Effect of exogenous auxin application on starch concentration during adventitious root formation of deciduous azalea 'Madame Debene' cuttings

Adventitious root formation is a process that requires large energy and carbon resources. Therefore, during the rooting of cuttings an adequate supply of carbohydrates is essentially important. Effect of exogenous auxin application on development of leafy stem cuttings of deciduous azalea cultivar 'Madame Debene', their starch concentration and overwintering were studied. The cuttings were treated with 1 or 2% indole-3-butyric acid (IBA) powders in talc, or talc only as control. The application of IBA significantly promoted rooting process favouring more rapid root development and increasing root weight. In all treatments, the starch concentration in cutting leaves increased during the first two months, which was followed by a decrease that coincided with an intense root formation. During autumn, the starch concentration in leaves of all treatments continued to gradually decline because of the transport to the perennial parts of plants. In the cutting bases, starch concentration increased over 1.5 months, and later some fluctuations were observed. At the end of the growing season, a negative correlation between root weight and starch concentration in cutting bases was detected. In cuttings treated with 1% IBA, which had developed the most vigorous roots, the lowest starch concentration in the cutting bases, and the highest one in roots was observed. Though 2% IBA treatment promoted the most rapid rooting of cuttings, it showed inhibitory effect on further cutting development, negatively affecting: i) root growth, ii) accumulation of starch in cutting tissues, indirectly indicating that photosynthesis has been repressed. In the next spring, during the evaluation of cuttings that had resumed growth, significant differences among treatments were not detected. Results showed that the concentration of starch in cuttings was not critically low to negatively affect their overwintering success.