Submitted to: Genetic Resources and Crop Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/9/2003
Publication Date: 7/15/2003
Citation: MLIKI, A., GHORBEL, A., ZHANGYONG, S., STAUB, J.E. 2003. GENETIC DIVERSITY IN AFRICAN CUCUMBER (CUCUMIS SATIVUS L.) PROVIDES POTENTIAL FOR GERMPLASM ENHANCEMENT. GENETIC RESOURCES AND CROP EVOLUTION. 50:461-468. Interpretive Summary: Plants of different geographic regions (germplasm) can possess different levels of genetic diversity (differences in genes which are points on chromosomes that govern the appearance of living things). These genetic differences are the source of resistant and susceptible varieties to disease and pests. It is important to keep the germplasm of a crop species genetically diverse (to prevent genetic erosion of our plant heritage; decrease in genetic diversity due to man and environmental changes) and to know the genetic diversity of crop species. Such knowledge will allow humankind to use this valuable heritage more effectively in improving the yield and quality of crop species since genes can be transferred by controlled pollination by man. Cucumber is a crop with a relatively low genetic diversity when compared to other species. Cucumber originated in India and its wild relatives exist throughout the Middle East and Africa. It would be important to know and understand the genetic diversity of African cucumber varieties and compare that diversity with other cucumbers of worldwide origin. Therefore a study was designed to assess the genetic diversity of African cucumbers and determine if they would have potential for improving commercial cucumber. A collection of African varieties were compared with European, U.S., and Asian cucumbers for their biochemical similarities. African cucumbers were found to be very different biochemically and genetically from all other cucumber varieties tested. The information in this study can be used directly by plant breeders to increase the genetic diversity of commercial cucumber by selecting and African cucumber varieties for hybrid seed development. The U.S. cucumber grower will benefit directly from such broadening of the genetic diversity of cucumber by increasing their competitive ability in the worldwide market place.
Technical Abstract: Genetic diversity among 26 cucumber (Cucumis sativus L. var. sativus) accessions from five African countries [Algeria (1), Egypt (21), Ethiopia (2), Kenya (1), and Libya (1)] present in the U.S. National Plant Germplasm System (NPGS) were examined by assessing variation at 71 polymorphic random amplified polymorphic DNA (RAPD) loci. Genetic distances (GD; simple matching coefficient) were estimated among these African accessions and a reference array (RA) of 21 accessions representative of the genetic variation in cucumber. GD among African accessions ranged between 0.41 and 0.97. GD among accessions in the reference array ranged between 0.36 and 0.88. Multivariate analysis identified three distinct groupings (1-3) of African accessions; Group 1 contained 21 accessions (Egypt, Ethiopia and Libya), Group 2 consisted of two accessions (Kenya, Algeria), and Group 3 possessed three accessions (Egypt). These groupings were distinct from each other (P > 0.001). Accessions in Group 1 differed genetically from all other accessions examined (P > 0.01), and accessions in Groups 2 and 3 were uniquely associated with several RA accessions. While GD among accessions in Group 1 ranged between 0.52 and 0.90, distances among Group 2 accessions varied between 0.93 and 0.97. The GD between the two accessions in Group 3 was 0.65. An accession from Syria (PI 181874) and from one Turkey (PI 199383) were genetically more similar to accessions in Group 1 than to other accessions in the RA. Likewise, accessions in Group 2 were genetically similar to two RA accessions from China and a European glasshouse cucumber line, and Group 3 accessions showed genetic affinities with the U.S. market class cultivar Dasher II. Data suggest that some Egyptian accessions (Group 1) possess unique genetic variation, that this germplasm has potential for broadening the genetic base of commerical cucumber, and that further collection of African germplasm is likely to enhance genetic diversity of cucumber in NPGS.