ABSTRACT
The era of the green revolution has significantly improved rice yield productivity. However, with the growing population and decreasing arable land, rice scientists must find new ways to improve rice productivity. Although hundreds of rice yield-related QTLs were already mapped and some of them were cloned, only a few were utilized for actual systematic introgression breeding programs. In this study, the major yield QTLs Grain Number 1a (Gn1a) and Wealthy Farmer's Panicle (WFP) were introgressed and stacked in selected NERICA cultivars by marker-assisted backcross breeding (MABB). The DNA markers RM3360, RM3452, and RM5493 were used for foreground selection. At BC3F4 and BC3F5 generation, a combination of marker-assisted selection and phenotypic evaluation were carried out to select lines with target alleles and traits. Further, genotyping-by-sequencing (GBS) was conducted to validate the introgression and determine the recurrent parent genome recovery (RPGR) of the selected lines. The Gn1a and/or WFP introgression lines showed significantly higher numbers of spikelets per panicle and primary branching compared to the recurrent parents. In addition, lines with Gn1a and/or WFP alleles were comparatively similar to the recurrent parents (RP) in most yield-related traits. This study demonstrates the success of utilizing yield QTLs and marker-assisted selection to develop and improve rice cultivars.
ABSTRACT
Bacterial blight caused by Xanthomonas oryzae pv. oryzae (Xoo) is a major limiting factor to rice productivity worldwide. Genetic control through the identification of novel sources of bacterial blight resistance and their utilization in resistance breeding remains the most effective and economical strategy to manage the disease. Here we report the identification of a novel locus from the wild Oryza species, Oryza latifolia, conferring a race-specific resistance to Philippine Xoo race 9A (PXO339). The locus was identified from two introgression lines i.e. WH12-2252 and WH12-2256 that segregated from O. latifolia monosomic alien addition lines (MAALs). The discrete segregation ratio of susceptible and resistant phenotypes in the F2 (χ2[3:1] = 0.22 at p>0.05) and F3 (χ2[3:1] = 0.36 at p>0.05) populations indicates that PXO339 resistance in the MAAL-derived introgression lines (MDILs) is controlled by a single, recessive gene. Genotyping of a total of 216 F2, 1130 F3 and 288 F4 plants derived from crossing either of the MDILs with the recurrent parent used to generate the MAALs narrowed the candidate region to a 1,817 kb locus that extends from 10,425 to 12,266 kb in chromosome 12. Putative candidate genes that were identified by data mining and comparative sequence analysis can provide targets for further studies on mapping and cloning of the causal gene for PXO339 resistance in the MDILs. To our knowledge, this is the first report of a genetic locus from the allotetraploid wild rice, O. latifolia conferring race-specific resistance to bacterial blight.
