Meloidogyne spp. Population Diversity and Inoculum Density Influence Parasitism of Kiwifruit Plants

Kiwifruit (Actinidia spp.) has become a globally important crop, with A. chinensis var. deliciosa cv. Hayward being the most widely cultivated cultivar. Root-knot nematodes (RKNs, Meloidogyne spp.) are highly damaging plant parasites that are widespread in Portugal. Meloidogyne hapla predominates in the major production areas and occasionally co-occurs with M. arenaria and M. hispanica; however, the effects of these RKNs on kiwifruit performance and yield remain largely unclear. This study evaluated the reaction of Hayward and Tomuri cultivars to different Meloidogyne spp. and inoculum levels, focusing on plant–nematode interactions with distinct M. hapla populations. Kiwifruit’s reaction to RKN parasitism varied according to both the Meloidogyne spp. and the intraspecific variability of M. hapla. Meloidogyne arenaria and M. hispanica caused different impacts in kiwifruit cultivars. Intraspecific variation in M. hapla influenced the host reaction, with certain populations showing high parasitic rates. Gall numbers increased with M. hapla inoculum density, indicating that higher nematode populations intensify pressure on the host. Although few differences were observed between cultivars, M. arenaria had a greater impact on cv. Hayward (female), while M. hispanica affected cv. Tomuri (male) more strongly, showing the importance of investigating cultivar- and sex-specific responses to RKNs for effective management in kiwifruit. These findings highlight that susceptibility and tolerance in kiwifruit depend on the RKN species identity, intraspecific variability, population density and cultivar-specific responses, emphasizing the complexity of host–nematode interactions.