Marker-assisted selection

About: Marker-assisted selection is a research topic. Over the lifetime, 2898 publications have been published within this topic receiving 86943 citations.

An introduction to markers, quantitative trait loci (QTL) mapping and marker-assisted selection for crop improvement: The basic concepts

Abstract: Recognizing the enormous potential of DNA markers in plant breeding, many agricultural research centers and plant breeding institutes have adopted the capacity for marker development and marker-assisted selection (MAS). However, due to rapid developments in marker technology, statistical methodology for identifying quantitative trait loci (QTLs) and the jargon used by molecular biologists, the utility of DNA markers in plant breeding may not be clearly understood by non-molecular biologists. This review provides an introduction to DNA markers and the concept of polymorphism, linkage analysis and map construction, the principles of QTL analysis and how markers may be applied in breeding programs using MAS. This review has been specifically written for readers who have only a basic knowledge of molecular biology and/or plant genetics. Its format is therefore ideal for conventional plant breeders, physiologists, pathologists, other plant scientists and students.

Efficiency of marker-assisted selection in the improvement of quantitative traits.

Abstract: Molecular genetics can be integrated with traditional methods of artificial selection on phenotypes by applying marker-assisted selection (MAS). We derive selection indices that maximize the rate of improvement in quantitative characters under different schemes of MAS combining information on molecular genetic polymorphisms (marker loci) with data on phenotypic variation among individuals (and their relatives). We also analyze statistical limitations on the efficiency of MAS, including the detectability of associations between marker loci and quantitative trait loci, and sampling errors in estimating the weighting coefficients in the selection index. The efficiency of artificial selection can be increased substantially using MAS following hybridization of selected lines. This requires initially scoring genotypes at a few hundred molecular marker loci, as well as phenotypic traits, on a few hundred to a few thousand individuals; the number of marker loci scored can be greatly reduced in later generations. The increase in selection efficiency from the use of marker loci, and the sample sizes necessary to achieve them, depend on the genetic parameters and the selection scheme.

Genomic Selection for Crop Improvement

Abstract: Despite important strides in marker technologies, the use of marker-assisted selection has stagnated for the improvement of quantitative traits. Biparental mating designs for the detection of loci affecting these traits (quantitative trait loci [QTL]) impede their application, and the statistical methods used are ill-suited to the traits' polygenic nature. Genomic selection (GS) has been proposed to address these deficiencies. Genomic selection predicts the breeding values of lines in a population by analyzing their phenotypes and high-density marker scores. A key to the success of GS is that it incorporates all marker information in the prediction model, thereby avoiding biased marker effect estimates and capturing more of the variation due to small-effect QTL. In simulations, the correlation between true breeding value and the genomic estimated breeding value has reached levels of 0.85 even for polygenic low heritability traits. This level of accuracy is sufficient to consider selecting for agronomic performance using marker information alone. Such selection would substantially accelerate the breeding cycle, enhancing gains per unit time. It would dramatically change the role of phenotyping, which would then serve to update prediction models and no longer to select lines. While research to date shows the exceptional promise of GS, work remains to be done to validate it empirically and to incorporate it into breeding schemes.

A retrospective DNA marker assessment of the development of insect resistant soybean

Abstract: There has been limited success over the past 30 yr in the development of superior soybean cultivars [Glycine max (L.) Merr] with insect resistance. Success may be hampered by the quantitative nature of resistance and by linkage drag from resistant plant introduction (Pl) donor parents. Soybean insect resistance quantitative trait loci (SIR QTLs) have been identified from PI 229358 and PI 171451 by restriction fragment length polymorphism (RFLP) analysis. The objective of this study was to tag the SIR QTLs from PI 229358 with simple sequence repeat (SSR) markers and to determine the extent to which the SIR QTLs have been introgressed in registered cultivars, germplasm releases, or breeding lines that have resistance derived from this PI or from PI 171451. Marker analysis defined intervals by 5 centimorgans (cM) or less for a SIR QTL on linkage group D1b (SIR-D1b), and for SIR-G, SIR-H, and SIR-M. SIR QTLs were tracked through pedigrees by evaluating the inheritance of PI alleles at marker loci tightly linked to the QTLs during the phenotypic selection for insect resistance. It was inferred that at least 13 of the 15 SIR genotypes studied had introgressed SIR-M. PI genome introgression around SIR-M was measured to assess linkage drag. Some genotypes exhibited a dramatic reduction in the amount of linked PI genome, which likely occurred in response to phenotypic selection for agronomic performance as a means of reducing linkage drag. Only a few genotypes were inferred to possess SIR-G or SIR-H, and no genotypes possessed SIR-D1b. The results of this study indicate that marker-assisted selection for SIR QTLs is needed to introgress these loci into elite genetic backgrounds.

Marker-Assisted Selection in Plant Breeding: From Publications to Practice

Abstract: The volume of publications on the development and to a lesser extent the application of molecular markers in plant breeding has increased dramatically during the last decade. However, most of the publications result from investments from donors with a strategic science quality or biotech advocacy mandate leading to insufficient emphasis on applied value in plant breeding. Converting promising publications into practical applications requires the resolution of many logistical and genetical constraints that are rarely addressed in journal publications. This results in a high proportion of published markers failing at one or more of the translation steps from research arena to application domain. The rate of success is likely to increase due to developments in gene-based marker development, more efficient quantitative trait locus (QTL) mapping procedures, and lower cost genotyping systems. However, some fundamental issues remain to be resolved, particularly regarding complex traits, before marker-assisted selection realizes its full potential in public sector breeding programs. These include the development of high throughput precision phenotyping systems for QTL mapping, improved understanding of genotype by environment interaction and epistasis, and development of publicly available computational tools tailored to the needs of molecular breeding programs.