Q.Thornless Blackberry Cane
I have a new cane growing on my Thornless Blackberry plant and it has what looks like white trails traveling up the cane. There is nothing else showing up yet. The cane looks healthy other than the white trails going up the cane and crossing over each other. There is nothing I can feel, the cane feels like it should, but it just seems like this should not be there and might be something else coming down the line.
It is difficult to say from just a description.
This link may help you compare the markings on your canes; Anthracnose is a possible issue.
You can also take samples to your County Extension Office.