Seed osmopriming with PEG solutions in seeds of three infraspecific taxa of Pinus nigra: Impacts on germination, mitosis and nuclear DNA

A phenological characterisation of the Portuguese Pinus nigra stands performed in the 1980s considered them as belonging to subspecies laricio, salzmanni and nigra. Recently, six allochthonous P. nigra populations that represent the actual species distribution in Portugal were molecularly characterised and showed high genetic similarity to subsp. laricio vars. corsicana and calabrica, and genetic distance to subsp. salzmanni. P. nigra has a hard natural regeneration, and this problem will be enhanced under the more severe and frequent drought episodes projected to Europe. In this work, seeds of the P. nigra infraspecific taxa previously assigned to Portugal were osmoprimed with 10% and 20% polyethylene glycol (PEG) solutions to mimic water stress, and to analyse its impacts on germination, mitosis, and nuclear DNA of young needles. Hydroprimed seeds and resulting plantlets were used as controls. The osmotic stress imposed to the seeds delayed the germination in most of the cases, induced cell cycle anomalies, and caused DNA damage in needles. These impacts were more pronounced in subsp. laricio var. corsicana. The detection of osmotic stress effects from germination to the juvenile plantlet stage suggested a stress memory transmission between plant tissues. The 20% PEG osmopriming performed in var. corsicana seeds was lethal. Globally, this preliminary work suggested a differential water stress tolerance among the three P. nigra infraspecific taxa that should be exploited further, and provided probable explanations for their reduced natural regeneration and early mortality of pine seedlings that compromise afforestation/reforestation programs in Portugal and abroad.