How do I prevent my Passionfruit from suckering?

Dear Peter,

We purchased a passiflora edulis produced at your nursery. It has an abundance of fruit but they remain green. Will it turn black or are they ripe now? Please see picture attached.

Kind Regards Rob

These Passionfruit just don't look ripe yet and based on the fruit we have developing at home I'm pretty sure they need another month on the vine.
The plant at home reminds me about grafting.
There is a great deal of debate around the traps about the (Banana Passionfruit) rootstock suckering. There is no doubt that the Banana Passionfruit is a vigorous weed that will take over large spaces in a garden but having planted two seedling Passionfruit at home there is a lot of benefit in growing a well Grafted Passionfruit.
We have been growing seedling Passionfruit for 3 seasons now and we have found them to be extremely popular because gardeners want to avoid the suckering problems. We have also found them to be buggers to germinate, I'm working on the theory that the seed has to be very fresh otherwise it quickly loses viability. We will try to do our sowing as soon as we notice ripe fruit this year, ie. within the next month. If you have any germination tips I'm all ears (eyes if you would prefer to email me).
At home we planted 2 seedling grown plants when we first grew them 3 years back and had an exceptional harvest in the first season. Sadly as the second spring season came around one of our 2 plants collapsed and died, the other plant has survived but has not shown anything like its early vigour. Why? I suspect some form of root rotting that a grafted root system would have protected the plants against.
We can't claim much horticultural merit for our Grafted Passionfruit.  We buy in pre grafted plants, pot them up and grow for a few weeks to "finish" them. The magic here is our supplier uses a micro graft (my terminology). The grafting is done on very small, young plants and low on the rootstock's stem to minimise the chance of buds being left viable below the graft. To date we have had NO reports of suckering.

Sadly our relatively small batch of Grafted Passionfruit for Spring 2014 all sold very smartly and we will not have any more until mid-late Spring 2015. So please keep them in mind when you are thinking of Passionfruit and remember that non-grafted plants have the advantage of not suckering but that comes at the cost of vigour and productiveness... and grafted plants don't have to sucker.