ARS | Publication request: MOLECULAR METHODOLOGIES FOR IMPROVED GENETIC DIVERSITY ASSESSMENT IN CUCUMBER AND MELON

Submitted to: Acta Horticulturae
Publication Type: Proceedings
Publication Acceptance Date: May 1, 2002
Publication Date: November 15, 2002
Citation: Staub, J.E., Robbins, M.D., Chung, S., Lopez Sese, A. 2002. Molecular methodologies for improved genetic diversity assessment in cucumber and melon. Acta Horticulturae.

Technical Abstract: Morphological and biochemical descriptors have been used successfully in germplasm management. The role of molecular markers in genetic analysis is dependent their effectiveness, the cost of their implementation, and the ease of their creation, reproducibility and application. Deployment of marker technologies is greatly enhanced if markers are codominant (increased information), consistent (transferable across laboratories), and amendable to high throughput operations. Interpretation of results is made more meaningful if diversity assessments are standardized by uniform marker arrays (UMA) and historically based reference accessions (RA). Molecular marker technology has been applied to the assessment of genetic diversity of Cucumis species. Sixty-three mapped RAPD markers have been converted to more stable SCARs markers, and tested in multiplexing reactions (duplex to pentaplex) to increase assessment efficiency. PCR kinetics and its optimization play a major role in the success of multiplexing. SSR markers have been constructed and evaluated for their effectiveness when compared to RAPD, AFLP, and isozyme markers. Data indicate that the effectiveness of dominant (RAPD, AFLP) and codominant (isozyme and SSR) markers are equivalent in this regard. Two UMA (RAPD & SSR) have been developed based on their discriminatory power in Cucumis accessions of elite (commercial) and exotic (India, China, Mediterranean, Africa) origin. One UMA has been applied to the analysis of U.S., European, Spanish, and Japanese elite and African exotic germplasm to identify a unique set of RA in melon and distinct gene pools. Similarly, UMA and RA have been developed for cucumber to identify distinct African gene pools. This has allowed for development of databases that have been useful in the design of a Core collection for cucumber, and strategic planning for future germplasm assessment and collection in both species.