City & Guild Trade Goods Question

On pages 139 and 140 there’s the list of trade goods by region. Some of the goods are italicized. I cannot figure out why. Why in Southern France are salt and wine italicized and dye and slaves aren’t? What does it mean?

It says they're export the area is particularly renowned for (block of text at the top of page 140).

Man, I don't know how many times I read those two paragraphs certain it had to be in there, and missed it every time.