Pyramiding three bacterial blight resistance genes (xa5, xa13 and Xa21) using marker-assisted selection into indica rice cultivar PR106

Bacterial blight (BB) of rice caused by Xanthomonas oryzae pv. oryzae (Xoo) is a major disease of rice in several countries. Three BE resistance genes , xa5, xa13 and Xa21, were pyramided into cv. PR106, which is widely grown in Punjab, India, using marker-assisted selection. Lines of PR106 with pyra mided genes were evaluated after inoculation with 17 isolates of the pathog en from the Punjab and six races of Xoo from the Philippines. Genes in comb inations were found to provide high levels of resistance to the predominant Xoo isolates from the Punjab and six races from the Philippines. Lines of PR106 with two and three BE resistance genes were also evaluated under natu ral conditions at 31 sites in commercial fields. The combination of genes p rovided a wider spectrum of resistance to the pathogen population prevalent in the region; Xa21 was the most effective, followed by xa5. Resistance ge ne xa13 was the least effective against Xoo. Only 1 of the BB isolates, PX0 4, was virulent on the line carrying Xa21 but avirulent on the lines having xa5 and xa13 genes in combination with Xa21.