The Host Range and Pathogenic Potential Differences Between Aphelenchoides oryzae and Aphelenchoides pseudobesseyi

Foliar nematodes within the Aphelenchoides besseyi species complex are economically important plant parasites. Unfortunately, the species delimitation and their host range have been unclear because these nematodes were long considered a single species. In this study, we identified A. pseudobesseyi and A. oryzae, two foliar nematode populations collected in Taiwan. The identification was based on integrative morphological and molecular analysis. Morphological characterization revealed consistent differences in post-vulval uterine sac length and male spicule structure between the two species. Bayesian phylogenetic analyses of the D2 to D3 region of 28S rRNA and mitochondrial COI sequences separated the two populations into distinct, well-supported species clades. Host range assays also demonstrated clear differences in pathogenic potential. A. pseudobesseyi parasitized and reproduced on soybean, lima bean, cowpea, and multiple ornamental plants tested, including Saxifraga stolonifera and Sinningia speciosa, which are newly identified host records. In contrast, A. oryzae exhibited a restricted host range and was recovered only from rice plants. Fungal host range tests showed that both species reproduced on commercial mushroom Flammulina filiformis. Furthermore, A. oryzae also reproduces on Fusarium fujikuroi, a major rice seedborne pathogen, whereas no reproduction was observed on Lentinula edodes, Pleurotus ostreatus, or Volvariella volvacea mushroom. Together, these results clarify species boundaries within the A. besseyi complex and demonstrate their pronounced differences in host range. The broad host range and pathogenicity of A. pseudobesseyi highlight its potential economic importance in both field crop and ornamental plant production systems.