A Preliminary Study on the Phenotypic and PCR Evaluation of Candidate Transgenic Rice (Oryza sativa L.) Containing the Xa21 Gene for Bacterial Blight Resistance

Abstract

R1 plants derived from PR3B and IR58025B hybrid parental lines that were transformed with the Xa21 transgene were evaluated for their reaction to bacterial blight (BB) through leaf clipping method. Among the total number of PR3B plants 15.9% were resistant, 71.2% were intermediate and 13% were susceptible. On the contrary, 1.24% of the hybrid maintainer rice line IR58025B showed intermediate reaction while 98.76% were susceptibile. None showed resistance. Nineteen selected BB resistant PR3B R1 lines (resistant/ intermediate in Ro screening and resistant in R1 screening) were also subjected to morpho- agronomic characterization, hygromycin assay and PCR analysis. The lines were comparable to the untransformed PR3B hybrid line in agronomic traits such as culm number, culm length, and 100-grain weight but not in panicle length and spikelet sterility. Among the 19 lines tested 17 produced progenies with resistant and susceptible reactions to hygromycin, while 2 lines resulted into progenies that are all susceptible. The result suggests that only the 17 lines contain the hpt gene coding for hygromycin resistance. PCR results revealed that of the 19 lines only 11 were positive for the presence of Xa21 gene. Further tests in the succeeding generations in terms of presence and expression of the Xa21 gene, as well as morpho-agronomic traits are needed to be performed so that plants that are highly similar to the original parental lines but exhibiting resistance to BB can be identified.