Effect of relative humidity in in vitro culture on some growth characteristics of a plum rootstock during shoot proliferation and rooting and on plantlet survival

Explants of Mr.S 2/5,a clone selected from seedlings of Prunus cerasifera, under in vitro conditions were exposed to 70%, 80%, 90% and 100% relative humidity (RH) during shoot proliferation and rooting. The RH decrease during shoot proliferation caused a progressive reduction in shoot cluster fresh and dry weight and in shoot number, while chlorophyll content and the values of several anatomic leaf traits increased. The rooting process and growth of rooted shoots also showed a significant decrease, whilst a progressively increasing survival rate during acclimation was recorded in plantlets rooted at decreasing RH.