Which flour is used for dried pasta and originates from the southern portion of Italy?

Semolina flour is the correct choice because it is specifically made from durum wheat, which is a hard variety of wheat that thrives in the southern regions of Italy, such as Puglia and Calabria. This type of flour has a high protein content and a coarse texture, making it ideal for producing dried pasta. The characteristics of semolina contribute to the firmness and ability of dried pasta to hold its shape when cooked.

In contrast, all-purpose flour is more versatile but lacks the specific properties that make semolina the preferred choice for pasta-making. Sourdough flour is typically used in bread making and does not relate to pasta production. Whole wheat flour, while healthier than white flour, does not provide the same desirable texture or flavor that semolina does for dried pasta. Therefore, semolina is the flour that best fits the description in the question regarding its origin and purpose.