Quercetin and indole 3-butyric acid (IBA) as rooting inducers in Eucalyptus grandis × E. urophylla
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Vegetative propagation is the main form of Eucalyptus cutting production, but some clones are still difficult to propagate, including rooting. Auxins and co-factors such as flavonoids can improve root development. This study aimed to evaluate the effects of the flavonoid quercetin, either in the presence or absence of auxin, in different rooting stages of E. grandis × E. urophylla, using biochemical markers. Assessments of stem diameter, height, rooting, number of roots and root length were analyzed and the content of polyamines (PAs) (putrescine, spermidine and spermine), ascorbic acid, indole-3-acetic acid (IAA), quercetin and peroxidase activity were determined in leaves and roots. Indole-3-butyric acid (IBA) induced a higher PA content in roots and leaves mainly after 60 days, indicating that auxin can induce PA production and cell division rate, which is higher at this stage of development. The ascorbic acid content was increased in roots by IBA and quercetin increased the ascorbic acid content in roots and leaves, demonstrating the activation of the antioxidant mechanism of cells. A reduction in peroxidase activity following the addition of auxin and quercetin to roots after 90 days indicates a reduction in oxidative stress. Application of IBA induced the highest IAA content in roots. Both the roots and leaves showed detectable levels of quercetin. All treatments promoted changes in biochemical markers at any time-point, indicating that these substances can reduce oxidative stress and increase cell division. Other Eucalyptus clones must be tested to confirm the effect of quercetin and auxin on growth and root development.