Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2002
Publication Date: 3/20/2003
Citation: Fazio, G., Staub, J.E. 2003. Comparative analysis of response to phenotypic and marker-assisted selection for multiple lateral branching in cucumber (cucumis sativus l.). Theoretical and Applied Genetics. Interpretive Summary: The fruit yield of U.S. processing (pickling) cucumber reached a plateau in the 1980s, and has remained generally unchanged during the 1990s. Plant growth studies under field conditions suggests that this plateau is the consequence of complex chemical interactions in the plant due to its genetic constitution and the environment in which it is grown. In order to manipulate the DNA of cucumber such that this plateau can be over come, biotechnological genetic tools have been developed called DNA markers. These markers have been used to study complex genetic relationships in cucumber, and associations have been found among some of them and genes that control yield in cucumber. Experiments were designed to determine whether improvements in yield could be made in cucumber using these genetic markers. It has been previously shown in our laboratory that genetic markers could theoretically be useful in cucumber improvement. The experiments conducted allowed for the use of these genetic markers in critical comparisons that did, in fact, show that the use of such markers could increase the efficiency and effectiveness of cucumber breeding for improved yield. Data from these experiments show how the cucumber breeder can use genetic markers in plant improvement, thus making another tools available to produce hybrids quicker and with less expensive. The grower will be directly affected by the use of the genetic markers that have been evaluated since hybrids with improved yield will increase their competitiveness.
Technical Abstract: Yield increase in processing cucumber (Cucumis sativus L.) is positively correlated with increased number of fruit bearing branches. Multiple lateral branching (MLB) is a metric trait controlled by at least five effective factors. Breeding efficacy might be improved through marker-assisted selection (MAS) for MLB. Experiments were designed to independently confirm previously determined linkage of molecular markers [L18-2-H19A SNP, CSWTAAA01 SSR, CSWCT13 SSR, W7-2 RAPD, and BC-551 RAPD] to MLB, and to determine their utility in MAS. These markers were present in significantly higher frequency than expected (1 presence:3 absence; p < 0.001) in BC2 plants than those selected based on high MLB phenotype. However, markers that were considered selectively neutral fit the expected segregation of donor parent DNA in BC2 progeny. Markers linked to MLB were used in MAS of BC1 and BC2 plants to produce BC2MAS, and BC3MAS progeny. Means for MLB in MAS populations were compared with backcross populations developed through phenotypic selection (BC2PHE, BC3PHE) and by random mating where no selection had been applied (BC2RND, BC3RND). Statistical analysis showed no significant differences (p < 0.001) between means of phenotypic (BC2PHE = 3.02, BC3PHE = 3.29) and marker-aided selection (BC2MAS = 3.12, BC3MAS = 3.11) for MLB. However, both phenotypic and MAS populations were significantly higher that the random control (BC2RND = 2.27, BC3RND = 2.41) for MLB. Thus, given the observed response to selection and the rapid life-cycle of cucumber (four months), markers linked to MLB when used in MAS will likely be effective tools in cucumber improvement.