Root-Knot Nematode Resistance Sources for Kenaf: Multi-Genotype Screening Across Five Meloidogyne Species

Kenaf (Hibiscus cannabinus) is a versatile fiber crop known for rapid growth and high biomass productivity that is often cultivated in warm-season regions where root-knot nematodes (RKNs) are prevalent. Here, we compared eight kenaf genotypes with Hibiscus acetosella and Hibiscus sabdariffa to evaluate resistance versus susceptibility to five RKN (Meloidogyne spp.) populations in two replicated greenhouse trials. The nematode panel comprised globally dominant species (M. incognita races 2 and 4, M. javanica) and emerging high-impact threats in warm-season systems (M. floridensis and M. enterolobii), which overlap geographically with current and potential kenaf production. Reproduction and galling were quantified using eggs per system, eggs per gram of root, egg masses, gall index, and reproduction factor, and genotypic differences were assessed by nonparametric rank-based tests at α = 0.05. Across nematode species, H. acetosella and H. sabdariffa showed minimal reproduction and galling, whereas most kenaf genotypes were highly susceptible. Susceptibility was most pronounced to M. enterolobii and M. floridensis, and several kenaf lines (‘Whitten’, ‘G 14’, ‘G 32’, ‘Yue 74-3’) had the highest egg counts and near-maximal egg masses and galling. M. incognita race 2 and race 4 produced strong contrasts, with H. acetosella and H. sabdariffa remaining resistant while multiple kenaf lines exhibited heavy reproduction and severe galling. M. javanica followed a similar pattern, with ‘G 32’, ‘Yue 74-3’, ‘Whitten’, ‘G 14’, and ‘74200 I4’ being highly susceptible. These results identify H. acetosella ‘PI 500707’ and H. sabdariffa ‘X17’ as robust donors of RKN resistance and highlight the susceptibility of cultivated kenaf genotypes, underscoring urgent breeding and integrated management needs for kenaf in warm-season production regions.