Growing Pinus nigra Seedlings in Spinout™-Treated Containers Reduces Root Malformation and Increases Growth After Transplanting

Abstract

Abstract Root malformation originating during container production causes mechanical instability and plant mortality when those seedlings are transplanted. We investigated the effects of chemical (interior container surfaces treated with Spinout™ or not) or mechanical container modifications (vertical slits or no vertical slits), and the effects of substrate bulk density on the growth of Pinus nigra (Arnold) seedlings during plug production and after transplanting. Seedlings grown in compacted substrate had the greatest shoot, root and total plant dry weights five months after seeding in plug trays. However the incidence of root malformation was also greatest when seedlings were grown in compacted substrate. Unless root pruned, root malformations were retained after transplanting. Seedlings with unpruned roots grown in Spinout™-treated containers had higher regenerated root dry weight than those grown in untreated containers four months after transplanting. Root pruning before transplanting reduced growth of the seedlings regardless of container configuration and of substrate bulk density. Root regrowth and seedling quality after transplanting were greatest for seedlings grown in the treatment combination of no Spinout™, compacted substrate and no slits. Seedlings produced under natural photoperiods formed a resting bud when the seedlings were approximately 2.5 cm (1 in) tall in spring season. Within two weeks shoot elongation resumed, which resulted in branched seedlings. Root malformation can be induced during plug production and is retained after transplanting unless corrected by root pruning.