Global distributions and emergence of six major tropical root-knot nematodes

Abstract

Root-knot nematodes (RKN; Meloidogyne spp.) are among the most damaging plant-parasitic nematodes worldwide and present a growing threat to global food production as their geographical ranges expand. Despite their importance, the geographical distributions, proliferation risks and crop-level impacts of major RKN species remain poorly understood. Here we assess global habitat suitability for six economically significant or regulated tropical RKN species: M. arenaria, M. incognita, M. javanica, M. enterolobii, M. ethiopica and M. luci. We integrated statistical species distribution models (SDMs), mechanistic thermal-time development models and experimentally derived host-suitability metrics. Ensemble SDMs, parameterised using global occurrence records and soil-derived bioclimatic variables, indicate broad climatically suitable ranges for the four well-represented species (M. arenaria, M. incognita, M. javanica and M. enterolobii) across much of the tropics, subtropics and warm temperate regions. Suitability was lower in cooler northern latitudes and, to a degree, in the humid tropics. Predictions for M. ethiopica and M. luci remain uncertain due to limited occurrence data. Thermal-time phenological models, built from published estimates of base temperatures and Growing Degree-Day (GDD) requirements, revealed a strong latitudinal gradient in potential generation number, with life-cycle completion unlikely at higher latitudes. The risk to 26 globally important crops was evaluated by combining crop-specific reproduction factor and gall index data with global crop distribution maps, indicating highest potential impacts in southern Brazil, the central United States, parts of West and East Africa, eastern India and northern China. Together, our analyses show that most global agricultural land is suitable for the focal species establishment and proliferation, with risk shaped jointly by climate, soil conditions and crop hosts. Strengthening distributional surveys and experimentally quantifying species-specific thermal and host responses will be essential to anticipate and mitigate future threats from these crop pests under climate change.