Determining Redundancy of Current and Collected Short-Day, Onion Accessions

The mission of the U.S. National Plant Germplasm System is to maintain a representative and genetically-diverse collection of germplasm while doing so in an efficient manner. Reducing genetically-duplicate accessions and adding new and different germplasm to the collection maximizes genetic diversity. This study was conducted to determine redundancies in the current short-day, onion (Allium cepa L.) germplasm collection in the U.S. Some accessions appear to be duplicates as indicated by their similar cultivar names. Another objective of this project was to evaluate recently-collected germplasm to determine if there were duplications among them, as well as, between them and the current accessions in the collection. Thirty-six different germplasm accessions and collected cultivars, that were grouped into eight different similarity groups, were seeded in October of 2007 and in September of 2008. As plants of each entry neared maturity, plants from each accession were measured for 18 different morphological characters. These characters included bolting percentage, sheath length and diameter, plant and leaf height, leaf width and thickness, and time when 20% of plants in the plot had reached tops down (20% tops down), 50% tops down, and 80% tops down. Bulbs were harvested at 80% tops down, and at that time, harvest date, pink root disease severity, and bulb number, height and diameter were measured. Two weeks after harvest, average bulb weight, bulb firmness, and the percentage of bulbs with a single growing point were measured. For those groups that had a high degree of bolting, seven characters were measured from bolting plants. These characters included pink root disease severity, bulb height and diameter, shape index, scape length and diameter, and umbel diameter. Five accessions were identified as duplicates of one another and may be removed from the collection. Ten newly-collected lines were deemed to be different from accessions already in the collection and may add some diversity to the short-day onion collection. Of the traits measured, the most differences between entries were detected by bulb diameter and days to 20% tops down, while the fewest number of differences were detected by sheath length and uniformity of maturity.