Breeding the Thai jasmine rice variety KDML105 for non-age-related broad-spectrum resistance to bacterial blight disease based on combined marker-assisted and phenotypic selection

Abstract

Bacterial blight (BB) caused by Xanthomonas oryzae pv. oryzae is one of the most devastating diseases of rainfed lowland rice in Thailand. The gene Xa21 shows broad-spectrum resistance and has been widely utilized to improve BB resistance in rice worldwide. However, Xa21 is not fully expressed in the early stages of development (seedling stage). In this study, we attempted to improve the Thai jasmine rice variety KDML105 to obtain non-age-related broad-spectrum resistance to BB. The Xa21 gene and seedling resistance genes from rice variety IR1188 (a variety with non-age-related broad-spectrum resistance to BB) were introgressed into KDML105 through three rounds of marker-assisted backcrossing (MAB) and phenotypic selection. Sixty KDML105 backcross introgression lines (KBILs) carrying the Xa21 gene were successfully developed. They were used to evaluate seedling resistance against thirteen Xoo strains. Three seedling resistance (SR) loci inherited from IR1188 were identified on rice chromosomes 1 (RM302-RM212), 8 (RM210-RM149) and 11 (RM287-RM224). The agronomic characters of the KBILs were assessed by planting these lines in the paddy field at Kasetsart University in 2003. Phenotypic variation was observed in the agronomic traits of these lines. Seven KBILs carrying the Xa21 and multiple SR loci and also having a similar plant type to the original KDML105 were chosen for testing in multi-location trials at research stations in rainfed lowland environments. The trials were conducted in 10 and 11 locations in the North and Northeast of Thailand, respectively, between 2005 and 2006. The yield, agronomic traits, cooking quality and important diseases were examined and compared with those of the original KML105. All of the 7 KBILs had a cooking quality profile (aroma, amylose content, gel consistency and alkaline spreading value) and agronomic performance similar to the original KDML105. In 2007, four KBILs were planted in farmers’ fields at 5 locations. All BILs and the original KDML105 did not differ significantly in their agronomic performance. In this study, multiple loci for broad-spectrum seedling resistance were identified from the KBIL population developed by the integrated marker-assisted and phenotypic selection procedures (MAS and PS). These results facilitated the successful improvement of non-age-related broad-spectrum BB resistance in KDML105. The established non-age-related broad-spectrum BB-resistant KDML105 is currently recommended by Kasetsart University for planting in farmers’ fields where the crop is vulnerable to BB