Incidence and distribution of viruses in plants grown from different portions of seed yams (Dioscoreaspp.)
ChukwuemekaNkere1,2,3*, Gabriel Atiri2, JosephOnyeka3,Susan Seal4 and LavaKumar1
1. International Institute of Tropical Agriculture (IITA), PMB 5320, Ibadan, Nigeria
2. Department of Crop Protection and Environmental Biology, University of Ibadan, Ibadan, Nigeria
3. National Root Crops Research Institute (NRCRI) Umudike PMB 7006 Umuahia Nigeria.
4. Natural Resource Institute (NRI), Old Royal Naval College, Park Row, Greenwich, London SE10 9LS, UK
*
Yam (Dioscorea spp.) is a multi species clonally propagated crop cultivated for its edible tubers in West Africa. Tubers - whole yams or sliced portions (minisetts) - are used as planting materials. This study determined the frequency of four widely prevalent yam viruses in West Africa, Dioscoreabadnaviruses (DBV, Badnavirus), Yam mosaic virus (YMV, Potyvirus), Yam mild mosaic virus (YMMV, Potyvirus) and Cucumber mosaic virus (CMV, Cucumovirus), in plants grown from different portions of the seed yam tubers. Each of the 349 seed yam tubers from virus infected plants representing 38 varieties was sliced into three equal portions (apex, middle and base) of about 50 g each and they were planted in a screen house. Plantlets (N=1047) were evaluated for three RNA viruses using a multiplex RT-PCR and PCR using generic primers to badnaviruses. The rate of sprouting was highest for tubers portions from apex (92%) whilst the sprouting from middle and base tuber portions were 61.6% and 66.8%, respectively. The virus incidence (symptoms) was between 42.1 – 100% in different varieties assessed and the incidence of YMMV, CMV, YMV and DBV respectively were 5.5%, 10.1%, 67.8% and 95.2%. Frequency of virus infections ranged from 5% to 97% in plants grown from different tuber portions. Several plantlets from virus infected tubers were asymptomatic but tested positive to viruses in PCR assays. Some asymptomatic plants that tested negative to RNA viruses at early growth stage developed symptoms at later stages and were virus positive. Differences in virus incidence in plants generated from infected tubers provide a scope for generating virus free planting material.