Which plant parts can show visible symptoms of disease?

In the study of plant pathology, visible symptoms of disease can manifest across various parts of a plant. When a plant is affected, the following parts often show abnormal changes such as discoloration, curling, or structural malformation:

• Leaves: Often the primary focus of diagnosis, leaves may exhibit spots, blights, lesions, yellowing, or deformations like holes and curling.1
• Stems, Branches, and Trunks: These may develop sunken, swollen, or discolored areas known as cankers, as well as abnormal growths like galls or evidence of wood decay.1
• Roots: Symptoms include decay, discoloration, stunting, or the formation of galls caused by organisms like nematodes.1
• Blossoms and Fruits: These organs can show spots, rot, or premature death.12

Disease symptoms are categorized as either local—affecting a limited area like a leaf spot or gall—or systemic, which involve the entire plant, such as general wilting, dwarfing, or yellowing. It is important to note that similar symptoms can sometimes be caused by environmental factors rather than infectious pathogens.31