study was carried out to investigate these effects and their interactions with effects of the other factors in sub-tropical double cropping systems. When evaluated at constant spacing, seed tuber weight significantly affected tuber yield in all conditions under study although seed origin, variety, altitude and season muddled these effects in varying degrees. The effects of seed tuber weight could be attributed to more main stems per plant from heavier seed tubers, resulting in more tubers produced per plant and thus per Unit area. When number of sprouts was set equal per unit area, effect of weight of seed tubers on final tuber yield per unit area was absent in seed tuber weight range from 22 to 124g. However, lighter seed tubers tended to increase leaf area per plant thus compensating the lower plant stand, with larger progeny tubers achieved. If calculated at a per stem basis the numbers of tubers produced and the tuber yields were different for the seed weight treatments; these differences were confounded by seed age effects. The number of tubers produced per unit area largely determined plant yield because the varieties used produced few tubers per plant whereas variation was caused by seed weight or seed density.