Аннотация:We present a new model for the basic double-pionic fusion reaction pn → d + (ππ)0 in the energy region Tp = 1.0–1.4 GeV. The model takes into account the production of the I(JP) = 0(3+) dibaryon resonance recently observed experimentally in the above reaction and the subsequent decay of this resonance into d + (ππ)0 channel by two ways: through generation of an intermediate σ-meson and through an isovector I(JP) = 1(2+) dibaryon production. The interference of these two mechanisms is shown to give a strong near-threshold enhancement in the ππ invariant mass spectrum, i.e., the well-known ABC effect. The model proposed is consistent with the dibaryon concept for short-range NN interaction and tightly interrelated to the idea of chiral symmetry restoration in dense and/or highly excited hadronic systems, such as dibaryon states. We discuss possible extensions of the model to the reactions pd → 3He + (ππ)0 and dd → 4He + (ππ)0, where the ABC effect was also observed.