Gấc Momordica cochinchinensis-problem from root cuttings

[pineislander]

I am propagating the vine from root cuttings off well established plants, one male and one female. They have been in the pots over six months and while they quickly established roots to the bottom of the pots no top growth has begun.
In the picture you can see a round growth at the top which has formed on one but seems like undifferentiated tissue not a vine sprout. Does anyone have a suggestion for how to spark some top growth in these? They are held in a shade cloth house with ordinary water and soil, not much fertilizer.

[Chandramohan]

We normally establish new plants from vine cuttings about 5mm to 6mm thick. They sprout without any problem.