Fecund gynogenic lines from onion (Allium cepa L.) breeding materials

We report the successful production of large numbers of fecund spontaneous and induced doubled haploid (DH) onion lines from pungent and mild materials developed in our long day onion breeding program. Culture of 3-5 mm unopened flower buds on modified BDS medium was the most efficient and convenient method for recovery of gynogenic plants. Over 1100 gynogenic plants were produced from approximately 47,000 flowers cultured between 1999 and 2001. All groups of donors tested were responsive although the level of gynogenic response varied significantly among them. About 15% of the gynogenic plants recovered were spontaneous diploids. Most others (82%) were haploids, requiring induced chromosome doubling. High survival and doubling frequencies were achieved by colchicine treatment (200-400mg/l colchicine in liquid medium for 48 h) of whole basal explants from 2- to 4-month-old in vitro haploid plants. Some shifts in ploidy classes were seen after bulbs were vernalized and re-sprouted. Viable selfed seeds were recovered from many diploid as well as mixoploid and tetraploid gynogenic plants. The number of seeds per plant varied from 2 to over 600. Progeny from two induced and five spontaneous diploid lines that were grown for observation showed uniform growth, similar to highly inbred lines. Bulbs of these plants showed excellent uniformity in shape and color with little variation in bulb size, indicating their DH origin. Advantages and difficulties of application of DH techniques in onion breeding are discussed. (C) 2004 Elsevier Ireland Ltd. All rights reserved.