Articles
TROPHIC VERSUS ENVIRONMENTAL FACTORS CONTROLLING IN VITRO BULB FORMATION IN ONION AND GARLIC MICROPROPAGATED PLANTS
Testing day-length influence on bulbing made it possible to distinguish between spring and autumn garlic varieties.
The addition of incandescent lamps to the fluorescent light reduced the requirements in day-length in garlic and induced bulbing in onion provided they had at least 16h day-length.
Preliminary long exposures to 3–4°C to induce bulbing was ineffective in onion and very efficient in garlic varieties.
Combinations of long photoperiod (16 h), low R:FR ratio (< 2) and low temperature stages (3–4°C for 4 months) could let to bulb any variety of both species.
Cytokinins, high sucrose concentrations and ethephon have been experimented in onion and garlic cultures in parallel to light experiments.
Basal swelling of onion was obtained without light induction, only with high sucrose concentrations (> 80 g/1) or with ethephon (> 2 mg/1). An autumn garlic variety could form heavier bulbs with greater sucrose concentration, but spring varieties did not bulb at all as long as no cold treatment has been applied.
Day-length appeared to be the key factor for both species, and differences in low temperature requirements among garlic varieties were revealing similar behaviour in vitro and in the open air.
External signals from the environment established durable physiological changes it was not possible to induce by means of culture medium modifications.