Tropical nematodes in greenhouses
5 November 2020
A wide variety of nematodes can occur in greenhouse horticulture. Most of these are tropical species that are not found in field-grown crops. The nematode analysis for greenhouse horticulture takes this into account.
Root knot nematodes
“In vegetables grown under glass, the most common nematodes are the tropical Meloidogyne species M. javanica, M. incognita, and M. hapla (the northern root knot nematode,” says Natasje Poot, Product Manager Cultivation . “These are known to cause damage in crops such as tomato, cucumber, eggplant and sweet pepper.” In recent years, these nematodes have also been causing more and more problems in cut flower crops. Among the plants we receive infected samples of are chrysanthemum, gerbera and rose. The root knot nematode can also occur in substrate-based systems. The species most frequently found in substrate-grown roses is M. hapla.
Root knot nematodes affect the physiology of the plant. Giant cells form at the points where the nematodes penetrate into the roots. On the outside of the roots, these can be seen in the form of knots, or galls. The eggs are laid in and on the knots in a jelly-like matrix containing 300-500 eggs. The eggs only need a temperature of 5 to 10°C to hatch, which is always present in greenhouses.
Root lesion nematodes
Another species that regularly causes damaging greenhouse crops is Pratylenchus (the root lesion nematode). “Pratylenchus penetrans can cause damage in chrysanthemum, alstroemeria, sweet pepper, and tomato, among others. Tropical Pratylenchus species are also found: P. bolivianus occurs in alstroemeria, for example. This is relatively rare, but when a P. bolivianus infection does occur, it is often severe and can cause significant problems. Pratylenchus seems to cause fewer problems in a substrate-grown crop, although the nematodes can still be found there too.”
This type of nematode penetrates the root and tunnels deep into it. The cells through which it passes are sucked dry and die off. This is visible externally in the form of brown spots (lesions). The nematodes remain mobile their entire lives and can leave the dying roots and infest new roots. The eggs are laid individually in the soil or in the roots. Pratylenchus penetrans lays one or two eggs a day over a period of five weeks. In warm temperatures such as those found in greenhouses, the eggs can hatch in as little as 9 to 12 days.
Virus transmission by LX and trichodorids
Other nematodes mainly cause indirect damage to the crop by transmitting viruses. This is particularly the case with the species Longidorus and Xiphinema (LX) and trichodorids. Certain LX nematodes can transmit Arabis mosaic virus, strawberry latent ringspot virus, and tomato black ring virus.