Ethylene inhibitors enhance in vitro root formation from apple shoot cultures

Effects of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) and three ethylene inhibitors, AgNO₃, aminoethoxyvinyglycine (AVG) and CoCl₂, on root formation were tested in vitro using shoot cultures of the apple (Malus×domestica Borkh.) cultivar Royal Gala. ACC inhibited root formation by delaying root emergence and increasing callus formation at the bases of shoots. In contrast, ethylene inhibitors promoted root formation. Both AgNO₃ and AVG at the appropriate concentrations increased the percentage of shoots producing roots and reduced callus formation at the base of these shoots. AgNO₃ stimulated root emergence and enhanced root growth, while AVG increased the number of roots per shoot. CoCl₂ slightly increased root number and rooting efficiency. These promotive effects may result from a reduction in ethylene concentration or inhibition of ethylene action. The results found in this study may be used to improve the rooting efficiency of other apple cultivars and rootstocks, and possibly of other plant species. Received: 2 March 1997 / Revision received: 1 July 1997 / Accepted: 18 July 1997