Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:PS36 was used previously in a P. sojae genetic population study (Dorrance and Grünwald 2009), and P74-75 amplified interspecific polymorphic bands of P. sojae, P. rubi, and P. europea (Schena et al. 2008).
Category: