Question
I'm studying horticulture and came across a 3 different rose bushes with deformed leaves. The three leaves are joined together on the same petiole. It is not just one cane of the bush that is doing that it is only a few leaves over each bush. I am making the assumption that it is a virus but can not find anything about it.

Telissa
Brisbane, Australia

Answer
The only information I can give you which would explain what it might be is proliferation on a rose. However this is usually on the flower.
But what you describe could be rose proliferation but it could also be caused by the following.
Viruses can deform a rose plant leaf but there is usually abnormal colouring, steaks, dots.
Sucking insects such as aphids also cause deformed leaves.
Developing bud may have been injured by cold
Something effected the cells in the developmental stage of the leaf bud.
Proliferation in roses is not fully understood. All that is known is that something effects the apical dominance  regulation. High nitrates in the soil can cause it and many of the very double older roses such as Gallicas plus certain modern roses are genetically prone to it and will proliferate every year if certain climatic conditions are present in the spring.

http://www.classicroses.co.uk/articles/pests_and_diseases/proliferation_of_flowe...