Marker-assisted selection in back cross progenies for transfer of bacterial leaf blight resistance genes into a popular lowland rice cultivar

Bacterial blight (BB) disease caused by Xanthomonas oryzae pv. Oryzae (Xoo) is a wide spread disease of rice and causes significant yield losses. BB is predominant in lowland and waterlogged ecology. Many rice cultivars have been pyramided with resistant-gene combinations such as xa5, xa13 and Xa21 with durable resistance to BB. In this study, the target genes Xa21, xa13 and xa5 were selected in backcross progenies of Jalmagna and Swarna BB pyramid line using the markers pTA248, RG136 and xa5S, R (multiplex) during foreground selection. In foreground screening of BC1F1 progenies, fifteen plants were obtained with three BB resistant genes (xa5, xa13 and Xa21). The parents were screened with 236 rice microsatellite markers covering all the chromosomes to be used for background recovery of recurrent genome in the backcross progenies. Out of these markers, 120 were observed to be polymorphic for the two parents. Among the polymorphic markers, 60 best distinguishing markers were selected for background selection in the backcross progenies. As high as 85% recurrent genome content was observed in a foreground screened BC1F1 plant in background selection of the backcross progenies.