Bulbing response of Allium X wakegi Araki to temperature experienced prior to bulb formation

Bulbing response of Allium Xwakegi Araki cv. Kiharabansei No.1 to temperature prior to bulb formation was investigated. The plants exposed to 5 degreesC for 35 days were grown at 20 degreesC under photoperiods ranging from 11 to 14 hrs. The control plants were kept above 15 degreesC before the photoperiodic treatment. Regardless of the exposure to low temperature, the plants did not form bulbs under 11- and 12-hr photoperiods, whereas they did under a 14-hr photoperiod. Under 13- and 14-hr photoperiods, the plants exposed to low temperature had higher bulbing ratios (the maximum diameter of basal leaf sheath / the minimum neck diameter) and higher percentages of tillers with bulb scales (bladeless swollen leaves) than had the control plants. Low temperature exposure did not induce bulb formation of A. X wakegi, but shortened the critical photoperiod for bulb formation from 14 hrs to 13 hrs. When bulbs were stored between 1 and 25 degreesC for 50 days and grown at 20 degreesC under a 13 - hr photoperiod, storage at or below 15 degreesC promoted the formation of new bulbs. Storage at 10 degreesC was more effective than that at 15 degreesC, but below 10 degreesC, it exerted no additional effect. When bulbs were stored at 5 degreesC between 0 and 84 days and grown at 20 degreesC under a 13 - hr photoperiod, the formation of new bulbs was promoted as the cold storage period was extended. The promotive effect of low temperature on bulb formation was weakened by subsequent exposure to 25 - 35 degreesC