ARS | Publication request: Marker-Assisted Selection in Cucumber

Submitted to: International Congress of Plant Molecular Biology
Publication Type: Abstract Only
Publication Acceptance Date: January 10, 2007
Publication Date: March 1, 2007
Citation: Staub, J.E. 2007. Marker-Assisted Selection in Cucumber [abstract]. International Congress of Plant Molecular Biology. p. 4.

Technical Abstract: Even though the short life cycle (3 months), low chromosome number (2n=2x=14) and small genomic size (~880 Mega base pairs, 750-1000 cM) of cucumber (Cucumis sativus L.) makes it an attractive model crop species for genomic analysis, its narrow genetic base (3-8% polymorphism) is an impediment for the implementation of marker-assisted selection (MAS) in this species. Nevertheless, the marker-trait associations that have been identified for yield and quality components have been used effectively in MAS. Gain from selection has been demonstrated in backcross introgression (2 cycles) of quantitative trait loci (QTL) for sex expression, lateral branch number, fruit size (length:diameter ratio), and fruit number. Population improvement during recurrent mass selection (3 cycles) for these QTL is dependent on the population under selection. During population development and line extraction gain from MAS is dependent on trait correlations, map position of QTL and their relative contribution to trait expression, and genotype x environment (GxE) and epistatic (E) interactions. MAS strategies based on empirical examination of genetic parameters of populations (e.g., variance components and generation means analyses), assessment of nearly-isogenic lines has allowed for the assessment of GE and E effects. Such assessments indicate that although QTL can be antagonistic, there are environment independent yield QTL that can be effectively used in MAS. Given the species’ narrow genetic base, the identification of marker-trait associations will continue to be extremely expensive and time consuming. However, such associations when identified will likely pay large dividends for use in MAS. MAS for quantitative trait improvement will require a population-specific evaluation of genotypic background, and an understanding of physiology (source-sink relationships), epistasis, and heritabilities.