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:N6 medium, developed by Chu (1978) for rice anther culture, has been used with some modifications to induce callus and somatic embryos from Citrus anthers (Germanà and Chiancone 2003; Benelli et al. 2010).
Category: