Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2004
Publication Date: 7/30/2004
Citation: Volk, G.M., A.D. Henk and C.M. Richards. 2004. Genetic Diversity among US garlic clones as detected using AFLP methods. Journal of the American Society for Horticultural Science 129(4):559-569.
Interpretive Summary: Several hundred garlic cultivars are grown in the United States, primarily by small-scale farmers. Since garlic plants do not produce seeds under standard growing conditions, garlic is vegetatively propagated. Individual cloves are planted in the field in the fall and bulbs are harvested during the summer months. Garlic plants are very responsive to the environment. Growth habit is affected by moisture, altitude, latitude, soil type, and growth conditions. As a result, cultivar appearance will vary depending on the farm on which it is grown. Over hundreds of years, cultivars have been renamed by growers, so many genetically-identical accessions may have different names. By using genetic analyses, we determined the extent of duplication within the National Plant Germplasm System garlic collection and within many common cultivars. Overall, approximately 50% of the garlic cultivars are genetically-identical to one another, using our methods. We also found that our genetic analyses correlated well with the garlic classification system often used by growers.
Technical Abstract: Garlic (Allium sativum L.) has been clonally propagated for thousands of years because it does not produce seed under standard cultivated conditions. A single garlic accession frequently displays a high degree of phenotypic plasticity that is likely to be dependent upon soil type, moisture, latitude, altitude, and cultural practices. The diversity observed by collectors has occasionally led to the renaming of varieties as they are exchanged among growers and gardeners. As a result, there are numerous garlic varieties available both commercially and within the USDA National Plant Germplasm System (NPGS) that may be identical genotypically, yet have unique cultivar names. To address this possibility, we performed amplified fragment length polymorphism (AFLP) analysis on a comprehensive selection of 211 Allium sativum and Allium longicuspis accessions from NPGS and commercial sources. We used several statistical approaches to evaluate how these clonal lineages are genetically differentiated and how these patterns of differentiation correspond to recognized phenotypic classifications. These data suggest that while there are extensive duplications within the surveyed accessions, parsimony and distance based analyses reveal substantial diversity that is largely consistent with major phenotypic classes.