Optimised in vitro propagation protocol for the avocado rootstock ‘Duke 7’ (Persea americana Mill.): Sterilisation, proliferation and rooting

Micropropagation is considered an important technique for the large-scale production of genetically uniform and disease-free avocado rootstocks. However, the recalcitrant nature of avocado poses significant challenges during different stages of micropropagation, often limiting the efficiency of this method. This study aimed to develop and optimise surface sterilisation, shoot proliferation and rooting conditions in the micropropagation of ‘Duke 7’ clonal rootstock. In the establishment stage, four sterilising agents [sodium hypochlorite (NaOCl), mercuric chloride (HgCL₂), sodium merthiolate (Na-merthiolate), and sodium dichloroisocyanurate (NaDCC)] at different concentrations and exposure durations were evaluated. The most effective surface sterilisation treatment was 0.25% NaDCC for 20 min, providing the highest survival rate (87.50% ± 16.23%) with minimal contamination. During the shoot proliferation stage, 6-benzylaminopurine (BAP), kinetin (KIN), and thidiazuron (TDZ) were assessed at various concentrations. Maximum number of shoots (2.07 ± 0.07 per explant), shoot length (21.00 ± 1.05 mm), number of leaves (5.27 ± 0.26 per explant) and shoot growth index (3.13 ± 0.29/4.00) were achieved on modified MS medium containing 8.88 μM BAP. In the rooting stage, different concentrations of indole-3-butyric acid (IBA) and naphthalene acetic acid (NAA) were evaluated using the quick-dip method. The highest rooting rate (13.33% ± 0.79%) was obtained with the 10 mM IBA treatment; however, this rate remained relatively low for effective root induction. In conclusion, this study demonstrated improvements in the surface sterilisation and shoot proliferation stages of avocado micropropagation. However, rooting remains a critical limiting stage, with its success influenced by genotype and the applied auxin induction strategy.