Effect of Exogenous Ethylene (Ethephon), Auxin, Cytokinin and Gibberellin on the Sprouting of Dorman and Non-dormant Onion Bulbs (AIlium cepa L.)

The effect of ethylene (2-chIoroethylphosphonic acid), auxin (IAA: 1-naphtylacetic acid), cytokinin (BA: 6-benzylaminopurine) and gibberellin (GA3: gibeberellic acid) on sprouting of dormant (immediately after harvesting and drying) and non-dormant (kept at 5 - 6 °C and 70% relative humidity during 6 months, without any visible sprouts) onion bulbs was followed. In dormant bulbs, increased ethylene concentration, achieved by ethephon application, shortened the time necessary for sprouting from 22 to 19 weeks. A combination of ethephon with cold treatment (3 weeks at 9 °C and 90% relative humidity) led to a further decrease of sprouting time to 15 weeks. In non-dormant bulbs, the increase of ethylene level did not exhibit any significant effect on sprouting (ethephon treated bulbs sprouted after 7 weeks, control sprouted after 6 weeks). In dormant bulbs, the strongest induction of sprouting was observed with auxin treatment (0.1 mg NAA per bulb, sprouting after 12 weeks), followed by cytokinin (0.1 mg BA per bulb, sprouting after 14 weeks). Gibberellin (0.1 mg GA3 per bulb) was the least effective (21 weeks). In each case, the application of ethylene antagonist, silver thiosulphate, prolonged the dormancy (by 33%, 21% and 24% for NAA, BA and GA3, respectively). In non-dormant bulbs, plant hormones affected sprouting in the same order (3, 4 and 5 weeks respectively). The difference in sprouting time was not statistically significant. Again, the application of silver thiosulphate led to the prolongation of the sprouting time, which indicates probable indirect participation of ethylene in termination of dormancy