Walnut root-lesion nematode

Systematic position
Pratylenchus vulnus is a microscopic nematode belonging to the phylum Nematoda, class Chromadorea, order Rhabditida, and family Pratylenchidae. It is widely recognized as a major soil-borne pathogen that causes significant economic losses in various agricultural sectors, particularly in orchards and perennial nurseries.

Host range
This nematode has a very broad host range, making it a persistent problem for growers. It severely impacts fruit trees, including walnuts, almonds, cherries, plums, and peaches. Furthermore, it causes significant damage to viticulture (grapes), ornamental plants such as roses, and several nursery crops, often leading to decline and loss of vigor in established plantings.

Biology and lifecycle
Pratylenchus vulnus is a migratory endoparasite, meaning it feeds within the root cortex and moves freely between the root tissues and the surrounding soil. The life cycle comprises an egg stage, four juvenile stages, and the adult stage. The reproduction is amphimictic, and the population density can build up rapidly in sandy or loamy soils, especially in regions with mild temperatures throughout the year.

Symptoms and damage
The primary damage occurs as a result of nematode feeding, which destroys cortical cells and leads to the formation of necrotic lesions and cavities on the roots. These lesions provide entry points for secondary pathogens, such as fungi and bacteria, leading to root rot. Infected plants exhibit symptoms like stunting, chlorosis, reduced fruit yield, and, in severe cases, the gradual death of the entire plant.

Management strategies
Effective management requires an integrated approach:

• Selection of certified nematode-free planting material to prevent introduction.
• Implementation of pre-plant soil fumigation in heavily infested nursery fields.
• Use of nematode-resistant rootstocks for fruit tree production.
• Crop rotation with non-host cover crops to suppress nematode populations in the soil.
• Maintaining soil health through organic amendments that encourage beneficial microbial activity.