The Leafy-Stem-Buried Etiolation Contributed to the High Efficiency of Rootstock Vegetative Propagation in Avocado (Persea americana)

Because of their tolerance to root rot and many abiotic stresses, rootstocks are generally required for commercial avocado production. However, cutting and air-layering, which are popular methods of vegetative propagation for producing large numbers of uniform and genetically identical plants, have been unsuccessful for years. To develop a practical and efficient rooting procedure for selected avocado clonal rootstocks, the present research investigated the effects of various factors on rooting cutting. Shoots were divided into three groups (air layering, direct cutting, and stem-buried etiolation) and treated with different combinations (plant growth regulators, PGRs; soaking time; and culture media), in which orthogonal or randomized-block designs were used. The rooting rate, average root length, average root number, average root dry weight, and rooting quality (Q value) were used as evaluation indicators. The results show that etiolation treatment of the mother shoot is the requisite condition for avocado shoot rooting. In addition, the rooting effect of etiolated cuttings was strongly impacted by PGR type, concentration, and soaking time, whereas no significant differences were detected among the culture media. Among these factors, the roots and the survival rates of etiolated cuttings of two hard-to-root varieties were optimal under the following conditions: indolebutyric acid concentration of 2500 mg/L, dipping duration for 5 s, and perlite:vermiculite culture at 1:1. The rooting rate of ‘Dusa’ was generally greater than that of ‘Duke 7’ and reached 82%.