Postgermination drenches with PEG-8000 reduce growth of salvia and marigolds

We previously found that incorporation of PEG-8000 into the growing medium delayed germination and resulted in shorter seedlings. However, in that study, we were unable to determine whether the reduced height was merely the effect of delayed germination or of reduced elongation after germination. To answer this question, we studied whether postgermination drenches with PEG-8000 can reduce seedling height. Annual salvia (Salvia splendens F. Sellow. ex Roem. & Shult. 'Bonfire') and French marigold (Tagetes patula L. 'Boy Orange') seedlings were treated with drenches of PEG-8000: 0, 15, 20, 30, 42, 50, 62, 72, or 83 g-L-1. At least 20% of seedlings treated with 62 to 83 g-L-1 of PEG-8000 were dead 14 d after treatment. Salvia and marigolds treated with the remaining PEG-8000 concentrations were up to 34% and 14% shorter than untreated seedlings, respectively. Leaf water (Psi(w)) and turgor potential (Psi(p)) also decreased for salvia which were grown with greater concentrations of PEG-8000 one probable cause of the observed reduction in elongation. Since the PEG-8000 in this study was applied after germination, it is clear that PEG-8000 does not reduce elongation merely by delaying germination, but also by reducing the elongation rate. Thus, postgermination drenches with PEG-8000 can be used to produce shorter seedlings.