EFFECTS OF SERIAL PLANTING OF SEED YAM TUBERS ON VIRUS INCIDENCE AND YAM TUBER DEGENERATION

Vegetative propagation of yam (Dioscorea spp.) with seed tubers is done to ensure uniformity of crop growth and yield. The objective of this study was to evaluate the effect of serial planting of seed yam on virus incidence and tuber degeneration in the Southern Guinea Savanna agro-ecologies of Nigeria. This study was conducted during the wet seasons of 2010 to 2012 at Kwara State and Abuja Federal Capital Territory (Abuja-FCT) in Nigeria. TDa 05/00129 and TDr 89/02665 yam bred lines from the International Institute of Tropical Agriculture, Ibadan, and three popular local varieties from each of Kwara State and Abuja Federal Capital Territory (Abuja- FCT) were used in the study. Harvested seed yams were tested for Yam mosaic virus (YMV), Yam mild mottle virus (YMMV), Dioscorea alata bacilliform viruses (DaBV) and Cucumber mosaic virus (CMV). Data obtained for germination percentage, virus incidence and tuber yields were subjected to ANOVA with mean separation done using Tukey HSD method in SPSS version 24. Viruses YMV, YMMV and DaBV were detected in seed yam as single or mixed infections. High virus incidence was associated with low tuber yield while low virus infection was associated with high tuber yield for most yam varieties. However, TDa 05/00129 produced high tuber yield inspite of high incidence of viruses in the tubers, indicating adaptation of this variety. There was progressive increase in virus population in yam seeds from the first to the third year of study with concurrent degeneration of seed yam and low yield at harvest.