Identification of recombinant inbred lines against rice blast (Pyricularia grisea (Cooke) Sacc.)

Identification of recombinant inbred lines for resistance to rice blast was made using six common isolates (Ca65, Ca89, IK81-25, M64-1-3-9-1, CBN9214-1 and PO6-6) under screenhouse condition. Results revealed that out of 202 lines evaluated for resistance, 181 lines were resistant to all isolates of rice blast pathogen tested. Of the 181 lines, 49 lines were highly resistant. These results indicated the presence of resistant genes against rice blast in the recombinant inbred lines (RIL). Due to variation of reaction among the RIL against the six isolates of rice blast pathogen, highly resistant lines were selected. Thirteen lines had highly resistant reaction to Ca65, namely: LxT 39, LxT 257, LxT 165, LxT 76, Lxt 73, LxT 77, Lxt 237, LxT 272, LxT 120, LxT 254, LxT 93, LxT 94, and LxT 96. Using the isolate Ca89, eight lines were highly resistant. These were LxT 39, LxT 21, LxT 265, LxT 326, LxT 65, LxT 66, LxT 324 and LxT 37. Meanwhile, isolate IK81-25 had five lines that showed highly resistant reaction. These were LxT 257, LxT 149, LxT 235, LxT 283, and Lxt 189. In contrast, evaluation of lines against M64-1-3-9-1 revealed only line LxT 364 was highly resistant to the disease. Twenty-five lines showed highly resistant reaction to isolate CBN9214-1. Highly resistant reactions to the disease were observed in lines LxT 73, LxT 360, LxT 113 and LxT 387 using isolate PO6-6. Furthermore, LxT 39 was the most resistant line with no disease symptom to isolates Ca65, Ca89 and CBN9214-1. LxT 165 and LxT 76 had no lesion to isolates Ca65 and CBN9214-1. LxT 21 was highly resistant to isolates Ca89 and CBN9214-1. LxT 257 was highly resistant to Ca65 and IK81-25. LxT 73 was resistant to Ca65 and PO6-6. The rest of the entries showed highly resistant reaction to only one isolate. When using the different isolates, M64-2-3-9-1 was the most virulent. When isolate CBN9214-1 was used, more lines were observed to have highly resistant reaction. Under blast nursery evaluation, majority of the lines was rated resistant LxT 392, LxT 403 and LxT 447 were highly resistant to the disease in all weeks of evaluation. During the different weeks of evaluation, a decreasing number of resistant lines and increasing number of susceptible lines to the disease were observed. For detailed evaluation of resistant lines against a disease, evaluation should be made up to panicle blast stage because there are lines that change the reaction up to the later stages of rice growth and development.