Prevalence and Molecular Diversity of Plant-Parasitic Nematodes of Yam ( Dioscorea spp.) in China, with Focus on Merlinius spp.

There is little information about nematode pests associated with yam in China. Between 2020 and 2021, surveys of yam fields were conducted to investigate the abundance and prevalence of plant-parasitic nematodes in major yam growing areas. A total of 110 bulk soil samples from the yam rhizosphere and 48 yam tubers were collected from seven counties in Jiangxi and Shandong provinces. Standard protocols were used to extract nematodes from soil and tubers and identified at the genus level. In this study, 16 species and 13 nematode genera were recorded. The five most prominent species on the yam rhizosphere according to mean population densities were Pratylenchus coffeae (291/individuals), Meloidogyne (262/individuals), Rotylenchulus reniformis (225/individuals), Merlinius (224/individuals), and Helicotylenchus dihystera (171/individuals). In the tubers, the three most prominent species were Pratylenchus coffeae (415/individuals), Meloidogyne (331/individuals), and Rotylenchulus reniformis (115/individuals). These species were verified with appropriate molecular analysis. The high prevalence of the ectoparasite ( Merlinius spp.) on the rhizosphere of yam also revealed that Merlinius spp. May be more important to yam than previously thought. Morphological and molecular analyses further confirmed the identity of the species as Merlinius brevidens and were characterized for the first time on yam in China. Minor morphometrical differences (slightly longer body and stylet) were observed in Chinese populations of M. brevidens compared to the original description. Additionally, this study reveals that M. brevidens isolated from China showed a higher nucleotide sequence in the ITS region compared to M. brevidens populations from India. This finding provides baseline information on the nematode pest occurrence on yam in China and calls for effective management.