Pythium species and cold storage affect the root growth potential and survival of loblolly (Pinus taeda L.) and slash pine (Pinus elliottii Engelm.) seedlings

When bareroot Southern pine (Pinus) seedlings are lifted in the fall and placed in cold storage for more than one week, survival is generally lower than when seedlings are lifted and stored during the winter. The combination of root wounding at the time of lifting with the presence of Pythium in the soil, the cool, moist conditions in cold storage encourage Pythium growth that results in seedling mortality after outplanting. Loblolly pine (Pinus taeda L.) and slash pine (Pinus elliottii Engelm.) seedlings were inoculated with either Pythium dimorphum orPythium irregulare, cold stored for 3 weeks, and placed in a hydroponic system (aerated aquariums). Seedling Root growth potential (RGP was measured as the number, length, volume, surface area, and diameter of new roots and survival was recorded 4 months after outplanting. Both Pythium species reduced the number of new roots and root length, root surface area, and root volume in slash pine. P. irregulare reduced the number of new roots, root length, and root surface area andP. dimorphum reduced the number of new roots on loblolly pine. Although, P. irregulare lowered RGP, it did not reduce loblolly pine survival. In contrast, P. irregulare inoculation did reduce the survival of slash pine seedlings after outplanting.   Key words: Pythium dimorphum, Pythium irregular, root collar diameter; bareroot.