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The root-lesion nematodes (RLN), Pratylenchusspp., are among the major plant-parasitic nematodes affecting yam (Dioscoreaspp.) production in West Africa. The distribution and diversity of RLN species associated with yam was investigated through a soil and tuber survey of the main producing areas in Nigeria and Ghana. Pratylenchusspp. were detected in the yam rhizosphere in 59% of 81 soil samples from Ghana and 39% of 114 soil samples from Nigeria. Pratylenchusspp. were detected in 24 of 400 tubers examined, in combination with root-knot nematodes (Meloidogynespp.) and their associated damage of galls and crazy roots (79%), and with yam nematode (Scutellonema bradys) and their associated damage of dry rot (17%), although no specific additional symptoms were observed for Pratylenchusspp. Species of Pratylenchuswere identified by their morphological features and by sequences of the D2-D3 region of the 28 S rDNA gene and the mitochondrial cytochrome oxidase I gene (COI). Pratylenchus brachyuruswas the most frequent RLN species in both the rhizosphere and tubers of yam. Pratylenchus hexincisuswas recovered from one tuber collected in Nigeria. While further investigations are required to establish the host status of yam for this nematode, this appears to be the first record of P. hexincisuson yam. The present taxonomical status of P. scribneriand P. hexincisusis discussed.

The morphological and molecular characterisations of two lance nematode species isolated from the rhizosphere of banana, Hoplolaimus seinhorstiand H. pararobustus, are provided based on an integrative study that includes light and scanning electron microscopy, phylogenetic analysis and two tree-based molecular species delimitation methods (GMYC and bPTP). Nineteen new sequences were obtained, including 5 partial 18S rRNA, 6 D2-D3 of 28S rRNA, 1 ITS rRNA and 7 COImtDNA (the first COIsequences of H. seinhorstiand H. pararobustus), and an updated morphological character comparison of 37 Hoplolaimusspecies is presented. The tree-based molecular species-delimitation approaches employed gave markedly differing results, and also showed remarkable discrepancies among the investigated genes, although the bPTP output was found to agree well with established morphological species delimitations. Both species-delimitation approaches did, however, provide the same output for the COImtDNA sequences, and the COImtDNA gene sequence was also found to correspond better to established morphological species. It is therefore recommended by this paper as representing the most suitable barcode marker for Hoplolaimusspecies identification. This integrative study also resulted in the corrective reassignment of 17 gene sequences that were previously unidentified or incorrectly classified, as well as concluding that H. pararobustusconsists of two cryptic species.

The root-knot nematodes (RKN), Meloidogynespp., represent an important threat to yam (Dioscoreaspp.) production in West Africa. With the aim to establish the diversity of RKN species affecting yam tubers, for control and resistance screening purposes, surveys were conducted in the main yam producing areas of Nigeria. Galled tubers (N = 48) were collected from farmers’ stores and markets in nine states in Nigeria and in one district in Ghana. RKN isolated from yam tubers were identified using enzyme phenotyping (esterase and malate dehydrogenase) and mitochondrial DNA (mtDNA) NADH dehydrogenase subunit 5 (Nad5) barcoding. Examination of 48 populations revealed that yam tubers were infested by Meloidogyne incognita(69%), followed by M. javanica(13%), M. enterolobii(2%), and M. arenaria(2%). Most of the tubers sampled (86%) were infected by a single species, and multiple species of RKN were detected in 14% of the samples. Results of both identification methods revealed the same species, confirming their accuracy for the identification of these tropical RKN species. In addition to M. incognita, M. javanica, and M. enterolobii, we report for the first time M. arenariainfecting yam tubers in Nigeria. This finding extends the list of yam pests and calls for caution when developing practices for yam pest management.