The this work was improve in vitro rooting percentage and quality of the apple rootstock 'Marubakaido' (Malus prunifolia Borkh.) through reduction of the damaging effects caused by excess auxin during rooting period. Shoots with three pair leaves (2.5 - 3.0 cm) derived from the in vitro multiplication process were utilized. The medium used had MS vitamins and salts MS/2, 100mg/l-1 myo-inositol, 30 g/l'1 sucrose and 6 g/l-1 agar. The pH was adjusted to 5,9 before adding the agar. The shoots remained 2, 4 and 6 days in the dark under three IBA concentrations as follows: 0; 1.0 and 3.0 muM. After that period they transferred to a medium without growth regulator and displayed in a growth chamber at 25 ±2° C, 16 hour photoperiod and 2000 lux. The lack of IBA or its lowest concentration reduced the rooting as the darkening period increased showing a negative linear effect. For the highest auxin level it was not observed any difference in the rooting for all the darkening periods witch presented over 80% rooting. Shoots treated witch IBA showed a higher number of roots as the darkening periods increased. It was observed that roots formed mainly in the base shoots soars. Plantlets showed gradual increase in leaf area witch the increase and IBA concentration and the period remained in the dark. The highest survival percentage occurred with higher IBA treated explants. The highest plantlet quality were obtained with 6 days darkening period under 3.0 muM IBA. Although the svstem IBA/darkness seems to improve quality it requires further manipulation of the individual explants and a renewed medium is also required.
darkness; IBA; in vitro rooting; Malus
