Bolting in onion bulb crops as influenced by cultivars and transplanting dates

Bolting reduces the quality and commercial yield of bulb onion, however, seed production is directly dependent on flower induction and bolting. Field experiments were conducted during two cropping seasons 2013-14 and 2014-15 at the Agricultural Research Institute, Swat, Pakistan to study the effects of three onion cultivars with five transplanting dates on bolting and marketable yield of onion. Seedlings of three onion cultivars were transplanted on five different dates with 15 days interval in a randomized complete block design. Onion cultivars varied in their susceptibility to bolting. Cultivar Swat-1 took significantly maximum days to bolting initiation and recorded a minimum bolting percentage compared to ‘Saryab Red’ and ‘Chiltan-89’. Early transplanting took 108.06 days to bolting initiation. The Bolting percentage was maximum at early transplanting and reduced with delay in transplanting from 25th November to 25th December. Bolting has not been recorded at late, (10th and 25th January) transplanting irrespective of the cultivar. Compare to ‘Saryab Red’ and ‘Chiltan-89’, ‘Swat-1’ has maximum plant height, leaves per plant, bulb diameter, bulb weight, total and marketable yield ton ha-1. Bulb diameter, bulb weight, days to maturity, and total yield ton ha-1 was maximum at early transplanting and decreased with delay in transplanting. Marketable yield was maximum at mid transplanting date (25th December); attributed to less bolting and percent cull compared to early transplanting. Unmarketable yield at early transplanting was largely due to bolting while at late transplanting it was due to small ungraded bulbs.