Physiological studies on the adventitious root formation in cuttings of Portulaca grandiflora HOOK. I

Abstract

The causes of adventitious root formation in cutting have been studied by many workers since the last century. However, the problems in cutting have not been solved yet.The studies reported here deal with these problems using Portulaca grandiflora which shows the green, reddish or red stem color. The differences in stem color result in the differences of rooting power. Namely, the cutting with red color shows good rooting power, while the cutting with green color poor, and that with reddish color medium. The fact that the root inducing substance is present in leaves was comfirmed by an experiment as follows. Cuttings with red color were divided into two groups. One group was consisted of intact cuttings, while the other of cuttings with leaves removed. When roots initiate in each group, the base of each cutting was cut off, and each cutting was returned into a flask with water. The intact cutting without basal treatment, the control, were compared with the two groups. The control cuttings showed good results of rooting, while leafless cuttings with basal treatment showed no root. On the other hand, the intact cuttings with basal treatment showed the retardation of rooting. The results suggest the movement of root inducing substance from the leaves to basal portion.To ascertain how many leaves are necessary to induce the root was the next problem. Then, rooting percentage, mean root number and mean root length of the cuttings with 0, 1, 5, 10, 20 or over 30 leaves were observed.From the results of this series of experiments, it was demonstrated that 5 leaves are enough for 100 percent rooting and rooting of 50 percent was obtained even in one-leaved cutting.Changing the duration from the time of making cuttings to the time of removing leaves, the rooting percentage, number of roots and length of roots of cuttings were compared. The earlier the removing of the leaves from cuttings, the fewer the number of roots initiated.From the view point that the root inducing substance moves from leaves to basal part of cutting, an assumption that the longer the leaves remain attached to cutting the less the root promoting substance in leaves, may be made. This was proved as follows. Alcohol extracts from the leaves which were removed from cuttings were applied to the cutting with leaves removed. The extract from leaves remained on the cutting longer was less effective on root formation than that from leaves removed earlier.