Population Structure And Species Delimitation Of Rice White Tip Nematode, Aphelenchoides Besseyi (Nematoda: Aphelenchoididae), In China

Aphelenchoides besseyi is a major nematode pathogen in rice known as the causal agent of white tip disease. In the present study, A. besseyi was recovered from 32 seed samples collected from the major rice-growing regions in China. Nine mitochondrial COI haplotypes and 95 ITS genotypes were identified, suggesting a high genetic diversity and endemism level of A. besseyi in China. Therefore, A. besseyi is likely to have experienced a long history of host-parasite coevolution in China, rather than being recently introduced from other countries. The results of population structure analysis indicated the presence of four clusters within Chinese A. besseyi, but these did not correspond to their geographic distribution. Haplotype H2 was found to be the most widespread. Haplotypes H9 and H13 were most genetically divergent and have been recognized as two cryptic species by molecular species delimitation methods, and with limited support from morphometric measurements. The COI-based phylogeny suggested the ability to parasitize rice has independently evolved at least four times in the genus Aphelenchoides.