On defect groups for generalized blocks of the symmetric group

In a paper of 2003, B. K\"ulshammer, J. B. Olsson and G. R. Robinson defined $\ell$-blocks for the symmetric groups, where $\ell >1$ is an arbitrary integer. In this paper, we give a definition for the defect group of the principal $\ell$-block. We then check that, in the Abelian case, we have an analogue of one of M. Brou\'e's conjectures.