Plant Disease Symptoms Overview

Disease Symptoms

• Discoloration: Change in natural green color, can be mosaic (specific spots) or yellowing (entire affected area)
• Spotting and Perforation of Leaves: Death of plant tissue, spots vary in shape, size, and color
• Blight: Rapid death of large plant parts, can lead to death of branches, leaves, flowers, and fruits. Example: Late blight in tomatoes & potatoes.
• Canker: Death of surface layer of affected part, leads to cracking and wounds that don't heal
• Rot: Death & decomposition of plant tissue, frequently affects water-rich or food storage parts. Example: Black rot in onions
• Wilting: Plant loses more water than it absorbs, resulting in loss of turgidity. Two types: Permanent wilting (pathological) and temporary wilting. Example: Fusarmic wilt in tomatoes
• Stunting/Atrophy: Plant size reduction (stunting) or affected part size reduction (atrophy) due to lack of food or water
• Tumors: Disorder in plant growth regulators leading to rapid cell division or increased cell size. Example: Crown gall in trees.
• Rust: Pockets filled with parasite beneath the plant skin, forming raised spots that can burst. Example: Yellow rust in wheat.
• Scab: Death of superficial spots on plant part, spots are raised and rough, result from increased growth of tissue followed by explosion and transformation into cork tissues. Example: Ordinary scab in potatoes.

Pathological Signs:

• Presence of the pathogen or its structures: Examples include mycelium, spores, sclerotia, bacterial growths.
• Example: Powdery mildew in grapes.

Microorganisms

• Are found everywhere, including water, air, soil, and food.
• Are absent or rare in places exposed to sunlight or treated with disinfectants like alcohol, Dettol, and chlorine.
• Are specialized, meaning they can only infect specific organisms.
• Microbes infecting plants cannot infect humans or animals and vice versa.

Harmful Microbes

• Some microbes can be harmful to humans, but only if precautions aren't taken.
• The biggest dangers are the toxins produced by microbes, which can lead to diseases like cancer and damage to vital organs like the kidneys and liver.

Beneficial Microbes

• Microbes are vital in producing baked goods, dairy products, and antibiotics.
• They decompose dead organisms and help increase soil fertility.
• Some microbes are edible.
• Microbes like Azotobacter and Rhizobium fix nitrogen, which helps legumes grow and increases soil fertility.

Plant Pathology

• The science dedicated to understanding the relationship between a plant and its pathogen.
• Aims to understand how pathogens impact plant health.

Plant Diseases

• Any deviation in a plant's natural behavior, causing changes in its appearance, physiological functions, or tissue composition.
• Typically caused by pathogens.