Adventitious Root Formation without Rooting Medium in Etiolated Shoots of 'Duke' Avocado (Persea americana) Growing on Nurse Plants

On etiolated shoots of avocado 'Duke'growing on nurse plants placed in normal light conditions, pre-rooting treatments (PRT) were applied at the middle section of the basal part of the shoots that remained etiolated as they were covered with aluminium foil. The objective was to test the possibility to promote better rooting conditions in these shoots, still connected to the mother plant, when they have to be used as layers or cuttings. Two trials were carried out under nursery conditions, between fall 2008 and summer 2009. In the first, two PRT were tested: 5000 and 10000 mg/L of indolebutyric acid (IBA) solutions (50% water, 50% alcohol). Treatments were applied using a wood splinter soaked in the IBA solution and then nailed in the shoots. After 45 days, the best results were observed with the highest dose reaching 56.6% of shoots with roots in early stages of growth, while with 5000 mg/L of IBA only 43.3% of shoots that had formed emerging roots structures were observed. In the second trial we evaluated four PRT: 1) IBA at 10000 mg/L applied with a fine brush. 2) As in 1 + nailed wood splinter soaked in 10000 mg/L of IBA. 3) As in 1 + a hole of 5 mm in diameter on the shoot. 4) As in 1 + small metal wire piece of 5 mm in diameter nailed in the shoots. After 65 days, the highest percentage of shoots with roots in early stages of growth was obtained in treatment 2 with 60%, followed by treatment 4 (40%), then treatments 3 with 25% and finally treatment 1 with the IBA solution alone (20%). In both trials, the control treatment, only stem covered with aluminum foil, showed no formation of any structure, keeping only the etiolated tissue.