| dc.description.abstract | Using IRRI rice near-isogenic lines, 106 isolates of Xanthomonas oryzae pv. oryzue (Xoo) isolated from diseased plants from Bekasi and Karawang Districts in the dry season of 1994 were separated into 12 pathotypes. All of them could be rcgarded as complex pathotypes. The simplest pathotype (pathotype I) has at least three genes for virulence to overcome Xa-1, Xa-11, and Xa-14 resistance genes, respectively. Pathotype V, the most dominant pathotype (46.23%), has at least seven virulence genes to overcome Xa-1, Xa-2, Xa3, Xa-4, Xa-10, Xa-11, and Xa-14, while the most virulent one (pathotype XII) has at least 10 virulence genes to overcome Xa-1, Xa-2, Xa-3, Xa-4, xa-5, Xa-7, Xa-10, Xa-1 1, Xa-14, and Xa-21. With the exception of pathotypes I and 11, which were only detected from IR 64 in a location with the irrigation scheme IV, the distribution of Xoo pathotypes were not affected by rice cultivars and the irrigation scheme1 planting time in each location. Out of ten resistance genes used in this study, only xr-5, Xa-7, and Xa-21 are relatively effective against the majority of the Xoo isolates, so that these resistance genes can be incorporated into our rice breeding program. Since Xoo pathotype having the ability to overcome the combination of these resistance genes already occurred in nature, however, xa-5, Xa-7, and Xa-21 should not be used in a gene pyramiding fashion. Due to the lower percentage of Xoo pathotypes having the ability to overcome Xa-7, we postulated that the addition of virulence genes to overcome X8-7 occurred after the integration of virulence genes to overcome xa-5 and Xa-21 into the Xoo population. | id |
