IN-VITRO AXILLARY SHOOT PROLIFERATION OF APPLE ROOTSTOCKS UNDER DIFFERENT ETHYLENE CONDITIONS

Ethylene effect on in vitro shoot proliferation of two apple rootstock s, MM111 and M9, was studied. Ethylene biosynthesis was proportionally stimulated by increasing concentrations of the precursor 1-aminocyclo propane-1-carboxylic acid (ACC). When 25 mu M or more ACC was applied without any control of the headspace of culture vessels, shoot prolife ration of both rootstocks was negatively affected. However, when shoot cultures were transferred to ACC-supplemented medium after the second week of culture, ACC had no effect. Supplementing the medium with ami noethoxyvinylglycine (AVG), an inhibitor of ethylene biosynthesis, tog ether with the application of gas traps inside the flasks, significant ly enhanced axillary shoot formation and elongation. Steady and high e xogenous concentrations of ethylene in the culture flasks had negative effects on shoot proliferation. MM111 appeared to be more sensitive t o ethylene than M9. For AVG a threshold dose was noticed, beyond which phytotoxic effects were induced.