Abstract
This experiment was conducted with the aim of introgressing multiple resistance genes against bacterial leaf blight (BLB) and blast diseases through marker-assisted backcross breeding. Two dominant (Xa4 and Xa21) and two recessive (xa5 and xa13) BLB resistance genes were introgressed into a Malaysian elite rice variety Putra-1 with genetic background of three blast resistance (Piz, Pi2 and Pi9) genes and high yielding. Eight polymorphic tightly linked functional and SSR markers were used for foreground selection of target genes. 79 polymorphic SSR markers were used in background selection. The plants were challenged at initial stage of breeding and challenged again at BC2F2 with the most virulent Malaysian pathotypes of Xoo (P7.7) and Magnaporthe oryzae (P7.2) to test their resistance. Results obtained from foreground marker analysis showed that the BC1F1 and BC2F1 both fitted into the Mendel’s single gene segregation ratio of 1:1 for both Xoo and blast resistance. At BC2F2, result obtained indicated that foreground marker segregation fitted into the expected Mendelian ratio of 1:2:1 for blast resistance only. Marker-assisted background selection revealed high percentage of recurrent parent genome recovery (95.9%). It was concluded that resistance to Xoo pathotype P7.7 in IRBB60 was neither due to two independent gene action nor epistasis but substantially due to single nuclear gene action. Also, the inheritance of blast resistance in the pyramided lines to pathotype P7.2 was also attributed to single gene action. The incorporation of four bacterial leaf blight and three blast resistance genes (Xa4+xa5+xa13+Xa21+Pi9+Pi2+Piz) in the newly developed lines provides for broad spectrum and durable resistance against the two major diseases studied.
