  The approximate tree decays B- -> pi- pi0/rho- rho0 may serve as benchmark
channels for testing the various theoretical descriptions of the strong
interaction dynamics in hadronic B meson decays. The ratios of hadronic and
differential semileptonic B -> pi l nu/rho l nu decay rates at maximum recoil
provide particularly clean probes of the QCD dynamics. We confront the recent
NNLO calculation in the QCD factorization framework with experimental data and
find support for the factorization assumption. A detailed analysis of all
tree-dominated B -> pi pi/pi rho/rho rho decay modes seems to favour somewhat
enhanced colour-suppressed amplitudes, which may be accommodated in QCD
factorization by a small value of the first inverse moment of the B meson
light-cone distribution amplitude, lambda_B ~ 250 MeV. Precise measurements of
the B -> rho l nu spectrum could help to clarify this point.
