entire plant wilts and dies. Initial symptoms may include the wilting of single leaves and smaller stems. Infected plants may produce a creamy white bacterial ooze when cut.
It is a derivative of the most rich fatty acid in the lipids of leaf membranes, alpha-linolenic acid. When plants experience mechanical wounding or herbivory, JA is synthesized de novo and induces genome-wide changes in gene expression. [5] JA travels through plants via the phloem, and accumulates in vascular tissue. [6]
Bacterial soft rots are caused by several types of bacteria, but most commonly by species of gram-negative bacteria, Erwinia, Pectobacterium, and Pseudomonas. It is a destructive disease of fruits, vegetables, and ornamentals found worldwide, and affects genera from nearly all the plant families.
Bacterial wilt is a disease of the vascular tissue. When a plant is infected, E. tracheiphila multiplies within the xylem, eventually causing mechanical blockage of the water transport system. The first sign of infection, which appears about five days after acquisition, is the wilting of individual leaves on a single stem.
Net necrosis of potato is the result of infection by potato leaf roll virus (PLRV). This symptom is caused by the selective death and damage to cells in the vascular tissues of the tuber. The fact that only specific cells within the tuber are affected by this problem while others remain normal causes the characteristic net symptom.