Leaf parsley growth and productivity are often affected by pathogen infection. Root-knot nematodes of the genus Meloiogyne are common pathogens reported on leaf parsley. The response of leaf parsley to Meloidogyne species in tropical and subtropical regions is quite known, while in temperate regions, comparable information is still scarce. In this study, we evaluated the host status and response of three flat-leaf (Laica, Laura, Gigante d’Italia) and three curly-leaf (Grüne Perle, Orfeo, Sombre) parsley cultivars to Meloidogyne species from temperate regions, i.e., M. hapla, M. chitwoodi, and M. fallax, as well as to the southern root-knot nematode M. incognita. Evaluation was based on measuring plant biomass and nematode reproduction nine weeks after nematode inoculation. Our results showed that all four Meloidogyne species did not cause the reduction in leaf parsley growth under the given experimental conditions. Regarding the host status of leaf parsley cultivars for Meloidogyne, results were variable. All six parsley cultivars were found to be good hosts for M. hapla. Regarding M. chitwoodi, the host status could not be clarified properly; however, each cultivar allowed nematode reproduction at least in one experiment. For M. fallax, flat-leaf parsley turned out to be less susceptible than curly-leaf parsley; and for M. incognita, Orfeo, Laura, and Laica were classified as good hosts, Grüne Perle and Sombre as poor hosts, and Gigante d’Italia as a non-host. Amongst all tested cultivars, Gigante d’Italia was found to be the least susceptible cultivar due to its poor host status for M. chitwoodi and non-host status for M. fallax and M. incognita. Infection with M. hapla, M. chitwoodi, and M. incognita, but not with M. fallax, resulted in distinct gall formation on the roots of all six leaf parsley cultivars.

Mentha is a cosmopolitan genus of medicinal and aromatic plants, which is characterised by the essential oils in its leaves and its therapeutic and aromatic qualities. Mint species are usually cultivated as a perennial crop and therefore susceptible for various pests and diseases. Root-knot nematodes of the genus Meloidogyne are one of the pathogens that can reproduce on mint and cause plant growth reduction. To better understand the pathogenicity of Meloidogyne on mint we studied whether an increasing number of Meloidogyne affects plant growth and essential oil content in the leaves. For our greenhouse experiments, we selected peppermint (Mentha x piperita ˈMultimenthaˈ) as the major mint variety cultivated in Central Europe and the root-knot nematode M. hapla that can pose a major threat in temporal regions. In addition, we evaluated the pathogenicity and reproduction of M. chitwoodi, M. fallax and M. incognita on peppermint and other commonly grown mint varieties in Central Europe, i.e. Mentha x piperita ˈFränkische Blaueˈ, apple mint (M. rotundifolia) and spearmint (M. spicata). None of the studied root-knot nematode species had a negative impact on plant growth of peppermint ˈMultimenthaˈ. However, high densities of M. hapla caused a reduction in the essential oil content. In conclusion, peppermint ˈMultimenthaˈ turned out to be a good host for M. hapla, but a non-host for M. chitwoodi, M. fallax and M. incognita. Plant growth of all four mint varieties was not affected by M. hapla infestation. In addition, peppermint ˈMultimenthaˈ and spearmint were more susceptible to M. hapla than apple mint and peppermint ˈFränkische Blaueˈ.

Synergistic interactions between soil-borne fungi and plant-parasitic nematodes can cause significantly more damage to a crop than either pathogen alone. For peppermint, synergistic interactions between Verticillium dahliae and plant-parasitic nematodes have only been described for the migratory endoparasite Pratylenchus, whereas there is no information for such interactions for ectoparasitic or sedentary endoparasitic nematodes. To determine whether species of these nematode groups co-occur with V. dahliae on peppermint, and to evaluate whether their interactions with V. dahliae on peppermint are synergistic, we conducted a field survey and three greenhouse experiments. In the field survey, we confirmed the presence of V. dahliae in infected plants and detected eight plant-parasitic nematode species in the soil associated with peppermint. Among the detected taxa were the sedentary endoparasite Meloidogyne hapla and the ectoparasite Paratylenchus projectus, with the latter found at particularly high densities. Both such species were selected for greenhouse experiments. The synergistic effect was assessed primarily on the basis of symptom severity and a measure of plant development. Furthermore, we employed isolation and qPCR to detect and quantify V. dahliae in peppermint stem base, stem and leaf samples. Results suggested potential synergistic interactions between V. dahliae and both nematodes, which was associated with increased wilt symptoms and reduced plant growth. The qPCR and isolation approaches confirmed the presence of V. dahliae and suggested that both nematodes influence V. dahliae distribution within a plant, as differences in Ct values between stem base and stem varied among treatments. In V. dahliae alone, no consistent differences were observed. In V. dahliae-M. hapla, Ct values were higher in the stem than in the stem base, whereas in V. dahliae-P. projectus, variable responses were observed depending on the inoculation order. In conclusion, the results demonstrated the cooccurrence of V. dahliae with different plant-parasitic nematodes on peppermint and indicated the potential synergistic interactions with M. hapla and P. projectus. However, whether such synergistic effects also occur under field conditions still needs to be proven.