Article

Marker assisted selection for biotic stress resistance in wheat and rice

Indian Journal of Genetics and Plant Breeding (Impact Factor: 0.19). 01/2009; 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: A widely grown but rust susceptible Indian wheat variety HD2932 was improved for multiple rust resistance by marker-assisted transfer of genes Lr19, Sr26 and Yr10. Foreground and background selection processes were practised to transfer targeted genes with the recovery of the genome of HD2932. The near-isogenic lines (NILs) of HD2932 carrying Lr19, Sr26 and Yr10 were individually produced from two backcrosses with recurrent parent HD2932. Marker-assisted background selection of NILs with 94.38-98.46% of the HD2932 genome facilitated rapid recovery of NILs carrying Lr19, Sr26 and Yr10. In the BC2F2 generation, NILs were intercrossed and two gene combinations of Lr19+Yr10, Sr26 + Yr10 and Lr19+Sr26 were produced. A total of 16 progeny of two gene combinations of homozygous NILs of HD2932 have been produced, which are under seed increase for facilitating the replacement of the susceptible HD2932 with three of the sixteen improved backcross lines with resistance to multiple rusts.
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