The effects of IAA and tetcyclacis on tuberization in potato (Solanum tuberosum L.) shoot cultures in vitro

Potato (Solanum tuberosum cv. Desiree) shoots grown in vitro in continuous darkness or in long days (LDs), were used to investigate indole-3-acetic acid (IAA) effects on stolon initiation and tuber formation, combining IAA with increased or decreased gibberellin levels. An increased gibberellin (GA) level was achieved by the applying 1 mu M GA(3), while decreased gibberellin level was presumably realized by the adding 3 mu M tetcyclacis (Tc). About 15% of potato shoots developed stolons both in LDs and in darkness. Stolon initiation was stimulated by GA(3) in darkness and by Tc in LDs. Tuber formation was strongly inhibited in LDs and by GA(3) both in light and darkness, but stimulated in darkness at low GA level. Exceptionally, tuber formation occurred in LDs at the highest Tc concentrations, in about 25% of explants. Indole-3-acetic acid alone stimulated stolon formation in LDs, both in the presence or absence of GA(3). IAA alone also stimulated tuber formation in dark-grown shoots, but could not overcome the inhibitory effect of LDs. Indications that, depending on their concentration ratio, IAA may interact with GA(3) in different tuberization phases, have been discussed.