Article

Marker assisted selection for biotic stress resistance in wheat and rice

Indian Journal of Genetics and Plant Breeding (Impact Factor: 0.19). 12/2009; 69:305-314.

ABSTRACT

Abstract
Use of molecular markers has emerged as a powerful and
efficient approach to complement traditional plant
breeding for improving crops. An array of molecular
markers are now available that include RFLP that is based
on Southern blot hybridization and, RAPD, ISSR, SSR and
STS are based on polymerase chain reaction. The AFLP
and CAPS markers are the other PCR based markers
involving pre and post amplification restriction digestion,
respectively. The most recent marker system is single
nucleotide polymorphism (SNP) that utilizes the vast DNA
sequence resources available in different crop species.
Each of these markers has its own strengths and
limitations. Markers are being used in several different
aspects of crop improvement including estimation of
genetic diversity, construction of high density genome
maps, mapping and tagging of genes, map-based isolation
of genes and marker assisted selection (MAS). MAS is
carried out for transferring target gene(s) from one genetic
background to another using tightly linked markers
(foreground selection). MAS is also carried out to quickly
recover recurrent parent genome in backcross breeding
using a large number of either random or mapped markers
having whole genome coverage (background selection).
Hence, MAS requires markers tightly linked to the genes
for the target traits as well as high-density genome maps
in crops of interest. This condition is not fulfilled in all
crops and traits. The Division of Genetics, IARI has taken
a lead in this approach in breeding for rust resistance in
wheat, blight and blast resistance in rice. MAS has been
effectively employed in pyramiding identified genes
involving short breeding cycles through background and
foreground selection thereby adding resistance to
established cultivars of each crop.

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    ABSTRACT: Backcross lines of high yielding cultivar HD2687 developed earlier carrying leaf rust resistance genes Lr19 and Lr28 were utilized to pyramid the two genes using marker assisted selection. Background analysis using 602 SSR markers was done to compare the genotypic background of backcrossed lines with recipient variety HD2687 as well as the donor genotypes Cook*61C80-1 and CS2A12M#412. Backcross lines of HD2687 with Lr19 and Lr28 i.e. HD2687+Lr19 and HD2687+ Lr28 showed 89 and 92.1 percent genomic similarity with HD2687. The two backcross lines were crossed and plants carrying both Lr19and Lr28were identified in F2 generation. Background analysis of 51 plants carrying both Lr19 and Lr28 was undertaken using polymorphic SSR markers to identify plants with better recovery of HD2687 background. Although, Lr19and Lr28 individually are ineffective against leaf rust pathotypes 77-8 and 77-10 but pyramided lines are expected to provide resistance against all the races.
    Full-text · Article · Nov 2011 · Indian Journal of Genetics and Plant Breeding
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Backcross lines of high yielding cultivar HD2687 developed earlier carrying leaf rust resistance genes Lr19 and Lr28 were utilized to pyramid the two genes using marker assisted selection. Background analysis using 602 SSR markers was done to compare the genotypic background of backcrossed lines with recipient variety HD2687 as well as the donor genotypes Cook*61C80-1 and CS2A12M#412. Backcross lines of HD2687 with Lr19 and Lr28 i.e. HD2687+Lr19 and HD2687+ Lr28 showed 89 and 92.1 percent genomic similarity with HD2687. The two backcross lines were crossed and plants carrying both Lr19and Lr28were identified in F2 generation. Background analysis of 51 plants carrying both Lr19 and Lr28 was undertaken using polymorphic SSR markers to identify plants with better recovery of HD2687 background. Although, Lr19and Lr28 individually are ineffective against leaf rust pathotypes 77-8 and 77-10 but pyramided lines are expected to provide resistance against all the races.
    Full-text · Article · Nov 2011 · Indian Journal of Genetics and Plant Breeding
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    ABSTRACT: Genetic markers have long been used for characterization of plant genetic diversity and exploitation in crop improvement. The advent of DNA marker technology (during 1980s) has revolutionized crop breeding research as it has enabled the breeding of elite cultivars with targeted selection of desirable gene or gene combinations in breeding programmes. DNA markers are considered better over traditional morphology and protein-based markers because they are abundant, neutral, reliable, convenient to automate and cost-effective. Over the years, DNA marker technology has matured from restriction based to PCR based to sequence based and to eventually the sequence itself with the emergence of novel genome sequencing technologies. Trait mapping has been the foremost application of molecular markers in plant breeding. Genomic locations of numerous genes or quantitative trait loci (QTLs) associated with agronomically important traits have been determined in several crop plants using linkage or association mapping approaches. Plant breeders always look for an easy, rapid and reliable method of selection of desirable plants in breeding populations. Conventionally, desirable plants are selected based on phenotypic observations. The phenotypic selection for complex agronomic traits is difficult, unpredictable and challenging. Once the marker-trait association is correctly established, the gene-or QTL-linked markers can be used to select plants carrying desirable traits, the process called marker-assisted selection (MAS). Marker-assisted backcrossing (MABC) has been widely used for transferring single major gene or combination of major genes into the background of elite cultivar; the process refers to gene pyramiding. Marker-assisted recurrent selection (MARS) and genome-wide association analysis (GWA) are considered potential MAS strategies for improvement of complex traits but still remain as theoretical possibilities in plant breeding. Though molecular markers and MAS have promises for improved plant breeding process, the marker-trait associations or QTLs are statistical associations, which are influenced by several factors such as trait heritability, phenotyping methods, marker density, population type and other experimental conditions that might lead to false positives. Therefore, a cautiously optimistic approach is necessary to consider MAS in crop breeding programmes. In this chapter, the potentials of genetic markers in plant breeding are described.
    No preview · Article · Jan 2015
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