Expression levels of three bacterial blight resistance genes against K3a race of Korea by molecular and phenotype analysis in japonica rice (O. sativa L.)

Abstract

Bacterial blight, caused by Xanthomonas oryzae pv. oryzae (Xoo) is a destructive disease of rice in the major rice growing countries of Asia. In 2003, a serious bacterial blight epidemic occurred in the southwestern coastal areas in Korea, causing significant yield loss due to the emergence of a new race, K3a. IR24 near-isogenic lines containing Xa4, xa5, Xa7 and Xa21 genes conferred different degrees of resistance to the most virulent K3a isolate, HB01009 in an inoculation experiment in the greenhouse. Expression levels of the resistance genes, Xa4, xa5 and Xa21 were studied in two F2 populations derived from the crosses between elite japonica cultivars and an advanced backcross breeding line possessing Xa4, xa5 and Xa21 genes. F2 progenies segregated for K3a resistance (R) and susceptible (S) phenotypes in a ratio of 3(R):1(S) indicated that K3a resistance was controlled by a major dominant gene. Three PCR markers tightly linked to the resistance genes Xa4, xa5 and Xa21 confirmed the presence of the genes and their interaction with each gene. This study demonstrated that the Xa21 gene dominantly contributed to K3a resistance. However, the Xa4 gene also contributed to the full expression of resistance. The level of expression of strong resistance to K3a race was attributed to the presence of Xa21 and Xa4 genes irrespective of the presence of xa5 gene. Our results suggest that the R-gene combinations of Xa4+Xa21 could be a useful and effective strategy toward improving resistance to K3a race of Korean japonica cultivars.

Development of breeding lines with three pyramided resistance genes that confer broad-spectrum bacterial blight resistance and their molecular analysis in rice

“…Mangeumbyeo is a japonica cultivar with good grain and cooking quality and high yield potential but it is highly susceptible to BB races. An IRBB57 NIL carrying Xa4 , xa5 and Xa21 genes in an IR24 genetic background conferred strong resistance to all Korean BB races, including K3a (Jeung et al 2006 ; Suh et al 2009a ). We have introduced the three BB resistance genes ( Xa4 + xa5 + Xa21 ) from IRBB57 into Mangeumbyeo through simultaneous foreground and phenotypic selection.…”

“…As a result, increasing attention has focused on the accumulation of major disease resistance genes in crop plants. Pyramided lines carrying two, three or four bacterial blight resistance genes showed broad-spectrum and higher resistance than the lines with a single resistance gene (Gu et al 2005 ; Jeung et al 2006 ; Kim et al 2009 ; Singh et al 2001 ; Suh et al 2009a ). However, conventional breeding methods to improve rice cultivars for BB resistance have not found much success (Shin et al 2011 ).…”

“…Molecular markers can be used to identify and pyramid favorable (or deleterious) and multiple alleles for biotic and abiotic stress resistance in a collection of diverse genotypes (Jena and Mackill, 2008 ; Lee et al 2003 ; Singh et al 2001 ; Suh et al 2009a ). Marker-assisted selection (MAS) for pyramiding important genes along with rapid background recovery of the recurrent parent, while maintaining the exquisite quality characteristics of rice, could be an effective approach for rice improvement (Shanti et al 2010 ; Singh et al 2001 ; Suh et al 2009a ; Suh et al 2011 ; Sundaram et al 2008 ; Xu and Crouch, 2008 ; Ye 2010 ). Gene pyramiding is difficult using conventional breeding methods due to the dominance and epistasis effects of genes governing disease resistance.…”

“…oryzae ( Xoo ) isolates under artificial inoculation and field conditions showed that the combination of genes provided a wider spectrum of resistance to the pathogen populations prevalent in the region (Singh et al 2001 ). In a previous study, the IR24 NILs (IRBB lines) containing Xa4 , xa5 , Xa7 and Xa21 genes and their combinations conferred different degrees of resistance to K1, K2, K3 and K3a races in a field inoculation experiment in Korea (Jeung et al 2006 ; Kim et al 2009 ; Suh et al 2009a ). The resistance gene pyramid of Xa4 + xa5 + Xa21 would be the most effective strategy for improving Korean japonica cultivars for BB resistance (Jeung et al 2006 ; Kim et al 2009 ).…”

Preliminary genome-wide association mapping of rice bacterial leaf blight resistance loci using major Korean races of Xoo (Xanthomonas oryzae)

“…Among other nearest genes, Xa3/Xa26 have been reported for resistance against three races, including K1, K2, and K3 but susceptible to K3a (Kim et al, 2015). Moreover, Suh et al (2009) reported that plants having Xa4 and Xa21 genes conferred strong resistance to K3a race. Another unknown locus on chromosome 11 for K3a race was located between an expressed protein and tropinone reductase2 gene, which helps in oxidoreductase activity in the cells.…”