Influence of planting material and duration of bulb vernalisation on bolting of shallot (Allium cepa L. var. ascalonicum Backer)

Abstract

SummaryReproduction of shallot (Allium cepa L. var. ascalonicum Backer) through bulbs has a number of disadvantages such as the difficulty of storing bulbs and carry-over of diseases. Reproduction through seed avoids these problems. Seed production in shallot can be achieved either through bulb-to-seed or seed-to-seed methods by vernalising bulbs or growing plants, respectively. To investigate the relative performance of these planting materials, intact bulbs (B) above the critical size for juvenility, plants raised from seeds (PS), and plants raised from bulbs (PB) of two shallot cultivars, ‘Ambition F1’ and ‘Matador F1’, were treated at 8°C and 12°C for 60 d at the post-juvenile stage. Each experimental unit consisted of 25 plants. The percentage of bolting in PS (88%) and PB (97%) was significantly higher than in B (64%). PS had significantly taller and thicker inflorescences, and more florets per umbel compared to PB and B. On average, PB, PS and B produced 6, 3.7 and 2.3 inflorescences per plant, respectively. Due to the low percentage of bolting in vernalised bulbs, an experiment to increase the percentage of bolting by extending the duration of the vernalisation period was initiated. Bulbs of cultivars ‘Ambition F1’ and ‘Matador F1’, and of seven other shallot cultivars that are vegetatively propagated, were treated at 8°C for 30, 60 and 90 d. However, none of the vegetatively propagated shallot cultivars flowered. ‘Ambition F1’ and ‘Matador F1’ showed about 60% bolting, irrespective of the duration of vernalisation period. Therefore, vernalisation of growing plants in the post-juvenile stage at 8°C or 12°C under 16 h photoperiod for a period of 60 d is recommended for high bolting.