Effect of auxins on the rooting of the avocado rootstock 'Duke 7'

Clonal propagation of avocado rootstocks through etiolated shoot rooting represents a key strategy to enhance genetic uniformity, plant health, and productivity in commercial orchards. However, its success largely depends on the rooting phase, where auxins play a critical role. This study evaluated the effect of auxin-based rooting agents (types and concentrations) on root induction and quality in etiolated shoots of the ‘Duke 7’ rootstock. Five agents (IAA, NAA, IBA, K-IBA, and IBA + NAA combination) were tested at three concentrations (24.6, 34.4, and 44.2 mM) under a completely randomized factorial design (5 × 3) with three replicates per treatment. Morphological variables included rooting percentage, survival rate, root number/length/diameter, secondary root development, callus formation, and root quality index (RQI). Results revealed significant effects of agent type, concentration, and their interaction. NAA (34.4 mM) was the most effective for root number (55.3) and RQI (154.9 cm), albeit with high callus formation and reduced secondary roots. The IBA + NAA combination (34.4 mM) also showed high RQI (140.4 cm), with greater root length and less negative impact on root architecture. IBA alone achieved 100% rooting with moderate root development, balancing efficacy and physiological tolerance. Overall, intermediate concentrations of NAA and IBA + NAA yielded optimal results. These findings can refine clonal propagation protocols for ‘Duke 7’, with direct applications in commercial nurseries producing high-performance rootstocks.