Growth rate of the fastest growing mode of the general dispersion relation. The solid curves represent the limiting case of efficient condensation (black; Eq. (47)) and no condensation (red; Eq. (42)). From top to bottom, the three dashed blue curves are for 30, 3 and 0.01 respectively. Other numerical values are α_μγ_s = 2,β_cγ_s = 1.7, and (N_q/N_T)² = 30. When decreases, the medium undergoes a transition from a regime where the double-diffusive mode can grow (positive growth rate) to a regime where this instability is shut-down by condensation.