Detection and Identification of Plant Viruses Causing Severe Losses in Yam Production in Cross River State, Nigeria

Abstract

Yam (Dioscorea spp.) is an important food crop cultivated for its edible tubers in Cross River State, Nigeria. Surveys were conducted in during the 2022 planting season in Cross River State to detect and identify viruses infecting yams. Twenty-three farms were surveyed located across the three senatorial districts. Sampling was carried out on Dioscorea rotundata, D. cayenensis, D. alata,and D. Dumetorum and tested using the multiplex-reverse transcription polymerase chain reaction (RT-PCR) followed by gene sequence/phylogenetic analysis. The 23 samples tested positive for multiplex-reverse transcription polymerase chain reaction (RT-PCR).  Eight samples tested positive for Yam mosaic virus (YMMV), 10 samples tested for Cucumber mosaic virus (CMV) and 5 samples tested positive for Yam mild mosaic virus (YMMV). The sequence obtained for each sample when compared with other virus sequences available in the NCBI GenBank through BLASTn revealed that CMV was the predominant representing 43.5% of total viruses identified with sequence homologue ranging between 87 and 98% followed by YMV which constituted 34.8% of total viruses identified with sequence homologue ranging from 90 to 98%. YMMV was the least predominant constituting 21.7% of viruses identified with sequence homologue ranging from 90 to 98%. The phylogenetic analysis revealed that YMV clustered together with some potyvirus isolates found within the Africa sub-region while YMMV clustered with other potyviruses outside Africa. This finding explains that YMV recorded a higher percentage of infection than YMMV. This is the first report of wide-scale detection of viruses infecting yams in Nigeria.