DEVELOPMENT OF TOP SYSTEM IN RELATION TO TUBEROUS ROOT-FORMATION IN SWEET-POTATO .3. BRANCHING CHARACTERISTICS AND ITS VARIETAL DIFFERENCES

This study was conducted to present a quantitative analysis of the bra nching pattern of the sweet potato over growth time and its varietal d ifferences of the two cultivars, Shiroyutaka and Minamiyutaka. 1. Prim ary and secondary branches in Shiroyutaka were developed significantly during 30 to 60 days after planting. Most of such branches were forme d at the base of the plant, and they tended to have grown more rapidly than in the branches formed on the other part of the plant axes. In M inamiyutaka, on the other hand, branching ability was relatively low, especially very few branches were formed at the base of the plant. Bas ed on the difference in such a branching habit of the two cultivars, t he dry matter of the vegetative top in Shiroyutaka showed heavier than that of Minamiyutaka through all the growth period. 2. The diameter a t the base of the main stem was observed to increase in close relation to the development of the branches formed at the base of the plant. S hiroyutaka, compared with Minamiyutaka, increased its diameter signifi cantly during the growth periods of both primary and secondary branche s. This increase was owed mainly to the increase in the secondary vasc ular tissues. 3. The tuberous root yields in Shiroyutaka were higher t han in Minamiyutaka through each time of the growth stage. Based on th ese results, it is suggested that early development of the branches fo rmed at the base of the plant promoted the growth rate of the vegetati ve top and the yield of tuberous roots. Additionally, the increase in diameter at the base of the main stem might have some advantage in rel ation to the translocation of the substance.