Effect of aminoethoxyvinylglycine and 1-methylcyclopropene on leaf abscission and root formation in Corymbia and Eucalyptus cuttings

• Indole-3-butyric acid induces leaf drop in Corymbia and Eucalyptus cuttings.
• The percentages of cuttings that form roots are correlated with leaf retention.
• Ethylene inhibitors alleviate leaf drop in Corymbia but not Eucalyptus.
• Low doses of indole-3-butyric acid are recommended for eucalypt propagation.

Auxins such as indole-3-butyric acid (IBA) promote adventitious root formation in many woody-plant cuttings but auxins also induce leaf abscission by stimulating ethylene production. This study determined whether the ethylene synthesis inhibitor, aminoethoxyvinylglycine (AVG), or the ethylene perception inhibitor, 1-methylcyclopropene (MCP), could reduce leaf abscission, promote adventitious root formation, and increase growth of cuttings of two eucalypt hybrids treated with a high dose (8 g/kg) of IBA. In Corymbia torelliana × Corymbia citriodora, AVG and MCP alleviated IBA-induced leaf abscission in a dose-dependent manner, with the most effective AVG dose (375 mg/L) also increasing the percentage of cuttings that formed roots, and the most effective MCP dose (1200 nL/L) increasing the shoot weight of rooted cuttings. In Eucalyptus pellita × Eucalyptus grandis, most AVG and MCP doses did not alleviate leaf abscission, and no AVG or MCP dose significantly increased rooting percentage or shoot weight. However, rooting percentage was correlated with leaf retention in both eucalypt hybrids. A lower IBA dose is recommended for propagation of these eucalypts because AVG and MCP did not increase leaf retention, rooting percentage, root weight or shoot weight of cuttings treated with 8 g/kg IBA above those of cuttings treated with 3 g/kg IBA. Compared with untreated cuttings, 3 g/kg IBA increased rooted cutting production by 153% and 56%, adventitious root number by 3.6 and 1.0, and root weight by 29% and 86% in C. torelliana × C. citriodora and E. pellita × E. grandis, respectively.