Vol. 80 No: 6

Title:
Juvenility and bolting in shallot (Allium cepa L. var. ascalonicum Backer)

Authors:
G. TABOR, H. STUETZEL and A. ZELLEKE

pp: 751-759

Abstract:
In an attempt to produce seeds from shallots, vernalisation of growing plants was effective. However, young plants failed to flower before they attained a critical stage of development. To identify the stage of development at which plants bolt satisfactorily, 20 plants of each of three shallot varieties: one long-day (LD) cv. ´Matador F1`, and two shortday (SD) cvs., ´Tropix` and ´Rox F1`, were grown in two separate greenhouses maintained at approx. 18°C with 16 h or 12 h photoperiods, respectively, for periods of 120, 90, 60, 30 or 0 d (imbibed seeds). Seedlings and imbibed seeds were then vernalised in growth chambers at 8°C for 60 d. Logistic regression was used to predict the probability of bolting plants, and plant-to-plant variation was used to analyse the other data. Complete bolting was obtained in plants vernalised after attaining about the six-leaf stage (after 90 d) in cv. ´Tropix`, the 17 leaf-stage (120 d) in cv. ´Rox F1` and the 12 leaf-stage (120 d) in cv. ´Matador F1`. The corresponding total soluble carbohydrate (TSCHO) levels [in g 100 g^-1 sheath dry weight (DW)] were 7.8, 9.8 and 15.5, respectively. However, the percentages of bolting after 90 d of growth for cvs. ´Rox F1` and ´Matador F1` were 75% and 60%, respectively. Apart from their high percentage of bolting, plants which attained sufficient size also induced floral shoots and bolted shortly after the end of vernalisation. An increase of one inflorescence per plant was obtained as the time before treatment was increased from 90 to 120 d in the two SD cultivars. In addition, plants of the three cultivars vernalised after 120 d produced, on average, approx. 4.4, 1.38 and 0.52 inflorescences d^-1-1-1, respectively. A strong positive correlation was also observed between TSCHO content and the percentage of bolting. This study showed that vernalising shallot seedlings at 60 d, or younger, does not result in sufficient bolting.

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