Abstract
This study analyzed the genetic diversity of 18 Yam mild mosaic virus (YMMV, genus Potyvirus) isolates collected from field surveys in Ghana (N = 8) and Nigeria (N = 10) in 2012−13. The full coat protein (CP) encoding region of the virus genome was sequenced and used for comparison and phylogenetic analysis of the YMMV isolates available in the NCBI nucleotide database. The mean nucleotide (nt) diversity was 13.4% among the 18 isolates (17 from D. alata and one from D. rotundata), 11.4% within the isolates of Ghana and 7.4% within the isolates of Nigeria. The phylogenetic clustering of the 18 YMMV isolates did not show correlation with the country of origin, and they aligned with the reference sequences of four of the 11 YMMV monophyletic groups representing the cosmopolitan group and the African group of YMMV isolates. High sequence homology of 99% between the YMMV sequence from Nigeria (CP12-DaN6-1) and a previously reported sequence from Togo (GenBank Accession Number AF548514) suggests a prevalence of seed-borne virus spread within the region. Understanding YMMV sequence diversity in West Africa aid in the improvement of diagnostic assays necessary for virus indexing and seed certification.
Highlights
Yam (Dioscorea spp.) is an annual herbaceous vine with edible starchy tubers
Except for a single isolate from Ghana (YMMV-CP12-DrG296−31; D. rotundata), all the Yam mild mosaic virus (YMMV) isolates detected in this study were from D. alata
This study revealed a low prevalence of YMMV in Nigeria and Ghana, sequence diversity showed evidence of regional and international distribution of viruses through planting material exchange
Summary
Yam (Dioscorea spp.) is an annual herbaceous vine with edible starchy tubers. It is the fourth most important tuber crop, while in Africa, it is second after cassava by value and production [1,2]. Tubers of domesticated yam provide an essential source of carbohydrate for over 60 million people in tropical and subtropical regions, with 95% of global production deriving from West Africa [3]. YMMV was described as yam virus 1 (YV1) [8] and Dioscorea alata virus (DaV) [7]. The virus spreads mainly through the vegetative propagation of tubers or vine cuttings sourced from the virus infected plants. YMMV transmission by the aphid, Aphis craccivora Koch, has been reported [7], but the significance of the aphid vector in YMMV transmission has not been established
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