Varietal Differences in Root System and its Relationship with Shoot Development and Tuber Yield

Abstract

Ten varieties were grown under the field conditions at the two locations, and number, diameter and dry weight of root were measured at the 4th leaf stage, the initial flowering stage and the full leaf expanding stage. The results obtained are summarized as follows: 1. Number, diamcter and dry weight of root attained to the maximum value about the initial flowering stage, and maximum diameter and dry weight of root were greater in late varieties than in early ones. 2. Number of roots per plant indicated a positive correlation with shoot numbcr (r=0.743), but dry weight of root per plant was correlated with dry weight of root per stem (r=0.792), not with shoot number. Moreover, maximum root diameter and dry weight of root correlated positively with stem length, number of leaves on main stem and stem diameter. 3. Root dry weight of each variety reached the maximum value several weeks earlier than shoot dry weight at each location. 4. During the period from the 4th leaf stage to the initial flowering stage, there were distinct differences among varieties in root and tuber growth rates. The growth rates in late varieties were higher in root, but lower in tuber, compared with early ones, and there was a highly negative correlation between them. However, varietal differences in growth rate per plant were very litte except Shimakei No. 161, and not related with the earliness. In addition, growth rates in each organ were correlated with their distribution ratios, not with growth rate per plant. 5. Root dry weight was significantly correlated with tuber yield. However, leaf and stem dry weight were greater in late varieties than in early ones and showed also highly significant correlations with tuber yield. Therefore, it was assumed that the relationship between root system and tuber yield was not due to the direct contribution of root system, but due to the pleiotropic expression of the earliness.