Abstract
A microsatellite marker (SSR) was chosen to simulate a target allele and three criteria (02, 04 and 06 markers per chromosome) were tested to evaluate the most efficient parameters for performing marker-assisted backcross (MAB) selection. We used 53 polymorphic SSRs to genotype 186 BC1 maize (Zea mays L.) plants produced by crossing the inbred maize lines L-08-05 (donor parent) and L-14-4B (recurrent parent). The second backcross (BC2) generation was produced with 180 plants and screened with markers which were not recovered from the first backcross (BC1) generation. A total of 480 plants were evaluated in the third backcross (BC3) generation from which 48 plants were selected for parental genotype recovery. Recurrent genotype recovery averages in three backcross generations were compatible with those expected in BC4 or BC5, indicating genetic gain due to the marker-assisted backcrossing. The target marker (polymorphic microsatellite PHI037) was efficiently transferred. Six markers per chromosome showed a high level of precision for parental estimates at different levels of maize genome saturation and donor alleles were not present in the selected recovered pure lines. Phenotypically, the plants chosen based on this criterion (06 markers per chromosome) were closer to the recurrent parent than any other selected by other criteria (02 or 04 markers per chromosome). This approach allowed the understanding that six microsatellites per chromosome is a more efficient parameter than 02 and 04 markers per chromosome for deriving a marker-assisted backcross (MAB) experiment in three backcross generations.
Highlights
Backcross breeding in maize (Zea mays L.) has been extensively used to transfer favorable alleles for monogenic traits from donor genotypes to elite inbred lines (Openshaw et al, 1994) but high heritability polygenic traits have been transferred through this method (Rinke and Sentz, 1961; Shaver, 1976)
The plant breeding community is enthusiastic about marker-assisted selection, but a link between theory and practice is still missing
Parameters are defined and simulations represent suitable approaches providing a strong contribution to the goal of using marker-assisted backcrossing (MAB) in crop improvement
Summary
Backcross breeding in maize (Zea mays L.) has been extensively used to transfer favorable alleles for monogenic traits from donor genotypes to elite inbred lines (Openshaw et al, 1994) but high heritability polygenic traits have been transferred through this method (Rinke and Sentz, 1961; Shaver, 1976). The use of markers as a diagnostic tool was first proposed by Tanksley (1983) and reviewed by Melchinger et al (1990) and the term ‘foreground selection’ was suggested by Hospital and Charcosset (1997); and/or (ii) to identify individuals with a low proportion of undesirable genome from the donor parent, this approach being called ‘background selection’ and was first proposed by Tanskley et al (1989) and by Hillel et al (1990) and was further investigated by Hospital et al (1992) and later reviewed by Viescher et al (1996) Several software programs, such as the PLABSIM program (Frisch et al, 2000), are available to make selection predictions using simulations. Jarboe et al (1994) have used the maize genome as a model for simulation and reported that three backcross generations and 80 markers were needed to recover 99% of the recurrent parent genotype
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