African peanut pod nematode

The African peanut pod nematode Ditylenchus africanus belongs to the order Tylenchida, family Anguinidae. It is a microscopic roundworm with an elongated body characteristic of the Ditylenchus genus.

Identifying this pest in the field is extremely difficult due to its microscopic size. Accurate species identification requires laboratory techniques, such as microscopic examination of plant tissues or molecular diagnostics (PCR).

The nematode is capable of surviving in soil and plant debris in a state of anabiosis under unfavorable conditions. Larvae and adults can withstand long periods of drought, making them highly resilient pests.

The life cycle involves several larval stages, with the fourth larval stage being the infective one. Transmission typically occurs through infested seed material and soil carried on agricultural machinery.

This species is well-adapted to the climatic conditions of Southern Africa, but it poses a significant phytosanitary threat to other regions if imported via infested plant products.

The primary host crop for Ditylenchus africanus is the peanut (Arachis hypogaea). The nematode causes systemic damage by infiltrating the tissues of the pods, fruit, and subterranean parts of the plant.

Damage caused by the nematode results in stunted plant growth, leading to significant losses in biomass. In infested pods, seed formation is impaired, which reduces market value and nutritional quality.

Damaged tissues become entry points for secondary infections, including various fungal and bacterial pathogens. This often leads to pod rot directly in the soil, resulting in substantial crop loss.

Economic losses from this nematode can reach critical levels in regions where peanut cultivation is intensive. Infested fields require strict quarantine measures to prevent the spread of the parasite.

It is worth noting that the nematode can infect other plant species as well, serving as a latent reservoir of infection in field plots, which complicates complete eradication.

One of the typical signs is the deformation and the appearance of dark spots on the peanut shells. Upon opening the pods, the internal seed tissues may appear destroyed or necrotic.

Plants infested with the nematode often display signs of chlorosis and premature wilting. The root system may be poorly developed, and the overall development of the above-ground part is significantly delayed.

At early stages, symptoms are almost invisible; however, in cases of high infestation, mass death of ovaries can be observed. The harvest often shows visible signs of fruit necrosis.

• Yellowing and curling of leaves.
• Stunted growth compared to healthy plants.
• Dark spots on peanut pods and kernels.
• Softening of the internal tissue of the pod.
• Reduction in the weight of filled pods.

Visual inspection during harvest allows for the detection of pathological changes, although by that stage, a large portion of the crop may already be affected.

The primary control method is the use of high-quality, certified seed material that is free from nematodes. Inspecting planting material before sowing is a critical stage of protection.

Implementing crop rotation is an essential agronomic practice. Alternating peanuts with crops that are not hosts for Ditylenchus africanus helps to reduce the nematode population in the soil.

Thorough cleaning of agricultural machinery when moving from infested fields to clean areas prevents the transfer of cysts and larvae through soil residues.

The use of chemical plant protection products (nematicides) is limited due to high costs and environmental risks. In some countries, such products are used only when infestation density is very high.

Destroying plant debris after harvest and deep plowing help reduce the number of sites where the nematode can overwinter and maintain its viability.