The new seedlings that were just moved out of the greenhouse are always the most susceptible (see photo below).
Even some of the very mature roses got hit pretty hard. Below is a photo of foliage drop from 'Osiana', a cut-flower variety that appears to be very susceptible.
However, some of the newer seedlings are showing little or no downy mildew. The first below is a seedling of 'Darlow's Enigma', followed by a seedling 2 generations down from "Basye's Thornless", and a rugosa seedling.
The last photo shown below is of a crested seedling that is surprisingly showing a good amount of downy mildew tolerance.