Effects of Citric Acid, Sucrose, and Proton Concentration in Suppressing Defoliation in Hibiscus Plants Grown under Low-illumination Conditions

Abstract

Potted young hibiscus (Hibiscus rosa-sinensis ‘Italian Red’) plants were placed in a postharvest environment under low-illumination conditions in a room from 22 July to 31 Dec. 2003. On treatment with a mineral nutrition (MN) solution, 19% of their leaves remained intact after 8 weeks, but all the leaves were lost after 12 weeks from the time of placement. Incorporation of citric acid (CA) into the MN solution at a final concentration of 5 mm considerably suppressed the defoliation so that 57% of the leaves remained intact after 8 weeks and 53% did so after 12 weeks from the time of placement. Furthermore, treatment with 3% sucrose (SUC) instead of CA also considerably suppressed the defoliation, with 26% of the leaves remaining intact for more than 8 weeks and 20% remaining intact for more than 12 weeks. Neither the CA nor the SUC solution was effective in maintaining the hibiscus plants for more than 20 weeks under low illumination. However, treatment with MN solution containing CA and SUC was highly effective in suppressing defoliation. About 60% of the leaves on the plants that were treated with the solution were retained for the entire 24-week period. The proton concentration of the organic solution was found to be a critical factor that affected plant maintenance. The plants survived only on treatment with a solution of pH 5.0, but not with one with a pH of 6.0 or 7.0.