Abstract
The root-lesion nematodes (RLN), Pratylenchus spp., are among the major plant-parasitic nematodes affecting yam (Dioscorea spp.) 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. Pratylenchus spp. were detected in the yam rhizosphere in 59% of 81 soil samples from Ghana and 39% of 114 soil samples from Nigeria. Pratylenchus spp. were detected in 24 of 400 tubers examined, in combination with root-knot nematodes (Meloidogyne spp.) 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 Pratylenchus spp. Species of Pratylenchus were 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 brachyurus was the most frequent RLN species in both the rhizosphere and tubers of yam. Pratylenchus hexincisus was 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. hexincisus on yam. The present taxonomical status of P. scribneri and P. hexincisus is discussed.
Highlights
M (Kunth) Pax., D. bulbifera L. and D. esculenta (Lour.) Burk
Twenty-four tubers were infected with Pratylenchus spp., of which, 19 tubers (79%) had galling and crazy root damage caused by the root-knot nematode (Meloidogyne spp.), 4 tubers (17%) showed dry rot symptoms caused by the yam nematode (Scutellonema bradys) while no symptoms were observed in one tuber, which had a density of 50 specimens of Pratylenchus brachyurus, per 5 g of yam peels (Figure 1D)
Twenty-eight populations from 12 yam tubers and 16 rhizosphere samples were studied using morphological and molecular data, which resulted in the identification of Pratylenchus brachyurus and P. hexincisus (Taylor and Jenkins, 1957) and P. zeae (Graham, 1951)
Summary
M (Kunth) Pax., D. bulbifera L. and D. esculenta (Lour.) Burk. yam plays an important socio-cultural role among communities and its cultivation and sale serve as a major income-generating activity for the people in yam-growing areas (Onwueme and Charles, 1994). Yam production is constrained by numerous biotic factors, of which plant-parasitic nematodes are among the most damaging They affect yield and tuber quality, reducing yam production and tuber storability (Ayensu and Coursey, 1972; Bridge et al, 2005; Coyne and Affokpon, 2018). It was observed that Pratylenchus spp. were associated with the galls and crazy roots caused by root-knot nematodes, or with dry rot caused by S. bradys, with no specific additional symptoms (Kolombia et al, 2016a). The Pratylenchus populations obtained from yam tuber tissue and yam rhizosphere were morphologically characterized and molecularly confirmed by sequencing of the D2-D3 of 28 S rDNA and mitochondrial COI genes
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