Inheritance of bacterial blight resistance in the rice cultivar Ajaya and high-resolution mapping of a major QTL associated with resistance.

Directorate of Rice Research, Rajendranagar, Hyderabad 500 030, AP, India.
Genetics Research (Impact Factor: 2). 12/2011; 93(6):397-408. DOI: 10.1017/S0016672311000577
Source: PubMed

ABSTRACT The cultivar Ajaya (IET 8585) exhibits durable broad-spectrum resistance to bacterial blight (BB) disease of rice and is widely used as a resistance donor. The present study was carried out to decipher the genetics of BB resistance in Ajaya and map the gene(s) conferring resistance. Genetic analysis in the F2 indicated a quantitative/additive nature of resistance governed by two loci with equal effects. Linked marker analysis and allelic tests revealed that one of the resistance genes is xa5. Sequence analysis of a 244 bp region of the second exon of the gene-encoding Transcription factor IIAγ (the candidate gene for xa5) confirmed the presence of xa5. Bulked-segregant analysis (BSA) revealed the putative location of the two quantitative trait loci (QTLs)/genes associated with resistance on chromosomes 5 and 8. Composite interval mapping located the first locus on Chr. 5S exactly in the genomic region spanned by xa5 and the second locus (qtl BBR 8.1) on Chr. 8L. Owing to its differential disease reaction with a set of seven hyper-virulent isolates of Xanthomonas oryzae, a map location on Chr. 8L, which was distinct from xa13 and data from allelism tests, the second resistance locus in Ajaya was determined to be novel and was designated as xaAj. A contig map spanning xaAj was constructed in silico and the genomic region was delimited to a 13.5 kb physical interval. In silico analysis of the genomic region spanning xaAj identified four putatively expressed candidate genes, one of which could be involved in imparting BB resistance in Ajaya along with xa5.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: IR 58025A is a very popular wild-abortive cytoplasmic male sterile (WA-CMS) line of rice and is extensively used for hybrid rice breeding. However, IR 58025A and many hybrids derived from it possess mild aroma (undesirable in some parts of India) and are highly susceptible to bacterial blight (BB) and blast diseases. To improve IR 58025A for BB and blast resistance, we have introgressed a major dominant gene conferring resistance against BB (i.e. Xa21) and blast (i.e. Pi54) into IR 58025B, the maintainer line of IR 58025A. An introgression line of Samba Mahsuri (i.e. SM2154) possessing Xa21 and Pi54 genes in homozygous condition and fine-grain type was used as donor parent, and backcross breeding strategy was adopted for targeted introgression of the resistance genes. PCR-based molecular markers tightly linked to Xa21 and Pi54 were used for selection of BB- and blast-resistant lines, while closely linked markers were used for identification of backcross-derived plants devoid of Rf4 and aroma. At BC2F5, four backcross-derived lines possessing resistance against BB and blast, devoid of aroma, high yield, short plant stature, long-slender grain type and with recurrent parent genome recovery ranging from 88.8% to 98.6% were selected and advanced for further evaluation. The improved versions of IR 58025B, viz. SB54-11-143-9-44-5, SB54-11-143-9-44-98, SB54-11-143-9-44-111 and SB54-11-143-9-44-171, behaved as perfect maintainers when testcrossed with WA-CMS lines. Agronomically superior lines of improved IR 58025B are being converted to CMS line through backcrossing for developing high-yielding and biotic stress-resistant rice hybrids.
    Plant Breeding 01/2013; · 1.18 Impact Factor

Full-text (2 Sources)

Available from
May 17, 2014