The Cornell onion breeding program, in cooperation with Lisa Earle, produced a series of doubled haploid created from long day onions adapted to New York state onion growing conditions. In 2006, the breeding program assessed a large number of unique doubled haploids, along with related mixaploids and haploids, and controls, for scape development, flower development, pollen viability, and seed set to analyze the resulting data for the effect of ploidy on bulb and reproductive characteristics. The largest bulbs and greatest frequency of fertile and fecund bulbs was found in true doubled haploids, rather than mixaploid or tetraploids. Sizable seed lots were produced for a number of the lines, facilitating replicated trials in 2007. The 2007 trials of pungent and mild lines demonstrated the uniformity of these lines, and the remarkable vigor and relative lack of inbreeding depression in a number of these lines, despite the absolute inbreeding of these lines. Several of the doubled haploid lines from the mild program showed good levels of mildness, a trait for which these lines should be fully uniform.

Much of the time and expense of onion breeding is the development of the inbred lines required for hybrid variety creation. The biennial flowering habit of onion slows the inbreeding process, resulting in times for inbred development of 10 to 12 years. Onion is also subject to severe inbreeding depressions, so as lines are inbred, the lines become increasingly less vigorous and produce less seed. Inbred development has been accelerated in other vegetable crops, notably broccoli and other Brassica crops, by the generation of doubled haploid lines. These doubled haploid lines can also be more uniform and vigorous that inbred lines created by traditional means. However the methods used to generated doubled haploids of the Brassica species does not work for onion. The ability to produce inbred lines by the creation of DH would therefore be of particular advantage for onions, considering the long development time of this crop species. This would have a major impact on development of improved open pollinated (OP) onion lines as well as hybrids. Production of DH from interspecific hybrids or heterozygous plants derived from such hybrids would also aid the introgression of important traits such as disease resistance.

The Cornell onion breeding program has cooperated withLisa Earle in a program developing and testing onion doubled haploids. Earle's lab modified and developed methods so that they could sucessfully culture unpollinated onion flowers from the onion breeding program to generate a large number of doubled haploid plantlets, as well as related haploid, mixaploids and tetraploids. The breeding program carefully handled the resulting plants, growing them to bulbing, characterizing the bulbs, and treating them through vernalization to induce flowering. In 2006, a large number of doubled haploids, along with controls, mixaploids and haploids, were assessed for scape development, flower development, pollen viability, and seed set to analyze the resulting data for the effect of ploidy on bulb and reproductive characteristics. The largest bulbs and greatest frequency of fertile and fecund bulbs was found in true doubled haploids, rather than mixaploid or tetraploids. Sizable seed lots were produced for a number of the lines, facilitating replicated trials in 2007. The 2007 trials of pungent and mild lines demonstrated the uniformity of these lines, and the remarkable vigor and relative lack of inbreeding depression in a number of these lines, despite the absolute inbreeding of these lines. Several of the doubled haploid lines from the mild program showed good levels of mildness, a trait for which these lines should be fully uniform.

Public or commercial onion breeding programs could use the information generated by this project to efficently and effectively use doubled haploid production to accelerate the process of developing new onion varities. This would enable them to more rapidly produce the improved onion varities needed to support the onion industry. Similarly, the doubled haploid lines generated in this program would be useful in creating more vigourous and uniform long day onion hybrids for use in NYS and other locations in US and internationally that use long day onion varieties. The doubled haploid lines will also be useful tools for molecular work in onion genetics. Some of these lines have already been used by a colleague to test molecular markers being used to create onion genetic maps.

onion breeding, doubled haploid production

Lisa Earle (Plant Breeding and Genetics)