Effects of Rootstock on the Yield, Mineral Nutrition and Hormone Level in Xylem Sap in Eggplant

Abstract

Eggplants, cv. Hayabusa, Kokuyou and Beikokudaimaru, grown either on their own roots or on the rootstocks, cv. VF, Akanasu and Torubamu, were used to study the effects of rootstock on the yield of eggplant in relation to the number of thick roots, mineral flux and hormone levels in xylem sap.
1. All of three varieties grafted on VF showed the highest yield and the most vigorous growth, and more thick roots were found on those plants. Own-root plants produced lower yields with fewer thick roots than grants. There was a close positive correlation between the number of thick roots and yield.
2. Xylem exudation rate and mineral flux in xylem sap were the highest in the plants grafted on VF. The mineral flux, especially nitrogen, was closely correlated with yield.
3. Cytokinin, gibberellin-like substances and indole-acetic acid levels were the greatest in the xylem sap of plants grafted on VF rootstock, which produced the highest yield. The difference in yield between rootstocks was significantly attributed to difference in cytokinin production, depending on the number of thick roots.
4. From these results, it may be concluded that the growth and yield of eggplant was affected by mineral absorption and hormones especially cytokinin production of rootstocks via many thick roots.