The 2011 ASHS Annual Conference

Since onions were first domesticated, many different germplasm pools within Allium cepa have been developed. Some of these different germplasms are distinguished by their daylength bulbing sensitivity. Among those different germplasms, short-day onions, those is classified as bulbing when 8-12 hours of daylength are reached, differ in their bulb shape and size, soluble solid content and amount of reducing sugars in their fleshy scales, number and color of dry bulb scale layers, local adaptation, and disease and stress resistance. Determining the genetic relatedness within and between short-day onion germplasm pools would be helpful in understanding the development of these germplasms and entries found within them. Entries were selected that grouped into the following germplasm pools: Bermuda, Creole (red, yellow, white), Grano (red, yellow, white), Italian Red Torpedo, and White Mexican. Forty accessions were evaluated at ten microsatellite loci, and relationships among the accessions were graphically displayed in a neighbor-joining tree and using the program STRUCTURE. The entry selected as an outlier for this analysis, PI 239633, did not group with any of the germplasm pools suggesting that this entry is quite different genetically than the short-day entries tested even though this entry exhibits many short-day characteristics. There appeared to be few genetic similarities between entries in different germplasm pools. Many entries within a germplasm pool, e.g. Creole, grouped together while entries in other germplasm pools e.g. Grano diverged from one another. White and yellow Grano type entries exhibited introgression from other germplasm pools. White Grano entries separated into three genetically distinct groups. ‘New Mexico Yellow Grano PRR’ appeared to be genetically distinct from other Yellow Grano entries. Within the Bermuda pool, ‘Eclipse L303’ appeared to be genetically different than other ‘Eclipse’ entries.