Identification, diversity, and distribution of Meloidogyne spp. in vegetable fields of South Georgia, USA

Abstract

Root-knot nematode (RKN; Meloidogyne spp.) is the most prevalent plant-parasitic nematode in vegetable fields of Georgia, with an incidence of 67.3%. Since aggressive RKN species are reported in the southeastern United States, molecular-based identification of RKN species was conducted on soil samples taken from a nematode surveillance study in 2018 from 292 RKN-infested vegetable fields in South Georgia. The RKN-infested soil was potted with tomato cv. Rutgers and individual nematode females were isolated from galled roots and subjected to species-specific PCR and mitochondrial haplotype-based RKN species identification. The incidence (%), mean, and maximum relative abundance (second-stage juveniles per 100 cm3 of soil) of the 5 RKN species identified consisted of M. incognita (91.9, 486, 14144), M. arenaria (36.0, 707, 14144), M. floridensis (2.2, 909, 5264), M. javanica (5.5, 352, 1488), and M. haplanaria (0.7, 8, 14). A large proportion of fields (29%) had mixed populations of M. incognita and M. arenaria which may reflect the region’s long history of cotton and peanut cultivation. For unknown reasons, mixed populations of M. incognita and M. arenaria were associated with higher population densities. Meloidogyne incognita is the most important RKN species in vegetable fields followed by M. arenaria, therefore, pure or mixed populations of these species should be addressed in nematode management programs. Although at a lower incidence, the newly detected species, M. floridensis and M. haplanaria, have the potential to become a major threat since they reproduce on vegetables with Mi-resistant genes.