Adventitious root formation ‘in vitro’ in apple rootstocks (Malus pumila) I. Factors affecting the length of the auxin‐sensitive phase in M.9

Abstract

The length of the auxin‐sensitive phase of root initiation ‘in vitro’ in the apple rootstock M.9 (Malus pumila Mill.) has been determined using the auxins indol‐3yl‐acettc acid (IAA) at 2.8 × 10−5M and indol‐3yl‐butyric acid (IBA) at 1.5 × 10−5M in the presence and absence of 10−3M phloroglucinol (PG). PG synergised IBA‐induced rooting after 4 days exposure, but contact times exceeding 8 days decreased root number. In contrast, PG consistently synergised IAA‐induced rooting in the dark for contact periods up to 13 days with the highest rooting being recorded at 9 days. An irradiance of 20 W m−2 from fluorescent lamps halved IAA‐induced rooting irrespective of the presence or absence of PG. The culture of shoots at temperatures of 22,25 and 29°C during the root initiation phase (auxin present) and the root emergence phase (auxin absent) produced no difference in rooting response. In the presence of PG the use of liquid culture in place of agar‐solidified culture during the auxin‐sensitive phase reduced root number but not rooting percentage.