Sustainable Management of Tropical Nematodes
D. De Waele, A. Elsen, L. Van der Veken and S. Moorthy

Culturing nematodes (D. De Waele and A. Elsen)
Because plant-parasitic nematodes are obligate biotrophic organisms that require living host tissues as food source, they are difficult to culture, especially monoxenically. This difficulty has seriously limited the study of these organisms as plant pathogens. In addition, working with tropical nematodes increases the difficulty since no field populations are available. Therefore, it is necessary to maintain nematode populations using sterile culture techniques. In the Nematology Section several techniques, depending on the nematode species, are applied.
The migratory endoparasites, like Radopholus similis and Pratylenchus coffeae, are maintained on carrot discs and on alfalfa callus. The sedentary endoparasites, Meloidogyne javanica and M. incognita, are maintained on Ri T-DNA transformed tomato roots.

Cryopreservation (B. Panis and A. Elsen)
The maintenance of the different culturing systems is very time-consuming. Moreover, human error and changes and/or adaptations in virulence/ pathogenicity of the cultured nematode populations can occur. Therefore long-term storage, such as cryopreserving the nematodes, has many advantages. In the Nematology Section, a protocol was successfully developed to cryopreserve these tropical nematodes. The protocol consists of a two-step incubation with glycerol and a vitrifiction solution followed by rapid freezing. The storage in –80°C did not alter the reproductive fitness nor the virulence of the nematodes.

Screening for natural resistance (D. De Waele and A. Elsen)

Although nematode resistant and tolerant varieties are often used in many agricultural crops, this method of nematode management has so far been neglected in bananas and plantains.

To obtain broad resistance more varieties from the Musa gene pool and breeding programs have to be evaluated for resistance against R. similis, Pratylenchus spp. and Meloidogyne spp. During screening for resistance, nematologists encounter some problems, like variability in pathogenicity of the different nematode populations, absence of a standard screening procedure and the lack of information concerning the effect of root growth on resistance observations. These different topics are under investigation in the Nematology Section and in different locations overseas. A manual for field screening for nematode resistance is available online.

Biological control by arbuscular mycorrhizal fungi (D. De Waele and A. Elsen)

Arbuscular mycorrhizal fungi (AMF) are obligate symbionts of plants that biotrophically colonise the root cortex and develop an extramatrical mycelium which helps the plant to acquire water and mineral nutrients from the soil, in exchange for carbon as an energy source. The mycorrhizal fungi increase the ability of the plant to tolerate abiotic stress (e.g. drought, Al-toxicity), to control the spread of soil-borne pathogens and influence the photosynthetic and water relations of the plant. Mycorrhizal fungi can form associations with most plants. The association of AMF with plant-parasitic nematodes and the beneficial effect of the mycorrhizal symbiosis on plant growth and nematode resistance / tolerance leads to investigations into the potential of AMF to limit yield losses due to nematodes.