|Robbins, Matthew - UNIVERSITY OF WISCONSIN|
Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 15, 2009
Publication Date: August 30, 2009
Citation: Robbins, M.D., Staub, J.E. 2009. Comparative Analysis of Marker-Assisted and Phenotypic Selection for Yield Components in Cucumber. Theoretical and Applied Genetics 119:621-634 (doi:10.1007/s00122-009-1072-8). Interpretive Summary: The use of molecular biological techniques (laboratory oriented procedures) have been cited for their potential for increasing plant breeding efficiency and effectiveness (all analyses performed in the laboratory). Such techniques reduce the time required to select unique improved plants, thus lowering the cost of research and development. However, few controlled experiments exist which confirm or reject their direct applicability to plant breeding efficiency. Those that do exist are controversial since they provide different results. One such technique is molecular marker-assisted selection (MAS), which employes the association of DNA (the composition of chromosomes which control economically important plant traits) and plant traits (e.g., yield and quality). Cucumber is an important vegetable worldwide where the U.S. is the third largest producer of cucumbers for marker and private consumption. It would be useful to determine if MAS could be used to improve the breeding efficiency when compared to visual selection (without DNA analysis where selection is performed by visual inspection) of plants in the open-field. Thus, an experiment was conducted where MAS would be compared to visual selection of cucumber plants (VS). Four populations of plants were created using MAS and VS, and then the performance (yield and quality); these plants were compared in a replicated, open-field evaluation to determine which method of selection of plants was most effective (i.e., lower cost and reduced time for development of populations). It was determined that MAS was more efficient in some populations when compared to VS. Thus, MAS must be used stragetically in plant breeding to increase cucumber yield and quality since the success of MAS is dependent on the population being selected. The research provides the plant breeder with information and strategies to improve selection efficiency which ultimately will provide the grower with improved cultivars more rapidly. The more rapid introduction of novel cucumber cultivars (e.g., improved yield and quality) will increase the global competitiveness of the U.S. cucumber grower.
Technical Abstract: Theorectical studies suggest that marker-assisted selection (MAS) has case-specific advantages over phenotypic selection (PHE) for selection of quantitative traits. However, few studies have been conducted that empirically compare these selection methods in the context of a plant breeding program. For direct comparison of the effectiveness of MAS and PHE, four cucumber (Cucumis sativus L.; 2x=2x=14) inbred lines were intermated and then maternal bulks were used to create four base populations for recurrent mass selection. Each of these populations then underwent three cycles of PHE (open-field evaluations), MAS (genotyping at 18 marker loci), and random mating without selection (RAN). Both MAS and PHE were practiced for yield indirectly by selecting four yield-component traits controlled by quantitative trait loci (QTL) with 2-6 QTL per trait. These traits were multiple lateral branching (MLB), gynoecious sex expression (GYN), earlinesss (EAR), and fruit length to diameter ratio (L:D). Both MAS and PHE were useful for multi-trait improvement, but their effectiveness depended upon the traits and populations under selection. Both MAS and PHE provided improvements in all traits under selection in at least one population, except for EAR which did not respond to MAS. The populations with maternal parents that were inferior for a trait responded favorably to both MAS and PHE, while those with maternal parents of superior trait values either did not change or decreased during selection. Generally, PHE was most effective for GYN, EAR, and L:D, while MAS was most effective for MLB and provided the only increase in yield (fruit per plant).