Evaluation of backcrossed pyramiding lines of the yield-related gene and the bacterial leaf blight resistant genes.

The yield-related gene, WFP increases grain number by increasing the primary branch number per panicle in rice.In the present study, WFP was introgressed from ST-12 to IRBB60, a pyramiding line having the genes Xa4, xa5, xa13 andXa21 for BLB resistance in the IR24 genetic background. The pyramided lines PL-1, PL-4 and PL-5 that were included in theinitial BC2F2 selections based on their improved PBN were selected for further agronomic evaluation and generation advanceup to BC2F3. All three lines recorded significantly higher PBN and GN due WFP introgression, although the loss of at leasttwo BLB genes during the breeding process resulted in the variable response of the lines to the different BLB races. Amongthe lines, only PL-5 showed a significantly higher estimate of actual yield measured in terms of panicle weight per squaremeter compared to IRBB60. PL-5 also exhibited resistance to five out of the six BLB races used for resistance screening.Despite the negative effects in grain size, the improved yield estimates, as well as the validated BLB resistance of PL-5 makesit a suitable candidate for cultivar adoption under the tropical rice ecosystem of Southeast Asia.