List of some nematode species associated with potato.
Plant-parasitic nematodes are a significant factor limiting potato production and tuber quality in several regions where potato is produced. Overall, parasitic nematodes alone cause an estimated annual crop loss of $ 78 billion worldwide and an average crop yield loss of 10–15%. As a result, sustainable food production and food security are directly impacted by pests and diseases. Degrading land use with monocultures and unsustainable cropping practices have intensified problems associated with plant pathogens. Proper identification of nematode species and isolates is crucial to choose effective and sustainable management strategies for nematode infection. Several nematode species have been reported associated with potato. Among those, the potato cyst nematodes Globodera rostochiensis and G. pallida, the root-knot nematode Meloidogyne spp., the root lesion nematode Pratylenchus spp., the potato rot nematode Ditylenchus destructor and the false root-knot nematode Nacobbus aberrans are major species limiting potato yield and leading to poor tuber quality. Here, we report a literature review on the biology, symptoms, damage and control methods used for these nematode species.
- lesion nematodes
- potato cyst nematodes
- root-knot nematodes
- Solanum tuberosum
- yield loss
There has been increasing demand for food supply and food security. Unsustainable cropping production systems with monocultures, intensive planting and expansion of crops to newly opened areas have increased problems associated with new pests and diseases .
Nematodes are diverse, microscopic multicellular animals comprising free living to plant parasitic species. They parasitize a wide range of plant species, including monocots and dicots, and are one of the most limiting factors for major crops, causing substantial annual crop loss worldwide. Plant parasitic nematodes are a limiting factor for potato production and lead to decreased yield, physical and chemical changes in potato tubers, poor tuber quality and malformations, which overall make them unmarketable [3, 5, 6]. Nematodes alone can cause average yield losses in potato up to 12% . Nonetheless, potato yield losses due to nematode parasitism also depend on a combination of factors, including cultivar, favorable environment, soil structure, population density and time of planting, and could lead to a more severe decline in yield at particular cropping systems [3, 5, 8, 9, 10].
Several nematode species are found associated with potato; some of which cause significant yield losses, while others may cause minor injuries and are of local importance. The main nematode species associated with potato includes the yellow potato cyst nematode
Since pathogens such as plant parasitic nematodes represent major losses in agricultural systems, especially when the crops are not managed sustainably, the searches for information on the occurrence of nematodes in the production system, population density, species, level of damage and monitoring and management of these populations are essential in regions where crops will be set [3, 4]. In addition, reliable, fast and proper nematode diagnosis and specimen identification are mandatory for choosing adequate management control strategies and for avoiding spreading of exotic nematodes in quarantine materials.
The objective of this chapter is to report a literature review on major nematode species that affect potato growth, yield and quality worldwide and to point out methods normally used for their sustainable management in the field. We will focus on the main nematode species that cause mostly damage to potato, including (i) the potato cyst nematodes
|Common name||Species name|
|Potato cyst nematodes|
|Root lesion nematodes|
|Potato rot nematode|
|The false root-knot nematode|
|Bulb & stem nematode|
|Stubby root nematode|
|The reniform nematode|
2. Major nematode species affecting potato
2.1. Potato cyst nematodes (
Potato cyst nematodes (PCN)—the golden nematode
Mature females of PCN,
Field dissemination of PCN occurs through several ways, including irrigation water, rainfall runoff, infested soil particles, infested commercial seed potato tubers, contaminated packing of seed potato tubers, footwear, animal hooves, as well as with infested implements and machineries, among others [17, 18].
The host range of PCN includes potato, tomato (
PCN are considered major pest to potato production in which yield losses can vary from slight losses, reach up to 70% or to a complete loss . The level of damages and losses, however, depend on a combination of factors, including nematode population buildup, number of generations per year, length of potato growing season, soil temperature and host factors [20, 21]. In addition, due to non-specific symptoms in potato, especially above ground, losses are often not taken into account or attributed to adverse factors, such as other pathogens, inadequate plant nutrition and lack of soil moisture . Typical symptoms of nematode infestations occur in patches of poor growth in the field, modifying the genetic characteristics of the crop, causing smaller, curled and abnormally colored leaves, tending to show brown spots on the margins and reduction of the numbers and sizes of leaflets, which overall affect the photosynthesis .
Potato plants infected with
Once the nematodes are reported into potato fields, other management measures should be used in order to avoid their dissemination or to decrease their population level and thus improve yield. The success in decreasing their population level is variable and depends on the initial population density, soil type and plant genotype, among others. Generally, long-cycle potatoes planted in the fall and harvested in spring have more pronounced yield losses than short-cycle cultivars .
Control methods for PCN include the use of quarantine regulations, crop rotation and crop succession [15, 21] and the use of resistant varieties and nematicides. For instance, crop rotation with barley has showed reduction in
The use of resistant varieties against nematode infection is one of the most effective and environmentally safe methods to control their infection. Resistant varieties against
Trap plants can also be used to control these nematodes. These plants will trigger hatching of nematode eggs with posterior prevention from completing their cycle by destroying the host. The length of time is critical and plants should be destroyed at a proper time after planting in order to stop the nematode cycle . If plants are not destroyed or occur too late, the nematode population will build up. Some examples of the use of trap plants include the plant species
Alternatively, the use of antagonist plants can be used to control these nematodes. Antagonistic plants will initially stand nematode infection; however, later in their cycle, plant factors will stop their further development. The following plant species
Other control methods include soil solarization, especially in regions with warmer temperatures. Chemical control with nematicides has also being used in several regions with satisfactory rate of control. Products, such as carbamates, aldicarb and carbofuran, have been used successfully. However, soil solarization and the use of nematocides are costly, and nematicides may cause side effects to human and to the environment .
2.2. Root-knot nematodes (
Root-knot nematodes (RKNs),
This group of nematodes is highly diverse, mainly due to their variations in cytogenetics (aneuploidy and polyploidy states), types of reproduction (amphimixis to parthenogenesis), complex mode of parasitism (advanced interactions with their hosts), interspecific hybridization, cryptic species and wide host ranges [27, 29, 30, 31, 32].
Root-knot nematodes are endo-sedentary parasitic nematodes. The second-stage juvenile (J2) is the infective stage. After RKN hatch from eggs, the J2 migrates through the soil towards suitable root and uses special enzymes and the stylets to force penetration into the vascular cylinder where RKN establishes their feeding site by inducing hypertrophy and hyperplasia of a group of cells leading to swelling and formation of giant cells. On this site, nematode goes through three more ecdysis (molting) to become a swollen young female. Mature females begin laying eggs in the root, forming mass eggs wrapped in a gelatinous matrix. Each egg mass contains 400–500 eggs on average, and it is formed in the midst of cortical parenchyma or on the surface of the roots. The embryonic development of the nematode results in the first stage (J1), passing through an ecdysis (molting) in the egg, followed by the second stage (J2). Adult males do not feed on infected plants; they leave the roots and move freely in the soil until they die [4, 27].
Symptoms in the field include yellowing, stunting, wilting, brown spots and rotting of tubers. RKNs induce hypertrophy and hyperplasia of infected cells leading to swelling of tissues commonly known as galls. Affected tubers also develop galls, known as ‘popcorn’, which overall leads to low quality of tubers (Figure 1) [5, 33]. The number and sizes of galls vary depending on the susceptibility of the cultivars, population density and favorable temperatures . RKN-infected roots change their nutrient and water uptake, leading to pronounced poor growth and tuber quality and decreased yield. Commonly, there are high levels of intraspecific variation within
Often, the invasion of potato root system is non-damaging, but as soon as tubers begin to initiate, tubers are invaded by the infective second-stage juvenile (J2) and a rapid development and spread occur. Thus, if potato roots and tubers become infected early, several generations of the pathogen will occur before harvest, which typically is about 110 days after planting . However, this depends on each cultivar and the management systems. Potato production in warmer regions or in sandy soils with irrigation system will result in a mix of favorable temperatures, soil structure and moisture status, which may lead to a significant increase in the severity of RKN infections .
Losses caused by RKN infection may in extreme cases reach up to 100% in potato fields. Also, variable losses occur as a result of the planting season and the level of soil infestation .
RKN species have been increasingly found in association with potato crops in the tropics and subtropics, causing substantial economic impact due to crop losses depending mainly on the cultivars, favorable climate and nematode density present during planting [5, 8, 9, 27, 35, 36]. A few RKN species have been reported as increasing problems for potato cultivation in several regions worldwide, and the most important ones are
In temperate regions, i.e. North America, Europe and Australia,
In a survey for RKN species in potato fields in southern Brazil , it was found that
In a similar survey, , using multiple loci sequencing approaches such as the intergenic region (IGS), D2-D3 expansion segments within 28S rDNA and
The most effective, low cost, environmentally and healthy sound way to control RKN is to use resistant cultivars that stand good yield performance and have been tested for a particular region where potato is produced. However, currently there is no potato cultivar resistant to
The best characterized resistant gene against RKN in wild potato (
Alternatively, chemical nematicides have been used for the control of RKN in potato, especially in large cropping areas . Other control methods, include crop rotation or succession with non-host and poor hosts, even though they should be used carefully since RKN have a very wide host range and it could host other non RKN species, i.e.
2.3. The false root-knot nematode (
The false root-knot nematode
This species is a quarantine regulated pest to several regions and it is considered a serious pest to potato in which yield losses up to 55–90% have been reported [43, 44, 45]. This nematode species has been detected in greenhouses in England, Netherlands, Finland, Russia, India and China [43, 45]; however, it has not been found in the field of any other region outside North and South America  and may have been eradicated following its detection in Europe and Asia countries. In the Andean region of Peru and Bolivia, for instance,
Potato is the most significant host of
The life cycle of
Control methods for
2.4. Root lesion nematodes (
Root lesion nematodes
Management practices for
Some other plant species such as
The lack of crop rotation or succession with crops that are good hosts, such as soybeans, beans, corn, sorghum and several forage grasses, no-tillage system; the use of sandy to medium texture soils and poor nutrition of plants are some of the facts that may increase root lesion nematode-associated problems in potato. Favorable temperatures and humidity (ca. 20–25°C and 60–80% humidity) and excess of nitrogen fertilization also intensify problems associated with these nematodes .
2.5. The root rot nematode (
The symptoms caused by
The use of crop rotation for controlling
Other control measures for these nematodes include the use of nematode free field, nematode free seed potato tuber, and ultimately the use of chemical nematicides may be recommended.
2.6. The stubby-root nematodes (
The stubby-root nematodes,
Trichodorids have a wide distribution around the world, although some species are restricted to a particular region. Studies on the distribution and ecology of trichodorids, as well as the mechanisms involved in the transmission of certain viruses, may eventually result in new strategies for their control .
Even though there is a considerable amount of data reporting the impact of these nematodes as a plant parasite, their ability to vector certain viruses has increased their importance to the agriculture, when several species of Trichodoridae were identified as a viral vector . Thus, they are considered economically important for potato production, both because of their direct damage and due to the viruses they transmit. For instance,
TRV-infected potato plants exhibit systemic and local symptoms, such as necrosis, chlorosis and overall stunting. Affected potato tubers may exhibit necrotic lesions with brittle tissues and low quality commercial potato tubers may occur even when mild symptoms are seen .
Other symptoms associated with TRV infection include delayed emergence of plant and subsequent poor growth, reduced tuber weight and potato yield, high incidence of poor commercial potato tubers, with low dry matter content and oxidation of tuber post cooking .
On the whole, control methods for stubby-root nematodes include those listed for other species as well, i.e. prevention (the use of certified planting material, cleaning soil from machineries and equipments, preventing the movement of animals within infested fields), crop rotation, cultural practices and the use of nematicides .
3. Other minor nematode species
Other nematode species, including the sting nematode (
4. Overall strategies for managing nematodes in potato fields
The effective control of potato nematodes are overall difficult and complex due to the particular biology of these plant parasites—they inhabit soil, have a short life cycle, multiply fast and have a large population build up; there are just few plant genotypes resistant to them, and chemical nematicides have limited effect due to their interaction with soil components or are being avoided due to their side effects to human and to the environment . Therefore, control strategies for nematodes affecting potato should be planned carefully in order to succeed. The use of more than one control strategy (integrated management) is advised in order to optimize the control efficiency. Information required for proper nematode management, include: (i) proper diagnosis of nematode species and isolate; (ii) relationship between population density and yield losses; (iii) nematode biology (life cycle, environmental requirements, parasitism); (iv) host range; (v) population dynamics; (vi) efficiency of control methods and (vii) economic feasibility of control methods .
Generally used control strategies for potato nematodes are (i) planting in fields free of nematode pests, (ii) the use of certified nematode-free seed potato tubers, (iii) crop rotation and succession with non-host or poor host, (iv) fallow (including elimination of weeds), (v) antagonist plants, (vi) trap plants, (vii) resistant cultivars, (viii) avoidance to disseminate the nematodes, i.e. cleaning of tools and machineries, clean irrigation water and cleaning of footwear, (ix) planting potato at season that is less favored to nematode reproduction, i.e. dry and cold season, (x) quarantine regulations for exotic nematode species, i.e. potato cyst nematodes
5. Concluding remarks
Several nematode species are associated with potato and few of them negatively impact yield and tuber quality. Severe yield losses and poor tuber quality have been reported in most regions where potatoes are grown. The importance of these nematode species depends on their adaptation to each geographical region (local climate), plant host factors and management practices of potato crop. Other minor species may be a problem to local regions as well. Nematode species have unique biology, behavior and are usually difficulty to be managed or eradicated once they are introduced in a field. In addition, their morphological similarities make them difficult to be diagnosed. Nonetheless, proper nematode identification to species and isolate level are mandatory to choose the proper control method. Overall, these nematode problems in potato are better managed when integrated management practices are used, i.e. exclusion (quarantine regulations, certified plant material, use of clean equipment and machineries), cultural practices (crop rotation, succession, cover crops), genetic control, and ultimately by the use of nematicides. Therefore, for a sustainable cropping of potato cultivars, growers, extension services and researchers must consider these nematodes holistically, the impact they cause and whether these management practices are economically, environmentally and technically sound.