Potato Golden Cyst Nematode (Globodera rostochiensis) is a serious agricultural and quarantine pest. Cysts can live in soil for 30 years and the nematode can cause direct crop losses, increase pest control costs, constrain cropping patterns, and devalue infested land. Potatoes and tomatoes are the main crops of economic importance attacked by this pest. The nematode also reproduces on the roots of eggplant and on some wild solanaceous weeds.
Initially, crops will display patches of poor growth and plants in these patches may show chlorosis and wilting. When the tubers are harvested there will be a yield loss and tubers will be smaller.
To be confident that these symptoms are caused by potato cyst nematodes and to give an indication of population density, soil samples must be taken or the females or cysts must be observed directly on the host roots. In heavily infested soils, plants have reduced root systems and often grow poorly due to nutrient deficiencies and to water stress. Plants may senesce prematurely as they are more susceptible to infection by fungi such as Verticillium spp. when heavily invaded by potato cyst nematodes
Biology and Ecology
Eggs contained within cysts are the persistent stage of the life cycle; new cysts contain around 500 eggs. Some eggs are able to survive within the cyst for as long as 30 years, although by this time very few are viable.
The infective juveniles, as with most other cyst nematodes, penetrate the host root just behind the root tip. From this point the juveniles move up or down the root until they receive a specific signal, probably of a chemical nature, to set up a feeding site in the form of a syncytium.
Infective second-stage juveniles that penetrate the pericycle cells of the plant are more likely to become males, whereas those that penetrate the procambial cells tend to become females. Within a few hours of settling, the juvenile probes the selected cell inserts its stylet into it while remaining motionless for several hours; the stylet is then withdrawn and re-inserted into the same cell.
The life cycle takes approximately 45 days, during which time the males will molt and become vermiform, leave the host root and fertilize as many females as possible before dying about 10 days or so after first leaving the root (Evans, 1970). The females during this time have become saccate and their posterior ends have protruded through the root cortex, ready for mating.
Prevention and control
To prevent further spread of potato cyst nematodes into uninfested areas, several methods are used. These include legislation on the movement of seed potatoes, nursery stock, flower bulbs and soil. These apply internationally and nationally.
1. Check that machinery is thoroughly clean and free from plant debris.
2. Do not return soil to fields as it may cause infestation of potato cyst nematode to spread.
3. Clean soil from potato tubers and have the soil tested to be sure of non-transference of potato cyst nematode.
4. Make sure that laboratories that test soil for potato cyst nematode are properly qualified and that they test 500 g of soil per sample.
5. Grow susceptible and resistant varieties of potato alternately, thus reducing the possibility of selecting highly virulent or new pathotypes.
To reduce nematode population densities, non-host crops such as barley are grown between host crops.
Trap cropping has been used successfully for the reduction of cyst nematode populations (Halford, et al., 1999). Potatoes are grown in order to cause the second stage juveniles to hatch. These are given sufficient time to penetrate the roots and develop into young adults. By monitoring soil temperature from the date of planting, fertilization and formation of new eggs can be avoided by destroying the crop some 6 or even 7 weeks after planting, before too many heat units have accumulated. If crop destruction is left too late, the nematode density will increase. Using this method, G. rostochiensis populations have been reduced by more than 80% (Halford et al., 1999).
Solarization is a good method of killing nematodes in very hot climates. The soil is covered with two layers of polyethylene, allowing the soil underneath to heat up quickly.
Natural parasites and biological control options are being studied intensively in the search for natural ways of controlling plant parasitic nematode populations without the use of nematicides, which are highly toxic and a burden on the environment. These biological control agents are part of a grander objective to manage nematodes more effectively using a variety of biological strategies that include trap cropping and rotation.
Eng. Adnan Mafakheri