Growing a Granadilla Vine (Passion Fruit)?

I live in Cape Town, South Africa. In February (end of summer) I planted a young granadilla vine which has since had quite a lot of upward growth on the one main leader (about 2m/6ft), but has only developed one short lateral branch. Is this normal, and is there anything I should do to encourage lateral growth through pruning? It is now mid-winter here is SA.

Thanks so much :)

By Lauren