Submitted to: Journal of Theoretical and Applied Genetics
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/15/2005
Publication Date: 2/20/2006
Citation: Zicheng, F., Robbins, M.D., Staub, J.E. 2006. Population development by phenotypic selection with subsequent marker-assisted selection for line extraction in cucumber (Cucumis sativus l.). Journal of Theoretical and Applied Genetics. 112:843-855. Interpretive Summary: The emergence and continued refinement of molecular tools (biotechnology associated with DNA) in the last two decades has afforded unique opportunities for their use in the genome (make up of hereditary information in the plant cell) characterization and genetic improvement of many crop species. In cucumber, such DNA (the basic genetic units that direct the development of cells in an organism) technologies, are being developed by the USDA as an adjunct to the classical or conventional approaches used by plant breeders during crop improvement. These technologies do not involve the genetic modification of organisms (GMO), but rather use genetic information at the DNA level to improve the efficiency and effectiveness of classical plant breeding to allow for the more rapid release of improved commercial cultivars. However, little is known about how to integrate such DNA technologies (molecular markers) into cucumber breeding programs. Thus, a study was designed to provide information on these advanced technologies by comparing rate of progression to improved cultivars for yield related characteristics using classical and molecular makers technologies. If molecular marker technologies proved to be more efficient and effective than classical plant breeding methods, then those technologies would be candidates for use by commercial plant breeders during plant improvement. Results for this experiment indicates that classical and molecular methods for plant improvement were equally effective in producing cultivars with improved characteristics. However, since molecular methods are faster, there is a cost savings using this technology in certain situations. Thus, our results will be useful to plant breeders whose objective it is to incorporate yield-related characteristics into commercial cucumber. The incorporation of this technology will allow for more rapid release of unique high yielding cultivars which will in turn increase the competitiveness of U.S. growers on a global market place.
Technical Abstract: Cucumber (Cucumis sativus L.; 2n = 2x =14) has a narrow genetic base, and commercial yield of U.S. processing cucumber has plateaued in the last 15 years. Yield may be increased by altering plant architecture to produce unique early flowering (days to flower; DTF), female (gynoecious; GYN), highly branched (multiple lateral branching; MLB), long-fruited (length:diameter ratio; L:D) cultivars with diverse plant statures. The genetic map position of these quantitatively inherited yield component traits is known, and linked molecular markers may have utility in marker-assisted selection (MAS) programs to increase selection efficiency and effectiveness. Therefore, a base population (C0) created by intermating four distinctly different lines was subjected to three cycles (C1-C3) of phenotypic mass selection for DTF, GYN, MLB, and L:D. In tandem, two cycles of marker-assisted backcrossing for these traits began with C2 progeny to produce families (C2, F1, BC1) for line extraction, and for comparative analysis of gain from selection for phenotypic and marker-assisted selection. Allelic frequencies at marker loci were used to monitor selection-dependent changes during phenotypic and MAS selection. Similar gain from selection was detected as a result of phenotypic and MAS selection for MLB (~0.3 branches/cycle), and L:D (~0.1 unit increase/cycle) with concomitant changes in allelic frequency at linked marker loci. Although genetic gain was not realized for GYN during phenotypic selection, the percent gynoecy of plants subjected to MAS was increased (5.6 to 9.8% per cycle) depending upon the population examined. Selection-dependent changes in allele frequency were also detected at marker loci linked to female sex expression. MAS operated to fix favorable alleles that were not exploited by phenotypic selection in this population, indicating that MAS could be applied for altering plant architecture in cucumber to improve its yield potential.