The choice of the test has nothing to do with the degrees of freedom or the decision from the analysis. It depends only on how the experiment was run. How were the 12 samples collected from each variety? How could you justify pairing one sample of Variety = A with one sample of Variety = B? The pair of samples would have to have existed in the same blocking structure. Each pair must exist in a different blocking structure from all other pairs.
For example, I want to test a new sole for shoes. I give a pair of shoes to 50 people. Each person gets one shoe with the old sole and one with a new sole. The pairing is by person because each subject represents a blocking structure. On the other hand, if I gave a pair of shoes with new soles to 25 people and a pair of shoes with the old sole to another 25 people, there is no inherent or justifiable pairing.
The design of the experiment determines the appropriate test to use.