Citrus nematode

The citrus nematode (Tylenchulus semipenetrans) is a microscopic soil-borne parasite belonging to the order Tylenchida and the family Tylenchulidae. It is recognized as one of the most significant limiting factors in citrus production globally. The nematode specifically attacks the root systems of citrus trees, causing a slow decline in tree vigor and fruit yields.

The host range is primarily limited to the Rutaceae family, including all commercial citrus varieties, as well as some non-citrus crops like grapevines and olive trees. Once established in the soil, the nematode can survive for long periods, as it is highly adapted to the root zone environment of perennial woody plants.

The biological cycle is unique due to the semi-endoparasitic feeding habit of the female. After penetrating the root cortex with its head, the female remains stationary and forms a feeding site known as a nurse cell. The posterior part of the female's body remains outside the root and produces a gelatinous matrix containing eggs, which protects the offspring from desiccation and soil pressure.

Symptoms of infestation are often deceptive, appearing as general malnutrition. The infected roots exhibit a dirty appearance because soil particles stick to the gelatinous egg masses on the root surface. Over time, the affected tree shows reduced leaf size, chlorosis, significant fruit drop, and stunted growth. The damage to the root system compromises the plant's ability to absorb water and nutrients efficiently.

Effective management requires an integrated pest management (IPM) strategy:

• Planting certified nematode-free nursery stock in clean soil.
• Using resistant rootstocks such as Poncirus trifoliata or specific hybrids.
• Implementing soil solarization before planting new orchards.
• Applying chemical or biological nematicides during the growing season.
• Maintaining optimal soil health and moisture to support tree recovery.