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Fine-mapping and molecular marker development for Pi56(t), a NBS-LRR gene conferring broad-spectrum resistance to Magnaporthe oryzae in rice

The major quantitative trait locus qBR9.1 confers broad-spectrum resistance to rice blast, and was mapped to a *69.1 kb region on chromosome 9 that was inherited from resistant variety Sanhuangzhan No 2 (SHZ-2). Within this region, only one predicted disease resistance gene with nucleotide binding site and leucine-rich repeat (NBS-LRR) domains was found.

Yan Liu, Bin Liu, Xiaoyuan Zhu, Jianyuan Yang, Alicia Bordeos, Guoliang Wang, Jan E. Leach, Hei Leung

Theor Appl Genet (2013) 126:985–998

 

ABSTRACT

 

The major quantitative trait locus qBR9.1 confers broad-spectrum resistance to rice blast, and was mapped to a *69.1 kb region on chromosome 9 that was inherited from resistant variety Sanhuangzhan No 2 (SHZ-2). Within this region, only one predicted disease resistance gene with nucleotide binding site and leucine-rich repeat (NBS-LRR) domains was found. Specific markers corre-sponding to this gene cosegregated with blast resistance in F2 and F3 populations derived from crosses of susceptible variety Texianzhan 13 (TXZ-13) to SHZ-2 and the resistant backcross line BC-10. We tentatively designate the gene as Pi56(t).

 

Sequence analysis revealed that Pi56(t) encodes an NBS-LRR protein composed of 743 amino acids. Pi56(t) was highly induced by blast infection in resistant lines SHZ-2 and BC-10. The corresponding allele of Pi56(t) in the susceptible line TXZ-13 encodes a protein with an NBS domain but without LRR domain, and it was not induced by Magnaporthe oryzae infection. Three new cosegregat-ing gene-specific markers, CRG4-1, CRG4-2 and CRG4-3, were developed. In addition, we evaluated polymorphism of the gene-based markers among popular varieties from national breeding programs in Asia and Africa.

 

The presence of the CRG4-2 SHZ-2 allele cosegregated with a blast-resistant phenotype in two BC2F1families of SHZ-2 crossed to recurrent parents IR64-Sub1 and Swarna-Sub1. CRG4-1 and CRG4-3 showed clear polymorphism among 19 varieties, suggesting that they can be used in marker-assisted breeding to combine Pi56(t) with other target genes in breeding lines.

 

Introduction Rice blast disease, caused by the fungus Magnaporthe oryzae, is one of the most devastating diseases of rice worldwide (Kush and Jena2009; Liu et al. 2010). Rice yield losses of about 20–50 % occur in the absence of adequate resistance (Savary et al.2000). Because of the effectiveness of plant resistance (R) genes in preventing diseases, the incorporation of blast resistance genes into cultivars has been the most favored strategy in breeding. A majority of the major resistance genes with strong effects follow a model of gene-for-gene interaction (Jia et al. 2000). Because of this high specificity, when blast resis-tance of a cultivar is based on a single resistance gene, it can be rapidly overcome by the emergence of compatible races of the pathogen (Hittalmani et al. 2000).

 

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