EFFECTIVENESS OF INDOLEACETIC-ACID, INDOLEBUTYRIC-ACID AND NAPHTHALENEACETIC-ACID DURING ADVENTITIOUS ROOT-FORMATION IN-VITRO IN MALUS-JORK-9

We have examined in vitro rooting of apple 'Jork 9' shoots exposed for three weeks to each of the three auxins commonly used for ex vitro ro oting: indole-3-acetic acid (IAA), indole-3-butyric acid (IBA) and alp ha-naphthaleneacetic acid (NAA). During the initial five days of the r ooting treatment, the cultures were incubated in darkness. In this per iod, the root initials are formed. Then, the cultures were moved to th e Light. NAA resulted in a low (ca. 8 roots), and IAA or IBA in a high (ca. 15 roots) maximal root number. The maximal root number was reach ed at a wide range of IAA concentrations (10-100 mu M) but at only one concentration of IBA (10 mu M) or NAA (3 mu M). With NAA and IBA, gro wth of roots and shoots was much more inhibited than with IAA. For the se reasons, IAA is the preferable auxin for in vitro rooting of apple 'Jork 9' shoots.