Assessment of genetic relationships among sexual and asexual forms of Allium cepa using morphological traits and RAPD markers

The species Allium cepa includes two major crops on the basis of morphological traits and typical reproduction mode: sexually reproduced biennial onions and vegetatively propagated perennial shallots which rarely flower. In addition, the seed-propagated shallot, a recently released variety with intermediate phenotype for life history, has been described and used by breeders. A joint analysis using molecular markers (random amplified polymorphic DNA, RAPD) and morphological characters was undertaken for the assessment of genetic diversity and crop classification among Allium cepa genotypes. A morphological study describing growth and development was carried out on a nested sampling (34 accessions) from two geographical origins (European or tropical) and of different plant status (improved varieties or local ecotypes). Four primers generated 24 reproducibly scorable DNA bands which gave individual fingerprinting for representative accessions of both onions and shallots. Our results indicate that the seed-propagated shallot is more closely related to onions than to vegetatively propagated shallots and, moreover, reveal a geographical structure of genetic diversity. The evolutionary significance of these data is discussed.