3.3.1 Detection and Identification of Plant Diseases

Plants can exhibit a variety of symptoms when they are affected by diseases or nutrient deficiencies. Recognising these signs is crucial for diagnosing and treating plant health issues.

Common Signs of Plant Diseases:

• Stunted Growth: This often indicates a nitrate deficiency, which hampers the plant's ability to produce the proteins necessary for growth.
• Spots on Leaves: Black spot fungus on roses is a typical cause of leaf spotting.
• Areas of Decay: Black spot fungus on roses and blights on potatoes can lead to decayed or rotten areas on plants.
• Abnormal Growths: Crown galls, caused by bacterial infections, lead to unusual growths or swellings on the plant.
• Malformed Stems or Leaves: Aphid infestations can cause stems and leaves to become distorted or misshapen.
• Discolouration: A magnesium deficiency can cause yellowing of the leaves, known as chlorosis, while tobacco mosaic virus causes a mosaic pattern of discoloured patches.
• Pests on Leaves: Visible pests such as caterpillars can damage the leaves by feeding on them.

Methods for Identifying Plant Diseases:

• Gardening Manuals or Websites: These resources provide images and descriptions to help match symptoms to specific diseases.
• Laboratory Observation: By examining the infected plant in a lab, the specific pathogen causing the disease can be identified through microscopic analysis or culturing techniques.
• Monoclonal Antibody Testing: This advanced method uses monoclonal antibodies to detect specific pathogens, providing an accurate diagnosis.

Important Plant Diseases to Know:

1. Tobacco Mosaic Virus (TMV): A viral disease that causes discolouration and mottling of the leaves, affecting photosynthesis.
2. Black Spot: A fungal disease that causes black spots on rose leaves, leading to reduced photosynthesis and early leaf drop.
3. Aphids: Insects that feed on plant sap, causing damage and potentially transmitting other diseases.

Ion Deficiencies in Plants:

• Nitrate Deficiency:
  • Effect: Leads to stunted growth because nitrates are essential for converting sugars produced during photosynthesis into proteins, which are needed for growth.
• Magnesium Deficiency (Chlorosis):
  • Effect: Causes chlorosis, where leaves turn yellow while the veins remain green. Magnesium is crucial for the production of chlorophyll, the green pigment necessary for photosynthesis.