Principal blocks and p-radical groups

Let G be a finite group and k a field of characteristic p > 0. In this paper, we obtain several equivalent conditions to determine whether the principal block B0 of a finite p-solvable group G is p-radical, which means that B0 has the property that e0(kP)G is semisimple as a kG-module, where P is a Sylow p-subgroup of G, kP is the trivial kP-module, (kP)G is the induced module, and e0 is the block idempotent of B0. We also give the complete classification of a finite p-solvable group G which has not more than three simple B0-modules where B0 is p-radical.