NAME OF THE ORGANISM: Meloidogyne javanica (MELGJA)

Candidate

The root knot nematode M. japonica is known to infect olive trees. Plant parasitic nematodes move only short distances and, thus their dissemination can occur via water, wind and human activities such as the introduction of infected planting material or diffusion of infested soil with nursery practices.
Hamza et al. (2017) and Nico et al. (2002) suggested that the use of infected rooted plantlets was one of the likely major sources of root-knot nematode inoculum in the field. In Spain, a study in olive nurseries reported a high-percentage of root-knot nematodes in infected plantlets [Meloidogyne incognita (14.7%), M. javanica (11.2%), and M. arenaria (2.7%)] (Nico et al., 2002).
These nematodes occur in sporadic distributions in established orchards. Notably, three major parameters drive the distribution of Meloidogyne spp. in cultivated olives: cover vegetation on alley, irrigation and soil texture; but different species respond differently to them. In particular the presence of M. incognita is highly correlated with sandy loamy soils, the presence of M. javanica with irrigated soils and cover vegetation, while the presence of M. arenaria is correlated with the absence of cover vegetation on alley and absence of irrigation. These parameters likely influence the selection of each particular Meloidogyne species from a major dispersal source, such as the rooted plantlets used to establish the orchards (Archidona-Yuste et al., 2018).
Different management measures allow to reduce the importance of other pathways than plants for planting such as the use of new pest-free production sites to establish the planting material, management via soil disinfestation with fumigants prior to planting, soil solarization, use of special amendments (biofumigation), establishment of arbuscular mycorrhizal fungi in plant root systems (to protect plants against soilborne diseases through improvement of phosphorus (P) absorption), direct competition etc., the use of good practices to avoid moving soils between different production sites etc. (Castillo et al., 2010). Taking all these measures into consideration, plants for planting is considered to be a major pathway compared to others.

Yes

The root knot nematodes M. arenaria, M. incognita and M. javanica are known to damage cultivated olive trees, especially in nurseries where optimum irrigation conditions favour root proliferation and increased nematode population, and which have been shown to be more susceptible than older plants (Castillo et al., 2010; Ali et al., 2014). Pathogenicity assays under controlled environmental conditions demonstrated the potential of M. arenaria, M. incognita and M. javanica to damage olive rootstocks as well as self-rooted olive cultivars (Castillo et al., 2010). Meloidogyne sp. cause heavy root galling on olive trees, distorted feeder roots as well as plant growth retardation. At low infection levels, no disease symptoms are observed on the stems or leaves of nematode-infected planting stocks as compared with non-infected ones (Nico et al., 2002). On specific cultivars, e.g. Picual (one of the olive cultivars most extensively grown in the Mediterranean Basin), these nematodes can show a distinct yellowing affecting the uppermost leaves followed by partial defoliation (Castillo et al., 2010; Ali et al., 2014). Controlled experiments showed that root-knot nematodes Meloidogyne (e.g., M. arenaria, M. incognita and M. javanica) may be responsible for 5 to 10% crop losses, while the damage is often difficult to assign to plant parasitic nematodes (Ali et al., 2014). Studies on the pathogenicity of Meloidogyne spp. to olives suggest that main stem diameter is a highly sensitive parameter for assessing damage caused by M. arenaria and M. javanica (Castillo et al., 2010).
In Argentina, the etiology of a generalized olive drying syndrome (designated “seca”) was attributed to a disease complex involving M. javanica and several species of the soilborne fungus Fusarium, although a causal relationship has not been established (Castillo et al., 2010).
Indirect root damages are also reported to be related to nematode infection, whose penetration opens pathways to other soilborne pathogens (bacteria, fungi). The best example is the association of plant pathogenic nematodes such as M. incognita with the fungal pathogen Verticillium dahliae (Verticillium wilt). The presence of nematodes enhances the symptoms induced by the fungus (Ali et al., 2014).

Medium in nurseries (but appears to be lower in orchards)

No

Candidate

Damage to established olive orchards by nematode parasitism may not be clearly perceived because olive is an extremely vigorous plant able to thrive in relatively dry areas, which may obscure expression of symptoms from nematode attacks. However, modern olive production is based largely on the establishment of new high-input orchards intended to increase yields while reducing the time for investment recovery. This model, broadly adopted in new olive-producing areas of the Southern Hemisphere and the Mediterranean Basin, creates an environment conducive to diseases caused by or involving nematodes (Ali et al., 2014). The economic importance of these nematodes in olive cultivation has also increased in recent years because most chemical agents for the control of plant-parasitic nematodes have been banned due to environmental and health concerns (Castillo et al., 2010).

Candidate

The appropriate application of exclusion principles should lead to nematode-free nursery stock. Disinfestation of soil by any means cannot achieve total nematode control. The use of potting mixtures that are not fully disinfested reduces nematological risk, but could mask the presence of pathogen nematodes in seemingly healthy stock (Castillo et al., 2010).

Candidate