Determining Redundancy of Current and Collected ‘Yellow Grano' 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 also maximizes genetic diversity. This was part of a study conducted to determine redundancies in the current ‘Yellow Grano' onion (Allium cepa L.) germplasm in the U.S. collection. Some accessions appear to be duplicates as indicated by their similar cultivar names. An additional objective of this study was to evaluate recently-collected germplasm to determine if there are duplications among them, and between them and the current accessions in the collection. Eight ‘Yellow Grano' accessions and collected cultivars were seeded in October of 2007 and in September of 2008. This group consisted of seven accessions that were already a part of the germplasm collection, and one newly-collected ‘Yellow Grano' proposed to be added to the collection. 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. Three accessions in the current germplasm collection were determined to be duplicates of other accessions and may be removed from the collection. A newly-collected ‘Yellow Grano' was not different from the ‘Yellow Grano' entries already in the collection and would not add diversity to the collection. The most discriminating characters among this group were percent single centers, bulb diameter, shape index, and days to 20% tops down. The least discriminating characters were pink root incidence, sheath length and diameter, plant and leaf height, and leaf width and thickness.