Meloidogyne ethiopica
(Root-knot nematode)

M. ethiopica is a polyphagous pest and classed as a tropical and temperate root-knot nematode (RKN) species (Strajnar et al., 2011). M. ethiopica is considered a damaging species as it can multiply on many different types of plants (including both dicotyledons and monocotyledons). Originally considered a tropical species, it has been shown to survive outdoors in temperate areas also. The distribution in Africa is unknown.

Only in Chile is it considered an invasive nematode. In Chile it occurs over a range of ca 1000 km and has been detected from the Copiapó valley, ca 800 km north of Santiago, to Talca, ca 250 km south of Santiago and it is found on grapevine (Vitis vinifera), kiwi (Actinida deliciosa C.) and potatoes in 80% of samples (Carneiro et al., 2007) collected in this area. It was introduced in Brazil from Chile on kiwi seedlings, and despite not being invasive in Brazil it has caused serious economic problems to grapevine in Chile (Carneiro et al., 2007). Recently, this species has also been recorded on asparagus (Asparagus officinalis L.) in Peru (Murga-Gutierrezet al., 2012). In Europe it has been detected only in Slovenia, on greenhouse tomatoes (Solanum lycopersicum L.) (Širca et al., 2004). It was added to the EPPO Alert List in 2011.

As a root-knot nematode species, M. ethiopica can easily be transmitted with soil and plant root material. Infested soil and growing media, plants for planting, bulbs and tubers from countries where M. ethiopica occurs are the most probable pathways of introduction into different regions. Soil attached to machinery, tools, footwear or plant products is also another possible pathway. M. ethiopica is a polyphagous species and many of its host plants are of economic importance as they are cultivated as arable, vegetable, ornamental or fruit crops. The recent detection of this pest in Brazil, Chile and Slovenia clearly demonstrated that it has the potential to enter in different regions. Recent studies have showed that, despite its tropical origin, M. ethiopica has the potential to survive outdoors in a continental climate (hot summers and cold winters), even in areas where soil temperatures fall below zero during winter, as well as in sub-Mediterranean climate (Strajnar et al., 2011). This indicates that M. ethiopica could establish and spread in different regions of different countries. In addition, M. ethiopica could survive under glasshouse conditions across regions with a sub-Mediterranean or a continental climate. Once root-knot nematodes have been introduced, it is generally difficult to control or eradicate them. Only in EPPO regions has this nematode been listed as a quarantine pest (EPPO, 2011).

M. ethiopica is a tropical and temperate root-knot nematode species detected essentially on cultivated crops. It is a new pest in South America and Europe (Carneiro et al, 2003; 2007; Sirca et al., 2004). In Copiapo and Talca (Central Valley, Chile), where M. ethiopica is present, the weather is hot during the summer and cold during the winter. In Brazil, M. ethiopica occurrs in subtropical (Rio Grande do Sul, Santa Catarina and Paraná States) and tropical areas (Distrito Federal and São Paulo States).

Strajnar et al. (2009) examined its ability to survive in open fields located in regions with sub-Mediterranean and continental European climates. The outdoor field experiment consisted of two locations and extended over three growing seasons and two winter seasons. The results demonstrated that M. ethiopica was able to survive at both locations and also that it retained its infection ability despite several instances of temperatures falling below freezing.

M. ethiopica is considered as a damaging species as it can multiply on many different types of plants, incuding both dicotyledons and monocotyledons (Sirca et al., 2004).

M. ethiopica Whitehead, 1968 was described from a single egg mass culture on tomato (type host), Tanzania (type locality); cowpea was also given as a host. M. ethiopica was collected and reported again by Whitehead (1969) from the Mlalo region of Tanzania on bean (Vicia faba), black wattle (Acacia mearnsii), cabbage, pepper (Capsicum frutescens), potato, pumpkin and tobacco. O’ Bannon (1975) collected specimens from lettuce, soybean, sisal and three weeds (Ageratum conyzoides, Datura stramonium, Solanum nigrum) from Awasa Road, Ethiopa.

Glasshouse tests with agronomic crops important to Brazil revealed that rice cv. BR 410, soybean cv. Cristalina, peach cv. Capdebosq and grapevine (Vitis labrusca) cv. Niágara Rosa are good hosts, whereas wheat cv. BR4, apple rootstocks cvs Maruba and M7, pear rootstock Calleryana, strawberry cvs Dover and Vila Nova, raspberry cv. Tupi, mulberry cv. Batu, blueberry cv. Powderblue and grapevine (Vitis rupestris) cv. Rupestris du Lot are non-hosts (Carneiro et al., 2003). In another test, tomato cv. Rutgers, tobacco cv. NC95, pepper cv. California Wonder and watermelon cv. Charleston Gray were all found to be good hosts, whilst cotton cv. Deltapine 61 and peanut cv. Florunner were non-hosts (Carneiro et al., 2004). Recent surveys conducted in Brazil showed that M. ethiopica presented a restricted distribution in Rio Grande do Sul on kiwi (Somavila et al., 2011) and in Distrito Federal States on vegetables (Carneiro et al., 2008).

In 2003, M. ethiopica was reported for the first time in a tomato greenhouse in Slovenia. This was also the first record for Europe (Sirca et al., 2004).

Biochemical Study

Species-specific esterase phenotypes (E3) with three bands (Rm: 0.9, 1.05, 1.20) were observed in the three isolates from Brazil, Chile and Kenya, as well as a malate dehydogenase phenotype N1 (Rm 1,0), which is shared with several species of Meloidogyne (Carneiro et al., 2000).

Genetics

The reproduction of M. ethiopica is by mitotic parthenogesis and the chromosome number is 36-38 (Carneiro et al., 2004).

Reproductive biology

The following is taken from Moens et al. (2009):

Females lay eggs into gelatinous masses composed of a glycoprotein matrix, which is produced by rectal glands in the female. The glycoprotein matrix it keeps the eggs together and protects them against environmental extremes and predation. The egg masses are usually found on the surface of galled roots, although they may also be embedded within the gall tissue. The egg mass is initially soft, sticky and hyaline but becomes firmer and dark brown with age. Surprisingly, there has been only limited analysis of the glycoproteins (Sharon and Spiegel, 1993) or other components of the gelatinous matrix, despite its obvious importance. Within the egg, embryogenesis proceeds to the first-stage juvenile, which moults to the infective second-stage juvenile (J2). Hatch of the J2 is primarily dependent on temperature and sufficient moisture, although other factors, including root diffusate and generation, modify the hatching response so that the J2 hatch when conditions are favourable for movement and host location; according Somavilla (2011), the temperatures 25°C and 30°C are most favorable to M. ethiopica  J2 hatching. The ability of M. ethiopica to survive is enhanced by several physiological and biochemical adaptations, including delayed embryogenesis, quiescence and diapause, and lipid reserves that prolong viability until the J2 reaches and invades a host. In the soil, the J2 is vulnerable and needs to locate a host as rapidly as possible. J2 are attracted to roots, and there is evidence that when both resistant and susceptible plant roots are present the susceptible ones are more attractive.

The invasive J2 commences feeding after it has invaded the root, usually behind the root tip, and moved through the root to initiate and develop a permanent feeding site. The feeding of the J2 on protoxylem and protophloem cells induces these cells to differentiate into specialized nurse cells, which are called giant cells. Once a giant cell is initiated, the nematode becomes sedentary and enlarges greatly to assume a ‘sausage’ shape. Under favorable conditions, the J2 stage moults to the third-stage juvenile (J3) after ca14 days, then to the fourth-stage juvenile (J4), and finally to the adult stage. The combined time for the J3 and J4 stages is much shorter than for the J2 or the adult, and typically takes 4–6 days. J3 and J4 lack a functional stylet and do not feed. Males, when present, are vermiform and there is no evidence that they feed. Males may be found in parthenogenetic species when conditions are unfavorable for female development, such as when population densities are very high and presumably there is a limitation of food supply.

The initiation, development and maintenance of the giant cell is the subject of continuing investigation, facilitated by molecular techniques with the impetus of developing novel control strategies based on preventing giant cell formation or, more likely, development. These specialized feeding sites are remarkable for their complexity. They are greatly enlarged from typical phloem and xylem parenchyma, or cortical cells, with final cell volumes nearly 100-fold greater than normal root cells. The giant cells are functionally similar to syncytia induced by other plant-parasitic nematodes that have sedentary adult females.

Longevity

M. ethiopica required 67, 48 and 36 days to complete one reproduction cycle at mean daily temperatures of 18.3, 22.7 and 26.3ºC, respectively, in a study by Strajnar et al. (2011). Reproduction did not occur at 13.9ºC. On grape susceptible rootstock  M. ethiopica completed its life cycle in 27 days at 25ºC (Somavilla, 2011).

Activity Patterns

Strajnar et al. (2011) examined the survival ability of M. ethiopica in continental climate conditions that are characterised as mild, with hot summers and cold winters, as well as in a sub-Mediterranean climate characterised by hot summers and mild winters. M. ethiopica survived and maintained infection ability in open fields in European climate conditions, despite the fact that the winter temperatures fell below zero degrees several times. The survival of the nematode population was observed for two winters and three growing seasons. Root galling, an indicator of nematode infection, increased in the second growing season.

Population Size and Density

The population density is elevated on susceptible tomato plants, similar to other important root-knot nematode species like M. incognita, M. javanica and M. arenaria.

Nutrition

M. ethiopica is an obligatory plant parasite (hosts are listed Hosts/Species Affected).

Associations

The associations with wild plants are relevant to the survival or invasiveness in field conditions; however, this has not been very well studied.

Environmental Requirements

Strajnar et al. (2011) carried out four experiments in a growing chamber using a range of mean daily temperatures (13.9, 18.3, 22.7 and 26.3ºC). M. ethiopica required 67, 48 and 36 days to complete one reproduction cycle at mean daily temperatures of 18.3, 22.7 and 26.3ºC, respectively. Reproduction did not occur at the lowest temperature (13.9ºC). In a histological study conducted by Somavilla (2011) in root sections of grape susceptible rootstock inoculated with M. ethiopica, it was verified that the nematode could to penetrate, develope and complete its life cycle with 27 days of inoculation at 25ºC.

A characteristic esterase isozyme patterns E3 (Rm: 0.9, 1.05,1.20) can be used to provide a more rapid and reliable identification of M. ethiopica (Carneiro et al., 2003; 2004).

Roots and tubers should be inspected for small and large multiple galls. Females can be collected from inside the roots.

The correct identification of M. ethiopica requires a detailed study of the distinctive morphological features of females, males and second-stage juveniles (J2) (see Description). By comparing the populations from Brazil and Chile and the population sent as M. ethiopica from Kenya, it is possible to see that they present very similar morphological and morphometrical features, as well as the following common characters, as described for the population from Tanzania (Whitehead, 1968): the perineal patterns of females are highly variable, going from M. arenaria (Neal, 1889) Chitwood, 1949 to M. incognita (Kofoidand White, 1919) Chitwood, 1949, but are very similar to the examined types. Phasmids are large and distinct, with a conspicuous phasmidial canal, and are also observed in the three populations, a good diagnostic character for differentiating this species from M. arenaria and M. incognita (Golden, 1992). Head region of females set off with elevated squarish labial disc, usually marked by two or three annulations. Female stylet robust, curved dorsally with small stylet knobs and the shaft gradually widening posteriorly to near the junction with the stylet knobs. Head region of males set off and sometimes marked by annules on the three populations. Male stylet robust, knobs small, rounded, usually sloping backwards. Lateral fields with four incisures, areolated, the spicules more thickly walled with strongly ridged shafts. Head region of second-stage juveniles(J2) truncate, not set off from the body, without annulations. The tail is slender with the terminus rounded in a pointed thin tip. In combination, these characters are useful to differentiate M. ethiopica from other known Meloidogyne spp.

The population of M. ethiopica described by Whitehead (1968) from Tanzania, and the three other populations studied by Carneiro et al. (2004), differ in some morphological and morphometrical features. The male head region is either marked by two annules behind the head region (Tanzania) or sometimes marked by one or two annules (Kenya, Chile and Brazil). Other differences include: the length of male stylets (14.4–24.1 [21.4] µm in Tanzania vs 22.8-26.8 [24.8] µm in Kenya, Chile and Brazil); the stylet length of second-stage juveniles (J2) (9.1-10.9 [10.0] µm vs 11.2-13.5 [12.2] µm); the tail length of J2 (41.0-52.0 [47.0] µm vs 52.2-72.4 [61.7] µm), and the hyaline tail terminus length ([8.4] µm 12.0-15.5 [13.5] µm) (Jepson, 1987). However, many of the morphological characters used in the past to distinguish species, such as the number of annulations on the head region and many body measurements, have been found to be variable and unreliable for Meloidogyne species characterization (Esser et al., 1976; Franklin,1979; Jepson, 1983).

Based on morphological characteristics, M. ethiopica can be confused with M. incognita, M.arenaria and M. inornata. However, characteristic esterase isozyme patterns, known as E3, have been described for M. ethiopica to provide more rapid and reliable identification (Carneiro et al., 2003; 2004).

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

The use of toxic nematicides can contaminate soils and water and can impact human and animal health.

In Chile, the prohibition on producing seedlings in areas with root-knot nematodes, and on the movement of infested seedlings into new growing areas, seem not to be effective, considering that many nursery plants across the country are severely infected with M. ethiopica.

Preventing crop infection in the first instance is perhaps the single most important strategy to avoid or limit crop losses in terms of quality and yield. This is particularly true since the treatment of nematode-infected crops, or a ‘therapeutic’ approach, is essentially more complicated and costly for producers. The use of clean, healthy, nematode-free planting material is a prerequisite for good crop production and cannot be overemphasized. Within an overall cropping system, the physical removal or destruction of plant material infected with root-knot nematodes, particularly roots or tubers, should be considered.

Planting crops that are poor or non-hosts of root-knot nematodes in rotation in infested soil reduces nematode populations. For the management of M. ethiopica in infested soil Lima et al. (2009) recommend planting successions of different summer and winter non-host plants:

‘A. Mucuna deeringiana, Avena strigosa, Arachis hypogaea; B. Crotalaria spectabilis, Lolium multiflorum, Cajanus cajan ‘PPI 832’; C. Vigna unguiculata, Secale cereale ‘IPR 69’, Cotralaria apioclice; D. Ricinus communis ‘IAC 80’, Raphanus sativus ‘IPR 116’, Crotalaria grantiana; E. Crotalaria grantiana, Secale cereale ‘IPR 69’, Cajanus cajan ‘PPI 832’; F. Crotalaria grantiana, Lolium multiflorum, Mucuna deeringiana; G. Vigna unguiculata, Avena strigosa, Arachis hypogaea. These plant sequences should be adapted to different regions and areas where M. ethiopica is a major agricultural problem’ (Lima et al., 2009). Ricinus communis ‘BRS Energia’, ‘CPACT 40’, ‘AL Guarani’, ‘Sara’, ‘Lyra and ‘Nordestina’ can also be used (Santos and Gomes, 2011).

In case of perennial plants like grapevine, use resistant rootstocks: SO4, IAC 313, P1103 88d, Salt Creck, K5 BB Kober’s and Harmony (Somavilla et al., 2008). Other fruit perennial species as Eugenia involucrata, E. guabiju, E. uvalha, E. uniflora, Campomanesia xanthocarpa, Myciaria cauliflora, Morus nigra ‘Xavante’ and ‘Guarani’, Psidium cattleianum and Citrus sunki ‘Maravilha’ and ‘Tropical’ are also poor hosts of M. ehtiopica (Somavilla et al., 2009).

Informatio is lacking on the extent of the damage and the environmental and economic impacts this nematode may cause on its different host plants.

The associations with wild plants are relevant to the survival or invasiveness of M. ethiopica in field conditions, but have not been very well studied.

The development of a molecular marker to identify M. ethiopica would be beneficial, as would a study of the resistance of different crops like potato, soybean and kiwi.

15/03/12 Original text by:

Regina Maria Dechechi Gomes Carneiro, Embrapa Cenargen, Parque Estação Biológica, Av. W 5 Norte (final), C. Postal 02372, 70770-900 Brasília, Brazil

Marina Dechechi Gomes Carneiro, Embrapa Cenargen, Parque Estação Biológica, Av. W 5 Norte (final), C. Postal 02372, 70770-900 Brasília, Brazil