Submitted to: Genetic Resources and Crop Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2000
Publication Date: N/A
Citation: Interpretive Summary: Cucumber is grown in most temperate regions, and represents the fourth most widely grown vegetable crop in the world, after tomato, onion and cabbage. The center of origin of cucumber is India, and cucumber has been domesticated for about 3,000 BC. It probably was brought to western Europe via the "Silk Road" (through the Near East and Mediterranean) and Oceanic routes. Genetic material (cultivars) from India have been used extensively by plant breeders for the last 70 years. Studies have shown that the genetic diversity (differences between cultivars) of cucumber is limited. Plant breeders rely on genetic diversity to improve cucumber. Therefore, it is important to discover more genetic diversity, if it exists, in order to identify cultivars which can be used by plant breeders for cucumber improvement. Since Africa cucumbers have not been used extensively in cucumber improvement and this continent may be a source of unique genetic material, we designed a study to investigate the genetic diversity of Africa cucumbers. We found that African cucumbers are a rich source of genetic diversity, and that plant breeders could use this diversity to improve commercial cucumber. Data supplied by our study can be used by agriculturists to create plans for more efficient utilization of this crop and to plan for further collection of wild cucumbers (landraces) from Africa.
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 were examined by assessing variation at 71 polymorphic RAPD loci. Genetic distances (GD) were estimated among these African accessions and a reference array 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 between Group 2 accessions varied between 0.97 and 0.93. The GD between the two accessions in Group 3 was 0.65. An accession from Syria (PI 181874) and Turkey (PI 199383) was genetically more similar to accessions in Group 1 than other accessions in the RA. Further collection of African germplasm is likely to enhance genetic diversity of cucumber in NPGS.