One or more of the features that are needed to show you the maps functionality are not available in the web browser that you are using.
Please consider upgrading your browser to the latest version or installing a new browser.
More information about modern web browsers can be found at http://browsehappy.com/
Potato cyst nematodes, in common with other cyst nematodes, do not cause specific symptoms of infestation. 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.
Direct damage to roots and the yield of tubers
The infective second stage juveniles of both G. rostochiensis and G. pallida respond to environmental conditions when hatching. There is a short period of time for the second stage juvenile to locate a host root and begin the process of invasion, usually just behind the root tip. The juveniles then position themselves next to the stele within the root where, after a few hours, they will establish a feeding site (syncytium), which will become their nutrient source until their death. If a susceptible variety of potato is planted the plants will soon show signs of attack particularly when nematode density is high. In resistant plant varieties juveniles still hatch from the cyst and invade the plant roots, but they are unable successfully to establish a feeding site or syncytium. In this situation, males are more likely to be produced than females, as males have negligible nutrient requirements compared to females. Nevertheless, even resistant crops may show signs of attack.
The reduction in the yield of potato tubers, depending on the cultivar grown, is also related to or dependent on the plant's ability to tolerate the effects of nematode attack. The effects of potato cyst nematode on the plant include water stress and early senescence of the leaves. A heavily infested plant is unlikely to produce 100% ground cover with its reduced canopy of leaves. Many field studies have monitored the progression of ground cover by leaves and correlated the findings with yields (see Trudgill et al., 1998).
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.
The specific EPPO quarantine regulations (OEPP/EPPO, 1990; EPPO, 2007) for these nematodes require that fields in which seed potatoes or rooted plants for export are grown are inspected by taking soil samples according to an EPPO-recommended method (OEPP/EPPO, 1991; EPPO, 2007) and must be found free from viable cysts of both species of potato cyst nematode. The sampling must be performed after harvest and after removal of the previous potato crop.
Quarantine is a very necessary and often expensive way of attempting to limit the damage caused by disease organisms such as nematodes. Methods to limit or prevent the introduction of alien or existing pests by providing ways of very accurate identification plus sensible legislation (MAFF, 2000) are already used in many countries. Continuous records must be kept of previous land usage and crop rotations. Various organizations throughout the world help to back up the phytosanitary regulations.
The previous PCN Control Directive for the European Union was in place for several decades, over which time many practices within the potato industry have changed and a lot more has been learned from intensive studies on this pest. New European legislation was introduced on 1 July 2010. The revised Control Directive (2007/33/EC) was adopted by the Council of Ministers and has been published in the Official Journal of the European Communities in June 2007.
Physical barriers help to confine pests to their own locality, for example, seas, mountains and other natural phenomena. Trade is probably the keystone to the problem of spread (Parker, 2000). Trade is essential and, when it comes to the movement of soil and plants, is of unparalleled importance with regard to nematode quarantine. Plant parasitic nematodes occur worldwide on virtually every crop, and plant movement can probably be blamed for all potato cyst nematode occurrences outside South America.
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 a highly virulent or new pathotypes.
For further details, see Seinhorst (1986).
Rotation is frequently used to reduce population densities of the potato cyst nematodes, G. rostochiensis and G. pallida. The major hosts of these two species are restricted to the plant family Solanaceae, with the main commercial crops being potato, tomato and aubergine. When these crops are grown in monoculture for several seasons in infested soil, nematode densities can increase to extremely high levels and crop yields become uneconomical. To reduce nematode population densities, non-host crops such as barley are grown between host crops. Magnusson (1987) recorded an 87% decline in G. rostochiensis population density using this type of rotation. Whitehead (1995) also found good control of G. rostochiensis when barley was grown in infested microplots. The annual decline rate of potato cyst nematode in soil is variable, depending on the non-hosts used, the initial population density, various soil-related factors and the population under study. If the reduction of population densities by rotation alone is too slow, then additional means of control may be necessary, such as the use of resistant cultivars, trap cropping or nematicides.
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).
The use of resistant potato clones as trap crops has been used in field trials in Northern Ireland. Ten clones had a strong hatch-inducing effect and resistance to currently known PCN pathotypes. Some of these showed potential for further development to reduce high population levels of PCN in the field and for the organic potato market (Turner et al., 2006) Another solanaceous host, S. sisymbriifolium, acts in a similar way, stimulating hatch without the nematode being able to complete its life-cycle, with the added benefit of then being used as a green manure. The seed line of S. sisymbriifolium is probably important as seed lines used for trap cropping are listed by Scholtze (2000) as totally resistant to PCN, whereas two lines (nos. 72 and 121) were recorded as poor hosts (with less then 5 cysts per plant in a host test performed by Stelter (1987). Where the nematode density is reduced, there will be a significant yield benefit for any subsequent potato crop.
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. In Oman, Mani et al. (1993) found that 62 days of solarization reduced G. rostochiensis population density by 95%. In New York State, USA, 97% of nematode eggs were inactivated in the top 10 cm of soil (LaMondia and Brodie, 1984.). Solarization in cooler climates and at depths greater than 10 cm is much less effective.
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.
Work on biological control agents was started in the late 1930s (Linford et al., 1938) and still continues (Crump and Flynn, 1995; Segers et al., 1996; Crump, 2004). At present, there is still no commercial biological product available to control potato cyst nematodes. The majority of studies in the late 1990s have concentrated on the fungal control agents Pochonia, Hirsutella and Arthrobotrys and the bacterium Pasteuria.
Several workers (e.g. Roessner, 1986) have studied biological control of G. rostochiensis in pots and in vitro. Almost no field trial data are available. This is probably due in part to the logistics of such operations e.g. producing enough inoculum for field scale trials. Also, some tests do not produce the expected results for reasons as yet undefined, but are probably related in some way to the physiology or ecology of the nematode or to the host parasite relationship.
Pochoniachlamydosporia will infect young females in pots but is less effective when potatoes are grown in the presence of low nematode population densities.
Progress in the area of biological control requires a better understanding of the population dynamics of potato cyst nematodes and its parasites (Davies et al., 1991; Davies, 1998). A variety of factors, such as plant host, the action of root exudates, soil type and the mode of parasitism of the control organism, interact to determine success in the biological control of the nematode. Cyst nematodes may be more susceptible to infection at certain points in their life cycle. For example, the three major fungal parasites Pochonia chlamydosporia, Fusarium oxysporum and Cylindrocarpon destructans, have all been detected throughout the potato cyst nematode life cycle but the most active will vary at different times of the cycle (Crump, 1987).
At the molecular level, the high specificity known to occur between cyst nematodes and their plant hosts is important, in terms of intra- and inter-specific variation, particularly with regard to virulence and avirulence. Work by Segers et al. (1996) on the effect of a protease-like enzyme (designated VCPI), from the nematophagous fungus Pochonia chlamydosporia, showed that when this enzyme was used as a pre-treatment of Meloidogyne incognita eggs they became more susceptible to P. chlamydosporia. The same treatment applied to G. rostochiensis eggs gave no response.
In the last decade some products have come to market that have nematicidal effects, such as DiTera, a compound produced from the fermentation extracts of a bacterium. Paecilomyces chlamydosporia, a fungal biocontrol agent, is also available on the market. Most other potential biocontrol agents are still being tested or studied to overcome problems with delivery systems or application methods. Many other mutualistic bacterial and fungal endophytes probably exist in the agroecosystem that would greatly improve plant health while at the same time be detrimental to plant parasitic nematodes. However, many technologies are involved in discovering the most appropriate candidates for commercialisation (Sikora et al., 2007). With time, appropriate study of plant parasites, their molecular properties and modes of parasitism will improve biological control options and identify new ways forward.
Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources: