Physiological changes induced by hardening in seedlings of eucalyptus as a function of growth stages

Hardening appears as an interesting strategy to improve the quality of seedlings in forest nurseries, favoring their survival in the field. Thus, the objective of this research was to show the physiological alterations resulting from the application of methyl jasmonate and stem flexion in three stages of growth in Eucalyptus urograndis seedlings. The experiment was carried out in Marechal Cândido Rondon, Paraná, and Eucalyptus urograndis seedlings were used. Treatments consisted of weekly applications of methyl jasmonate (MeJA), daily imposition of stem flexion and a control treatment. Analyzes included quantification of flexural stiffness, lignin content in stems and roots, phenolic compounds in leaves and roots, electrolyte leakage in roots and field survival. In seedlings of Eucalyptus urograndis at 100 days after emergence (DAE) and at the three distances used to evaluate flexural rigidity, the highest averages were observed in seedlings submitted to chemical and mechanical treatments, coinciding with the increase in lignin content in the stem. In the roots, after quantifying the extravasation of electrolytes in Stage I, the means decreased with the application of treatments. In the field phase, there were no statistically significant differences between seedling survival assessments, quantified every 15 days, for a period of 90 days after planting. However, seedlings in Stage I were lost because they were too young and could not tolerate the stressful conditions observed in the field.