Bacterial blight resistance of transgenic IR72-Xa21 in field conditions

Three transgenic IR72 lines with Xa21 gene for bacterial blight resistance were evaluated in a contained transgenic field in the PhilRice Central Experiment station during the 2002 WS [wet season] to determine resistance to bacterial blight under field conditions, compare the agronomic performance of transgenic and non-transgenic rice, and assess the horizontal gene flow to non-targeted rice plants. Seeds of transgenic rice TT103 (IRRI transgenic line), IR72-82-3-13-2-2 and IR72-82-3-42-4-6 (PhilRice transgenic lines), untransformed IR72; IRBB 21, a conventionally bred line with Xa21 gene; and IR24, a susceptible control were evaluated. Bacterial blight susceptible purple rice was planted in between varieties (3 rows) and around the periphery of the field (10 rows) that served as buffer and indicators for horizontal Xa21 gene transfer. Sesbania trees planted outside the 1.2 m fence surrounding the field served as pollen barrier. Inoculation of PXO79 race 3 (Maligaya isolate) by clipping method was at maximum tillering stage and rating for percentage diseased leaf area (% dla) were at 14 and 21 days after. The agronomic traits: days to flowering and maturity, plant height at maturity, percentage productive tillers, panicle length, weight of 1,000 grains and the harvest index were obtained to determine possible phenotypic change between transgenic and non-transgenic IR72. The 2002 WS trial showed that the susceptible IR24 had the highest mean % dla as expected. The untransformed IR72, which contain some genes for resistance to X00, was intermediate, IRBB 21 was moderately resistant, and the transgenic lines were resistant to moderately resistant. Yield component data revealed that the transgenic lines were comparable to the untransformed IR72 in days to flowering and maturity, percent productive tillers, plant height, 1,000 grain weight and harvest index