Flowering physiology and some vegetative traits of short-day shallot: A comparison with bulb onion

The critical physiological age of shallot (Allium cepa var. aggregatum) gro wn from seed and sets, and the effect of temperature on stored bulbs and th e flowering habit were studied in Israel. Three short-day genotypes were gr own from seeds or sets. Prior to storage, bulbs were sorted according to si ze and incubated in low (5-10 degrees C), intermediate (13-20 degrees C) or high (30 degrees C) temperatures for various periods. Plants were grown in the open field and in the phytotron, and their vegetative and blooming dev elopment was investigated. Our findings show significant genotypic differen ces in flowering, cold treatment is essential for floral initiation; and th e length of the juvenile phase is tightly dependent on the environment. In the field, early-sown shallots had a faster growth rate, accumulated more m ass, and produced earlier and more auxiliary buds and side shoots than thos e from the late sowing. Shallots can be induced to flower by cold treatment in storage, the optimum temperature being 5-10 degrees C, whereas high and intermediate storage temperatures delay the development of the inflorescen ce. During growth, high temperatures may suppress already initiated inflore scences. Plants from larger sets flowered more readily than those from smal l ones, and genotypes varied significantly in their response to cold induct ion. The impact of genotype and environment on bulb and seed production as well as the similarities and differences in flowering habits between shallo t and bulb onion are discussed.