COMPARISON OF ROOTING METHODS FOR APPLE CULTIVARS IN VITRO
Micropropagated shoots of 27 apple cultivars have been rooted using either an agar-solidified low-salt medium containing organic supplements, a carbon source and auxin or a simplified liquid medium containing only a carbon source and auxin. Rooting percentages in agar and liquid medium were equivalent for most cultivars but several strains of 'Delicious' rooted better in agar. Although the original method developed using liquid medium gave significantly better rooting when the shoots were incubated at 30° C in the dark for 1 week, recent results using shoots from cultures several years older indicate that the dark treatment is not necessary. A 6-hr soak treatment in a higher auxin concentration works as well as a 7-day incubation in a very low concentration. Cuttings on which roots have been initiated in liquid medium can be inserted, under non-aseptic conditions, into preformed planting plugs in which previously initiated roots can elongate. Once the roots have developed, plants can be acclimated without disturbing the root system and transplanting can be delayed until shoot growth is well under way. Even then disturbance of the root system is minimized since the plug containing the rooted shoot is moved as a unit. Plants produced in this way are easier to establish in the greenhouse than those rooted in agar. Plants rooted in plugs in January, then planted in the nursery or field in June, have attained a height of 1.1 to 1.3 m by the end of the growing season.
Zimmerman, R.H., Yae, B.W. and Fordham, I. (1987). COMPARISON OF ROOTING METHODS FOR APPLE CULTIVARS IN VITRO. Acta Hortic. 212, 303-310