A field experiment was conducted at the Teaching and Research Farm of the Federal University of Agriculture, Makurdi, Nigeria in 2019 planting season to determine the effect of different seed size on the growth and yield of two indigenous water yam (Dioscorea alata) cultivars planted in nematode infested soil. The seed sizes (50g, 100g, 150g, 200g and 250g) of two water yam cultivars (Chokolo and Sudan) served as the treatment and was laid out in a Randomized Complete Block Design (RCBD). Results obtained showed that the two D. alata cultivars were significantly different, as evidenced by their reaction to root knot nematode (Meloidogyne incognita) infection, percentage emergence and vigor. Also, the yield attributes such as number of ware tubers and tuber yield were significantly different (P<0.05) for the two cultivars tested. The mean value of the yield parameters showed that 250g seed yam of Sudan cultivar gave the highest tuber yield (16.08t/ha) and number of tubers/plot. The result obtained on the nematode activity on the different treatments showed mild damage by the root-knot nematodes (M. incognita) on all the different treatments. Result of this study showed that the use of different seed size of water yam tubers has an impact on the tubers production but do not secure the plants from infection by M. incognita.
