Classification, Symptoms, and Nature of Damage Caused by Plant Nematodes

Plant-parasitic nematodes cause significant damage to crops worldwide. The damage caused by nematodes varies based on the species, plant host, and environmental conditions. Below is a classification of some important plant-parasitic nematodes, their symptoms, and the nature of damage they cause.

• Nematode Classification

Plant-parasitic nematodes are classified into various families based on their morphology, feeding habits, and life cycle. The major families involved in plant parasitism include:

• Family: Heteroderidae: Includes Cyst Nematodes (e.g., Heterodera spp.)
• Family: Meloidogynidae: Includes Root-knot Nematodes (e.g., Meloidogyne spp.)
• Family: Anguinidae: Includes Stem Nematodes (e.g., Anguina spp.)
• Family: Tylenchulidae: Includes Lesion Nematodes (e.g., Pratylenchus spp.)
• Family: Hoplolaimidae: Includes Stubby Root Nematodes (e.g., Trichodorus spp., Paratrichodorus spp.)
• Family: Radopholidae: Includes Banana Nematode (e.g., Radopholus spp.)

• Key Plant-Parasitic Nematodes, Symptoms, and Nature of Damage

Heterodera spp. (Cyst Nematodes)

• Common species: Heterodera avenae, Heterodera glycines (Soybean cyst nematode), Heterodera schachtii (Sugar beet cyst nematode).
• Symptomology:
  • Root Cysts: The female nematodes form a cyst that contains eggs. These cysts appear on the roots as small, lemon-shaped sacs.
  • Stunted Growth: Cyst formation leads to stunted root growth and nutrient uptake.
  • Yellowing: Above-ground symptoms often include yellowing or wilting of leaves, resembling nutrient deficiencies.
  • Root Damage: Roots may appear swollen with a cyst-like structure.

• Nature of Damage:
  • Cyst nematodes feed on root cells, leading to nutrient and water absorption problems.
  • The feeding induces galling, causing long-term damage to the root system, reducing the plant’s ability to take up nutrients.
  • In severe cases, this can cause complete plant death, particularly in heavily infested fields.

Meloidogyne spp. (Root-Knot Nematodes)

• Common species: Meloidogyne incognita, Meloidogyne javanica, Meloidogyne arenaria.
• Symptomology:
  • Root Galls: Characteristic root galls or knots develop around the feeding site of the nematode. These galls disrupt root development.
  • Yellowing: The plant shows yellowing of leaves (chlorosis) and may appear stunted.
  • Poor Growth: Plants exhibit reduced vigor and growth. In severe infestations, they may exhibit wilting.
  • Poor Root Development: The root system is unable to develop properly due to the formation of large galls.

• Nature of Damage:
  • Root-knot nematodes invade the roots and induce the formation of galls that interfere with water and nutrient absorption.
  • The feeding damage also creates entry points for pathogens like fungi and bacteria.
  • This results in reduced yields, especially in crops like tomato, cotton, tobacco, and potato.

Anguina spp. (Stem Nematodes)

• Common species: Anguina tritici (Wheat seed gall nematode), Anguina agrostis.
• Symptomology:
  • Seed Galls: These nematodes form galls on seeds, particularly in wheat. Infected seeds often become swollen and distorted.
  • Stunted Growth: Infested plants exhibit stunted growth and may show yellowing and leaf curling.
  • Blighting: Some plants may exhibit blighting symptoms due to extensive nematode damage.

• Nature of Damage:
  • Seed Gall Formation: The nematode feeds within the developing seed, causing it to become deformed and unviable.
  • Plant Growth Disruption: The feeding on young plant tissues results in poor germination and early plant death, reducing crop yields.
  • Economic Losses: Wheat and grasses are particularly affected, leading to significant economic losses in affected regions.

Radopholus spp. (Banana Nematodes)

• Common species: Radopholus similis (Banana root nematode), Radopholus citrophilus (Citrus nematode).
• Symptomology:
  • Root Rot: Radopholus spp. feed on the roots, causing them to become rotten and discolored.
  • Yellowing and Wilting: The plant may show yellowing and wilting, especially during periods of drought or stress.
  • Root Decay: As the nematode feeds, it disrupts the root system and causes significant root decay.

• Nature of Damage:
  • Radopholus spp. are known to cause root decay, which severely affects the plant’s ability to absorb water and nutrients.
  • In banana crops, the nematode contributes to corm rot, leading to poor fruit development and reduced yields.
  • Secondary infections: The decayed roots can be colonized by opportunistic pathogens, worsening the damage and further reducing crop yields.

Pratylenchus spp. (Lesion Nematodes)

• Common species: Pratylenchus penetrans (Root-lesion nematode), Pratylenchus brachyurus.
• Symptomology:
  • Root Lesions: Feeding creates lesions or necrotic areas on the roots, leading to decay and death of root tissue.
  • Stunting and Yellowing: Above-ground symptoms include yellowing and stunting.
  • Wilting: Plants may exhibit wilting, even under normal soil moisture conditions.

• Nature of Damage:
  • Lesion nematodes feed by penetrating root tissues, causing cell rupture and necrosis, leading to reduced root function.
  • This damage disrupts water and nutrient uptake, causing stunting, yellowing, and ultimately poor plant growth.
  • Lesion nematodes are often associated with secondary infections by fungal pathogens, such as Verticillium and Fusarium.