Poor development of grafted passionfruit

[Mikep]

Whilst I regard myself as a brown thumb and any plant I purchase as ultimately doomed, I have in the past had good success with passionfruit and so am disappointed at the peculiar development of my vine planted around 2 years ago. The root stock is substantial, but the grafted vine coming out of the root stock is puny, the vine leaves are yellowish and, for a passionfruit, sparse. I live in a low rainfall area but the vine gets plenty of watering, and fertilizing seems to have no effect. Do I just have a bad plant, or am I missing something. Advice would be welcomed. Thanks, Mike PS you have to turn your head on its side to get the right angle, sorry about that!