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.