The study of phanerogamic plant parasites and nematodes involves understanding how these organisms affect plants and the diseases they cause. Here’s an overview of both:

1. Phanerogamic Plant Parasites:

Phanerogams are flowering plants that reproduce by seeds, and some of these species are parasitic. These plants lack the ability to produce their own food through photosynthesis and instead rely on a host plant for nourishment. The parasitic phanerogams use specialized structures to connect to the host plant and draw nutrients.

Characteristics:

• They have specialized structures like haustoria that penetrate the host plant tissues.
• They are typically found in root, stem, or leaf parasitism.
• They can be holoparasitic (completely dependent on the host plant) or hemiparasitic (partially dependent, still photosynthesize).

Examples of Phanerogamic Plant Parasites:

• Cuscuta (Dodder):

  • A holoparasite that lacks chlorophyll and depends entirely on its host for nutrients. It attaches to the host plant using haustoria.
  • Diseases caused: Cuscuta species cause significant damage by weakening plants, reducing yield, and transmitting plant viruses.

• Striga (Witchweed):

  • A hemiparasitic plant that mainly parasitizes crops like maize, sorghum, and millet. It has chlorophyll and can photosynthesize but relies on the host for water and nutrients.
  • Diseases caused: Striga infestation leads to Striga wilt, characterized by stunted growth, yellowing, and reduced crop yields.

• Mistletoe (Viscum album):

  • A hemiparasite that attaches to trees and shrubs, drawing nutrients and water from the host plant.
  • Diseases caused: Mistletoe can cause damage to trees by weakening them, resulting in reduced growth and potential death of the host.

2. Nematodes:

Nematodes are microscopic, cylindrical worms that are found in soil or water. Some species of nematodes are plant-parasitic, feeding on plant roots, stems, and leaves.

Characteristics:

• They have a simple, elongated, unsegmented body with a protective cuticle.
• They are typically endoparasitic (living inside plant tissues) or ectoparasitic (feeding from the surface).
• Nematodes can cause damage directly by feeding on plant cells or indirectly by transmitting pathogens.

Types of Plant-Parasitic Nematodes:

• Root-Knot Nematodes (Meloidogyne spp.): These nematodes form galls or knots on plant roots, which interfere with water and nutrient absorption. Diseases caused: The affected plants may show yellowing, stunting, and wilting, and the root system becomes swollen with knots. Major crops affected include tomato, cotton, and soybean.

• Cyst Nematodes (Heterodera spp. and Globodera spp.): Cyst nematodes form cysts in the soil and on the roots of plants, causing root damage. Diseases caused: These nematodes affect potatoes, tomatoes, and soybeans, leading to poor root development, nutrient deficiency, and reduced yields.

• Lesion Nematodes (Pratylenchus spp.): Lesion nematodes feed on the roots, causing lesions or wounds. Diseases caused: Plants may show symptoms like stunted growth, wilting, and necrotic lesions. Commonly infects crops like banana, maize, and wheat.

• Stem Nematodes (Ditylenchus spp.): These nematodes infect the stems, leaves, or bulbs of plants. Diseases caused: They cause wilt diseases, such as citrus nematode wilt, affecting crops like garlic, onions, and peanut.

• Foliar Nematodes (Aphelenchoides spp.): Foliar nematodes feed on plant leaves and can lead to significant damage.Diseases caused: They cause yellowing and necrotic lesions on leaves, and plants may become more susceptible to other pathogens.