Meloidogyne enterolobii – Survival and distribution under temperate climate conditions within Europe.

Abstract

Meloidogyne enterolobii is one of the most destructive plant-parasitic nematodes (PPN). It was recently detected or intercepted in several European countries, raising concerns about its spread, mainly due to climate change which favors the proliferation of parasites. In this study, the survival of second-stage juveniles (J2) of three (3) root-knot nematode (RKN) species (namely: tropical PPN M. enterolobii as preferred species, M. incognita as tropical control RKN and M. chitwoodi as a control temperate RKN) was examined in vitro at four (4) different temperatures (5, 12, 20 and 25 °C) and five (5) periods (2, 4, 6, 8 and 10 weeks) in the absence of their host. The infectivity of the surviving nematodes was evaluated by inoculating them into tomato seedlings following two scenarios (inoculum obtained after extraction of the nematodes using the automatic zonal centrifuge and the inoculum obtained without extraction of the nematodes after incubation). One week post-inoculation, nematodes inside the roots were counted under a microscope after staining to facilitate observation. Data collected after nematode extraction showed significant variations in survival depending on species, temperatures, and incubation periods. In the final weeks of incubation, M. enterolobii showed greater resilience to high temperatures, while M. chitwoodi was more sensitive. In general, higher temperatures reduced nematode survival over time. For M. enterolobii, a significant difference was noted between 25 °C and 20 °C after 4 weeks of incubation. Survival generally declined over several weeks, influenced by nematode lifespan and the effectiveness of incubation conditions, with complex and non-linear interactions. All three Meloidogyne species had higher survival rates at temperatures below 20 °C, but the number of surviving nematodes declined sharply over time. Observation of the stained roots revealed great variability in the percentage of nematodes present inside the roots. Both studies confirm that temperature was a critical factor for root-knot nematode infectivity. In the infectivity test carried out after extraction of the nematodes, M. enterolobii had reached its maximum infectious power at 20 °C after two and six weeks incubation, while M. incognita and M. chitwoodi present peaks at different temperatures and periods, highlighting the optimal conditions of infectivity specific to each species. In the nematode infectivity test without extraction, M. enterolobii showed maximum and significant infectivity at 5 °C after seven (7) weeks of incubation, with more constant infectivity across temperatures after eight (8) weeks of incubation. M. incognita presented a relatively constant infectivity regardless of temperatures, with a slight drop at 25 °C after 7 weeks incubation and a significantly higher infectivity at 5 °C after 8 weeks observation. In contrast, M. chitwoodi reached a peak at 20 °C after 7 weeks and remained constant regardless of temperature after 8 weeks incubation. After ten weeks, no nematodes were observed in the roots, regardless of species or temperature. The climate projections for the cities of Gent and Bonn were produced using data from local weather stations and climate models based on different socio-economic scenarios (Shared Socio-economic Pathway: SSP). Projections of the future scenarios indicate a significant increase in Heat accumulation by 2085, stability in the Chill accumulation, and a reduction in the Frost duration, highlighting the importance of adapting nematode management strategies to these futures weather conditions. Given the survival and remaining infectivity of M. enterolobii at lower temperatures as shown in this research, its establishment in temperate regions is an eminent threat.