Characterization and reproduction of Paratylenchus enigmaticus from chrysanthemum in Korea

Paratylenchus enigmaticus is a recently described pin nematode species with a broad host range, but its occurrence and pathogenicity on chrysanthemum remain poorly understood. During a survey of spray chrysanthemum (Chrysanthemum × grandiflorum) fields in Icheon, Korea, populations of pin nematodes were detected in the rhizosphere and subsequently identified as P. enigmaticus through detailed morphological observations and molecular analyses of LSU D2–D3 and internal transcribed spacer (ITS) rRNA regions. Phylogenetic analyses confirmed a close relationship between the Korean population and previously described P. enigmaticus sequences from Canada and Spain. Pathogenicity assays revealed density-dependent reproduction on the chrysanthemum cultivar “Milky Star.” The reproduction factor (RF) was highest at the lowest inoculum density (Pi = 100; RF = 3.59 ± 0.54), declined at Pi = 1,000 (RF = 1.49 ± 0.69), and further decreased at Pi = 10,000 (RF = 0.37 ± 0.09). Plant growth parameters showed numerical variation among treatments but no significant differences. A host response assay using five chrysanthemum cultivars demonstrated successful reproduction of P. enigmaticus in all cultivars, although variation in RF was observed. Among them, “Pretty Purple” was classified as a poor host (RF ≤ 1), while the others were considered susceptible hosts (RF > 1). Our results document the first occurrence of P. enigmaticus in Korea, detected from a spray chrysanthemum field in Icheon, and demonstrate that it can utilize spray chrysanthemum as a host. However, its economic importance and potential to cause damage remain unclear, warranting additional investigations.