The currant tomatoes in our greenhouse had some leaves with a white waxy substance on the underside veins, making them curl and wilt. The stuff rubs off easily. Other varieties in the greenhouse are fine. Here's a pic of some of these leaves after they spent a day in a jar. Has anybody seen anything like it? Hopefully it doesn't matter now because since picking off affected leaves as I find them, I've seen no recurrence for two days, but just in case...

Here is a link that might be useful: