A new gene for resistance to race 6 of bacterial blight in rice, Oryza saliva L.

Most of our earlier studies on inheritance of resistance to bacterial blight (BB) were carried out using Philippine races 1,2, 3 and 4 of Xanthonionas oryzae pv. oryzac (Ogawa and Khush 1989). When race 6 of BB became available in 1980s, several rice varieties with resistance to this race were identified. A recessive gene for resistance to race 6 was identified in BJ1 (Ogawa et a!. 1987) and designated as xal3. Four other varieties e.g. AC19-l-1, Aus 274, Chinsurah Boro II and Kalimekri 77-5 were proposed to belong to this group (designated as BJ1 group) on the basis of their reaction pattern to races 1, 2,4 and 6 of BB (Ogawa eta!. 1987). On the basis of reaction pattern to four race, Ogawa et a!. (1991) suggested that Tepa 1 (Boro) may also belong to this group. Mir and Khush (1990) carried out genetic analysis of DV86 and concluded that a recessive gene conveys resistance to race 6 in this variety. Three other varieties, e.g. Long Grain, Aus 295 and DV85 are also resistant to race 6.

We crossed nine varieties having resistance to race 6 with BJ1 to confirm if they indeed have xal3 for resistance to race 6. As the results of Table 1 show, the F1s of Kalimekri 77-5, Chinsurah Boro II, Tepa 1 (Boro), Aus 274, AC19-l-land Long Grain were resistant and the F2 populations did not segregate for susceptibility. These results show that these six varieties have xal3 for resistance. On the other hand the F1s of BJ1 with DV85, DV86 and Aus 295 were susceptible and the F2 populations segregated in a ratio of 7:9 thereby showing that these three varieties have recessive genes for resistance to race 6 which segregate independently of xal3. The F1s of DV85 with DV86 and Aus 295 were resistant and the F2 populations did not segregate for susceptibility (Table 1). These results show that the recessive gene for resistance to race 6 identified in DV86 by Mir and Khush (1990) is non-allelic to and independent of xal3. Moreover, DV86, DV85 and Aus 295 have the same recessive gene for resistance. This gene is designated as xa24(t).

Ogawa, T., G.S. Busto, R.E. Tabien, 0.0. Romero, N. Endo and G.S. Khush, 1991. Grouping of rice cultivars based on reaction pattern to Philippine races of bacterial blight pathogen (Xanthomonas campestris pv. oryzae). Japan. J. Breed. 41: 109-119.

37. A new gene for resistance to race 6 of bacterial blight in rice, Oryza saliva L.G.S. KHUSH and E.R. ANGELES International Rice Research Institute, MCPO Box 3127, Makati City 1271, Philippines Most of our earlier studies on inheritance of resistance to bacterial blight (BB) were carried out using Philippine races 1,2, 3 and 4 of Xanthonionas oryzae pv. oryzac (Ogawa and Khush 1989). When race 6 of BB became available in 1980s, several rice varieties with resistance to this race were identified. A recessive gene for resistance to race 6 was identified in BJ1 (Ogawa et a!. 1987) and designated as xal3. Four other varieties e.g. AC19-l-1, Aus 274, Chinsurah Boro II and Kalimekri 77-5 were proposed to belong to this group (designated as BJ1 group) on the basis of their reaction pattern to races 1, 2,4 and 6 of BB (Ogawa eta!. 1987). On the basis of reaction pattern to four race, Ogawa et a!. (1991) suggested that Tepa 1 (Boro) may also belong to this group. Mir and Khush (1990) carried out genetic analysis of DV86 and concluded that a recessive gene conveys resistance to race 6 in this variety. Three other varieties, e.g. Long Grain, Aus 295 and DV85 are also resistant to race 6. We crossed nine varieties having resistance to race 6 with BJ1 to confirm if they indeed have xal3 for resistance to race 6. As the results of Table 1 show, the F1s of Kalimekri 77-5, Chinsurah Boro II, Tepa 1 (Boro), Aus 274, AC19-l-land Long Grain were resistant and the F2 populations did not segregate for susceptibility. These results show that these six varieties have xal3 for resistance. On the other hand the F1s of BJ1 with DV85, DV86 and Aus 295 were susceptible and the F2 populations segregated in a ratio of 7:9 thereby showing that these three varieties have recessive genes for resistance to race 6 which segregate independently of xal3. The F1s of DV85 with DV86 and Aus 295 were resistant and the F2 populations did not segregate for susceptibility (Table 1). These results show that the recessive gene for resistance to race 6 identified in DV86 by Mir and Khush (1990) is non-allelic to and independent of xal3. Moreover, DV86, DV85 and Aus 295 have the same recessive gene for resistance. This gene is designated as xa24(t). References Mir, G.N. and G.S. Khush, 1990. Genetics of resistance to bacterial blight in rice cultivar DV86. Crop Res. 3(2):194-198. Ogawa, T. and G.S. Khush, 1989. Major genes for resistance to bacterial blight in rice. p. 177-192, In Bacterial blight of rice. International Rice Research Institute, P.O. Box 933, Manila, Philippines. Ogawa, T., L. Lin, R.E. Tabien and G.S. Khush, 1987. Anew recessive gene for resistance to bacterial blight of rice. RON 4:98-100. Ogawa, T., G.S. Busto, R.E. Tabien, 0.0. Romero, N. Endo and G.S. Khush, 1991. Grouping of rice cultivars based on reaction pattern to Philippine races of bacterial blight pathogen (Xanthomonas campestris pv. oryzae). Japan. J. Breed. 41: 109-119.